diff mbox series

[V5,2/3] rust: Use llvm instead of rust-llvm

Message ID 20251015095914.2120664-2-Deepesh.Varatharajan@windriver.com
State Accepted, archived
Commit 9b0a3484626ecb5e58004572caac7a8e8f86980c
Headers show
Series [V5,1/3] rust: Increase QEMU size to 1024 MB | expand

Commit Message

Deepesh Varatharajan Oct. 15, 2025, 9:59 a.m. UTC
From: Deepesh Varatharajan <Deepesh.Varatharajan@windriver.com>

Updated the Rust build to depend on llvm instead.

*Summary of discussion with the rust upstream about using latest LLVM instead of Rust maintained LLVM fork.
https://internals.rust-lang.org/t/can-we-use-proper-clang-instead-of-llvm-fork-what-rust-uses/23489

*Upstream LLVM is generally compatible:
- Rust does support building with upstream (vanilla) LLVM, especially the latest
major release and the one or two preceding ones.
https://rustc-dev-guide.rust-lang.org/backend/updating-llvm.html#updating-llvm

*Impact on Yocto Rust upgrades:
- Rust upgrades shall always check for updates on rust forked llvm and backport
the relevant patches to llvm.

*Regarding the rust forked llvm local patches:
- There are no local patches on rust forked llvm other than the backported fixes
from llvm master.

*We are copying the natively built `llvm-config` binary into the target sysroot and running
it. However, this `llvm-config` has compile time dependencies on various other arch's LLVM
libraries because native-llvm is built for all oe-core supported targets.

Attempting to work around this by symlinking the missing libraries from the native sysroot
into the target sysroot leads to mixed architectures in the final `.rlib`. Specifically,
the object files extracted from those symlinked libraries within `librustc_llvm-<hash>.rlib`
are built for the host, while others are correctly built for the target This results in linker
failures due to file format not recognized.

To resolve this, we now build llvm-target also for all oe-core supported architectures in
addition to the native-llvm build. This ensures that `llvm-config` and all associated
libraries are built for the correct target, eliminating cross-architecture contamination
and linker issues.

*We are enabling -DLLVM_INSTALL_UTILS=ON to ensure essential LLVM utilities like FileCheck
are available, as they are required by the Rust build.

Without this, the build fails with an error as below:
| thread 'main' panicked at src/bootstrap/src/core/sanity.rs:315:21:
| FileCheck executable "poky/build/tmp/work/x86_64-linux/rust-native/1.90.0/recipe-sysroot
-native/usr/bin/FileCheck" does not exist

*We now add these flags "-Clink-arg=-lz -Clink-arg=-lzstd" because of this following

Comments

Khem Raj Oct. 17, 2025, 6:01 a.m. UTC | #1
I am seeing a build regression when using clang as default compiler

https://errors.yoctoproject.org/Errors/Details/885430/

PREFERRED_TOOLCHAIN_TARGET ?= "clang"
PREFERRED_TOOLCHAIN_SDK ?= "clang"
TOOLCHAIN_NATIVE:pn-rust ?= "clang"
TOOLCHAIN_NATIVE:pn-rust-native ?= "clang"
TOOLCHAIN_NATIVE:pn-nativesdk-rust ?= "clang"

On Wed, Oct 15, 2025 at 2:59 AM Varatharajan, Deepesh via
lists.openembedded.org
<deepesh.varatharajan=windriver.com@lists.openembedded.org> wrote:
>
> From: Deepesh Varatharajan <Deepesh.Varatharajan@windriver.com>
>
> Updated the Rust build to depend on llvm instead.
>
> *Summary of discussion with the rust upstream about using latest LLVM instead of Rust maintained LLVM fork.
> https://internals.rust-lang.org/t/can-we-use-proper-clang-instead-of-llvm-fork-what-rust-uses/23489
>
> *Upstream LLVM is generally compatible:
> - Rust does support building with upstream (vanilla) LLVM, especially the latest
> major release and the one or two preceding ones.
> https://rustc-dev-guide.rust-lang.org/backend/updating-llvm.html#updating-llvm
>
> *Impact on Yocto Rust upgrades:
> - Rust upgrades shall always check for updates on rust forked llvm and backport
> the relevant patches to llvm.
>
> *Regarding the rust forked llvm local patches:
> - There are no local patches on rust forked llvm other than the backported fixes
> from llvm master.
>
> *We are copying the natively built `llvm-config` binary into the target sysroot and running
> it. However, this `llvm-config` has compile time dependencies on various other arch's LLVM
> libraries because native-llvm is built for all oe-core supported targets.
>
> Attempting to work around this by symlinking the missing libraries from the native sysroot
> into the target sysroot leads to mixed architectures in the final `.rlib`. Specifically,
> the object files extracted from those symlinked libraries within `librustc_llvm-<hash>.rlib`
> are built for the host, while others are correctly built for the target This results in linker
> failures due to file format not recognized.
>
> To resolve this, we now build llvm-target also for all oe-core supported architectures in
> addition to the native-llvm build. This ensures that `llvm-config` and all associated
> libraries are built for the correct target, eliminating cross-architecture contamination
> and linker issues.
>
> *We are enabling -DLLVM_INSTALL_UTILS=ON to ensure essential LLVM utilities like FileCheck
> are available, as they are required by the Rust build.
>
> Without this, the build fails with an error as below:
> | thread 'main' panicked at src/bootstrap/src/core/sanity.rs:315:21:
> | FileCheck executable "poky/build/tmp/work/x86_64-linux/rust-native/1.90.0/recipe-sysroot
> -native/usr/bin/FileCheck" does not exist
>
> *We now add these flags "-Clink-arg=-lz -Clink-arg=-lzstd" because of this following
> diff otherwise we will get errors during link time.
>
> Setup in rust-llvm
> -DLLVM_ENABLE_ZLIB=OFF \
> -DLLVM_ENABLE_ZSTD=OFF \
> -DLLVM_ENABLE_FFI=OFF \
>
> Setup in llvm
> -DLLVM_ENABLE_FFI=ON \
>
> *When multilibs enabled:
>
> llvm-config expects static libraries to be located in the lib directory rather than
> lib64. However, since we are copying the natively built llvm-config to target sysroot
> and running it and llvm-config doesn't know anything about lib64 existence. To accommodate
> this without breaking multilib behavior, we are creating a symlink from 'lib' to 'lib64'
> directory.
>
> Previously, when we depended on rust-llvm, this worked because we specified:
> -DCMAKE_INSTALL_PREFIX:PATH=${libdir}/llvm-rust
>
> With this setup, llvm-config was installed inside ${libdir}/llvm-rust, which included
> its own bin and lib directories. Thus, llvm-config located in bin would correctly find
> the libraries in the adjacent lib directory.
>
> Even when multilib was enabled or not, llvm-config would still look for libraries under
> lib in this structure, so everything functioned as expected.
>
> Signed-off-by: Deepesh Varatharajan <Deepesh.Varatharajan@windriver.com>
> ---
>  meta/recipes-devtools/clang/llvm_git.bb   |  2 +-
>  meta/recipes-devtools/rust/rust_1.90.0.bb | 39 ++++++++++++++++++++---
>  2 files changed, 36 insertions(+), 5 deletions(-)
>
> diff --git a/meta/recipes-devtools/clang/llvm_git.bb b/meta/recipes-devtools/clang/llvm_git.bb
> index d2b060ff88..2f47af8d7a 100644
> --- a/meta/recipes-devtools/clang/llvm_git.bb
> +++ b/meta/recipes-devtools/clang/llvm_git.bb
> @@ -27,7 +27,6 @@ OECMAKE_SOURCEPATH = "${S}/llvm"
>  # https://github.com/llvm/llvm-project/blob/main/llvm/CMakeLists.txt
>  LLVM_TARGETS_GPU ?= "${@bb.utils.contains_any('DISTRO_FEATURES', 'opencl opengl vulkan', 'AMDGPU;NVPTX;SPIRV', '', d)}"
>  LLVM_TARGETS_TO_BUILD ?= "AArch64;ARM;BPF;Mips;PowerPC;RISCV;X86;LoongArch;${LLVM_TARGETS_GPU}"
> -LLVM_TARGETS_TO_BUILD:class-target ?= "${@get_clang_host_arch(bb, d)};BPF;${LLVM_TARGETS_GPU}"
>
>  LLVM_EXPERIMENTAL_TARGETS_TO_BUILD ?= ""
>
> @@ -37,6 +36,7 @@ HF[vardepvalue] = "${HF}"
>
>  EXTRA_OECMAKE += "-DCMAKE_BUILD_TYPE=MinSizeRel \
>                    -DLLVM_ENABLE_BINDINGS=OFF \
> +                  -DLLVM_INSTALL_UTILS=ON \
>                    -DLLVM_ENABLE_FFI=ON \
>                    -DLLVM_ENABLE_RTTI=ON \
>                    -DLLVM_TARGETS_TO_BUILD='${LLVM_TARGETS_TO_BUILD}' \
> diff --git a/meta/recipes-devtools/rust/rust_1.90.0.bb b/meta/recipes-devtools/rust/rust_1.90.0.bb
> index 5d804c7398..0319d73b93 100644
> --- a/meta/recipes-devtools/rust/rust_1.90.0.bb
> +++ b/meta/recipes-devtools/rust/rust_1.90.0.bb
> @@ -7,7 +7,7 @@ LIC_FILES_CHKSUM = "file://COPYRIGHT;md5=11a3899825f4376896e438c8c753f8dc"
>  inherit rust
>  inherit cargo_common
>
> -DEPENDS += "rust-llvm"
> +DEPENDS += "llvm"
>  # native rust uses cargo/rustc from binary snapshots to bootstrap
>  # but everything else should use our native builds
>  DEPENDS:append:class-target = " cargo-native rust-native"
> @@ -28,8 +28,8 @@ PV .= "${@bb.utils.contains('RUST_CHANNEL', 'stable', '', '-${RUST_CHANNEL}', d)
>
>  export FORCE_CRATE_HASH = "${BB_TASKHASH}"
>
> -RUST_ALTERNATE_EXE_PATH ?= "${STAGING_LIBDIR}/llvm-rust/bin/llvm-config"
> -RUST_ALTERNATE_EXE_PATH_NATIVE = "${STAGING_LIBDIR_NATIVE}/llvm-rust/bin/llvm-config"
> +RUST_ALTERNATE_EXE_PATH ?= "${STAGING_BINDIR}/llvm-config"
> +RUST_ALTERNATE_EXE_PATH_NATIVE = "${STAGING_BINDIR_NATIVE}/llvm-config"
>
>  # We don't want to use bitbakes vendoring because the rust sources do their
>  # own vendoring.
> @@ -188,6 +188,37 @@ python do_configure() {
>      bb.build.exec_func("setup_cargo_environment", d)
>  }
>
> +# llvm-config expects static libraries to be in the 'lib' directory rather than 'lib64' when
> +# multilibs enabled. Since we are copying the natively built llvm-config into the target sysroot
> +# and executing it there, it will default to searching in 'lib', as it is unaware of the 'lib64'
> +# directory. To ensure llvm-config can locate the necessary libraries, create a symlink from 'lib'
> +do_compile:append:class-target() {
> +    # Ensure llvm-config can find static libraries in multilib setup
> +    lib64_dir="${STAGING_DIR_TARGET}/usr/lib64"
> +    lib_dir="${STAGING_DIR_TARGET}/usr/lib"
> +
> +    if [ -d "$lib64_dir" ]; then
> +        # If lib does not exist, symlink it to lib64
> +        if [ ! -e "$lib_dir" ]; then
> +            ln -s lib64 "$lib_dir"
> +        fi
> +
> +        # Only do per-file symlinking if lib is a real directory (not symlink)
> +        if [ -d "$lib_dir" ] && [ ! -L "$lib_dir" ]; then
> +            for lib64_file in "${lib64_dir}"/libLLVM*.a; do
> +                if [ -e "$lib64_file" ]; then
> +                    lib_name=$(basename "${lib64_file}")
> +                    target_link="${lib_dir}/${lib_name}"
> +
> +                    if [ ! -e "${target_link}" ]; then
> +                        ln -s "../lib64/${lib_name}" "${target_link}"
> +                    fi
> +                fi
> +            done
> +        fi
> +    fi
> +}
> +
>  rust_runx () {
>      echo "COMPILE ${PN}" "$@"
>
> @@ -199,7 +230,7 @@ rust_runx () {
>      unset CXXFLAGS
>      unset CPPFLAGS
>
> -    export RUSTFLAGS="${RUST_DEBUG_REMAP}"
> +    export RUSTFLAGS="${RUST_DEBUG_REMAP} -Clink-arg=-lz -Clink-arg=-lzstd"
>
>      # Copy the natively built llvm-config into the target so we can run it. Horrible,
>      # but works!
> --
> 2.49.0
>
>
> -=-=-=-=-=-=-=-=-=-=-=-
> Links: You receive all messages sent to this group.
> View/Reply Online (#224888): https://lists.openembedded.org/g/openembedded-core/message/224888
> Mute This Topic: https://lists.openembedded.org/mt/115768136/1997914
> Group Owner: openembedded-core+owner@lists.openembedded.org
> Unsubscribe: https://lists.openembedded.org/g/openembedded-core/unsub [raj.khem@gmail.com]
> -=-=-=-=-=-=-=-=-=-=-=-
>
Deepesh Varatharajan Oct. 18, 2025, 6:42 a.m. UTC | #2
On 17-10-2025 11:31, Khem Raj wrote:
> CAUTION: This email comes from a non Wind River email account!
> Do not click links or open attachments unless you recognize the sender and know the content is safe.
>
> I am seeing a build regression when using clang as default compiler
>
> https://errors.yoctoproject.org/Errors/Details/885430/
>
> PREFERRED_TOOLCHAIN_TARGET ?= "clang"
> PREFERRED_TOOLCHAIN_SDK ?= "clang"
> TOOLCHAIN_NATIVE:pn-rust ?= "clang"
> TOOLCHAIN_NATIVE:pn-rust-native ?= "clang"
> TOOLCHAIN_NATIVE:pn-nativesdk-rust ?= "clang"
Hi Khem,

WIth the above mentioned conf in local.conf, I tried building rust for 
qemuarm and qemuarm64 quite
few times and the build completed successfully without any issues for 
both native and target. Do I need
to add any other layers on top of poky ? Do you have any branch where I 
can clone and reproduce the
issue ? Am I missing any step in reproducing the issue ?

Regards,
Deepesh
>
> On Wed, Oct 15, 2025 at 2:59 AM Varatharajan, Deepesh via
> lists.openembedded.org
> <deepesh.varatharajan=windriver.com@lists.openembedded.org> wrote:
>> From: Deepesh Varatharajan <Deepesh.Varatharajan@windriver.com>
>>
>> Updated the Rust build to depend on llvm instead.
>>
>> *Summary of discussion with the rust upstream about using latest LLVM instead of Rust maintained LLVM fork.
>> https://internals.rust-lang.org/t/can-we-use-proper-clang-instead-of-llvm-fork-what-rust-uses/23489
>>
>> *Upstream LLVM is generally compatible:
>> - Rust does support building with upstream (vanilla) LLVM, especially the latest
>> major release and the one or two preceding ones.
>> https://rustc-dev-guide.rust-lang.org/backend/updating-llvm.html#updating-llvm
>>
>> *Impact on Yocto Rust upgrades:
>> - Rust upgrades shall always check for updates on rust forked llvm and backport
>> the relevant patches to llvm.
>>
>> *Regarding the rust forked llvm local patches:
>> - There are no local patches on rust forked llvm other than the backported fixes
>> from llvm master.
>>
>> *We are copying the natively built `llvm-config` binary into the target sysroot and running
>> it. However, this `llvm-config` has compile time dependencies on various other arch's LLVM
>> libraries because native-llvm is built for all oe-core supported targets.
>>
>> Attempting to work around this by symlinking the missing libraries from the native sysroot
>> into the target sysroot leads to mixed architectures in the final `.rlib`. Specifically,
>> the object files extracted from those symlinked libraries within `librustc_llvm-<hash>.rlib`
>> are built for the host, while others are correctly built for the target This results in linker
>> failures due to file format not recognized.
>>
>> To resolve this, we now build llvm-target also for all oe-core supported architectures in
>> addition to the native-llvm build. This ensures that `llvm-config` and all associated
>> libraries are built for the correct target, eliminating cross-architecture contamination
>> and linker issues.
>>
>> *We are enabling -DLLVM_INSTALL_UTILS=ON to ensure essential LLVM utilities like FileCheck
>> are available, as they are required by the Rust build.
>>
>> Without this, the build fails with an error as below:
>> | thread 'main' panicked at src/bootstrap/src/core/sanity.rs:315:21:
>> | FileCheck executable "poky/build/tmp/work/x86_64-linux/rust-native/1.90.0/recipe-sysroot
>> -native/usr/bin/FileCheck" does not exist
>>
>> *We now add these flags "-Clink-arg=-lz -Clink-arg=-lzstd" because of this following
>> diff otherwise we will get errors during link time.
>>
>> Setup in rust-llvm
>> -DLLVM_ENABLE_ZLIB=OFF \
>> -DLLVM_ENABLE_ZSTD=OFF \
>> -DLLVM_ENABLE_FFI=OFF \
>>
>> Setup in llvm
>> -DLLVM_ENABLE_FFI=ON \
>>
>> *When multilibs enabled:
>>
>> llvm-config expects static libraries to be located in the lib directory rather than
>> lib64. However, since we are copying the natively built llvm-config to target sysroot
>> and running it and llvm-config doesn't know anything about lib64 existence. To accommodate
>> this without breaking multilib behavior, we are creating a symlink from 'lib' to 'lib64'
>> directory.
>>
>> Previously, when we depended on rust-llvm, this worked because we specified:
>> -DCMAKE_INSTALL_PREFIX:PATH=${libdir}/llvm-rust
>>
>> With this setup, llvm-config was installed inside ${libdir}/llvm-rust, which included
>> its own bin and lib directories. Thus, llvm-config located in bin would correctly find
>> the libraries in the adjacent lib directory.
>>
>> Even when multilib was enabled or not, llvm-config would still look for libraries under
>> lib in this structure, so everything functioned as expected.
>>
>> Signed-off-by: Deepesh Varatharajan <Deepesh.Varatharajan@windriver.com>
>> ---
>>   meta/recipes-devtools/clang/llvm_git.bb   |  2 +-
>>   meta/recipes-devtools/rust/rust_1.90.0.bb | 39 ++++++++++++++++++++---
>>   2 files changed, 36 insertions(+), 5 deletions(-)
>>
>> diff --git a/meta/recipes-devtools/clang/llvm_git.bb b/meta/recipes-devtools/clang/llvm_git.bb
>> index d2b060ff88..2f47af8d7a 100644
>> --- a/meta/recipes-devtools/clang/llvm_git.bb
>> +++ b/meta/recipes-devtools/clang/llvm_git.bb
>> @@ -27,7 +27,6 @@ OECMAKE_SOURCEPATH = "${S}/llvm"
>>   # https://github.com/llvm/llvm-project/blob/main/llvm/CMakeLists.txt
>>   LLVM_TARGETS_GPU ?= "${@bb.utils.contains_any('DISTRO_FEATURES', 'opencl opengl vulkan', 'AMDGPU;NVPTX;SPIRV', '', d)}"
>>   LLVM_TARGETS_TO_BUILD ?= "AArch64;ARM;BPF;Mips;PowerPC;RISCV;X86;LoongArch;${LLVM_TARGETS_GPU}"
>> -LLVM_TARGETS_TO_BUILD:class-target ?= "${@get_clang_host_arch(bb, d)};BPF;${LLVM_TARGETS_GPU}"
>>
>>   LLVM_EXPERIMENTAL_TARGETS_TO_BUILD ?= ""
>>
>> @@ -37,6 +36,7 @@ HF[vardepvalue] = "${HF}"
>>
>>   EXTRA_OECMAKE += "-DCMAKE_BUILD_TYPE=MinSizeRel \
>>                     -DLLVM_ENABLE_BINDINGS=OFF \
>> +                  -DLLVM_INSTALL_UTILS=ON \
>>                     -DLLVM_ENABLE_FFI=ON \
>>                     -DLLVM_ENABLE_RTTI=ON \
>>                     -DLLVM_TARGETS_TO_BUILD='${LLVM_TARGETS_TO_BUILD}' \
>> diff --git a/meta/recipes-devtools/rust/rust_1.90.0.bb b/meta/recipes-devtools/rust/rust_1.90.0.bb
>> index 5d804c7398..0319d73b93 100644
>> --- a/meta/recipes-devtools/rust/rust_1.90.0.bb
>> +++ b/meta/recipes-devtools/rust/rust_1.90.0.bb
>> @@ -7,7 +7,7 @@ LIC_FILES_CHKSUM = "file://COPYRIGHT;md5=11a3899825f4376896e438c8c753f8dc"
>>   inherit rust
>>   inherit cargo_common
>>
>> -DEPENDS += "rust-llvm"
>> +DEPENDS += "llvm"
>>   # native rust uses cargo/rustc from binary snapshots to bootstrap
>>   # but everything else should use our native builds
>>   DEPENDS:append:class-target = " cargo-native rust-native"
>> @@ -28,8 +28,8 @@ PV .= "${@bb.utils.contains('RUST_CHANNEL', 'stable', '', '-${RUST_CHANNEL}', d)
>>
>>   export FORCE_CRATE_HASH = "${BB_TASKHASH}"
>>
>> -RUST_ALTERNATE_EXE_PATH ?= "${STAGING_LIBDIR}/llvm-rust/bin/llvm-config"
>> -RUST_ALTERNATE_EXE_PATH_NATIVE = "${STAGING_LIBDIR_NATIVE}/llvm-rust/bin/llvm-config"
>> +RUST_ALTERNATE_EXE_PATH ?= "${STAGING_BINDIR}/llvm-config"
>> +RUST_ALTERNATE_EXE_PATH_NATIVE = "${STAGING_BINDIR_NATIVE}/llvm-config"
>>
>>   # We don't want to use bitbakes vendoring because the rust sources do their
>>   # own vendoring.
>> @@ -188,6 +188,37 @@ python do_configure() {
>>       bb.build.exec_func("setup_cargo_environment", d)
>>   }
>>
>> +# llvm-config expects static libraries to be in the 'lib' directory rather than 'lib64' when
>> +# multilibs enabled. Since we are copying the natively built llvm-config into the target sysroot
>> +# and executing it there, it will default to searching in 'lib', as it is unaware of the 'lib64'
>> +# directory. To ensure llvm-config can locate the necessary libraries, create a symlink from 'lib'
>> +do_compile:append:class-target() {
>> +    # Ensure llvm-config can find static libraries in multilib setup
>> +    lib64_dir="${STAGING_DIR_TARGET}/usr/lib64"
>> +    lib_dir="${STAGING_DIR_TARGET}/usr/lib"
>> +
>> +    if [ -d "$lib64_dir" ]; then
>> +        # If lib does not exist, symlink it to lib64
>> +        if [ ! -e "$lib_dir" ]; then
>> +            ln -s lib64 "$lib_dir"
>> +        fi
>> +
>> +        # Only do per-file symlinking if lib is a real directory (not symlink)
>> +        if [ -d "$lib_dir" ] && [ ! -L "$lib_dir" ]; then
>> +            for lib64_file in "${lib64_dir}"/libLLVM*.a; do
>> +                if [ -e "$lib64_file" ]; then
>> +                    lib_name=$(basename "${lib64_file}")
>> +                    target_link="${lib_dir}/${lib_name}"
>> +
>> +                    if [ ! -e "${target_link}" ]; then
>> +                        ln -s "../lib64/${lib_name}" "${target_link}"
>> +                    fi
>> +                fi
>> +            done
>> +        fi
>> +    fi
>> +}
>> +
>>   rust_runx () {
>>       echo "COMPILE ${PN}" "$@"
>>
>> @@ -199,7 +230,7 @@ rust_runx () {
>>       unset CXXFLAGS
>>       unset CPPFLAGS
>>
>> -    export RUSTFLAGS="${RUST_DEBUG_REMAP}"
>> +    export RUSTFLAGS="${RUST_DEBUG_REMAP} -Clink-arg=-lz -Clink-arg=-lzstd"
>>
>>       # Copy the natively built llvm-config into the target so we can run it. Horrible,
>>       # but works!
>> --
>> 2.49.0
>>
>>
>> -=-=-=-=-=-=-=-=-=-=-=-
>> Links: You receive all messages sent to this group.
>> View/Reply Online (#224888): https://lists.openembedded.org/g/openembedded-core/message/224888
>> Mute This Topic: https://lists.openembedded.org/mt/115768136/1997914
>> Group Owner: openembedded-core+owner@lists.openembedded.org
>> Unsubscribe: https://lists.openembedded.org/g/openembedded-core/unsub [raj.khem@gmail.com]
>> -=-=-=-=-=-=-=-=-=-=-=-
>>
Khem Raj Oct. 18, 2025, 5:11 p.m. UTC | #3
On Fri, Oct 17, 2025 at 11:42 PM Deepesh Varatharajan
<deepesh.varatharajan@windriver.com> wrote:
>
>
> On 17-10-2025 11:31, Khem Raj wrote:
> > CAUTION: This email comes from a non Wind River email account!
> > Do not click links or open attachments unless you recognize the sender and know the content is safe.
> >
> > I am seeing a build regression when using clang as default compiler
> >
> > https://errors.yoctoproject.org/Errors/Details/885430/
> >
> > PREFERRED_TOOLCHAIN_TARGET ?= "clang"
> > PREFERRED_TOOLCHAIN_SDK ?= "clang"
> > TOOLCHAIN_NATIVE:pn-rust ?= "clang"
> > TOOLCHAIN_NATIVE:pn-rust-native ?= "clang"
> > TOOLCHAIN_NATIVE:pn-nativesdk-rust ?= "clang"
> Hi Khem,
>
> WIth the above mentioned conf in local.conf, I tried building rust for
> qemuarm and qemuarm64 quite
> few times and the build completed successfully without any issues for
> both native and target. Do I need
> to add any other layers on top of poky ? Do you have any branch where I
> can clone and reproduce the
> issue ? Am I missing any step in reproducing the issue ?
>

Yeah, I missed a setting which I think could be the reason

TC_CXX_RUNTIME = "llvm"


> Regards,
> Deepesh
> >
> > On Wed, Oct 15, 2025 at 2:59 AM Varatharajan, Deepesh via
> > lists.openembedded.org
> > <deepesh.varatharajan=windriver.com@lists.openembedded.org> wrote:
> >> From: Deepesh Varatharajan <Deepesh.Varatharajan@windriver.com>
> >>
> >> Updated the Rust build to depend on llvm instead.
> >>
> >> *Summary of discussion with the rust upstream about using latest LLVM instead of Rust maintained LLVM fork.
> >> https://internals.rust-lang.org/t/can-we-use-proper-clang-instead-of-llvm-fork-what-rust-uses/23489
> >>
> >> *Upstream LLVM is generally compatible:
> >> - Rust does support building with upstream (vanilla) LLVM, especially the latest
> >> major release and the one or two preceding ones.
> >> https://rustc-dev-guide.rust-lang.org/backend/updating-llvm.html#updating-llvm
> >>
> >> *Impact on Yocto Rust upgrades:
> >> - Rust upgrades shall always check for updates on rust forked llvm and backport
> >> the relevant patches to llvm.
> >>
> >> *Regarding the rust forked llvm local patches:
> >> - There are no local patches on rust forked llvm other than the backported fixes
> >> from llvm master.
> >>
> >> *We are copying the natively built `llvm-config` binary into the target sysroot and running
> >> it. However, this `llvm-config` has compile time dependencies on various other arch's LLVM
> >> libraries because native-llvm is built for all oe-core supported targets.
> >>
> >> Attempting to work around this by symlinking the missing libraries from the native sysroot
> >> into the target sysroot leads to mixed architectures in the final `.rlib`. Specifically,
> >> the object files extracted from those symlinked libraries within `librustc_llvm-<hash>.rlib`
> >> are built for the host, while others are correctly built for the target This results in linker
> >> failures due to file format not recognized.
> >>
> >> To resolve this, we now build llvm-target also for all oe-core supported architectures in
> >> addition to the native-llvm build. This ensures that `llvm-config` and all associated
> >> libraries are built for the correct target, eliminating cross-architecture contamination
> >> and linker issues.
> >>
> >> *We are enabling -DLLVM_INSTALL_UTILS=ON to ensure essential LLVM utilities like FileCheck
> >> are available, as they are required by the Rust build.
> >>
> >> Without this, the build fails with an error as below:
> >> | thread 'main' panicked at src/bootstrap/src/core/sanity.rs:315:21:
> >> | FileCheck executable "poky/build/tmp/work/x86_64-linux/rust-native/1.90.0/recipe-sysroot
> >> -native/usr/bin/FileCheck" does not exist
> >>
> >> *We now add these flags "-Clink-arg=-lz -Clink-arg=-lzstd" because of this following
> >> diff otherwise we will get errors during link time.
> >>
> >> Setup in rust-llvm
> >> -DLLVM_ENABLE_ZLIB=OFF \
> >> -DLLVM_ENABLE_ZSTD=OFF \
> >> -DLLVM_ENABLE_FFI=OFF \
> >>
> >> Setup in llvm
> >> -DLLVM_ENABLE_FFI=ON \
> >>
> >> *When multilibs enabled:
> >>
> >> llvm-config expects static libraries to be located in the lib directory rather than
> >> lib64. However, since we are copying the natively built llvm-config to target sysroot
> >> and running it and llvm-config doesn't know anything about lib64 existence. To accommodate
> >> this without breaking multilib behavior, we are creating a symlink from 'lib' to 'lib64'
> >> directory.
> >>
> >> Previously, when we depended on rust-llvm, this worked because we specified:
> >> -DCMAKE_INSTALL_PREFIX:PATH=${libdir}/llvm-rust
> >>
> >> With this setup, llvm-config was installed inside ${libdir}/llvm-rust, which included
> >> its own bin and lib directories. Thus, llvm-config located in bin would correctly find
> >> the libraries in the adjacent lib directory.
> >>
> >> Even when multilib was enabled or not, llvm-config would still look for libraries under
> >> lib in this structure, so everything functioned as expected.
> >>
> >> Signed-off-by: Deepesh Varatharajan <Deepesh.Varatharajan@windriver.com>
> >> ---
> >>   meta/recipes-devtools/clang/llvm_git.bb   |  2 +-
> >>   meta/recipes-devtools/rust/rust_1.90.0.bb | 39 ++++++++++++++++++++---
> >>   2 files changed, 36 insertions(+), 5 deletions(-)
> >>
> >> diff --git a/meta/recipes-devtools/clang/llvm_git.bb b/meta/recipes-devtools/clang/llvm_git.bb
> >> index d2b060ff88..2f47af8d7a 100644
> >> --- a/meta/recipes-devtools/clang/llvm_git.bb
> >> +++ b/meta/recipes-devtools/clang/llvm_git.bb
> >> @@ -27,7 +27,6 @@ OECMAKE_SOURCEPATH = "${S}/llvm"
> >>   # https://github.com/llvm/llvm-project/blob/main/llvm/CMakeLists.txt
> >>   LLVM_TARGETS_GPU ?= "${@bb.utils.contains_any('DISTRO_FEATURES', 'opencl opengl vulkan', 'AMDGPU;NVPTX;SPIRV', '', d)}"
> >>   LLVM_TARGETS_TO_BUILD ?= "AArch64;ARM;BPF;Mips;PowerPC;RISCV;X86;LoongArch;${LLVM_TARGETS_GPU}"
> >> -LLVM_TARGETS_TO_BUILD:class-target ?= "${@get_clang_host_arch(bb, d)};BPF;${LLVM_TARGETS_GPU}"
> >>
> >>   LLVM_EXPERIMENTAL_TARGETS_TO_BUILD ?= ""
> >>
> >> @@ -37,6 +36,7 @@ HF[vardepvalue] = "${HF}"
> >>
> >>   EXTRA_OECMAKE += "-DCMAKE_BUILD_TYPE=MinSizeRel \
> >>                     -DLLVM_ENABLE_BINDINGS=OFF \
> >> +                  -DLLVM_INSTALL_UTILS=ON \
> >>                     -DLLVM_ENABLE_FFI=ON \
> >>                     -DLLVM_ENABLE_RTTI=ON \
> >>                     -DLLVM_TARGETS_TO_BUILD='${LLVM_TARGETS_TO_BUILD}' \
> >> diff --git a/meta/recipes-devtools/rust/rust_1.90.0.bb b/meta/recipes-devtools/rust/rust_1.90.0.bb
> >> index 5d804c7398..0319d73b93 100644
> >> --- a/meta/recipes-devtools/rust/rust_1.90.0.bb
> >> +++ b/meta/recipes-devtools/rust/rust_1.90.0.bb
> >> @@ -7,7 +7,7 @@ LIC_FILES_CHKSUM = "file://COPYRIGHT;md5=11a3899825f4376896e438c8c753f8dc"
> >>   inherit rust
> >>   inherit cargo_common
> >>
> >> -DEPENDS += "rust-llvm"
> >> +DEPENDS += "llvm"
> >>   # native rust uses cargo/rustc from binary snapshots to bootstrap
> >>   # but everything else should use our native builds
> >>   DEPENDS:append:class-target = " cargo-native rust-native"
> >> @@ -28,8 +28,8 @@ PV .= "${@bb.utils.contains('RUST_CHANNEL', 'stable', '', '-${RUST_CHANNEL}', d)
> >>
> >>   export FORCE_CRATE_HASH = "${BB_TASKHASH}"
> >>
> >> -RUST_ALTERNATE_EXE_PATH ?= "${STAGING_LIBDIR}/llvm-rust/bin/llvm-config"
> >> -RUST_ALTERNATE_EXE_PATH_NATIVE = "${STAGING_LIBDIR_NATIVE}/llvm-rust/bin/llvm-config"
> >> +RUST_ALTERNATE_EXE_PATH ?= "${STAGING_BINDIR}/llvm-config"
> >> +RUST_ALTERNATE_EXE_PATH_NATIVE = "${STAGING_BINDIR_NATIVE}/llvm-config"
> >>
> >>   # We don't want to use bitbakes vendoring because the rust sources do their
> >>   # own vendoring.
> >> @@ -188,6 +188,37 @@ python do_configure() {
> >>       bb.build.exec_func("setup_cargo_environment", d)
> >>   }
> >>
> >> +# llvm-config expects static libraries to be in the 'lib' directory rather than 'lib64' when
> >> +# multilibs enabled. Since we are copying the natively built llvm-config into the target sysroot
> >> +# and executing it there, it will default to searching in 'lib', as it is unaware of the 'lib64'
> >> +# directory. To ensure llvm-config can locate the necessary libraries, create a symlink from 'lib'
> >> +do_compile:append:class-target() {
> >> +    # Ensure llvm-config can find static libraries in multilib setup
> >> +    lib64_dir="${STAGING_DIR_TARGET}/usr/lib64"
> >> +    lib_dir="${STAGING_DIR_TARGET}/usr/lib"
> >> +
> >> +    if [ -d "$lib64_dir" ]; then
> >> +        # If lib does not exist, symlink it to lib64
> >> +        if [ ! -e "$lib_dir" ]; then
> >> +            ln -s lib64 "$lib_dir"
> >> +        fi
> >> +
> >> +        # Only do per-file symlinking if lib is a real directory (not symlink)
> >> +        if [ -d "$lib_dir" ] && [ ! -L "$lib_dir" ]; then
> >> +            for lib64_file in "${lib64_dir}"/libLLVM*.a; do
> >> +                if [ -e "$lib64_file" ]; then
> >> +                    lib_name=$(basename "${lib64_file}")
> >> +                    target_link="${lib_dir}/${lib_name}"
> >> +
> >> +                    if [ ! -e "${target_link}" ]; then
> >> +                        ln -s "../lib64/${lib_name}" "${target_link}"
> >> +                    fi
> >> +                fi
> >> +            done
> >> +        fi
> >> +    fi
> >> +}
> >> +
> >>   rust_runx () {
> >>       echo "COMPILE ${PN}" "$@"
> >>
> >> @@ -199,7 +230,7 @@ rust_runx () {
> >>       unset CXXFLAGS
> >>       unset CPPFLAGS
> >>
> >> -    export RUSTFLAGS="${RUST_DEBUG_REMAP}"
> >> +    export RUSTFLAGS="${RUST_DEBUG_REMAP} -Clink-arg=-lz -Clink-arg=-lzstd"
> >>
> >>       # Copy the natively built llvm-config into the target so we can run it. Horrible,
> >>       # but works!
> >> --
> >> 2.49.0
> >>
> >>
> >> -=-=-=-=-=-=-=-=-=-=-=-
> >> Links: You receive all messages sent to this group.
> >> View/Reply Online (#224888): https://lists.openembedded.org/g/openembedded-core/message/224888
> >> Mute This Topic: https://lists.openembedded.org/mt/115768136/1997914
> >> Group Owner: openembedded-core+owner@lists.openembedded.org
> >> Unsubscribe: https://lists.openembedded.org/g/openembedded-core/unsub [raj.khem@gmail.com]
> >> -=-=-=-=-=-=-=-=-=-=-=-
> >>
Ross Burton Oct. 20, 2025, 11:23 a.m. UTC | #4
Hi,

> On 15 Oct 2025, at 10:59, Varatharajan, Deepesh via lists.openembedded.org <deepesh.varatharajan=windriver.com@lists.openembedded.org> wrote:
> Updated the Rust build to depend on llvm instead.

Because I was curious, I looked at the build stats before and after this series being merged. Here are the diffs for cputime and walltime when I built llvm-native/rust-llvm-native and rust-native:

  PKG                           TASK                   ABSDIFF  RELDIFF  CPUTIME1 -> CPUTIME2
- rust-llvm-native              do_compile           -12241.8s  -100.0%  12241.8s -> 0.0s
- rust-llvm-native              do_unpack               -31.4s  -100.0%     31.4s -> 0.0s
- rust-llvm-native              do_configure             -9.4s  -100.0%      9.4s -> 0.0s
- rust-llvm-native              do_populate_sysroot      -6.2s  -100.0%      6.2s -> 0.0s
+ llvm-project-source-21.1.3    do_patch                  5.8s    +inf%      0.0s -> 5.8s
  rust-native                   do_populate_sysroot       9.5s  +323.0%      2.9s -> 12.5s
+ llvm-native                   do_configure             12.9s    +inf%      0.0s -> 12.9s
+ llvm-native                   do_populate_sysroot      18.6s    +inf%      0.0s -> 18.6s
+ llvm-project-source-21.1.3    do_unpack                20.0s    +inf%      0.0s -> 20.0s
+ llvm-tblgen-native            do_configure             29.0s    +inf%      0.0s -> 29.0s
+ llvm-tblgen-native            do_compile              593.1s    +inf%      0.0s -> 593.1s
  rust-native                   do_install             1724.2s   +26.1%   6611.3s -> 8335.5s
+ llvm-native                   do_compile            12051.6s    +inf%      0.0s -> 12051.6s

  PKG                           TASK          ABSDIFF  RELDIFF  WALLTIME1 -> WALLTIME2
- rust-llvm-native              do_compile    -401.1s  -100.0%     401.1s -> 0.0s
- rust-llvm-native              do_unpack      -23.0s  -100.0%      23.0s -> 0.0s
  rust-native                   do_unpack      -21.3s   -42.5%      50.3s -> 28.9s
- rust-llvm-native              do_configure    -9.0s  -100.0%       9.0s -> 0.0s
+ llvm-project-source-21.1.3    do_unpack        7.0s    +inf%       0.0s -> 7.0s
+ llvm-native                   do_configure    12.3s    +inf%       0.0s -> 12.3s
+ llvm-tblgen-native            do_configure    28.5s    +inf%       0.0s -> 28.5s
+ llvm-tblgen-native            do_compile      30.1s    +inf%       0.0s -> 30.1s
  rust-native                   do_install      33.4s    +6.0%     553.4s -> 586.8s
+ llvm-native                   do_compile     378.0s    +inf%       0.0s -> 378.0s

For llvm vs rust-llvm, I’ve a local tweak to not build some of the GPU backends (as they take a long time) so it’s actually comparing like-for-like, and it’s good to see that the compile time is close.  It’s slightly faster in llvm even though it’s building more backends, so I’m glad my build tweaking was useful.

However, rust-native takes 26% more cpu time (just 6% more wall time, due to parallelisation).  I’m wondering if this is fallout from using -Os instead of -O2, or something else about how we’re building rust-llvm vs llvm.  Insights welcome, but I’ll likely fire a test build without -Os to see how that impacts the numbers later.

Cheers,
Ross
Ross Burton Oct. 20, 2025, 2:40 p.m. UTC | #5
On 20 Oct 2025, at 12:23, Ross Burton via lists.openembedded.org <ross.burton=arm.com@lists.openembedded.org> wrote:
> 
> Hi,
> 
>> On 15 Oct 2025, at 10:59, Varatharajan, Deepesh via lists.openembedded.org <deepesh.varatharajan=windriver.com@lists.openembedded.org> wrote:
>> Updated the Rust build to depend on llvm instead.
> 
> Because I was curious, I looked at the build stats before and after this series being merged. Here are the diffs for cputime and walltime when I built llvm-native/rust-llvm-native and rust-native:
> 
>  PKG                           TASK                   ABSDIFF  RELDIFF  CPUTIME1 -> CPUTIME2
> - rust-llvm-native              do_compile           -12241.8s  -100.0%  12241.8s -> 0.0s
> - rust-llvm-native              do_unpack               -31.4s  -100.0%     31.4s -> 0.0s
> - rust-llvm-native              do_configure             -9.4s  -100.0%      9.4s -> 0.0s
> - rust-llvm-native              do_populate_sysroot      -6.2s  -100.0%      6.2s -> 0.0s
> + llvm-project-source-21.1.3    do_patch                  5.8s    +inf%      0.0s -> 5.8s
>  rust-native                   do_populate_sysroot       9.5s  +323.0%      2.9s -> 12.5s
> + llvm-native                   do_configure             12.9s    +inf%      0.0s -> 12.9s
> + llvm-native                   do_populate_sysroot      18.6s    +inf%      0.0s -> 18.6s
> + llvm-project-source-21.1.3    do_unpack                20.0s    +inf%      0.0s -> 20.0s
> + llvm-tblgen-native            do_configure             29.0s    +inf%      0.0s -> 29.0s
> + llvm-tblgen-native            do_compile              593.1s    +inf%      0.0s -> 593.1s
>  rust-native                   do_install             1724.2s   +26.1%   6611.3s -> 8335.5s
> + llvm-native                   do_compile            12051.6s    +inf%      0.0s -> 12051.6s
> 
>  PKG                           TASK          ABSDIFF  RELDIFF  WALLTIME1 -> WALLTIME2
> - rust-llvm-native              do_compile    -401.1s  -100.0%     401.1s -> 0.0s
> - rust-llvm-native              do_unpack      -23.0s  -100.0%      23.0s -> 0.0s
>  rust-native                   do_unpack      -21.3s   -42.5%      50.3s -> 28.9s
> - rust-llvm-native              do_configure    -9.0s  -100.0%       9.0s -> 0.0s
> + llvm-project-source-21.1.3    do_unpack        7.0s    +inf%       0.0s -> 7.0s
> + llvm-native                   do_configure    12.3s    +inf%       0.0s -> 12.3s
> + llvm-tblgen-native            do_configure    28.5s    +inf%       0.0s -> 28.5s
> + llvm-tblgen-native            do_compile      30.1s    +inf%       0.0s -> 30.1s
>  rust-native                   do_install      33.4s    +6.0%     553.4s -> 586.8s
> + llvm-native                   do_compile     378.0s    +inf%       0.0s -> 378.0s
> 
> For llvm vs rust-llvm, I’ve a local tweak to not build some of the GPU backends (as they take a long time) so it’s actually comparing like-for-like, and it’s good to see that the compile time is close.  It’s slightly faster in llvm even though it’s building more backends, so I’m glad my build tweaking was useful.
> 
> However, rust-native takes 26% more cpu time (just 6% more wall time, due to parallelisation).  I’m wondering if this is fallout from using -Os instead of -O2, or something else about how we’re building rust-llvm vs llvm.  Insights welcome, but I’ll likely fire a test build without -Os to see how that impacts the numbers later.

Followup, comparing current master to master but with LLVM built as RelWithDebInfo instead of MinSizeRel:

  PKG                   TASK                  ABSDIFF   RELDIFF  CPUTIME1 -> CPUTIME2
  rust-native           do_install           -1690.4s    -20.3%   8335.5s -> 6645.1s
  llvm-native           do_compile            6081.7s    +50.5%  12051.6s -> 18133.3s

Cumulative cputime:
  4117.4s    +19.5%    5:52:36.1 (21156.1s) -> 7:01:13.5 (25273.5s)


  PKG                   TASK                 ABSDIFF   RELDIFF  WALLTIME1 -> WALLTIME2
  rust-native           do_install             24.0s     +4.1%     586.8s -> 610.8s
  llvm-native           do_compile            238.9s    +63.2%     378.0s -> 616.8s

Cumulative walltime:
  251.3s    +22.8%    18:24.7 (1104.7s) -> 22:36.0 (1356.0s)

So rust builds a bit faster, but LLVM is a lot slower to build, with a net result that the build is actually slower overall.  I’m happy with the choice to use MinSizeRel in LLVM. 

Ross
Khem Raj Oct. 20, 2025, 3:11 p.m. UTC | #6
On Mon, Oct 20, 2025 at 7:40 AM Ross Burton via lists.openembedded.org
<ross.burton=arm.com@lists.openembedded.org> wrote:
>
> On 20 Oct 2025, at 12:23, Ross Burton via lists.openembedded.org <ross.burton=arm.com@lists.openembedded.org> wrote:
> >
> > Hi,
> >
> >> On 15 Oct 2025, at 10:59, Varatharajan, Deepesh via lists.openembedded.org <deepesh.varatharajan=windriver.com@lists.openembedded.org> wrote:
> >> Updated the Rust build to depend on llvm instead.
> >
> > Because I was curious, I looked at the build stats before and after this series being merged. Here are the diffs for cputime and walltime when I built llvm-native/rust-llvm-native and rust-native:
> >
> >  PKG                           TASK                   ABSDIFF  RELDIFF  CPUTIME1 -> CPUTIME2
> > - rust-llvm-native              do_compile           -12241.8s  -100.0%  12241.8s -> 0.0s
> > - rust-llvm-native              do_unpack               -31.4s  -100.0%     31.4s -> 0.0s
> > - rust-llvm-native              do_configure             -9.4s  -100.0%      9.4s -> 0.0s
> > - rust-llvm-native              do_populate_sysroot      -6.2s  -100.0%      6.2s -> 0.0s
> > + llvm-project-source-21.1.3    do_patch                  5.8s    +inf%      0.0s -> 5.8s
> >  rust-native                   do_populate_sysroot       9.5s  +323.0%      2.9s -> 12.5s
> > + llvm-native                   do_configure             12.9s    +inf%      0.0s -> 12.9s
> > + llvm-native                   do_populate_sysroot      18.6s    +inf%      0.0s -> 18.6s
> > + llvm-project-source-21.1.3    do_unpack                20.0s    +inf%      0.0s -> 20.0s
> > + llvm-tblgen-native            do_configure             29.0s    +inf%      0.0s -> 29.0s
> > + llvm-tblgen-native            do_compile              593.1s    +inf%      0.0s -> 593.1s
> >  rust-native                   do_install             1724.2s   +26.1%   6611.3s -> 8335.5s
> > + llvm-native                   do_compile            12051.6s    +inf%      0.0s -> 12051.6s
> >
> >  PKG                           TASK          ABSDIFF  RELDIFF  WALLTIME1 -> WALLTIME2
> > - rust-llvm-native              do_compile    -401.1s  -100.0%     401.1s -> 0.0s
> > - rust-llvm-native              do_unpack      -23.0s  -100.0%      23.0s -> 0.0s
> >  rust-native                   do_unpack      -21.3s   -42.5%      50.3s -> 28.9s
> > - rust-llvm-native              do_configure    -9.0s  -100.0%       9.0s -> 0.0s
> > + llvm-project-source-21.1.3    do_unpack        7.0s    +inf%       0.0s -> 7.0s
> > + llvm-native                   do_configure    12.3s    +inf%       0.0s -> 12.3s
> > + llvm-tblgen-native            do_configure    28.5s    +inf%       0.0s -> 28.5s
> > + llvm-tblgen-native            do_compile      30.1s    +inf%       0.0s -> 30.1s
> >  rust-native                   do_install      33.4s    +6.0%     553.4s -> 586.8s
> > + llvm-native                   do_compile     378.0s    +inf%       0.0s -> 378.0s
> >
> > For llvm vs rust-llvm, I’ve a local tweak to not build some of the GPU backends (as they take a long time) so it’s actually comparing like-for-like, and it’s good to see that the compile time is close.  It’s slightly faster in llvm even though it’s building more backends, so I’m glad my build tweaking was useful.
> >
> > However, rust-native takes 26% more cpu time (just 6% more wall time, due to parallelisation).  I’m wondering if this is fallout from using -Os instead of -O2, or something else about how we’re building rust-llvm vs llvm.  Insights welcome, but I’ll likely fire a test build without -Os to see how that impacts the numbers later.
>
> Followup, comparing current master to master but with LLVM built as RelWithDebInfo instead of MinSizeRel:
>
>   PKG                   TASK                  ABSDIFF   RELDIFF  CPUTIME1 -> CPUTIME2
>   rust-native           do_install           -1690.4s    -20.3%   8335.5s -> 6645.1s
>   llvm-native           do_compile            6081.7s    +50.5%  12051.6s -> 18133.3s
>
> Cumulative cputime:
>   4117.4s    +19.5%    5:52:36.1 (21156.1s) -> 7:01:13.5 (25273.5s)
>
>
>   PKG                   TASK                 ABSDIFF   RELDIFF  WALLTIME1 -> WALLTIME2
>   rust-native           do_install             24.0s     +4.1%     586.8s -> 610.8s
>   llvm-native           do_compile            238.9s    +63.2%     378.0s -> 616.8s
>
> Cumulative walltime:
>   251.3s    +22.8%    18:24.7 (1104.7s) -> 22:36.0 (1356.0s)
>
> So rust builds a bit faster, but LLVM is a lot slower to build, with a net result that the build is actually slower overall.  I’m happy with the choice to use MinSizeRel in LLVM.

A large set of users of OE would not build compiler as often as some
system build engineers who build distros for them will do, so I wonder
how fast is resulting compiler in compiling applications, because in
such
settings it will be used in often and save a lot of time for users
such that spending extra time in compiling it in OE can be justified.
Of couse I am not recommending that
OE adopts that option as default.

>
> Ross
> -=-=-=-=-=-=-=-=-=-=-=-
> Links: You receive all messages sent to this group.
> View/Reply Online (#225121): https://lists.openembedded.org/g/openembedded-core/message/225121
> Mute This Topic: https://lists.openembedded.org/mt/115768136/1997914
> Group Owner: openembedded-core+owner@lists.openembedded.org
> Unsubscribe: https://lists.openembedded.org/g/openembedded-core/unsub [raj.khem@gmail.com]
> -=-=-=-=-=-=-=-=-=-=-=-
>
Deepesh Varatharajan Oct. 21, 2025, 6:09 a.m. UTC | #7
On 18-10-2025 22:41, Khem Raj wrote:
> CAUTION: This email comes from a non Wind River email account!
> Do not click links or open attachments unless you recognize the sender and know the content is safe.
>
> On Fri, Oct 17, 2025 at 11:42 PM Deepesh Varatharajan
> <deepesh.varatharajan@windriver.com> wrote:
>>
>> On 17-10-2025 11:31, Khem Raj wrote:
>>> CAUTION: This email comes from a non Wind River email account!
>>> Do not click links or open attachments unless you recognize the sender and know the content is safe.
>>>
>>> I am seeing a build regression when using clang as default compiler
>>>
>>> https://errors.yoctoproject.org/Errors/Details/885430/
>>>
>>> PREFERRED_TOOLCHAIN_TARGET ?= "clang"
>>> PREFERRED_TOOLCHAIN_SDK ?= "clang"
>>> TOOLCHAIN_NATIVE:pn-rust ?= "clang"
>>> TOOLCHAIN_NATIVE:pn-rust-native ?= "clang"
>>> TOOLCHAIN_NATIVE:pn-nativesdk-rust ?= "clang"
>> Hi Khem,
>>
>> WIth the above mentioned conf in local.conf, I tried building rust for
>> qemuarm and qemuarm64 quite
>> few times and the build completed successfully without any issues for
>> both native and target. Do I need
>> to add any other layers on top of poky ? Do you have any branch where I
>> can clone and reproduce the
>> issue ? Am I missing any step in reproducing the issue ?
>>
> Yeah, I missed a setting which I think could be the reason
>
> TC_CXX_RUNTIME = "llvm"
Hi Khem,

After adding the above in locl.conf, reproduced the issue. I've looked 
into the issue and
here’s what I found:

Currently, both rust-native and rust-target rely on the natively built 
llvm-config binary.
However, upon inspecting the runtime dependencies of llvm-config, I 
noticed the following:

$ ldd ./llvm-config
         linux-vdso.so.1 =>  (0x00007ffdec9eb000)
         libstdc++.so.6 => /usr/lib/x86_64-linux-gnu/libstdc++.so.6
         libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6
         libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1
         libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6

As shown, llvm-config is linked against libstdc++. Meanwhile, we're 
enforcing Rust to be
built using libc++, and this mismatch is causing symbol resolution 
issues at runtime.

To address the ABI mismatch, I tried building llvm-native with libc++ by 
introducing a
dependency on libcxx-native. However, this leads to a circular dependency:
     >llvm-native depends on libcxx-native
     >libcxx-native depends on clang-native
     >clang-native depends back on llvm-native
This cycle blocks the build.

One possible solution could be to create a separate llvm-config recipe 
that builds with a
dependency on libcxx-native, and have Rust depend on that version 
specifically.

Do we have any alternative ways to break this circular dependency?

Regards,
Deepesh
>
>
>> Regards,
>> Deepesh
>>> On Wed, Oct 15, 2025 at 2:59 AM Varatharajan, Deepesh via
>>> lists.openembedded.org
>>> <deepesh.varatharajan=windriver.com@lists.openembedded.org> wrote:
>>>> From: Deepesh Varatharajan <Deepesh.Varatharajan@windriver.com>
>>>>
>>>> Updated the Rust build to depend on llvm instead.
>>>>
>>>> *Summary of discussion with the rust upstream about using latest LLVM instead of Rust maintained LLVM fork.
>>>> https://internals.rust-lang.org/t/can-we-use-proper-clang-instead-of-llvm-fork-what-rust-uses/23489
>>>>
>>>> *Upstream LLVM is generally compatible:
>>>> - Rust does support building with upstream (vanilla) LLVM, especially the latest
>>>> major release and the one or two preceding ones.
>>>> https://rustc-dev-guide.rust-lang.org/backend/updating-llvm.html#updating-llvm
>>>>
>>>> *Impact on Yocto Rust upgrades:
>>>> - Rust upgrades shall always check for updates on rust forked llvm and backport
>>>> the relevant patches to llvm.
>>>>
>>>> *Regarding the rust forked llvm local patches:
>>>> - There are no local patches on rust forked llvm other than the backported fixes
>>>> from llvm master.
>>>>
>>>> *We are copying the natively built `llvm-config` binary into the target sysroot and running
>>>> it. However, this `llvm-config` has compile time dependencies on various other arch's LLVM
>>>> libraries because native-llvm is built for all oe-core supported targets.
>>>>
>>>> Attempting to work around this by symlinking the missing libraries from the native sysroot
>>>> into the target sysroot leads to mixed architectures in the final `.rlib`. Specifically,
>>>> the object files extracted from those symlinked libraries within `librustc_llvm-<hash>.rlib`
>>>> are built for the host, while others are correctly built for the target This results in linker
>>>> failures due to file format not recognized.
>>>>
>>>> To resolve this, we now build llvm-target also for all oe-core supported architectures in
>>>> addition to the native-llvm build. This ensures that `llvm-config` and all associated
>>>> libraries are built for the correct target, eliminating cross-architecture contamination
>>>> and linker issues.
>>>>
>>>> *We are enabling -DLLVM_INSTALL_UTILS=ON to ensure essential LLVM utilities like FileCheck
>>>> are available, as they are required by the Rust build.
>>>>
>>>> Without this, the build fails with an error as below:
>>>> | thread 'main' panicked at src/bootstrap/src/core/sanity.rs:315:21:
>>>> | FileCheck executable "poky/build/tmp/work/x86_64-linux/rust-native/1.90.0/recipe-sysroot
>>>> -native/usr/bin/FileCheck" does not exist
>>>>
>>>> *We now add these flags "-Clink-arg=-lz -Clink-arg=-lzstd" because of this following
>>>> diff otherwise we will get errors during link time.
>>>>
>>>> Setup in rust-llvm
>>>> -DLLVM_ENABLE_ZLIB=OFF \
>>>> -DLLVM_ENABLE_ZSTD=OFF \
>>>> -DLLVM_ENABLE_FFI=OFF \
>>>>
>>>> Setup in llvm
>>>> -DLLVM_ENABLE_FFI=ON \
>>>>
>>>> *When multilibs enabled:
>>>>
>>>> llvm-config expects static libraries to be located in the lib directory rather than
>>>> lib64. However, since we are copying the natively built llvm-config to target sysroot
>>>> and running it and llvm-config doesn't know anything about lib64 existence. To accommodate
>>>> this without breaking multilib behavior, we are creating a symlink from 'lib' to 'lib64'
>>>> directory.
>>>>
>>>> Previously, when we depended on rust-llvm, this worked because we specified:
>>>> -DCMAKE_INSTALL_PREFIX:PATH=${libdir}/llvm-rust
>>>>
>>>> With this setup, llvm-config was installed inside ${libdir}/llvm-rust, which included
>>>> its own bin and lib directories. Thus, llvm-config located in bin would correctly find
>>>> the libraries in the adjacent lib directory.
>>>>
>>>> Even when multilib was enabled or not, llvm-config would still look for libraries under
>>>> lib in this structure, so everything functioned as expected.
>>>>
>>>> Signed-off-by: Deepesh Varatharajan <Deepesh.Varatharajan@windriver.com>
>>>> ---
>>>>    meta/recipes-devtools/clang/llvm_git.bb   |  2 +-
>>>>    meta/recipes-devtools/rust/rust_1.90.0.bb | 39 ++++++++++++++++++++---
>>>>    2 files changed, 36 insertions(+), 5 deletions(-)
>>>>
>>>> diff --git a/meta/recipes-devtools/clang/llvm_git.bb b/meta/recipes-devtools/clang/llvm_git.bb
>>>> index d2b060ff88..2f47af8d7a 100644
>>>> --- a/meta/recipes-devtools/clang/llvm_git.bb
>>>> +++ b/meta/recipes-devtools/clang/llvm_git.bb
>>>> @@ -27,7 +27,6 @@ OECMAKE_SOURCEPATH = "${S}/llvm"
>>>>    # https://github.com/llvm/llvm-project/blob/main/llvm/CMakeLists.txt
>>>>    LLVM_TARGETS_GPU ?= "${@bb.utils.contains_any('DISTRO_FEATURES', 'opencl opengl vulkan', 'AMDGPU;NVPTX;SPIRV', '', d)}"
>>>>    LLVM_TARGETS_TO_BUILD ?= "AArch64;ARM;BPF;Mips;PowerPC;RISCV;X86;LoongArch;${LLVM_TARGETS_GPU}"
>>>> -LLVM_TARGETS_TO_BUILD:class-target ?= "${@get_clang_host_arch(bb, d)};BPF;${LLVM_TARGETS_GPU}"
>>>>
>>>>    LLVM_EXPERIMENTAL_TARGETS_TO_BUILD ?= ""
>>>>
>>>> @@ -37,6 +36,7 @@ HF[vardepvalue] = "${HF}"
>>>>
>>>>    EXTRA_OECMAKE += "-DCMAKE_BUILD_TYPE=MinSizeRel \
>>>>                      -DLLVM_ENABLE_BINDINGS=OFF \
>>>> +                  -DLLVM_INSTALL_UTILS=ON \
>>>>                      -DLLVM_ENABLE_FFI=ON \
>>>>                      -DLLVM_ENABLE_RTTI=ON \
>>>>                      -DLLVM_TARGETS_TO_BUILD='${LLVM_TARGETS_TO_BUILD}' \
>>>> diff --git a/meta/recipes-devtools/rust/rust_1.90.0.bb b/meta/recipes-devtools/rust/rust_1.90.0.bb
>>>> index 5d804c7398..0319d73b93 100644
>>>> --- a/meta/recipes-devtools/rust/rust_1.90.0.bb
>>>> +++ b/meta/recipes-devtools/rust/rust_1.90.0.bb
>>>> @@ -7,7 +7,7 @@ LIC_FILES_CHKSUM = "file://COPYRIGHT;md5=11a3899825f4376896e438c8c753f8dc"
>>>>    inherit rust
>>>>    inherit cargo_common
>>>>
>>>> -DEPENDS += "rust-llvm"
>>>> +DEPENDS += "llvm"
>>>>    # native rust uses cargo/rustc from binary snapshots to bootstrap
>>>>    # but everything else should use our native builds
>>>>    DEPENDS:append:class-target = " cargo-native rust-native"
>>>> @@ -28,8 +28,8 @@ PV .= "${@bb.utils.contains('RUST_CHANNEL', 'stable', '', '-${RUST_CHANNEL}', d)
>>>>
>>>>    export FORCE_CRATE_HASH = "${BB_TASKHASH}"
>>>>
>>>> -RUST_ALTERNATE_EXE_PATH ?= "${STAGING_LIBDIR}/llvm-rust/bin/llvm-config"
>>>> -RUST_ALTERNATE_EXE_PATH_NATIVE = "${STAGING_LIBDIR_NATIVE}/llvm-rust/bin/llvm-config"
>>>> +RUST_ALTERNATE_EXE_PATH ?= "${STAGING_BINDIR}/llvm-config"
>>>> +RUST_ALTERNATE_EXE_PATH_NATIVE = "${STAGING_BINDIR_NATIVE}/llvm-config"
>>>>
>>>>    # We don't want to use bitbakes vendoring because the rust sources do their
>>>>    # own vendoring.
>>>> @@ -188,6 +188,37 @@ python do_configure() {
>>>>        bb.build.exec_func("setup_cargo_environment", d)
>>>>    }
>>>>
>>>> +# llvm-config expects static libraries to be in the 'lib' directory rather than 'lib64' when
>>>> +# multilibs enabled. Since we are copying the natively built llvm-config into the target sysroot
>>>> +# and executing it there, it will default to searching in 'lib', as it is unaware of the 'lib64'
>>>> +# directory. To ensure llvm-config can locate the necessary libraries, create a symlink from 'lib'
>>>> +do_compile:append:class-target() {
>>>> +    # Ensure llvm-config can find static libraries in multilib setup
>>>> +    lib64_dir="${STAGING_DIR_TARGET}/usr/lib64"
>>>> +    lib_dir="${STAGING_DIR_TARGET}/usr/lib"
>>>> +
>>>> +    if [ -d "$lib64_dir" ]; then
>>>> +        # If lib does not exist, symlink it to lib64
>>>> +        if [ ! -e "$lib_dir" ]; then
>>>> +            ln -s lib64 "$lib_dir"
>>>> +        fi
>>>> +
>>>> +        # Only do per-file symlinking if lib is a real directory (not symlink)
>>>> +        if [ -d "$lib_dir" ] && [ ! -L "$lib_dir" ]; then
>>>> +            for lib64_file in "${lib64_dir}"/libLLVM*.a; do
>>>> +                if [ -e "$lib64_file" ]; then
>>>> +                    lib_name=$(basename "${lib64_file}")
>>>> +                    target_link="${lib_dir}/${lib_name}"
>>>> +
>>>> +                    if [ ! -e "${target_link}" ]; then
>>>> +                        ln -s "../lib64/${lib_name}" "${target_link}"
>>>> +                    fi
>>>> +                fi
>>>> +            done
>>>> +        fi
>>>> +    fi
>>>> +}
>>>> +
>>>>    rust_runx () {
>>>>        echo "COMPILE ${PN}" "$@"
>>>>
>>>> @@ -199,7 +230,7 @@ rust_runx () {
>>>>        unset CXXFLAGS
>>>>        unset CPPFLAGS
>>>>
>>>> -    export RUSTFLAGS="${RUST_DEBUG_REMAP}"
>>>> +    export RUSTFLAGS="${RUST_DEBUG_REMAP} -Clink-arg=-lz -Clink-arg=-lzstd"
>>>>
>>>>        # Copy the natively built llvm-config into the target so we can run it. Horrible,
>>>>        # but works!
>>>> --
>>>> 2.49.0
>>>>
>>>>
>>>> -=-=-=-=-=-=-=-=-=-=-=-
>>>> Links: You receive all messages sent to this group.
>>>> View/Reply Online (#224888): https://lists.openembedded.org/g/openembedded-core/message/224888
>>>> Mute This Topic: https://lists.openembedded.org/mt/115768136/1997914
>>>> Group Owner: openembedded-core+owner@lists.openembedded.org
>>>> Unsubscribe: https://lists.openembedded.org/g/openembedded-core/unsub [raj.khem@gmail.com]
>>>> -=-=-=-=-=-=-=-=-=-=-=-
>>>>
diff mbox series

Patch

diff otherwise we will get errors during link time.

Setup in rust-llvm
-DLLVM_ENABLE_ZLIB=OFF \
-DLLVM_ENABLE_ZSTD=OFF \
-DLLVM_ENABLE_FFI=OFF \

Setup in llvm
-DLLVM_ENABLE_FFI=ON \

*When multilibs enabled:

llvm-config expects static libraries to be located in the lib directory rather than
lib64. However, since we are copying the natively built llvm-config to target sysroot
and running it and llvm-config doesn't know anything about lib64 existence. To accommodate
this without breaking multilib behavior, we are creating a symlink from 'lib' to 'lib64'
directory.

Previously, when we depended on rust-llvm, this worked because we specified:
-DCMAKE_INSTALL_PREFIX:PATH=${libdir}/llvm-rust

With this setup, llvm-config was installed inside ${libdir}/llvm-rust, which included
its own bin and lib directories. Thus, llvm-config located in bin would correctly find
the libraries in the adjacent lib directory.

Even when multilib was enabled or not, llvm-config would still look for libraries under
lib in this structure, so everything functioned as expected.

Signed-off-by: Deepesh Varatharajan <Deepesh.Varatharajan@windriver.com>
---
 meta/recipes-devtools/clang/llvm_git.bb   |  2 +-
 meta/recipes-devtools/rust/rust_1.90.0.bb | 39 ++++++++++++++++++++---
 2 files changed, 36 insertions(+), 5 deletions(-)

diff --git a/meta/recipes-devtools/clang/llvm_git.bb b/meta/recipes-devtools/clang/llvm_git.bb
index d2b060ff88..2f47af8d7a 100644
--- a/meta/recipes-devtools/clang/llvm_git.bb
+++ b/meta/recipes-devtools/clang/llvm_git.bb
@@ -27,7 +27,6 @@  OECMAKE_SOURCEPATH = "${S}/llvm"
 # https://github.com/llvm/llvm-project/blob/main/llvm/CMakeLists.txt
 LLVM_TARGETS_GPU ?= "${@bb.utils.contains_any('DISTRO_FEATURES', 'opencl opengl vulkan', 'AMDGPU;NVPTX;SPIRV', '', d)}"
 LLVM_TARGETS_TO_BUILD ?= "AArch64;ARM;BPF;Mips;PowerPC;RISCV;X86;LoongArch;${LLVM_TARGETS_GPU}"
-LLVM_TARGETS_TO_BUILD:class-target ?= "${@get_clang_host_arch(bb, d)};BPF;${LLVM_TARGETS_GPU}"
 
 LLVM_EXPERIMENTAL_TARGETS_TO_BUILD ?= ""
 
@@ -37,6 +36,7 @@  HF[vardepvalue] = "${HF}"
 
 EXTRA_OECMAKE += "-DCMAKE_BUILD_TYPE=MinSizeRel \
                   -DLLVM_ENABLE_BINDINGS=OFF \
+                  -DLLVM_INSTALL_UTILS=ON \
                   -DLLVM_ENABLE_FFI=ON \
                   -DLLVM_ENABLE_RTTI=ON \
                   -DLLVM_TARGETS_TO_BUILD='${LLVM_TARGETS_TO_BUILD}' \
diff --git a/meta/recipes-devtools/rust/rust_1.90.0.bb b/meta/recipes-devtools/rust/rust_1.90.0.bb
index 5d804c7398..0319d73b93 100644
--- a/meta/recipes-devtools/rust/rust_1.90.0.bb
+++ b/meta/recipes-devtools/rust/rust_1.90.0.bb
@@ -7,7 +7,7 @@  LIC_FILES_CHKSUM = "file://COPYRIGHT;md5=11a3899825f4376896e438c8c753f8dc"
 inherit rust
 inherit cargo_common
 
-DEPENDS += "rust-llvm"
+DEPENDS += "llvm"
 # native rust uses cargo/rustc from binary snapshots to bootstrap
 # but everything else should use our native builds
 DEPENDS:append:class-target = " cargo-native rust-native"
@@ -28,8 +28,8 @@  PV .= "${@bb.utils.contains('RUST_CHANNEL', 'stable', '', '-${RUST_CHANNEL}', d)
 
 export FORCE_CRATE_HASH = "${BB_TASKHASH}"
 
-RUST_ALTERNATE_EXE_PATH ?= "${STAGING_LIBDIR}/llvm-rust/bin/llvm-config"
-RUST_ALTERNATE_EXE_PATH_NATIVE = "${STAGING_LIBDIR_NATIVE}/llvm-rust/bin/llvm-config"
+RUST_ALTERNATE_EXE_PATH ?= "${STAGING_BINDIR}/llvm-config"
+RUST_ALTERNATE_EXE_PATH_NATIVE = "${STAGING_BINDIR_NATIVE}/llvm-config"
 
 # We don't want to use bitbakes vendoring because the rust sources do their
 # own vendoring.
@@ -188,6 +188,37 @@  python do_configure() {
     bb.build.exec_func("setup_cargo_environment", d)
 }
 
+# llvm-config expects static libraries to be in the 'lib' directory rather than 'lib64' when
+# multilibs enabled. Since we are copying the natively built llvm-config into the target sysroot
+# and executing it there, it will default to searching in 'lib', as it is unaware of the 'lib64'
+# directory. To ensure llvm-config can locate the necessary libraries, create a symlink from 'lib'
+do_compile:append:class-target() {
+    # Ensure llvm-config can find static libraries in multilib setup
+    lib64_dir="${STAGING_DIR_TARGET}/usr/lib64"
+    lib_dir="${STAGING_DIR_TARGET}/usr/lib"
+
+    if [ -d "$lib64_dir" ]; then
+        # If lib does not exist, symlink it to lib64
+        if [ ! -e "$lib_dir" ]; then
+            ln -s lib64 "$lib_dir"
+        fi
+
+        # Only do per-file symlinking if lib is a real directory (not symlink)
+        if [ -d "$lib_dir" ] && [ ! -L "$lib_dir" ]; then
+            for lib64_file in "${lib64_dir}"/libLLVM*.a; do
+                if [ -e "$lib64_file" ]; then
+                    lib_name=$(basename "${lib64_file}")
+                    target_link="${lib_dir}/${lib_name}"
+
+                    if [ ! -e "${target_link}" ]; then
+                        ln -s "../lib64/${lib_name}" "${target_link}"
+                    fi
+                fi
+            done
+        fi
+    fi
+}
+
 rust_runx () {
     echo "COMPILE ${PN}" "$@"
 
@@ -199,7 +230,7 @@  rust_runx () {
     unset CXXFLAGS
     unset CPPFLAGS
 
-    export RUSTFLAGS="${RUST_DEBUG_REMAP}"
+    export RUSTFLAGS="${RUST_DEBUG_REMAP} -Clink-arg=-lz -Clink-arg=-lzstd"
 
     # Copy the natively built llvm-config into the target so we can run it. Horrible,
     # but works!