Re: [PATCH v3 04/29] x86: assembly, use ENDPROC for functions

From: Josh Poimboeuf
Date: Fri May 19 2017 - 15:50:51 EST


On Fri, May 19, 2017 at 11:17:24AM +0200, Jiri Slaby wrote:
> On 05/17/2017, 03:23 PM, Jiri Slaby wrote:
> >> So the initial CFI state is different between the two types of
> >> "functions". And there are a lot of other differences. C-type
> >> functions have to follow frame pointer conventions, for example. So
> >> your FUNC_START macro (and objtool) would have to somehow figure out a
> >> way to make a distinction between the two. So it would probably work
> >> out better if we kept the distinction between C-type functions and other
> >> code.
> >
> > Ok, that makes a lot of sense.
>
> A quick question:
> Do you consider these to be C-type functions?
>
> ENTRY(function_hook)
> ret
> END(function_hook)
>
> or this?
>
> ENTRY(native_load_gs_index)
> pushfq
> DISABLE_INTERRUPTS(CLBR_ANY & ~CLBR_RDI)
> SWAPGS
> movl %edi, %gs
> SWAPGS
> popfq
> ret
> END(native_load_gs_index)
>
> Both are called from C, but they do not setup frame pointer etc.

Yeah, those are valid C-type functions. Setting up the frame pointer is
optional for leaf functions (i.e. functions which don't call other
functions).

--
Josh