diff mbox series

musl: read ld-musl-$ARCH.path from /etc with usrmerge

Message ID 20261022025520.234942-2-mark.yang@lge.com
State New
Headers show
Series musl: read ld-musl-$ARCH.path from /etc with usrmerge | expand

Commit Message

mark.yang Oct. 22, 2026, 2:55 a.m. UTC 
From: "mark.yang" <mark.yang@lge.com>

Make the dynamic linker read /etc/ld-musl-$ARCH.path when PT_INTERP
points to /usr/lib.

Non-multilib builds do not notice the problem today. We are working
towards musl with multilib. There a 64-bit program with /usr/lib in
PT_INTERP loads the lib32 copy of a library from /usr/lib and fails
with "Exec format error".

With usrmerge the dynamic linker is /usr/lib/ld-musl-$ARCH.so.1, and
gcc and clang put this path into PT_INTERP. musl drops the last two
components of PT_INTERP and appends /etc/ld-musl-$ARCH.path to the
rest. This gives /usr/etc/ld-musl-$ARCH.path, which does not exist.

ld-musl-$ARCH.path is the musl counterpart of ld.so.conf. It lists the
directories where the dynamic linker looks for shared libraries after
LD_LIBRARY_PATH and RPATH, and when present it replaces the built-in
default path.

The musl recipe installs it in /etc with base_libdir and libdir of the
variant. The file name carries the architecture, so each multilib
variant has its own list, and a 64-bit program would search
/usr/lib64 only.

When the file is not found, musl falls back to its default path.
Patch 0002 sets it to syslibdir:libdir, see 2da79f021b ("musl: Create
default library search path based on configuration").

Reference: https://git.openembedded.org/openembedded-core/commit/?id=2da79f021b5525ea5b56a86563905a67fc958fa5

Without multilib the libraries are in /usr/lib, which the default path
covers, so nothing shows. A 64-bit multilib build gets
/usr/lib:/usr/lib64 and looks in /usr/lib first, so a 64-bit program
loads the lib32 copies of its libraries from there and fails.

Treat a /usr prefix as the root, so /usr/lib/ld-musl-$ARCH.so.1 reads
/etc/ld-musl-$ARCH.path like /lib/ld-musl-$ARCH.so.1 does. Without
usrmerge PT_INTERP starts with /lib, and nothing changes.

  PT_INTERP                        file musl opens
                                   before                                     after
  /usr/lib/ld-musl-aarch64.so.1    /usr/etc/ld-musl-aarch64.path (missing)    /etc/ld-musl-aarch64.path
  /lib/ld-musl-aarch64.so.1        /etc/ld-musl-aarch64.path                  /etc/ld-musl-aarch64.path

Signed-off-by: mark.yang <mark.yang@lge.com>
---
 ...ath-file-from-etc-when-the-loader-is.patch | 35 +++++++++++++++++++
 meta/recipes-core/musl/musl_git.bb            |  1 +
 2 files changed, 36 insertions(+)
 create mode 100644 meta/recipes-core/musl/musl/0004-ldso-read-the-.path-file-from-etc-when-the-loader-is.patch

Comments

Khem Raj Oct. 22, 2026, 5:35 a.m. UTC | #1 
I think you might want to look
into 0002-ldso-Use-syslibdir-and-libdir-as-default-pathes-to-l.patch
The recipe sets --syslibdir=${nonarch_base_libdir}, which is right for
where the loader lives
this patch then builds the fallback search path from that same value,
giving /usr/lib:/usr/lib64 for a 64-bit multilib build.
That fallback is wrong whenever the .path file is missing or unreadable. I
wonder if this patch
should use ${base_libdir} for the search path. then you wont need this
patch.

instead of hardcoding /usr A sturdier option is to pass
-DSYSCONFDIR='"${sysconfdir}"'

Upstream-status says Inappropriate but I think any distro that uses
usrmerge will have this problem
worth checking with upstream musl community.

On Wed, Oct 21, 2026 at 7:55 PM mark.yang via lists.openembedded.org
<mark.yang=lge.com@lists.openembedded.org> wrote:

> From: "mark.yang" <mark.yang@lge.com>
>
> Make the dynamic linker read /etc/ld-musl-$ARCH.path when PT_INTERP
> points to /usr/lib.
>
> Non-multilib builds do not notice the problem today. We are working
> towards musl with multilib. There a 64-bit program with /usr/lib in
> PT_INTERP loads the lib32 copy of a library from /usr/lib and fails
> with "Exec format error".
>
> With usrmerge the dynamic linker is /usr/lib/ld-musl-$ARCH.so.1, and
> gcc and clang put this path into PT_INTERP. musl drops the last two
> components of PT_INTERP and appends /etc/ld-musl-$ARCH.path to the
> rest. This gives /usr/etc/ld-musl-$ARCH.path, which does not exist.
>
> ld-musl-$ARCH.path is the musl counterpart of ld.so.conf. It lists the
> directories where the dynamic linker looks for shared libraries after
> LD_LIBRARY_PATH and RPATH, and when present it replaces the built-in
> default path.
>
> The musl recipe installs it in /etc with base_libdir and libdir of the
> variant. The file name carries the architecture, so each multilib
> variant has its own list, and a 64-bit program would search
> /usr/lib64 only.
>
> When the file is not found, musl falls back to its default path.
> Patch 0002 sets it to syslibdir:libdir, see 2da79f021b ("musl: Create
> default library search path based on configuration").
>
> Reference:
> https://git.openembedded.org/openembedded-core/commit/?id=2da79f021b5525ea5b56a86563905a67fc958fa5
>
> Without multilib the libraries are in /usr/lib, which the default path
> covers, so nothing shows. A 64-bit multilib build gets
> /usr/lib:/usr/lib64 and looks in /usr/lib first, so a 64-bit program
> loads the lib32 copies of its libraries from there and fails.
>
> Treat a /usr prefix as the root, so /usr/lib/ld-musl-$ARCH.so.1 reads
> /etc/ld-musl-$ARCH.path like /lib/ld-musl-$ARCH.so.1 does. Without
> usrmerge PT_INTERP starts with /lib, and nothing changes.
>
>   PT_INTERP                        file musl opens
>                                    before
>    after
>   /usr/lib/ld-musl-aarch64.so.1    /usr/etc/ld-musl-aarch64.path
> (missing)    /etc/ld-musl-aarch64.path
>   /lib/ld-musl-aarch64.so.1        /etc/ld-musl-aarch64.path
>     /etc/ld-musl-aarch64.path
>
> Signed-off-by: mark.yang <mark.yang@lge.com>
> ---
>  ...ath-file-from-etc-when-the-loader-is.patch | 35 +++++++++++++++++++
>  meta/recipes-core/musl/musl_git.bb            |  1 +
>  2 files changed, 36 insertions(+)
>  create mode 100644
> meta/recipes-core/musl/musl/0004-ldso-read-the-.path-file-from-etc-when-the-loader-is.patch
>
> diff --git
> a/meta/recipes-core/musl/musl/0004-ldso-read-the-.path-file-from-etc-when-the-loader-is.patch
> b/meta/recipes-core/musl/musl/0004-ldso-read-the-.path-file-from-etc-when-the-loader-is.patch
> new file mode 100644
> index 0000000000..bcc0c71c3b
> --- /dev/null
> +++
> b/meta/recipes-core/musl/musl/0004-ldso-read-the-.path-file-from-etc-when-the-loader-is.patch
> @@ -0,0 +1,35 @@
> +From 29727534313c4955d2231344711fddd1e93af1c2 Mon Sep 17 00:00:00 2001
> +From: "mark.yang" <mark.yang@lge.com>
> +Date: Wed, 21 Oct 2026 18:57:49 +0900
> +Subject: [PATCH] ldso: read the .path file from /etc when the loader is in
> + /usr/lib
> +
> +musl looks for ld-musl-$ARCH.path in the etc directory next to the
> +directory of the dynamic linker, as named by PT_INTERP. With usrmerge
> +OE puts /usr/lib/ld-musl-$ARCH.so.1 into PT_INTERP, so musl opens
> +/usr/etc/ld-musl-$ARCH.path while the file is installed in /etc.
> +
> +Treat a /usr prefix as the root, so /usr/lib/ld-musl-$ARCH.so.1 reads
> +/etc/ld-musl-$ARCH.path like /lib/ld-musl-$ARCH.so.1 does.
> +
> +Upstream-Status: Inappropriate [oe-core specific]
> +Signed-off-by: mark.yang <mark.yang@lge.com>
> +---
> + ldso/dynlink.c | 4 ++++
> + 1 file changed, 4 insertions(+)
> +
> +diff --git a/ldso/dynlink.c b/ldso/dynlink.c
> +index 0fdc9e7c..dfc772e3 100644
> +--- a/ldso/dynlink.c
> ++++ b/ldso/dynlink.c
> +@@ -1136,6 +1136,10 @@ static struct dso *load_library(const char *name,
> struct dso *needed_by)
> +                                       for (s=t=z=ldso.name; *s; s++)
> +                                               if (*s=='/') z=t, t=s;
> +                                       prefix_len = z-ldso.name;
> ++                                      /* With usrmerge the loader is
> /usr/lib/ld-musl-*,
> ++                                       * but the .path file stays in
> /etc. */
> ++                                      if (prefix_len == 4 && !memcmp(
> ldso.name, "/usr", 4))
> ++                                              prefix_len = 0;
> +                                       if (prefix_len < PATH_MAX)
> +                                               prefix = ldso.name;
> +                               }
> diff --git a/meta/recipes-core/musl/musl_git.bb b/meta/recipes-core/musl/
> musl_git.bb
> index 212bda1f29..f901b6e8da 100644
> --- a/meta/recipes-core/musl/musl_git.bb
> +++ b/meta/recipes-core/musl/musl_git.bb
> @@ -14,6 +14,7 @@ SRC_URI = "git://git.musl-libc.org/musl;branch=master \
>
> file://0001-Make-dynamic-linker-a-relative-symlink-to-libc.patch \
>
> file://0002-ldso-Use-syslibdir-and-libdir-as-default-pathes-to-l.patch \
>
> file://0003-tools-version.sh-fall-back-to-VERSION-when-git-descr.patch \
> +
>  file://0004-ldso-read-the-.path-file-from-etc-when-the-loader-is.patch \
>            "
>
>  PROVIDES += "virtual/libc virtual/libiconv virtual/libintl virtual/crypt"
>
> -=-=-=-=-=-=-=-=-=-=-=-
> Links: You receive all messages sent to this group.
> View/Reply Online (#248409):
> https://lists.openembedded.org/g/openembedded-core/message/248409
> Mute This Topic: https://lists.openembedded.org/mt/121878787/1997914
> 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 --git a/meta/recipes-core/musl/musl/0004-ldso-read-the-.path-file-from-etc-when-the-loader-is.patch b/meta/recipes-core/musl/musl/0004-ldso-read-the-.path-file-from-etc-when-the-loader-is.patch
new file mode 100644
index 0000000000..bcc0c71c3b
--- /dev/null
+++ b/meta/recipes-core/musl/musl/0004-ldso-read-the-.path-file-from-etc-when-the-loader-is.patch
@@ -0,0 +1,35 @@ 
+From 29727534313c4955d2231344711fddd1e93af1c2 Mon Sep 17 00:00:00 2001
+From: "mark.yang" <mark.yang@lge.com>
+Date: Wed, 21 Oct 2026 18:57:49 +0900
+Subject: [PATCH] ldso: read the .path file from /etc when the loader is in
+ /usr/lib
+
+musl looks for ld-musl-$ARCH.path in the etc directory next to the
+directory of the dynamic linker, as named by PT_INTERP. With usrmerge
+OE puts /usr/lib/ld-musl-$ARCH.so.1 into PT_INTERP, so musl opens
+/usr/etc/ld-musl-$ARCH.path while the file is installed in /etc.
+
+Treat a /usr prefix as the root, so /usr/lib/ld-musl-$ARCH.so.1 reads
+/etc/ld-musl-$ARCH.path like /lib/ld-musl-$ARCH.so.1 does.
+
+Upstream-Status: Inappropriate [oe-core specific]
+Signed-off-by: mark.yang <mark.yang@lge.com>
+---
+ ldso/dynlink.c | 4 ++++
+ 1 file changed, 4 insertions(+)
+
+diff --git a/ldso/dynlink.c b/ldso/dynlink.c
+index 0fdc9e7c..dfc772e3 100644
+--- a/ldso/dynlink.c
++++ b/ldso/dynlink.c
+@@ -1136,6 +1136,10 @@ static struct dso *load_library(const char *name, struct dso *needed_by)
+ 					for (s=t=z=ldso.name; *s; s++)
+ 						if (*s=='/') z=t, t=s;
+ 					prefix_len = z-ldso.name;
++					/* With usrmerge the loader is /usr/lib/ld-musl-*,
++					 * but the .path file stays in /etc. */
++					if (prefix_len == 4 && !memcmp(ldso.name, "/usr", 4))
++						prefix_len = 0;
+ 					if (prefix_len < PATH_MAX)
+ 						prefix = ldso.name;
+ 				}
diff --git a/meta/recipes-core/musl/musl_git.bb b/meta/recipes-core/musl/musl_git.bb
index 212bda1f29..f901b6e8da 100644
--- a/meta/recipes-core/musl/musl_git.bb
+++ b/meta/recipes-core/musl/musl_git.bb
@@ -14,6 +14,7 @@  SRC_URI = "git://git.musl-libc.org/musl;branch=master \
            file://0001-Make-dynamic-linker-a-relative-symlink-to-libc.patch \
            file://0002-ldso-Use-syslibdir-and-libdir-as-default-pathes-to-l.patch \
            file://0003-tools-version.sh-fall-back-to-VERSION-when-git-descr.patch \
+           file://0004-ldso-read-the-.path-file-from-etc-when-the-loader-is.patch \
           "
 
 PROVIDES += "virtual/libc virtual/libiconv virtual/libintl virtual/crypt"