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Date: Tue, 18 Aug 2020 19:43:07 -0400 From: Arvind Sankar <nivedita@...m.mit.edu> To: Andrew Morton <akpm@...ux-foundation.org>, Linus Torvalds <torvalds@...ux-foundation.org> Cc: Nick Desaulniers <ndesaulniers@...gle.com>, linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com Subject: [PATCH] lib/string.c: Disable tree-loop-distribute-patterns gcc can transform the loop in a naive implementation of memset/memcpy etc into a call to the function itself. This optimization is enabled by -ftree-loop-distribute-patterns. This has been the case for a while (see eg [0]), but gcc-10.x enables this option at -O2 rather than -O3 as in previous versions. Add -ffreestanding, which implicitly disables this optimization with gcc. It is unclear whether clang performs such optimizations, but hopefully it will also not do so in a freestanding environment. This by itself is insufficient for gcc if the optimization was explicitly enabled by CFLAGS, so also add a flag to explicitly disable it. [0] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56888 Signed-off-by: Arvind Sankar <nivedita@...m.mit.edu> --- lib/Makefile | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/lib/Makefile b/lib/Makefile index e290fc5707ea..80edea49613f 100644 --- a/lib/Makefile +++ b/lib/Makefile @@ -15,11 +15,18 @@ KCOV_INSTRUMENT_debugobjects.o := n KCOV_INSTRUMENT_dynamic_debug.o := n KCOV_INSTRUMENT_fault-inject.o := n +# string.o implements standard library functions like memset/memcpy etc. +# Use -ffreestanding to ensure that the compiler does not try to "optimize" +# them into calls to themselves. +# The optimization pass that does such transformations in gcc is +# tree-loop-distribute-patterns. Explicitly disable it just in case. +CFLAGS_string.o := -ffreestanding $(call cc-option,-fno-tree-loop-distribute-patterns) + # Early boot use of cmdline, don't instrument it ifdef CONFIG_AMD_MEM_ENCRYPT KASAN_SANITIZE_string.o := n -CFLAGS_string.o := -fno-stack-protector +CFLAGS_string.o += -fno-stack-protector endif # Used by KCSAN while enabled, avoid recursion. -- 2.26.2
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