Linus reported the following objtool warning:
kernel/signal.o: warning: objtool: .altinstr_replacement+0x54: call without
frame pointer save/setup
The warning is valid. It's caused by the fact that gcc placed the call
instruction in alternative_call_2()'s inline asm before the frame
pointer setup, which breaks frame pointer convention and can result in a
bad stack trace.
Force a stack frame to be created before the call instruction by listing
the stack pointer as an output operand in the inline asm statement.
Reported-by: Linus Torvalds <torva...@linux-foundation.org>
Signed-off-by: Josh Poimboeuf <jpoim...@redhat.com>
---
arch/x86/include/asm/alternative.h | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/arch/x86/include/asm/alternative.h
b/arch/x86/include/asm/alternative.h
index e77a644..1b02038 100644
--- a/arch/x86/include/asm/alternative.h
+++ b/arch/x86/include/asm/alternative.h
@@ -217,10 +217,14 @@ static inline int alternatives_text_reserved(void *start,
void *end)
*/
#define alternative_call_2(oldfunc, newfunc1, feature1, newfunc2, feature2, \
output, input...) \
+{ \
+ register void *__sp asm(_ASM_SP); \
asm volatile (ALTERNATIVE_2("call %P[old]", "call %P[new1]", feature1,\
"call %P[new2]", feature2) \
- : output : [old] "i" (oldfunc), [new1] "i" (newfunc1), \
- [new2] "i" (newfunc2), ## input)
+ : output, "+r" (__sp) \
+ : [old] "i" (oldfunc), [new1] "i" (newfunc1), \
+ [new2] "i" (newfunc2), ## input); \
+}
/*
* use this macro(s) if you need more than one output parameter
--
2.7.4
