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[V2,1/2] rust: Use clang instead of rust-llvm

Message ID 20250926100120.3731171-1-Deepesh.Varatharajan@windriver.com
State New
Headers show
Series [V2,1/2] rust: Use clang instead of rust-llvm | expand

Commit Message

Deepesh Varatharajan Sept. 26, 2025, 10:01 a.m. UTC 
From: Deepesh Varatharajan <Deepesh.Varatharajan@windriver.com>

Updated the Rust build to depend on Clang 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 clang's 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 now add these flags "-Clink-arg=-lz -Clink-arg=-lzstd" because of this following

Comments

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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 clang
-DLLVM_ENABLE_FFI=ON \
-DLLVM_ENABLE_ZSTD=ON \

*When multilibs enabled:

llvm-config expects static libraries to be located in the lib directory rather than
lib64. However, since LLVM is built as a non-multilib component, the lib directory
doesn't contain any library files. To accommodate this without breaking multilib
behavior, we copy the required library files appropriately.

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.

*Changes needs to be done when llvm splits from clang:
In rust recipe:
Update the dependency from:
DEPENDS += "ninja-native clang" to DEPENDS += "ninja-native llvm"

In llvm recipe:
Apply the same changes that were made in the Clang recipe, as those
configurations have now been moved to the LLVM recipe after the split.

Signed-off-by: Deepesh Varatharajan <Deepesh.Varatharajan@windriver.com>
---
 meta/recipes-devtools/clang/clang_git.bb     |  4 ++--
 meta/recipes-devtools/clang/common-clang.inc |  6 +++---
 meta/recipes-devtools/rust/rust-source.inc   |  1 -
 meta/recipes-devtools/rust/rust_1.90.0.bb    | 18 ++++++++++++++----
 4 files changed, 19 insertions(+), 10 deletions(-)

diff --git a/meta/recipes-devtools/clang/clang_git.bb b/meta/recipes-devtools/clang/clang_git.bb
index 53bca1c24f..3e117b308b 100644
--- a/meta/recipes-devtools/clang/clang_git.bb
+++ b/meta/recipes-devtools/clang/clang_git.bb
@@ -83,7 +83,6 @@  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 ?= ""
 
@@ -107,6 +106,7 @@  EXTRA_OECMAKE += "-DLLVM_ENABLE_ASSERTIONS=OFF \
                   -DLLVM_ENABLE_PIC=ON \
                   -DCLANG_DEFAULT_PIE_ON_LINUX=ON \
                   -DLLVM_BINDINGS_LIST='' \
+		  -DLLVM_INSTALL_UTILS=ON \
                   -DLLVM_ENABLE_FFI=ON \
                   -DLLVM_ENABLE_ZSTD=ON \
                   -DFFI_INCLUDE_DIR=$(pkg-config --variable=includedir libffi) \
@@ -137,7 +137,7 @@  EXTRA_OECMAKE:append:class-target = "\
                   -DCMAKE_AR=${STAGING_BINDIR_TOOLCHAIN}/${TARGET_PREFIX}llvm-ar \
                   -DCMAKE_NM=${STAGING_BINDIR_TOOLCHAIN}/${TARGET_PREFIX}llvm-nm \
                   -DCMAKE_STRIP=${STAGING_BINDIR_TOOLCHAIN}/${TARGET_PREFIX}llvm-strip \
-                  -DLLVM_TARGET_ARCH=${HOST_ARCH} \
+                  -DLLVM_TARGET_ARCH=${@get_clang_target_arch(bb, d)} \
                   -DLLVM_DEFAULT_TARGET_TRIPLE=${TARGET_SYS}${HF} \
                   -DLLVM_HOST_TRIPLE=${TARGET_SYS}${HF} \
                   -DLLVM_LIBDIR_SUFFIX=${LLVM_LIBDIR_SUFFIX} \
diff --git a/meta/recipes-devtools/clang/common-clang.inc b/meta/recipes-devtools/clang/common-clang.inc
index bf3a63914a..c22e3c1b19 100644
--- a/meta/recipes-devtools/clang/common-clang.inc
+++ b/meta/recipes-devtools/clang/common-clang.inc
@@ -30,10 +30,10 @@  def get_clang_arch(bb, d, arch_var):
     elif re.match('aarch64$', a):                      return 'AArch64'
     elif re.match('aarch64_be$', a):                   return 'AArch64'
     elif re.match('mips(isa|)(32|64|)(r6|)(el|)$', a): return 'Mips'
-    elif re.match('riscv32$', a):                      return 'RISCV'
-    elif re.match('riscv64$', a):                      return 'RISCV'
+    elif re.match('riscv32$', a):                      return 'riscv32'
+    elif re.match('riscv64$', a):                      return 'riscv64'
     elif re.match('p(pc|owerpc)(|64)', a):             return 'PowerPC'
-    elif re.match('loongarch64$', a):                  return 'LoongArch'
+    elif re.match('loongarch64$', a):                  return 'loongarch64'
     else:
         bb.fatal("Unhandled architecture %s" % arch_val)
         return ""
diff --git a/meta/recipes-devtools/rust/rust-source.inc b/meta/recipes-devtools/rust/rust-source.inc
index cf8274b443..ac814c67b6 100644
--- a/meta/recipes-devtools/rust/rust-source.inc
+++ b/meta/recipes-devtools/rust/rust-source.inc
@@ -7,7 +7,6 @@  SRC_URI += "https://static.rust-lang.org/dist/rustc-${RUST_VERSION}-src.tar.xz;n
             file://oeqa-selftest-Increase-timeout-in-process-sigpipe-ru.patch;patchdir=${RUSTSRC} \
             file://0001-src-core-build_steps-tool.rs-switch-off-lto-for-rust.patch;patchdir=${RUSTSRC} \
             file://revert-link-std-statically-in-rustc_driver-feature.patch;patchdir=${RUSTSRC} \
-            file://0001-libunwind-Use-gcs-instead-of-gcs-target-attribute.patch;patchdir=${RUSTSRC} \
             file://0001-riscv32-Define-plain-syscalls-as-their-time64-varian.patch;patchdir=${RUSTSRC} \
 "
 SRC_URI[rust.sha256sum] = "6bfeaddd90ffda2f063492b092bfed925c4b8c701579baf4b1316e021470daac"
diff --git a/meta/recipes-devtools/rust/rust_1.90.0.bb b/meta/recipes-devtools/rust/rust_1.90.0.bb
index 5d804c7398..c2cb8f8829 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 += "ninja-native clang"
 # 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 +188,16 @@  python do_configure() {
     bb.build.exec_func("setup_cargo_environment", d)
 }
 
+#llvm-config expecting static libraries in 'lib' instead of 'lib64'.
+#Since LLVM is built as a non-multilib component, the 'lib' directory 
+#doesn't have any library files when multilibs enabled. So, copying 
+#library files without impacting multilib behavior.
+do_compile:append:class-target() {
+if [ -d ${STAGING_DIR_TARGET}/usr/lib64 ]; then
+    cp ${STAGING_DIR_TARGET}/usr/lib64/libLLVM*.a ${STAGING_DIR_TARGET}/usr/lib/.
+fi
+}
+
 rust_runx () {
     echo "COMPILE ${PN}" "$@"
 
@@ -199,7 +209,7 @@  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!