[PATCH v2] kbuild: expand inlining hints with -fdiagnostics-show-inlining-chain

[Justin Stitt <justinstitt@google.com>]

Clang recently added -fdiagnostics-show-inlining-chain [1] to improve
the visibility of inlining chains in diagnostics. This is particularly
useful for CONFIG_FORTIFY_SOURCE where detections can happen deep in
inlined functions.

Add this flag to KBUILD_CFLAGS under a cc-option so it is enabled if the
compiler supports it. Note that GCC does not have an equivalent flag as
it supports a similar diagnostic structure unconditionally.

Link: https://github.com/llvm/llvm-project/pull/174892 [1]
Link: https://github.com/ClangBuiltLinux/linux/issues/1571
Signed-off-by: Justin Stitt <justinstitt@google.com>
---
Changes in v2:
- Move to always enable option if compiler supports it (thanks Nathan,
  Kees)
- Change commit title and message
- Link to v1: https://lore.kernel.org/r/20260327-kbuild-show-inlining-v1-1-730ac2cae571@google.com
---
 Makefile | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/Makefile b/Makefile
index e1279c4d5b24..4972b23fb77f 100644
--- a/Makefile
+++ b/Makefile
@@ -973,6 +973,10 @@ KBUILD_CFLAGS	+= $(call cc-option, -fno-stack-clash-protection)
 # Get details on warnings generated due to GCC value tracking.
 KBUILD_CFLAGS	+= $(call cc-option, -fdiagnostics-show-context=2)
 
+# Show inlining notes for __attribute__((warning/error)) call chains.
+# GCC supports this unconditionally while Clang 23+ provides a flag.
+KBUILD_CFLAGS	+= $(call cc-option, -fdiagnostics-show-inlining-chain)
+
 # Clear used registers at func exit (to reduce data lifetime and ROP gadgets).
 ifdef CONFIG_ZERO_CALL_USED_REGS
 KBUILD_CFLAGS	+= -fzero-call-used-regs=used-gpr

---
base-commit: 7df48e36313029e4c0907b2023905dd7213fd678
change-id: 20260327-kbuild-show-inlining-557d31d2293a

Best regards,
-- 
Justin Stitt <justinstitt@google.com>