On 21/01/2016 23:49, Josh Poimboeuf wrote:
> With some configs, gcc doesn't inline test_cc().  When that happens, it
> doesn't create a stack frame before inserting the call instruction.
> This breaks frame pointer convention if CONFIG_FRAME_POINTER is enabled
> and 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.

If an __always_inline allocation works, that would be better.

Paolo

> Signed-off-by: Josh Poimboeuf <jpoim...@redhat.com>
> Cc: Gleb Natapov <g...@kernel.org>
> Cc: Paolo Bonzini <pbonz...@redhat.com>
> Cc: k...@vger.kernel.org
> ---
>  arch/x86/kvm/emulate.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index aa4d726..7dba65a 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -972,11 +972,13 @@ static int em_bsr_c(struct x86_emulate_ctxt *ctxt)
>  static u8 test_cc(unsigned int condition, unsigned long flags)
>  {
>       u8 rc;
> +     register void *__sp asm(_ASM_SP);
>       void (*fop)(void) = (void *)em_setcc + 4 * (condition & 0xf);
>  
>       flags = (flags & EFLAGS_MASK) | X86_EFLAGS_IF;
>       asm("push %[flags]; popf; call *%[fastop]"
> -         : "=a"(rc) : [fastop]"r"(fop), [flags]"r"(flags));
> +         : "=a"(rc), "+r"(__sp)
> +         : [fastop]"r"(fop), [flags]"r"(flags));
>       return rc;
>  }
>  
> 

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