Re: gcc corrections for better pie support

["Peter S. Mazinger" <ps dot m at gmx dot net>]

On Wed, 10 Nov 2004, Richard Sandiford wrote:

> "Peter S. Mazinger" <ps.m@gmx.net> writes:
> > On Wed, 10 Nov 2004, Richard Sandiford wrote:
> >> Thiemo Seufer <ica2_ts@csv.ica.uni-stuttgart.de> writes:
> >> > Richard Sandiford wrote:
> >> >> So the current handling of __PIC__ is inconsistent.  What does it mean
> >> >> for mips*-linux-gnu targets?  Does it mean:
> >> >> 
> >> >>    (1) That position independent code has been explicitly selected?
> >> >>        If so, then flag_pie || flag_shlib seems like the right condition.
> >> >> 
> >> >>    (2) That abicalls code is selected?  If so, then the current specs are
> >> >>        wrong, because "gcc -fno-pic" generates abicalls code.
> >> >> 
> >> >> But I suppose the current definition is closest to (2).  If (2) is indeed
> >> >> what we want, then another alternative would be to guard the __PIC__
> >> >> definition in linux.h with TARGET_ABICALLS.
> >> >
> >> > Currently in use on MIPS linux are:
> >> >  - PIC + abicalls for the whole userland. __PIC__ is always expected to
> >> >    be defined. Executables are always PIC. This is the toolchain default.
>                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> >> 
> >> Executables are created from position-independent objects, but the
> >> executables themselves are not PIC.  They have a fixed load address
> >> and are not relocatable.  Hence...
> >
> > This is not quite true, I have access to a mips box running uclibc and I 
> > can build PIE executables, these are relocatable (I know though that such 
> > test can't be done on glibc, because it fails w/ undefs)
> 
> I was talking specifically about the default here, not what happens when
> you use -fpie or -fPIE (note the highlighted context).  It _is_ true that
> mips*-linux-gnu does not create position-independent executables by default.

true for all archs

> 
> FWIW (in case this is what you're suggesting) I think making uclibc
> targets generate PIE by default would be a mistake.

No, I don't suggest that, it would be too troublesome to have it like that
(many text relocations on other archs where PIC is not default)

> 
> Anyway (and thanks to Thiemo for his reply), it looks like we're getting
> close agreement on the __PIC__=abicalls thing.  Going back to your patch,
> I think the summary is:
> 
>   - Remove the __PIC__ handling from spec strings and guard the
>     TARGET_OS_CPP_BUILTINS definition with TARGET_ABICALLS.

what to do w/ lines 52-54, MASK_ABICALLS (comment and define)

Peter

> 
>   - Make the assembler spec pass -KPIC unless -mno-abicalls is used.
> 
> Richard
> 
> 

-- 
Peter S. Mazinger <ps dot m at gmx dot net>           ID: 0xA5F059F2
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