[FFmpeg-devel] TEXTRELs in fft_mmx.asm (was Re: [PATCH] split-radix FFT)

[Dominik 'Rathann' Mierzejewski]

On Monday, 03 November 2008 at 05:44, Loren Merritt wrote:
> On Sat, 1 Nov 2008, Dominik 'Rathann' Mierzejewski wrote:
> 
> >... these 6 macros seem to be causing textrels even on x86_64.
> >I've already given up on avoiding textrels in FFmpeg on x86_32,
> >but on x86_64 this is the only problematic case.
> 
> First blacklist everything Drepper has ever written, and explain in your 
> own words why you want to avoid textrels. If it's just to stop selinux 
> from complaining at you, then screw it, I'm not willing to spend any code 
> on that.

Not really. I wouldn't want to sacrifice performance, either.

> The only reason I support PIC on x86_64 is that ld.so doesn't support 
> 32bit textrels in 64bit shared libs. That ld.so bug does not extend to 
> prevent 64bit textrels, so I see no reason to avoid them.
> 
> Then, does this work?

I'll check that ASAP, thanks. I figured it would be something like that.

> According to readelf, .rodata is loaded into the 
> main RX section. I could use .rel.data.ro, but that needs an ifdef for 
> non-elf. I could use .data, but that's counterproductive if your reason 
> for disliking textrels involves the duplication of memory pages.

That's one of the reasons. The other is not having memory pages that
are both writable and executable, which provides an additional level
of security against "arbitrary code execution"-type bugs, IIUC.
If we can have that without too much work and without losing performance,
then I'm all for it.

Regards,
R.

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