[PATCH] kbuild: pass -fno-pic when probing for -mfentry

[PATCH] kbuild: pass -fno-pic when probing for -mfentry

[Ricardo Ribalda]

Some distros (namely Debian) configure their 32-bit toolchain with
--enable-default-pie.

To properly probe for -mfentry on them we need to pass -fno-pic,
otherwise allmodconfig will fail with:

./arch/x86/include/asm/ftrace.h:9:3: error: #error Compiler does not support fentry?

Fixes: 454e00cf8ee5 ("kbuild: avoid re-running compiler and linker probes")
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
---
I found this while testing next with media-ci.

Full logs:
https://gitlab.freedesktop.org/linux-media/users/ribalda/-/jobs/113299249#L4729
---
 scripts/Kconfig.toolchain | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/scripts/Kconfig.toolchain b/scripts/Kconfig.toolchain
index b0b9a663ddbe..53b361cf365a 100644
--- a/scripts/Kconfig.toolchain
+++ b/scripts/Kconfig.toolchain
@@ -170,8 +170,10 @@ config CC_HAS_MNOP_MCOUNT
 	def_bool $(cc-option,-mnop-mcount)
 
 # s390-linux-gnu-gcc did not support -mfentry until gcc-9.
+# 32-bit x86 gcc does not support -mfentry in combination with -fpic, which will
+# be enabled by default when gcc is configured with --enable-default-pie.
 config CC_HAS_MFENTRY
-	def_bool $(cc-option,-mfentry)
+	def_bool $(cc-option,-fno-pic -mfentry)
 
 config LD_OPT_FORCE_GROUP_ALLOCATION
 	def_string "$(ld-option-str,--force-group-allocation)"

---
base-commit: 3d229ce89862b8e82d71a9e11d6f840ca272a6d6
change-id: 20261020-pie-6774df20b0fa

Best regards,
-- 
Ricardo Ribalda <ribalda@chromium.org>

Re: [PATCH] kbuild: pass -fno-pic when probing for -mfentry

[Lorenzo Stoakes (ARM)]

On Tue, Oct 20, 2026 at 06:10:52AM +0000, Ricardo Ribalda wrote:
> Some distros (namely Debian) configure their 32-bit toolchain with
> --enable-default-pie.
>
> To properly probe for -mfentry on them we need to pass -fno-pic,
> otherwise allmodconfig will fail with:
>
> ./arch/x86/include/asm/ftrace.h:9:3: error: #error Compiler does not support fentry?
>
> Fixes: 454e00cf8ee5 ("kbuild: avoid re-running compiler and linker probes")
> Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>

Thanks! Makes sense to me, so:

Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>

> ---
> I found this while testing next with media-ci.
>
> Full logs:
> https://gitlab.freedesktop.org/linux-media/users/ribalda/-/jobs/113299249#L4729
> ---
>  scripts/Kconfig.toolchain | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/scripts/Kconfig.toolchain b/scripts/Kconfig.toolchain
> index b0b9a663ddbe..53b361cf365a 100644
> --- a/scripts/Kconfig.toolchain
> +++ b/scripts/Kconfig.toolchain
> @@ -170,8 +170,10 @@ config CC_HAS_MNOP_MCOUNT
>  	def_bool $(cc-option,-mnop-mcount)
>
>  # s390-linux-gnu-gcc did not support -mfentry until gcc-9.
> +# 32-bit x86 gcc does not support -mfentry in combination with -fpic, which will
> +# be enabled by default when gcc is configured with --enable-default-pie.
>  config CC_HAS_MFENTRY
> -	def_bool $(cc-option,-mfentry)
> +	def_bool $(cc-option,-fno-pic -mfentry)
>
>  config LD_OPT_FORCE_GROUP_ALLOCATION
>  	def_string "$(ld-option-str,--force-group-allocation)"
>
> ---
> base-commit: 3d229ce89862b8e82d71a9e11d6f840ca272a6d6
> change-id: 20261020-pie-6774df20b0fa
>
> Best regards,
> --
> Ricardo Ribalda <ribalda@chromium.org>
>

--
Cheers, Lorenzo