Re: [PATCH] crypto: ecc - Unbreak the build on arm with CONFIG_KASAN_STACK=y

[Nathan Chancellor <nathan@kernel.org>]

On Wed, Apr 08, 2026 at 08:15:49AM +0200, Lukas Wunner wrote:
> Andrew reports the following build breakage of arm allmodconfig,
> reproducible with gcc 14.2.0 and 15.2.0:
> 
>   crypto/ecc.c: In function 'ecc_point_mult':
>   crypto/ecc.c:1380:1: error: the frame size of 1360 bytes is larger than 1280 bytes [-Werror=frame-larger-than=]
> 
> gcc excessively inlines functions called by ecc_point_mult() (without
> there being any explicit inline declarations) and doesn't seem smart
> enough to stay below CONFIG_FRAME_WARN.
> 
> clang does not exhibit the issue.
> 
> The issue only occurs with CONFIG_KASAN_STACK=y because it enlarges the
> frame size.  This has been a controversial topic a couple of times:
> 
> https://lore.kernel.org/r/CAK8P3a3_Tdc-XVPXrJ69j3S9048uzmVJGrNcvi0T6yr6OrHkPw@mail.gmail.com/
> 
> Prevent gcc from going overboard with inlining to unbreak the build.
> The maximum inline limit to avoid the error is 101.  Use 100 to get a
> nice round number per Andrew's preference.
> 
> Reported-by: Andrew Morton <akpm@linux-foundation.org> # off-list
> Signed-off-by: Lukas Wunner <lukas@wunner.de>
> ---
>  crypto/Makefile | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/crypto/Makefile b/crypto/Makefile
> index 04e269117589..b3ac7f29153e 100644
> --- a/crypto/Makefile
> +++ b/crypto/Makefile
> @@ -181,6 +181,11 @@ obj-$(CONFIG_CRYPTO_ZSTD) += zstd.o
>  obj-$(CONFIG_CRYPTO_ECC) += ecc.o
>  obj-$(CONFIG_CRYPTO_ESSIV) += essiv.o
>  
> +# Avoid exceeding stack frame due to excessive gcc inlining in ecc_point_mult()
> +ifeq ($(ARCH)$(CONFIG_KASAN_STACK)$(LLVM),army)

Please use proper Kconfig variables here.

  ifeq ($(CONFIG_ARM)$(CONFIG_KASAN_STACK)$(CONFIG_CC_IS_GCC),yyy)

Which is both more robust, as $(LLVM) may not be set but CC=clang could
be, and it is clearer (in my opinion). If all supported versions of GCC
support this flag, you could drop the cc-option at that point.

> +CFLAGS_ecc.o += $(call cc-option,-finline-limit=100)
> +endif
> +
>  ecdh_generic-y += ecdh.o
>  ecdh_generic-y += ecdh_helper.o
>  obj-$(CONFIG_CRYPTO_ECDH) += ecdh_generic.o
> -- 
> 2.51.0
>