[bug#43591] [PATCH core-updates] gnu: glibc-final: Catch all cases of a glibc user not requesting 64-bit offsets and then using readdir.

[Marius Bakke]

Danny Milosavljevic <dannym@scratchpost.org> writes:

> Hi Marius,
>
> On Thu, 24 Sep 2020 20:17:14 +0200
> Marius Bakke <marius@gnu.org> wrote:
>
>> As mentioned in that issue, and which this patch states on no uncertain
>> terms, a workaround is to use -D_FILE_OFFSET_BITS=64 on 32-bit platforms.
>
> Yeah.  The problem is how to find all those places where we need to add it,
> and how to keep finding them as we maintain stuff (read: as upstream changes
> stuff).
>
>> Won't this break _everything_ that uses readdir() without 64-bit
>> offsets?
>
> That's the goal of that patch.  Because it won't work at runtime anyway, when
> run on a guix x86_64 build machine, building for ARM (which is the usual way
> we build stuff for ARM).

Why is this not an issue with i686 on x86_64 kernels?  Or armhf on
AArch64?  This problem only manifests when using QEMUs syscall
emulation, right?

> Maybe we can find out whether dirent.h is #included for compiling for one of
> the main Guix platforms (I prefer this latter solution, if possible).
>
> It's either that or we stop qemu transparent emulation on the build farm,
> because the result isn't reliable.  This time it was "caught" because of
> an overabundance of caution on behalf of the glibc people.  We won't be
> so lucky next time.

Arguably running code for foreign architectures through QEMU binfmt is
something of a hack.  Mandating that every package *must* be patched to
support it seems user-hostile.  I'm more in favor of dropping it on the
build farm, or just keep fixing things on a per-package basis.

A less user-hostile solution could perhaps be to (setenv "CFLAGS"
"-D_FILE_OFFSET_BITS=64") on 32-bit architectures in gnu-build-system.
Not sure whether that could cause any adverse effects.  But again, I
don't like the idea of optimizing for QEMUs user-mode emulation.

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