[Mesa-dev] [PATCH] configure: Enable large file support for the 32-bit platforms

[Lauri Kasanen]

On Fri, 31 Jan 2014 13:28:48 -0800
Carl Worth <cworth at cworth.org> wrote:

> Lauri Kasanen <cand at gmx.com> writes:
> >> 32-bit use is on the increase due to Steam; avoid any surprises
> >> and make Mesa LFS-aware.
> ...
> >>  AC_PROG_MKDIR_P
> >> +AC_SYS_LARGEFILE
> 
> Hi Lauri,
> 
> Can you describe a bit more what failure modes you encounter without
> AC_SYS_LARGEFILE in place? I just haven't dealt with this macro, (nor
> the resulting compiler options), before and am wanting to understand
> things a bit better.

It uses the experience gathered in autoconf to enable large file
support on all platforms. For 32-bit Linux, it adds -D_LARGEFILE_SOURCE
and -D_FILE_OFFSET_BITS=64. For other platforms, other magic is used.
On 64-bit linux, it is a no-op.

This means that all IO calls automatically and transparently handle
files above 2gb. Without this, you get a cap at 2gb for both read and
write, which can be quite unexpected.

I hit this in some submitted memory traces from 32-bit platforms. They
were capped at exactly UINT_MAX bytes. This code is not in mesa, but
it's not hard to imagine other dumps, or perhaps reading a big binary
shader exceeding 2gb.

> > Ping. Having this done in autoconf is much better than the current
> > hardcoding done in vmware svga build files.
> 
> Does that suggest that the patch should also be removing some of these
> hard-coded options?

Yes. I didn't do it, because I've no way to test the SVGA driver.

- Lauri