This is the mail archive of the
gcc@gcc.gnu.org
mailing list for the GCC project.
Re: BUG: GCC-4.4.x changes the function frame on some functions
- From: Steven Rostedt <rostedt at goodmis dot org>
- To: Frederic Weisbecker <fweisbec at gmail dot com>
- Cc: David Daney <ddaney at caviumnetworks dot com>, Linus Torvalds <torvalds at linux-foundation dot org>, Andrew Haley <aph at redhat dot com>, Richard Guenther <richard dot guenther at gmail dot com>, Thomas Gleixner <tglx at linutronix dot de>, Ingo Molnar <mingo at elte dot hu>, "H. Peter Anvin" <hpa at zytor dot com>, LKML <linux-kernel at vger dot kernel dot org>, Andrew Morton <akpm at linux-foundation dot org>, Heiko Carstens <heiko dot carstens at de dot ibm dot com>, feng dot tang at intel dot com, Peter Zijlstra <peterz at infradead dot org>, jakub at redhat dot com, gcc at gcc dot gnu dot org
- Date: Thu, 19 Nov 2009 15:05:41 -0500
- Subject: Re: BUG: GCC-4.4.x changes the function frame on some functions
- References: <alpine.LFD.2.00.0911191607440.24119@localhost.localdomain> <alpine.LFD.2.00.0911190934070.2793@localhost.localdomain> <1258653562.22249.682.camel@gandalf.stny.rr.com> <84fc9c000911191003t244eb864o3d5b355ab5485f@mail.gmail.com> <4B058CCD.8050605@redhat.com> <alpine.LFD.2.00.0911191039470.2793@localhost.localdomain> <alpine.LFD.2.00.0911191041471.2793@localhost.localdomain> <alpine.LFD.2.00.0911191047350.2793@localhost.localdomain> <4B05982B.6060200@caviumnetworks.com> <1258658886.22249.874.camel@gandalf.stny.rr.com> <20091119194625.GE4967@nowhere>
- Reply-to: rostedt at goodmis dot org
On Thu, 2009-11-19 at 20:46 +0100, Frederic Weisbecker wrote:
> On Thu, Nov 19, 2009 at 02:28:06PM -0500, Steven Rostedt wrote:
> > <function>:
> > call __fentry__
> > [...]
> >
> >
> > -- Steve
>
>
> I would really like this. So that we can forget about other possible
> further suprises due to sophisticated function prologues beeing before
> the mcount call.
>
> And I guess that would fix it in every archs.
Well, other archs use a register to store the return address. But it
would also be easy to do (pseudo arch assembly):
<function>:
mov lr, (%sp)
add 8, %sp
blr __fentry__
sub 8, %sp
mov (%sp), lr
That way the lr would have the current function, and the parent would
still be at 8(%sp)
>
> That said, Linus had a good point about the fact there might other uses
> of mcount even more tricky than what does the function graph tracer,
> outside the kernel, and those may depend on the strict ABI assumption
> that 4(ebp) is always the _real_ return address, and that through all
> the previous stack call. This is even a concern that extrapolates the
> single mcount case.
As I am proposing a new call. This means that mcount stay as is for
legacy reasons. Yes I know there exists the -finstrument-functions but
that adds way too much bloat to the code. One single call to the
profiler is all I want.
>
> So I wonder that actually the real problem is the lack of something that
> could provide this guarantee. We may need a -real-ra-before-fp (yeah
> I suck in naming).
Don't worry, so do the C compiler folks, I mean, come on "mcount"?
-- Steve