Re: PATCH: Also check for `movl %esp, %ebp' for x32

Mark Kettenis
2012-05-02T21:44:18Z

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> Date: Sun, 29 Apr 2012 11:37:49 -0700
> From: "H.J. Lu" <hjl.tools@gmail.com>
>
> On Tue, Apr 24, 2012 at 9:27 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
> > On Tue, Apr 17, 2012 at 7:30 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
> >> On Tue, Apr 17, 2012 at 4:43 AM, Mark Kettenis <mark.kettenis@xs4all.nl> wrote:
> >>>> Date: Tue, 10 Apr 2012 13:29:53 -0700
> >>>> From: "H.J. Lu" <hongjiu.lu@intel.com>
> >>>>
> >>>> Hi,
> >>>>
> >>>> X32 may use `movl %esp, %ebp' in prologue.  This patch checks it for
> >>>> x32.  Tested on Linux/x86-64.  OK for trunk?
> >>>
> >>> Sorry, but I'm not sure it is a good idea to mix ABIs in the code like
> >>> that.  Up until now, I've made a conscious attempt to keep the i386
> >>> and amd64 ABIs seperated out as much as possible.  Can you post a
> >>> complete diff of the -tdep.c related changes to support x32 in GDB,
> >>> such that I can judge where this is heading?
> >>
> >> Here is the complete x32 GDB patch:
> >>
> >> http://sourceware.org/ml/gdb-patches/2012-04/msg00476.html
> >>
> >
> > Hi Mark,
> >
> > Have you looked at my change?
> >
> > Thanks.
>
> Ping.

Sorry; been travelling too much lately...

I did have a look at it, but still have some questions.

> Hi,
>
> X32 may use `movl %esp, %ebp' in prologue. This patch checks it for
> x32. Tested on Linux/x86-64. OK for trunk?

But the prologues generated by various compilers are expected to be
otherwise the same for both the x32 ABI and the normal 64-bit ABI? I
guess x32 has to use "pushq %rbp" as "pushl %ebp" isn't available.
And I guess you want to keep the stack 16-byte aligned anyway. I
suppose that "movq %rsp, %rbp" is still ok for x32, but "movl %esp,
%ebp" can be encoded in less bytes, so it might be a bit more
efficient for x32.

But what about the stack align code that we check for in
amd64_analyze_stack_align()? Wouldn't that be different for x32 as
well?