Commit 4548f63e authored Mar 09, 2016 by Josh Poimboeuf Committed by Paolo Bonzini May 10, 2016

x86/kvm: Add stack frame dependency to fastop() inline asm

The kbuild test robot reported this objtool warning [1]:

  arch/x86/kvm/emulate.o: warning: objtool: fastop()+0x69: call without frame pointer save/setup

The issue seems to be caused by CONFIG_PROFILE_ALL_BRANCHES.  With that
option, for some reason gcc decides not to create a stack frame in
fastop() before doing the inline asm call, which can result in a bad
stack trace.

Force a stack frame to be created if CONFIG_FRAME_POINTER is enabled by
listing the stack pointer as an output operand for the inline asm
statement.

This change has no effect for !CONFIG_PROFILE_ALL_BRANCHES.

[1] https://lists.01.org/pipermail/kbuild-all/2016-March/018249.html



Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

parent 5e1b59ab

arch/x86/kvm/emulate.c

+5 −1

Original line number	Diff line number	Diff line
		@@ -5110,13 +5110,17 @@ static void fetch_possible_mmx_operand(struct x86_emulate_ctxt *ctxt,

		static int fastop(struct x86_emulate_ctxt ctxt, void (fop)(struct fastop *))
		{
		register void *__sp asm(_ASM_SP);
		ulong flags = (ctxt->eflags & EFLAGS_MASK) \| X86_EFLAGS_IF;

		if (!(ctxt->d & ByteOp))
		fop += __ffs(ctxt->dst.bytes) * FASTOP_SIZE;

		asm("push %[flags]; popf; call *%[fastop]; pushf; pop %[flags]\n"
		: "+a"(ctxt->dst.val), "+d"(ctxt->src.val), [flags]"+D"(flags),
		[fastop]"+S"(fop)
		[fastop]"+S"(fop), "+r"(__sp)
		: "c"(ctxt->src2.val));

		ctxt->eflags = (ctxt->eflags & ~EFLAGS_MASK) \| (flags & EFLAGS_MASK);
		if (!fop) /* exception is returned in fop variable */
		return emulate_de(ctxt);

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