Per commit b3f11af9b2ce ("arm64: ftrace: forbid CALL_OPS with
CC_OPTIMIZE_FOR_SIZE"), GCC is silently ignoring `-falign-functions=N`
when passed `-Os`, causing functions to be improperly aligned. This
doesn't seem to be a problem with Clang though, where enabling CALL_OPS
with CC_OPTIMIZE_FOR_SIZE doesn't spit out any warnings at boot about
misaligned patch-sites. Only forbid CALL_OPS if GCC is used and we're
optimizing for size so that CALL_OPS can be used with clang optimizing
for size.
Cc: Jason Ling <[email protected]>
Cc: Florian Fainelli <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Nathan Chancellor <[email protected]>
Cc: Nick Desaulniers <[email protected]>
Cc: Bill Wendling <[email protected]>
Cc: Justin Stitt <[email protected]>
Cc: <[email protected]>
Fixes: b3f11af9b2ce ("arm64: ftrace: forbid CALL_OPS with CC_OPTIMIZE_FOR_SIZE")
Signed-off-by: Stephen Boyd <[email protected]>
---
arch/arm64/Kconfig | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index aa7c1d435139..6b96d75a3a3d 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -198,7 +198,7 @@ config ARM64
if DYNAMIC_FTRACE_WITH_ARGS && DYNAMIC_FTRACE_WITH_CALL_OPS
select HAVE_DYNAMIC_FTRACE_WITH_CALL_OPS \
if (DYNAMIC_FTRACE_WITH_ARGS && !CFI_CLANG && \
- !CC_OPTIMIZE_FOR_SIZE)
+ (CC_IS_CLANG || !CC_OPTIMIZE_FOR_SIZE))
select FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY \
if DYNAMIC_FTRACE_WITH_ARGS
select HAVE_SAMPLE_FTRACE_DIRECT
base-commit: 6613476e225e090cc9aad49be7fa504e290dd33d
--
https://chromeos.dev
On Thu, Feb 22, 2024 at 10:40:29PM -0800, Stephen Boyd wrote:
> Per commit b3f11af9b2ce ("arm64: ftrace: forbid CALL_OPS with
> CC_OPTIMIZE_FOR_SIZE"), GCC is silently ignoring `-falign-functions=N`
> when passed `-Os`, causing functions to be improperly aligned. This
> doesn't seem to be a problem with Clang though, where enabling CALL_OPS
> with CC_OPTIMIZE_FOR_SIZE doesn't spit out any warnings at boot about
> misaligned patch-sites. Only forbid CALL_OPS if GCC is used and we're
> optimizing for size so that CALL_OPS can be used with clang optimizing
> for size.
>
> Cc: Jason Ling <[email protected]>
> Cc: Florian Fainelli <[email protected]>
> Cc: Mark Rutland <[email protected]>
> Cc: Nathan Chancellor <[email protected]>
> Cc: Nick Desaulniers <[email protected]>
> Cc: Bill Wendling <[email protected]>
> Cc: Justin Stitt <[email protected]>
> Cc: <[email protected]>
> Fixes: b3f11af9b2ce ("arm64: ftrace: forbid CALL_OPS with CC_OPTIMIZE_FOR_SIZE")
> Signed-off-by: Stephen Boyd <[email protected]>
Seems reasonable to me.
Reviewed-by: Nathan Chancellor <[email protected]>
I wonder if that GCC issue is resolved with '-fmin-function-alignment'
that is being introduced in GCC 14 [1]. If it is, I suspect this
conditional could actually be CONFIG_CC_HAS_SANE_FUNCTION_ALIGNMENT
instead of CONFIG_CC_IS_CLANG, but that can obviously happen as a clean
up later down the road (more just food for thought for the arm64 folks,
not sure how much '-Os' is used in general)
[1]: https://git.kernel.org/masahiroy/linux-kbuild/c/5270316c9fec8cc99aa0e0a258509c5c7f789d12
> ---
> arch/arm64/Kconfig | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index aa7c1d435139..6b96d75a3a3d 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -198,7 +198,7 @@ config ARM64
> if DYNAMIC_FTRACE_WITH_ARGS && DYNAMIC_FTRACE_WITH_CALL_OPS
> select HAVE_DYNAMIC_FTRACE_WITH_CALL_OPS \
> if (DYNAMIC_FTRACE_WITH_ARGS && !CFI_CLANG && \
> - !CC_OPTIMIZE_FOR_SIZE)
> + (CC_IS_CLANG || !CC_OPTIMIZE_FOR_SIZE))
> select FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY \
> if DYNAMIC_FTRACE_WITH_ARGS
> select HAVE_SAMPLE_FTRACE_DIRECT
>
> base-commit: 6613476e225e090cc9aad49be7fa504e290dd33d
> --
> https://chromeos.dev
>
On Thu, 22 Feb 2024 22:40:29 -0800, Stephen Boyd wrote:
> Per commit b3f11af9b2ce ("arm64: ftrace: forbid CALL_OPS with
> CC_OPTIMIZE_FOR_SIZE"), GCC is silently ignoring `-falign-functions=N`
> when passed `-Os`, causing functions to be improperly aligned. This
> doesn't seem to be a problem with Clang though, where enabling CALL_OPS
> with CC_OPTIMIZE_FOR_SIZE doesn't spit out any warnings at boot about
> misaligned patch-sites. Only forbid CALL_OPS if GCC is used and we're
> optimizing for size so that CALL_OPS can be used with clang optimizing
> for size.
>
> [...]
Applied to arm64 (for-next/misc), thanks!
[1/1] arm64: ftrace: Don't forbid CALL_OPS+CC_OPTIMIZE_FOR_SIZE with Clang
https://git.kernel.org/arm64/c/a743f26d03a9
--
Catalin