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Re: gas: Question about .cfi_startproc and nested labels
- From: "Jan Beulich" <JBeulich at suse dot com>
- To: "Martin Galvan" <martin dot galvan at tallertechnologies dot com>
- Cc: <binutils at sourceware dot org>
- Date: Mon, 17 Nov 2014 09:58:14 +0000
- Subject: Re: gas: Question about .cfi_startproc and nested labels
- Authentication-results: sourceware.org; auth=none
- References: <CAOKbPbapLucqZDJfr6Bu0DdV8HZQxiZPAfF0ki8V_oGqs97vxw at mail dot gmail dot com>
>>> On 17.11.14 at 06:09, <martin.galvan@tallertechnologies.com> wrote:
> Hi there! I'm trying to add some CFI directives to an existing ARM
> code, and I noticed sometimes we have stuff like this:
>
> some_label:
> ...
>
> some_other_label:
> ...
>
> END
>
> where "END" is a macro that expands to the appropriate epilogue/return
> instructions. If we want to mark those labels as functions, I know
> .cfi_endproc should be placed right after the END macro, but what
> about .cfi_startproc? I'm thinking of doing something like:
>
> some_label:
> .cfi_startproc
> ...
>
> some_other_label:
> .cfi_startproc
> ...
>
> END
> .cfi_endproc
>
> However, I'm not sure if that would be right. Will gas realize
> some_label and some_other_label are meant to be different functions?
No - these two directives have to strictly alternate. I.e. you'd need
another .cfi_endproc right before the second label, or drop the
.cfi_startproc right after it. Note that to the unwinder it doesn't
really matter whether some internal label of a function is externally
callable - all it cares about is that the unwinder state is correct at
that (as well as any other) point.
Jan