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Commit 317c2ce7 authored by Josh Poimboeuf's avatar Josh Poimboeuf Committed by Ingo Molnar
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x86/alternatives: Add stack frame dependency to alternative_call_2() 



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-and-tested-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20160923214939.j5o7c67nhepzmh3t@treble


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 71f5443e

arch/x86/include/asm/alternative.h

+6 −2
Original line number Diff line number Diff line
@@ -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