Enable GCC 16's coming "-fdiagnostics-show-context=2" option[1] to provide enhanced diagnostic information for value-tracking warnings, which displays the control flow chain leading to the diagnostic. This covers our existing use of -Wrestrict and -Wstringop-overread, and gets us closer to enabling -Warray-bounds, -Wstringop-overflow, and -Wstringop-truncation.
The context depth of 2 provides the immediate decision path that led to the problematic code location, showing conditional checks and branch decisions that caused the warning. This will help us understand why GCC's value-tracking analysis triggered the warning and makes it easier to determine whether warnings are legitimate issues or false positives. For example, an array bounds warning will now show the conditional statements (like "if (i >= 4)") that established the out-of-bounds access range, directly connecting the control flow to the warning location. This is particularly valuable when GCC's interprocedural analysis can generate warnings that are difficult to understand without seeing the inferred control flow. Link: https://github.com/gcc-mirror/gcc/commit/6faa3cfe60ff9769d1bebfffdd2c7325217d7389 [1] Signed-off-by: Kees Cook <[email protected]> --- Cc: Gustavo A. R. Silva <[email protected]> Cc: Nathan Chancellor <[email protected]> Cc: Nicolas Schier <[email protected]> Cc: Masahiro Yamada <[email protected]> Cc: Miguel Ojeda <[email protected]> Cc: <[email protected]> --- Makefile | 3 +++ 1 file changed, 3 insertions(+) diff --git a/Makefile b/Makefile index d14824792227..d97452441cd0 100644 --- a/Makefile +++ b/Makefile @@ -940,6 +940,9 @@ KBUILD_CFLAGS += $(call cc-option,-fzero-init-padding-bits=all) # for the randomize_kstack_offset feature. Disable it for all compilers. 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) + # 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 -- 2.34.1
