Re: [tip:x86/asm] objtool: Handle GCC stack pointer adjustment bug

[H. Peter Anvin]

On 08/30/17 02:43, tip-bot for Josh Poimboeuf wrote:
> 
> Those warnings are caused by an unusual GCC non-optimization where it
> uses an intermediate register to adjust the stack pointer.  It does:
> 
>   lea    0x8(%rsp), %rcx
>   ...
>   mov    %rcx, %rsp
> 
> Instead of the obvious:
> 
>   add    $0x8, %rsp
> 
> It makes no sense to use an intermediate register, so I opened a GCC bug
> to track it:
> 
>   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81813
> 
> But it's not exactly a high-priority bug and it looks like we'll be
> stuck with this issue for a while.  So for now we have to track register
> values when they're loaded with stack pointer offsets.
> 

This seems like a good reason to try to extract this information from
the DWARF data *if available*?

	-hpa