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authorNick Desaulniers <ndesaulniers@google.com>2019-08-07 15:15:32 -0700
committerThomas Gleixner <tglx@linutronix.de>2019-08-08 08:25:52 +0200
commit4ce97317f41d38584fb93578e922fcd19e535f5b (patch)
tree89b6f51ed094af29da06cacc19e3766d07458810 /arch/x86/boot/string.c
parent7468a4eae541ce5aff65595aa502aa0a4def6615 (diff)
downloadlinux-4ce97317f41d38584fb93578e922fcd19e535f5b.tar.bz2
x86/purgatory: Do not use __builtin_memcpy and __builtin_memset
Implementing memcpy and memset in terms of __builtin_memcpy and __builtin_memset is problematic. GCC at -O2 will replace calls to the builtins with calls to memcpy and memset (but will generate an inline implementation at -Os). Clang will replace the builtins with these calls regardless of optimization level. $ llvm-objdump -dr arch/x86/purgatory/string.o | tail 0000000000000339 memcpy: 339: 48 b8 00 00 00 00 00 00 00 00 movabsq $0, %rax 000000000000033b: R_X86_64_64 memcpy 343: ff e0 jmpq *%rax 0000000000000345 memset: 345: 48 b8 00 00 00 00 00 00 00 00 movabsq $0, %rax 0000000000000347: R_X86_64_64 memset 34f: ff e0 Such code results in infinite recursion at runtime. This is observed when doing kexec. Instead, reuse an implementation from arch/x86/boot/compressed/string.c. This requires to implement a stub function for warn(). Also, Clang may lower memcmp's that compare against 0 to bcmp's, so add a small definition, too. See also: commit 5f074f3e192f ("lib/string.c: implement a basic bcmp") Fixes: 8fc5b4d4121c ("purgatory: core purgatory functionality") Reported-by: Vaibhav Rustagi <vaibhavrustagi@google.com> Debugged-by: Vaibhav Rustagi <vaibhavrustagi@google.com> Debugged-by: Manoj Gupta <manojgupta@google.com> Suggested-by: Alistair Delva <adelva@google.com> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Tested-by: Vaibhav Rustagi <vaibhavrustagi@google.com> Cc: stable@vger.kernel.org Link: https://bugs.chromium.org/p/chromium/issues/detail?id=984056 Link: https://lkml.kernel.org/r/20190807221539.94583-1-ndesaulniers@google.com
Diffstat (limited to 'arch/x86/boot/string.c')
-rw-r--r--arch/x86/boot/string.c8
1 files changed, 8 insertions, 0 deletions
diff --git a/arch/x86/boot/string.c b/arch/x86/boot/string.c
index 401e30ca0a75..8272a4492844 100644
--- a/arch/x86/boot/string.c
+++ b/arch/x86/boot/string.c
@@ -37,6 +37,14 @@ int memcmp(const void *s1, const void *s2, size_t len)
return diff;
}
+/*
+ * Clang may lower `memcmp == 0` to `bcmp == 0`.
+ */
+int bcmp(const void *s1, const void *s2, size_t len)
+{
+ return memcmp(s1, s2, len);
+}
+
int strcmp(const char *str1, const char *str2)
{
const unsigned char *s1 = (const unsigned char *)str1;