PR79066, non-PIC code generated for powerpc glibc with -fpic

Alan Modra amodra@gmail.com
Tue Jan 17 02:52:00 GMT 2017


On Mon, Jan 16, 2017 at 01:49:36PM -0600, Segher Boessenkool wrote:
> On Mon, Jan 16, 2017 at 03:50:01PM +1030, Alan Modra wrote:
> > > > > Okay for trunk if there is nothing unexpected.  Thanks!
> > > > 
> > > > I guess I should at least build glibc.
> > > 
> > > Yes exactly, something big that uses pic -- it is pretty obvious it won't
> > > change anything for non-pic.
> > 
> > glibc built fine without elf_high/elf_low with no regressions in its
> > testsuite.
> 
> I meant comparing the generated code, sorry.

libc.so had differences in debug sections due to libgcc source paths
being different, but other than that there were no differences.

> > However, there is a problem in rs6000_emit_allocate_stack
> > -fstack-limit-symbol=SYMBOL code.  This now might ICE if someone tries
> > to use the option with -fpic/PIC.  I reckon the option combination to
> > be little used, so it shouldn't hurt to disable -fstack-limit-symbol
> > for PIC.  (We were generating non-PIC for the trap, so we probably
> > would have gotten a complaint about text relocs in shared libraries.)
> > 
> > This revised patch has been bootstrapped and regression tested as
> > before, and tested with glibc too.  OK?
> > 
> > 	PR target/79066
> > 	* config/rs6000/rs6000.md (elf_high, elf_low): Disable when pic.
> > 	* config/rs6000/rs6000.c (rs6000_emit_allocate_stack): Don't allow
> > 	symbolic stack limit when pic.
> > testsuite/
> > 	* gcc.target/powerpc/pr79066.c: New.
> > 
> > diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c
> > index 11394b2..2dd6bbe 100644
> > --- a/gcc/config/rs6000/rs6000.c
> > +++ b/gcc/config/rs6000/rs6000.c
> > @@ -27668,7 +27668,8 @@ rs6000_emit_allocate_stack (HOST_WIDE_INT size, rtx copy_reg, int copy_off)
> >  	}
> >        else if (GET_CODE (stack_limit_rtx) == SYMBOL_REF
> >  	       && TARGET_32BIT
> > -	       && DEFAULT_ABI == ABI_V4)
> > +	       && DEFAULT_ABI == ABI_V4
> > +	       && !flag_pic)
> >  	{
> >  	  rtx toload = gen_rtx_CONST (VOIDmode,
> >  				      gen_rtx_PLUS (Pmode,
> 
> Please at least make it sorry() for ABI_V4 && flag_pic.  Or what does it
> result in with the patch as-is?

I think we're OK as is.  A warning is emitted "stack limit expression
is not supported".

-- 
Alan Modra
Australia Development Lab, IBM



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