unable to build i386 glibc: lld: error: relocation refers to a symbol in a discarded section

[andrewrk]

$ ./zig test ../test/stage1/behavior.zig -target i386-linux-gnu -lc
lld: error: relocation refers to a symbol in a discarded section: __x86.get_pc_thunk.bx
>>> defined in /home/andy/.cache/zig/stage1/o/QwPOfrBzzIXOEPuFhvbaQ4pBmiZk1vZIjVDP_sy7CCeeXOl8s6Zh8l0nMcfprTj6/crti.o
>>> referenced by crti.S:68 (/home/andy/Downloads/zig/lib/libc/glibc/sysdeps/i386/crti.S:68)
>>>               /home/andy/.cache/zig/stage1/o/QwPOfrBzzIXOEPuFhvbaQ4pBmiZk1vZIjVDP_sy7CCeeXOl8s6Zh8l0nMcfprTj6/crti.o:(.init+0x5)
>>> referenced by crti.S:88 (/home/andy/Downloads/zig/lib/libc/glibc/sysdeps/i386/crti.S:88)
>>>               /home/andy/.cache/zig/stage1/o/QwPOfrBzzIXOEPuFhvbaQ4pBmiZk1vZIjVDP_sy7CCeeXOl8s6Zh8l0nMcfprTj6/crti.o:(.fini+0x5)

[LemonBoy]

Oh this is a nice one, there are a few problems:

• The get_pc_thunk stubs are actually emitted by gcc when PIC is emitted...
• ...but clang doesn't follow this convention (afaik they're replaced by some inline code)...
• ...anyways, glibc used to define __x86.get_pc_thunk.bx in a .gnu.linkonce section...
• ...that lld correctly discards, hence the error...
• ...but glibc devs changed that piece of code to use a comdat section instead...
• ...and that fix was shipped with glibc 2.32 that Zig supports...
• ...but Update to glibc 2.32 #6212 forgot to update the sysdeps folder!

Many issues (#3340, #3287, #2256, #4927 and this one) have the same root cause in common, missing/stale files in sysdeps.

@andrewrk the instructions on the wiki page should be updated, I don't see sysdeps being mentioned at all.
The last update was made in 697b123, a while ago. Shipping a mix of old and new header files is no good.

[zhaozg]

Ref by #7440

[FireFox317]

@andrewrk Can we make sure that we do the thing that @LemonBoy said in the comment above (#4926 (comment)) before the release of zig 0.8.0? This issue currently causes a lot of problems, as can be seen by all the linked comments in this issue.

[sundbp]

Hi. I'm a potential first time zig contributor. I was going to have a go at adding support for glibc-2.33 to play nicely on Arch. In doing so I was pointed towards this ticket. If someone could add a bit of color about the sysdeps issue I'll have a go at fixing scripts and making a PR for glibc-2.33 and a separate PR for updated glibc-2.32 with fixed sysdeps. Hopefully fixing scripts will make the wiki entry be "correct", otherwise I'll update the wiki as well to be complete. (https://github.com/ziglang/zig/wiki/Updating-libc). So any input on the sysdeps would be great! @LemonBoy

[LemonBoy]

Well the first step is finding out what to copy (all the .h files and some crt-related .S files) and the following one to update glibc and check if all the linked errors are solved.

[sundbp]

Is there any example of a correct set of sysdeps file to use as guidance that you're aware of?

[LemonBoy]

Not really, ideally every file that's copied by make install is potentially interesting (with a caveat, the set of installed files varies between target architectures).

[sundbp]

So I managed to build and sync the headers as per the wiki. I've then looked at all the files in lib/libc/glibc to see what there should be sync'd with the new version. It isn't only sysdeps as noted. The following list of files has no match in the glibc 2.33 dir:

No such file: include/libc-modules.h
No such file: sysdeps/alpha/nptl/bits/pthreadtypes-arch.h
No such file: sysdeps/powerpc/nptl/bits/pthreadtypes-arch.h
No such file: sysdeps/s390/nptl/bits/pthreadtypes-arch.h
No such file: sysdeps/x86/bits/select.h
No such file: sysdeps/ia64/nptl/bits/pthreadtypes-arch.h
No such file: sysdeps/microblaze/nptl/bits/pthreadtypes-arch.h
No such file: sysdeps/sh/nptl/bits/pthreadtypes-arch.h
No such file: sysdeps/init_array/crtn.S
No such file: sysdeps/init_array/crti.S
No such file: sysdeps/unix/alpha/sysdep.h
No such file: sysdeps/unix/mips/mips64/n32/sysdep.h
No such file: sysdeps/unix/mips/mips64/n64/sysdep.h
No such file: sysdeps/unix/sysv/linux/alpha/bits/stat.h
No such file: sysdeps/unix/sysv/linux/hppa/pthread.h
No such file: sysdeps/unix/sysv/linux/powerpc/bits/stat.h
No such file: sysdeps/unix/sysv/linux/powerpc/powerpc32/sysdep.h
No such file: sysdeps/unix/sysv/linux/generic/bits/stat.h
No such file: sysdeps/unix/sysv/linux/s390/bits/stat.h
No such file: sysdeps/unix/sysv/linux/x86/bits/stat.h
No such file: sysdeps/unix/sysv/linux/mips/mips64/n32/sysdep.h
No such file: sysdeps/unix/sysv/linux/mips/mips64/n64/sysdep.h
No such file: sysdeps/unix/sysv/linux/mips/bits/stat.h
No such file: sysdeps/unix/sysv/linux/ia64/bits/stat.h
No such file: sysdeps/unix/sysv/linux/microblaze/bits/stat.h
No such file: sysdeps/unix/sysv/linux/sparc/bits/stat.h
No such file: sysdeps/unix/sysv/linux/m68k/bits/stat.h
No such file: sysdeps/sparc/nptl/bits/pthreadtypes-arch.h
No such file: sysdeps/arm/nptl/bits/pthreadtypes-arch.h
No such file: csu/abi-note.S
No such file: csu/abi-tag.h

How should I interpret that? Are these files no longer required due to changes in glibc? Do they come from elsewhere?

I see that e.g. libc-modules.h is referenced in glibc.zig, and looks generated by a tool. Where does this file come from?

[LemonBoy]

How should I interpret that?

Open this and start searching.
I'll get you started, have you seen this commit?
And this one?
And this one?
Oh and this one too

[sundbp]

I was afraid that'd be the case - go through things manually until it makes sense basically.

The one thing I'm a bit lost on is how libc-modules.h is created. It doesn't exist inside of my multi directory and seems to be automatically generated. I'll need to work out how to generate it properly.

[LemonBoy]

$(common-objpfx)libc-modules.h: $(common-objpfx)libc-modules.stmp; @:
$(common-objpfx)libc-modules.stmp: $(..)scripts/gen-libc-modules.awk \
				   $(common-objpfx)soversions.i
	$(AWK) -v buildlist="$(subst -,_,$(built-modules))" -f $^ > ${@:stmp=T}
	$(move-if-change) ${@:stmp=T} ${@:stmp=h}
	touch $@

[sundbp]

Indeed. I'm putting this on ice for a bit - spoke to @andrewrk about it briefly and it's complex enough that it'll be time better spent by someone else. Thanks for your help - I learnt a fair amount in the process either way :)

[andrewrk]

@andrewrk the instructions on the wiki page should be updated, I don't see sysdeps being mentioned at all.

I've done as you requested.

Many issues (#3340, #3287, #2256, #4927 and this one) have the same root cause in common, missing/stale files in sysdeps.

There are no more stale files. Here are updates for each of these issues:

• RISC-V is stuck on glibc using an undocumented GAS feature that clang does not support: unable to build glibc for target riscv64-linux-gnu #3340 (comment)
• -target arm-linux-gnueabihf -mcpu=generic+v8a is in the same place it was before, it just needs a few more files copied over from upstream.
• powerpc is actually looking pretty good. The next issue is that behavior tests are failing at runtime: problem compiling for 32bit powerpc targets #2256 (comment)
• mipsel-linux-gnueabihf is down to undefined symbol: __mips_syscall5: unable to build mipsel glibc: fatal error: 'entry.h' file not found #4927 (comment)