Bug#932287: glib2.0: FTBFS on mips64el: linking 32-bit code with 64-bit code

[Simon McVittie]

Control: severity -1 normal

On Thu, 18 Jul 2019 at 16:04:36 +0800, YunQiang Su wrote:
> Simon McVittie <smcv at debian.org> 于2019年7月18日周四 上午2:03写道：
> > Looks like plain objcopy produces MIPS-I objects, whereas invoking it
> > in the normal way via the compiler frontend produces MIPS64r2 objects:
> >
> > (sid_mips64el-dchroot)smcv at eller ~/glib % file debian/build/deb/gio/tests/bcb7ac7@@actions at exe/actions.c.o
> > debian/build/deb/gio/tests/bcb7ac7@@actions at exe/actions.c.o: ELF 64-bit LSB relocatable, MIPS, MIPS64 rel2 version 1 (SYSV), with debug_info, not stripped
> > (sid_mips64el-dchroot)smcv at eller ~/glib % file debian/build/deb/gio/tests/test_resources2.o
> > debian/build/deb/gio/tests/test_resources2.o: ELF 64-bit LSB relocatable, MIPS, MIPS-I version 1 (SYSV), not stripped

For now I've disabled that test via
debian/patches/GIO-tests-Don-t-do-clever-tricks-with-objcopy.patch. Please
drop that patch if you want to test potential fixes.

> I guess you are right, objcopy doesn't alter the object file correctly.
> We need to patch it.

Here's a minimal reproducer, which demonstrates that the problem is
actually in (how GLib invokes) ld, not objcopy:

Create an ordinary object file with 4 bytes of data named "foo", for
comparison:

$ cat > 932287.c <<EOF
int foo = 0x12345678;
EOF
$ cc -c -o 932287.o 932287.c
$ file 932287.o
932287.o: ELF 64-bit LSB relocatable, MIPS, MIPS64 rel2 version 1 (SYSV), not stripped
$ objdump -x 932287.o
...

Create an object file from a raw binary with 4 bytes of data named "foo":

$ xxd -r - 932287.bin <<EOF
00000000: 7856 3412
EOF
$ ld -r -b binary 932287.bin -o 932287-raw.o
$ file 932287-raw.o
932287-raw.o: ELF 64-bit LSB relocatable, MIPS, MIPS-I version 1 (SYSV), not stripped
$ objdump -x 932287-raw.o
...
$ objcopy --add-symbol foo=.data:0 932287-raw.o 932287-with-symbol.o
$ file 932287-with-symbol.o
932287-with-symbol.o: ELF 64-bit LSB relocatable, MIPS, MIPS-I version 1 (SYSV), not stripped
$ objdump -x 932287-with-symbol.o
...

Presumably when ld is invoked via the gcc compiler driver it does something
that is more suitable for mips64el?

Regards,
    smcv