Re: [PATCH][libgcc] Fix PR81080, build libgcov with large file support

[Joseph Myers <joseph at codesourcery dot com>]

On Wed, 14 Jun 2017, Richard Biener wrote:

> The following patch makes sure we build the 32bit multilib libgcov with
> large file support on x86_64-linux.  libgcov.h ends up using auto-host.h
> via including tconfig.h which is only valid for the main multilib
> (and on x86_64 doesn't need explicit large-file support defines).  That
> libgcc ends up using that is probably from times where it wasn't at
> the toplevel, some files already include auto-target.h generated by
> libgcc configure but most do so after including tsystem.h which is
> of course too late.  I suppose libgcc files shouldn't include tconfig.h
> from gcc/, but that's a change going to far for this bug ;)

tconfig.h shouldn't include host-specific configure test results (as the 
relevant bits of config.in should be conditioned on USED_FOR_TARGET), 
though that doesn't mean everything is indeed properly conditioned (and 
ideally we'd avoid configuration information from the gcc/ directory 
needing to be used in target libraries at all).

> Other than libgcov libgomp, libcilkrts, libmpx and libstdc++
> are similarly affected (they use fopen on the 32bit multilib)
> but not fixed.  libubsan, libasan, libssp, libbacktrace and libgfortran
> use open.  While libgfortran configury has AC_SYS_LARGEFILE, the
> open use leaks in through libbacktrace (ubsan/asan might have the
> same issue, didn't investigate).  libbacktrace lacks AC_SYS_LARGEFILE.

In general, watch out for off_t etc. as part of the ABI for such libraries 
(in which case AC_SYS_LARGEFILE could break the ABI).  And if the code 
uses fseek/ftell, it needs to change to fseeko/ftello (where available) to 
handle large offsets.

-- 
Joseph S. Myers
joseph@codesourcery.com