sys-apps/nix and app-text/lowdown-nix fail to link with CFLAGS=-flto: ld: ...ccsAsSAj.ltrans0.ltrans.o:(.debug_info+0x2f): undefined reference to `document.c....' #19

drnfc · 2022-06-06T20:53:15Z

Not sure if this is the right place to ask this, but I am having issues emerging nix.
here's my portage build log:

https://pastebin.com/VYV27NJR

things I've tried:

disabling LTO
installing nix v2.8.1

trofi · 2022-06-06T21:00:29Z

It's the right place. Welcome! :) Let's try to figure out why it fails.

Is it a fresh sys-apps/nix install? Or an upgrade of some existing version? I'll try to reproduce locally as well.

Posting build snippet here to ease the search:

$ x86_64-pc-linux-gnu-g++ -o /var/tmp/portage/sys-apps/nix-2.9.0/image/usr/lib64/libnixcmd.so -shared  -L/var/tmp/portage/sys-apps/nix-2.9.0/image/usr/lib64 -lnixstore -Wl,-rpath,/usr/lib64  -L/var/tmp/portage/sys-apps/nix-2.9.0/image/usr/lib64 -lnixutil -Wl,-rpath,/usr/lib64  -L/var/tmp/portage/sys-apps/nix-2.9.0/image/usr/lib64 -lnixexpr -Wl,-rpath,/usr/lib64 -latomic_ops -lgc -lpthread -ldl  -L/var/tmp/portage/sys-apps/nix-2.9.0/image/usr/lib64 -lnixmain -Wl,-rpath,/usr/lib64  -L/var/tmp/portage/sys-apps/nix-2.9.0/image/usr/lib64 -lnixfetchers -Wl,-rpath,/usr/lib64 -L/usr/lib64 -Wl,-O1 -Wl,--as-needed -Wl,--no-copy-dt-needed-entries src/libcmd/command.o src/libcmd/common-eval-args.o src/libcmd/installables.o src/libcmd/legacy.o src/libcmd/markdown.o src/libcmd/repl.o -leditline -L/usr/lib64/lowdown-nix/lib -llowdown -lm -pthread -Wl,-z,defs -Wl,-soname=libnixcmd.so 
/usr/lib/gcc/x86_64-pc-linux-gnu/11.3.0/../../../../x86_64-pc-linux-gnu/bin/ld: /var/tmp/portage/sys-apps/nix-2.9.0/temp/ccP05pSk.ltrans0.ltrans.o:(.debug_info+0x2f): undefined reference to `buffer.c.69cd1d9b'
/usr/lib/gcc/x86_64-pc-linux-gnu/11.3.0/../../../../x86_64-pc-linux-gnu/bin/ld: /var/tmp/portage/sys-apps/nix-2.9.0/temp/ccP05pSk.ltrans0.ltrans.o:(.debug_info+0x4a): undefined reference to `buffer.c.69cd1d9b'
/usr/lib/gcc/x86_64-pc-linux-gnu/11.3.0/../../../../x86_64-pc-linux-gnu/bin/ld: /var/tmp/portage/sys-apps/nix-2.9.0/temp/ccP05pSk.ltrans0.ltrans.o:(.debug_info+0x57): undefined reference to `buffer.c.69cd1d9b'
...

drnfc · 2022-06-06T21:01:06Z

It is a fresh install, and wow, thanks for the quick response

trofi · 2022-06-06T21:08:12Z

While nix itself is being built without LTO one of it's library depends does build with LTO and final driver fails to resolve it: buffer.c.69cd1d9b. That usually happens if one of libraries is statically linked.

It likely comes from /usr/lib64/lowdown-nix/lib/liblowdown.a from app-text/lowdown-nix (it does not provide dynamic library equivalent). As a workaround you can try rebuilding it without LTO as well and see if it helps.

Or if you suspect app-text/lowdown-nix was built before a compiler upgrade you can just rebuild it first and see if it's enough.

trofi · 2022-06-06T21:11:16Z

Meanwhile I reproduced locally similar failure with -flto:

# CFLAGS="-O2 -flto" CXXFLAGS="-O2 -flto" LDFLAGS="-O2 -flto" emerge -v1 app-text/lowdown-nix sys-apps/nix
...
x86_64-pc-linux-gnu-g++ -o /dev/shm/portage/sys-apps/nix-2.9.0/image/usr/lib64/libnixcmd.so -shared  -L/dev/shm/portage/sys-apps/nix-2.9.0/image/usr/lib64 -lnixstore -Wl,-rpath,/usr/lib64  -L/dev/shm/portage/sys-apps/nix-2.9.0/image/usr/lib64 -lnixutil -Wl,-rpath,/usr/lib64  -L/dev/shm/portage/sys-apps/nix-2.9.0/image/usr/lib64 -lnixexpr -Wl,-rpath,/usr/lib64 -latomic_ops -lgc -lpthread -ldl  -L/dev/shm/portage/sys-apps/nix-2.9.0/image/usr/lib64 -lnixmain -Wl,-rpath,/usr/lib64  -L/dev/shm/portage/sys-apps/nix-2.9.0/image/usr/lib64 -lnixfetchers -Wl,-rpath,/usr/lib64 -L/usr/lib64 -O2 -flto -Wl,--no-copy-dt-needed-entries src/libcmd/command.o src/libcmd/common-eval-args.o src/libcmd/installables.o src/libcmd/legacy.o src/libcmd/markdown.o src/libcmd/repl.o -leditline -L/usr/lib64/lowdown-nix/lib -llowdown -lm -pthread -Wl,-z,defs -Wl,-soname=libnixcmd.so
/usr/lib/gcc/x86_64-pc-linux-gnu/12.1.0/../../../../x86_64-pc-linux-gnu/bin/ld: /dev/shm/portage/sys-apps/nix-2.9.0/temp/ccsAsSAj.ltrans0.ltrans.o:(.debug_info+0x2f): undefined reference to `document.c.7180b45a'
/usr/lib/gcc/x86_64-pc-linux-gnu/12.1.0/../../../../x86_64-pc-linux-gnu/bin/ld: /dev/shm/portage/sys-apps/nix-2.9.0/temp/ccsAsSAj.ltrans0.ltrans.o:(.debug_info+0x4a): undefined reference to `document.c.7180b45a'
/usr/lib/gcc/x86_64-pc-linux-gnu/12.1.0/../../../../x86_64-pc-linux-gnu/bin/ld: /dev/shm/portage/sys-apps/nix-2.9.0/temp/ccsAsSAj.ltrans0.ltrans.o:(.debug_info+0x57): undefined reference to `document.c.7180b45a'
/usr/lib/gcc/x86_64-pc-linux-gnu/12.1.0/../../../../x86_64-pc-linux-gnu/bin/ld: /dev/shm/portage/sys-apps/nix-2.9.0/temp/ccsAsSAj.ltrans0.ltrans.o:(.debug_info+0x64): undefined reference to `document.c.7180b45a'

Looking as well.

drnfc · 2022-06-06T21:16:44Z

completely disabling lto and recompiling lowdown-nix fixed my issue. Now I just got to figure out the minimum number of settings to change and I'll report to the lto-overlay, as this is an LTO issue, not a nix one. Thanks for the help.

trofi · 2022-06-06T21:29:45Z

Adding FEATURES="nostrip" when building lowdonw-nix is enough to restore LTO build. I guess it's a form of https://bugs.gentoo.org/603594. Do you have AR=gcc-ar RANLIB=gcc-ranlib or equivalent set in your environment? (emerge --info app-text/lowdown-nix should tell)

drnfc · 2022-06-06T21:32:44Z

no I don't seem to have those set in my environment.

trofi · 2022-06-06T21:40:14Z

Maybe it's OK. Chances are that binutils automatically discover linker plugin and use it.

trofi · 2022-06-06T21:51:06Z

Gentoo uses the following to strip files:

strip: x86_64-pc-linux-gnu-strip --strip-unneeded -N __gentoo_check_ldflags__ -R .comment -R .GCC.command.line -R .note.gnu.gold-version

   /usr/lib64/lowdown-nix/bin/lowdown
   /usr/lib64/lowdown-nix/bin/lowdown-diff
   /usr/lib64/lowdown-nix/lib/liblowdown.a

x86_64-pc-linux-gnu-strip: /dev/shm/portage/app-text/lowdown-nix-1.0.0/image/usr/lib64/lowdown-nix/lib/stPl3K5x/autolink.o: plugin needed to handle lto object

I think it hints at missing plugin load. Worth exploring if strip --strip-unneeded is supposed to keep .o files alive after stripping. I suspect it does not interact that well with LTO bytecode.

trofi · 2022-06-06T22:21:46Z

Gentoo uses the following to strip files:

strip: x86_64-pc-linux-gnu-strip --strip-unneeded -N __gentoo_check_ldflags__ -R .comment -R .GCC.command.line -R .note.gnu.gold-version

   /usr/lib64/lowdown-nix/bin/lowdown
   /usr/lib64/lowdown-nix/bin/lowdown-diff
   /usr/lib64/lowdown-nix/lib/liblowdown.a

x86_64-pc-linux-gnu-strip: /dev/shm/portage/app-text/lowdown-nix-1.0.0/image/usr/lib64/lowdown-nix/lib/stPl3K5x/autolink.o: plugin needed to handle lto object

The log is misleading. Those strip flags are used only for ELF files. .a files followdifferent path:

+ x86_64-pc-linux-gnu-strip -g /dev/shm/portage/app-text/lowdown-nix-1.0.0/image/usr/lib64/lowdown-nix/lib/liblowdown.a
x86_64-pc-linux-gnu-strip: /dev/shm/portage/app-text/lowdown-nix-1.0.0/image/usr/lib64/lowdown-nix/lib/st9KFBGP/autolink.o: plugin needed to handle lto object
+ gcc-ranlib /dev/shm/portage/app-text/lowdown-nix-1.0.0/image/usr/lib64/lowdown-nix/lib/liblowdown.a

Looking at the binutils source only ar and nm can autoload LTO plugins. I think it's expected that FEATURES=strip (uses strip) and FEATURES=splitdebug (uses objcopy) both can break LTO .a archives.

What I'm not sure about is whether strip -g is guaranteed to work on .a/.o files. I could see how LTO's dwarf sections could contain not just debug info.

https://sourceware.org/PR21479 implies it might work, but is a "minefield".

trofi · 2022-06-07T18:43:11Z

Filed https://gcc.gnu.org/PR105877 to see if we can clarify it upstream.

By default portage runs 'strip -g' on .a files. This is known to break liblowdown.a when it's built with -flto: #19 Chances are it's a toolchain bug (or a limitation of LTO): https://gcc.gnu.org/PR105877 Reported-by: drnfc Bug: https://gcc.gnu.org/PR105877 Closes: #19

trofi · 2022-06-08T06:51:22Z

Meanwhile f9afe32 should allow building nix with lto.

trofi changed the title ~~emake failed~~ sys-apps/nix and app-text/lowdown-nix fail to link with CFLAGS=-flto: ld: ...ccsAsSAj.ltrans0.ltrans.o:(.debug_info+0x2f): undefined reference to `document.c....' Jun 6, 2022

drnfc closed this as completed Jun 6, 2022

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sys-apps/nix and app-text/lowdown-nix fail to link with CFLAGS=-flto: ld: ...ccsAsSAj.ltrans0.ltrans.o:(.debug_info+0x2f): undefined reference to `document.c....' #19

sys-apps/nix and app-text/lowdown-nix fail to link with CFLAGS=-flto: ld: ...ccsAsSAj.ltrans0.ltrans.o:(.debug_info+0x2f): undefined reference to `document.c....' #19

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sys-apps/nix and app-text/lowdown-nix fail to link with CFLAGS=-flto: ld: ...ccsAsSAj.ltrans0.ltrans.o:(.debug_info+0x2f): undefined reference to `document.c....' #19

sys-apps/nix and app-text/lowdown-nix fail to link with CFLAGS=-flto: ld: ...ccsAsSAj.ltrans0.ltrans.o:(.debug_info+0x2f): undefined reference to `document.c....' #19

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