From: Nick Desaulniers ndesaulniers@google.com
[ Upstream commit 24845dcb170e16b3100bd49743687648c71387ae ]
-Wframe-larger-than= requires stack frame information, which the frontend cannot provide. This diagnostic is emitted late during compilation once stack frame size is available.
When building with LTO, the frontend simply lowers C to LLVM IR and does not have stack frame information, so it cannot emit this diagnostic. When the linker drives LTO, it restarts optimizations and lowers LLVM IR to object code. At that point, it has stack frame information but doesn't know to check for a specific max stack frame size.
I consider this a bug in LLVM that we need to fix. There are some details we're working out related to LTO such as which value to use when there are multiple different values specified per TU, or how to propagate these to compiler synthesized routines properly, if at all.
Until it's fixed, ensure we don't miss these. At that point we can wrap this in a compiler version guard or revert this based on the minimum support version of Clang.
The error message is not generated during link: LTO vmlinux.o ld.lld: warning: stack size limit exceeded (8224) in foobarbaz
Cc: Sami Tolvanen samitolvanen@google.com Reported-by: Candle Sun candlesea@gmail.com Suggested-by: Fangrui Song maskray@google.com Signed-off-by: Nick Desaulniers ndesaulniers@google.com Signed-off-by: Kees Cook keescook@chromium.org Link: https://lore.kernel.org/r/20210312010942.1546679-1-ndesaulniers@google.com Signed-off-by: Sasha Levin sashal@kernel.org --- Makefile | 5 +++++ 1 file changed, 5 insertions(+)
diff --git a/Makefile b/Makefile index a20afcb7d2bf..476ab5b3adc2 100644 --- a/Makefile +++ b/Makefile @@ -912,6 +912,11 @@ CC_FLAGS_LTO += -fvisibility=hidden
# Limit inlining across translation units to reduce binary size KBUILD_LDFLAGS += -mllvm -import-instr-limit=5 + +# Check for frame size exceeding threshold during prolog/epilog insertion. +ifneq ($(CONFIG_FRAME_WARN),0) +KBUILD_LDFLAGS += -plugin-opt=-warn-stack-size=$(CONFIG_FRAME_WARN) +endif endif
ifdef CONFIG_LTO