[Buildroot] [PATCH] package/musl: fix build for POWER10 and later

[Buildroot] [PATCH] package/musl: fix build for POWER10 and later

[Yegor Yefremov]

When targeting POWER10 or POWER11, gcc generates pc-relative code by
default, and the resulting C functions do not preserve the TOC pointer.
musl's powerpc64 assembly calls or tail-calls C functions assuming the
TOC-based ABI (bl without a following nop in crt_arch.h, b __dlsym in
dlsym.s, b __setjmp_toc in setjmp.s/sigsetjmp.s), so the linker cannot
insert the needed TOC save/restore stubs and linking libc.so fails:

  dlstart.c:(.text+0x24): call to `_dlstart_c' lacks nop, can't restore toc; (toc save/adjust stub)
  ld: final link failed: bad value

Build musl with -mno-pcrel for POWER10 and POWER11, so musl itself is
built as TOC-based code. Applications can still be built with
pc-relative code and link against it.

The issue has been reported upstream [1], as musl does not accept
AI-assisted patches.

This issue has been present since commit 3523e1ac79c1
("arch/Config.in.powerpc: add Power10 CPU type"), which made it possible
to build musl with -mcpu=power10 (and later power11, added by commit
da1b45dd00fd ("arch/Config.in.powerpc: add Power11 CPU type")). It
therefore affects 2026.08 and later, including 2026.08.x.

Fixes:
https://autobuild.buildroot.org/results/1342da7c9258a93eada96f92f53a643e316ce7f6

[1] https://www.openwall.com/lists/musl/2026/11/15/2

Fixes: 3523e1ac79c15c5199a15589692e269191abd546 ("arch/Config.in.powerpc: add Power10 CPU type")
Assisted-by: Claude:claude-opus-5-5
Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>
---
 package/musl/musl.mk | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/package/musl/musl.mk b/package/musl/musl.mk
index cb9f7f8870..b6e0ae6d97 100644
--- a/package/musl/musl.mk
+++ b/package/musl/musl.mk
@@ -49,6 +49,13 @@ ifeq ($(BR2_ARM_INSTRUCTIONS_THUMB),y)
 MUSL_EXTRA_CFLAGS += -marm
 endif
 
+# The powerpc64 assembly code assumes TOC-based C code, but gcc
+# generates pc-relative code by default for POWER10 and later, which
+# makes linking libc.so fail.
+ifeq ($(BR2_powerpc_power10)$(BR2_powerpc_power11),y)
+MUSL_EXTRA_CFLAGS += -mno-pcrel
+endif
+
 define MUSL_CONFIGURE_CMDS
 	(cd $(@D); \
 		$(TARGET_CONFIGURE_OPTS) \
-- 
2.34.1

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Re: [Buildroot] [PATCH] package/musl: fix build for POWER10 and later

[Thomas Petazzoni via buildroot]

On Sun, Nov 15, 2026 at 07:58:03AM +0100, Yegor Yefremov wrote:
> When targeting POWER10 or POWER11, gcc generates pc-relative code by
> default, and the resulting C functions do not preserve the TOC pointer.
> musl's powerpc64 assembly calls or tail-calls C functions assuming the
> TOC-based ABI (bl without a following nop in crt_arch.h, b __dlsym in
> dlsym.s, b __setjmp_toc in setjmp.s/sigsetjmp.s), so the linker cannot
> insert the needed TOC save/restore stubs and linking libc.so fails:
> 
>   dlstart.c:(.text+0x24): call to `_dlstart_c' lacks nop, can't restore toc; (toc save/adjust stub)
>   ld: final link failed: bad value
> 
> Build musl with -mno-pcrel for POWER10 and POWER11, so musl itself is
> built as TOC-based code. Applications can still be built with
> pc-relative code and link against it.
> 
> The issue has been reported upstream [1], as musl does not accept
> AI-assisted patches.
> 
> This issue has been present since commit 3523e1ac79c1
> ("arch/Config.in.powerpc: add Power10 CPU type"), which made it possible
> to build musl with -mcpu=power10 (and later power11, added by commit
> da1b45dd00fd ("arch/Config.in.powerpc: add Power11 CPU type")). It
> therefore affects 2026.08 and later, including 2026.08.x.
> 
> Fixes:
> https://autobuild.buildroot.org/results/1342da7c9258a93eada96f92f53a643e316ce7f6
> 
> [1] https://www.openwall.com/lists/musl/2026/11/15/2

Funnily enough, I had already reported the issue to upstream musl:

  https://www.openwall.com/lists/musl/2026/11/05/3

> Fixes: 3523e1ac79c15c5199a15589692e269191abd546 ("arch/Config.in.powerpc: add Power10 CPU type")
> Assisted-by: Claude:claude-opus-5-5
> Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>

Applied to master, thanks!

Thomas
-- 
Thomas Petazzoni, co-owner and CEO, Bootlin
Embedded Linux and Kernel engineering and training
https://bootlin.com
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