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Date:   Wed, 30 Aug 2017 12:23:24 -0700
From:   "H. Peter Anvin" <>
Subject: Re: [tip:x86/asm] objtool: Handle GCC stack pointer adjustment bug

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:
> 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*?


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