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lib/string.c: Use freestanding environment

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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, 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.

Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56888
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Arvind Sankar 2020-08-19 10:08:16 -04:00 committed by Linus Torvalds
parent 394b19d6cb
commit 33d0f96ffd
1 changed files with 6 additions and 1 deletions
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7
lib/Makefile
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@ -15,11 +15,16 @@ 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.
CFLAGS_string.o := -ffreestanding
# 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.