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

[Lukas Wunner]

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@xxxxxxxxxxxxxx/

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@xxxxxxxxxxxxxxxxxxxx> # off-list
Signed-off-by: Lukas Wunner <lukas@xxxxxxxxx>
---
 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)
+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