Re: Incorrect line info in printf for powerpc-eabisim -mhard-foat

[Michael Eager <eager at eagercon dot com>]

Hi --

I don't think that a fix in GDB would be appropriate.
GDB is doing exactly what it should -- it places a breakpoint
at the first line in the function.

GCC should not output a line entry in the middle of the prologue.


Luis Machado wrote:
> Hi,
>
> Yes, this is exactly what i was chasing some time ago. The GCC fix i had
> in mind (it just changes the ordering of statements) didn't get through
> since it dealt with arch-independent code and there was fear that this
> would break architectures other than PPC (or have the potential to do
> so).
>
> The breakpoint is placed at the wrong place due to the branch
> instruction in the prologue. GDB just assumes that the second BB is real
> code (not prologue anymore) since GCC never provided any useful
> information on where exactly the prologue ends.
>
> Original thread is here:
> http://gcc.gnu.org/ml/gcc-patches/2009-02/msg01213.html
>
> A fix on GDB's side proved to be harder than in GCC's side (since we're
> already assuming things, it would just be another workaround).
>
> Luis
>
> On Tue, 2009-07-21 at 08:38 -0500, Peter Bergner wrote:
> > On Thu, 2009-07-16 at 13:55 -0700, Michael Eager wrote:
> > > I've tracked down a failure in gdb to hit a breakpoint
> > > set at printf to the the breakpoint being placed incorrectly.
> > >
> > > Here is the code generated for printf with -mhard-float:
> > >
> > > 	.loc 1 29 0
> > > 	.cfi_startproc
> > > .LVL0:
> > > 	mflr 0
> > > 	stwu 1,-112(1)
> > > .LCFI0:
> > > 	.cfi_def_cfa_offset 112
> > > 	stw 5,24(1)
> > > 	stw 0,116(1)
> > > 	stw 6,28(1)
> > > 	stw 7,32(1)
> > > 	stw 8,36(1)
> > > 	stw 9,40(1)
> > > 	stw 10,44(1)
> > > 	bne- 1,.L2              <<<  - 1
> > > 	.cfi_offset 65, 4
> > > 	.loc 1 29 0		<<<  - 2
> > > 	stfd 1,48(1)            <<<  - 3
> > > 	stfd 2,56(1)
> > > 	stfd 3,64(1)
> > > 	stfd 4,72(1)
> > > 	stfd 5,80(1)
> > > 	stfd 6,88(1)
> > > 	stfd 7,96(1)
> > > 	stfd 8,104(1)
> > > .L2:
> > > 	.loc 1 34 0
> > >
> > > Gdb places a breakpoint at printf() at the stfd instruction (3).
> > > This appears to be because of the .loc at (2).  When the code is
> > > executed, the branch (1) is taken, jumping over the the breakpoint.
> > > I think that the .loc at (2) should not be generated, since it is
> > > in the middle of the prologue code.
> > Luis, isn't there a bugzilla regarding this?  This seems to me to
> > be similar to what you had been looking at.
> >
> > Peter


--
Michael Eager	 eager@eagercon.com
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