107728 – _umoddi3.o has reference to the unwinder at -O0

Bug 107728 - _umoddi3.o has reference to the unwinder at -O0

Summary: _umoddi3.o has reference to the unwinder at -O0

Status:	UNCONFIRMED

Alias:	None

Product:	gcc
Classification:	Unclassified
Component:	libgcc (show other bugs)
Version:	12.2.0

Importance:	P3 normal
Target Milestone:	---
Assignee:	Not yet assigned to anyone

URL:
Keywords:	build

Depends on:
Blocks:

Reported:	2022-11-16 21:43 UTC by Thomas Petazzoni
Modified:	2022-11-24 17:31 UTC (History)
CC List:	1 user (show)

See Also:
Host:
Target:	sh4eb-buildroot-linux-gnu
Build:
Known to work:
Known to fail:
Last reconfirmed:

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Description Thomas Petazzoni 2022-11-16 21:43:23 UTC

We've started doing builds with -O0 in Buildroot, and we get build failures in glibc that look like this:


/home/autobuild/autobuild/instance-11/output-1/host/lib/gcc/sh4eb-buildroot-linux-gnu/11.3.0/../../../../sh4eb-buildroot-linux-gnu/bin/ld: /home/autobuild/autobuild/instance-11/output-1/build/glibc-2.36-66-ga1dc0be03c9dd850b864bd7a9c03cf8e396eb7ca/build/elf/librtld.os: in function `__register_frame':
/home/autobuild/autobuild/instance-11/output-1/build/host-gcc-initial-11.3.0/build/sh4eb-buildroot-linux-gnu/libgcc/../../../libgcc/unwind-dw2-fde.c:138: undefined reference to `malloc'
/home/autobuild/autobuild/instance-11/output-1/host/lib/gcc/sh4eb-buildroot-linux-gnu/11.3.0/../../../../sh4eb-buildroot-linux-gnu/bin/ld: /home/autobuild/autobuild/instance-11/output-1/build/glibc-2.36-66-ga1dc0be03c9dd850b864bd7a9c03cf8e396eb7ca/build/elf/librtld.os: in function `__register_frame_table':
/home/autobuild/autobuild/instance-11/output-1/build/host-gcc-initial-11.3.0/build/sh4eb-buildroot-linux-gnu/libgcc/../../../libgcc/unwind-dw2-fde.c:186: undefined reference to `malloc'
/home/autobuild/autobuild/instance-11/output-1/host/lib/gcc/sh4eb-buildroot-linux-gnu/11.3.0/../../../../sh4eb-buildroot-linux-gnu/bin/ld: /home/autobuild/autobuild/instance-11/output-1/build/glibc-2.36-66-ga1dc0be03c9dd850b864bd7a9c03cf8e396eb7ca/build/elf/librtld.os: in function `__deregister_frame_info_bases':
/home/autobuild/autobuild/instance-11/output-1/build/host-gcc-initial-11.3.0/build/sh4eb-buildroot-linux-gnu/libgcc/../../../libgcc/unwind-dw2-fde.c:246: undefined reference to `free'
/home/autobuild/autobuild/instance-11/output-1/host/lib/gcc/sh4eb-buildroot-linux-gnu/11.3.0/../../../../sh4eb-buildroot-linux-gnu/bin/ld: /home/autobuild/autobuild/instance-11/output-1/build/glibc-2.36-66-ga1dc0be03c9dd850b864bd7a9c03cf8e396eb7ca/build/elf/librtld.os: in function `__deregister_frame':
/home/autobuild/autobuild/instance-11/output-1/build/host-gcc-initial-11.3.0/build/sh4eb-buildroot-linux-gnu/libgcc/../../../libgcc/unwind-dw2-fde.c:260: undefined reference to `free'
/home/autobuild/autobuild/instance-11/output-1/host/lib/gcc/sh4eb-buildroot-linux-gnu/11.3.0/../../../../sh4eb-buildroot-linux-gnu/bin/ld: /home/autobuild/autobuild/instance-11/output-1/build/glibc-2.36-66-ga1dc0be03c9dd850b864bd7a9c03cf8e396eb7ca/build/elf/librtld.os: in function `start_fde_sort':
/home/autobuild/autobuild/instance-11/output-1/build/host-gcc-initial-11.3.0/build/sh4eb-buildroot-linux-gnu/libgcc/../../../libgcc/unwind-dw2-fde.c:449: undefined reference to `malloc'
/home/autobuild/autobuild/instance-11/output-1/host/lib/gcc/sh4eb-buildroot-linux-gnu/11.3.0/../../../../sh4eb-buildroot-linux-gnu/bin/ld: /home/autobuild/autobuild/instance-11/output-1/build/host-gcc-initial-11.3.0/build/sh4eb-buildroot-linux-gnu/libgcc/../../../libgcc/unwind-dw2-fde.c:449: undefined reference to `malloc'
/home/autobuild/autobuild/instance-11/output-1/host/lib/gcc/sh4eb-buildroot-linux-gnu/11.3.0/../../../../sh4eb-buildroot-linux-gnu/bin/ld: /home/autobuild/autobuild/instance-11/output-1/build/glibc-2.36-66-ga1dc0be03c9dd850b864bd7a9c03cf8e396eb7ca/build/elf/librtld.os: in function `end_fde_sort':
/home/autobuild/autobuild/instance-11/output-1/build/host-gcc-initial-11.3.0/build/sh4eb-buildroot-linux-gnu/libgcc/../../../libgcc/unwind-dw2-fde.c:629: undefined reference to `free'
/home/autobuild/autobuild/instance-11/output-1/host/lib/gcc/sh4eb-buildroot-linux-gnu/11.3.0/../../../../sh4eb-buildroot-linux-gnu/bin/ld: /home/autobuild/autobuild/instance-11/output-1/build/glibc-2.36-66-ga1dc0be03c9dd850b864bd7a9c03cf8e396eb7ca/build/elf/librtld.os: in function `abort':
(.text+0x2345c): undefined reference to `__pthread_mutex_lock'
/home/autobuild/autobuild/instance-11/output-1/host/lib/gcc/sh4eb-buildroot-linux-gnu/11.3.0/../../../../sh4eb-buildroot-linux-gnu/bin/ld: (.text+0x23464): undefined reference to `__pthread_mutex_unlock'
/home/autobuild/autobuild/instance-11/output-1/host/lib/gcc/sh4eb-buildroot-linux-gnu/11.3.0/../../../../sh4eb-buildroot-linux-gnu/bin/ld: (.text+0x2346c): undefined reference to `__pthread_mutex_lock'
collect2: error: ld returned 1 exit status
make[3]: *** [Makefile:1339: /home/autobuild/autobuild/instance-11/output-1/build/glibc-2.36-66-ga1dc0be03c9dd850b864bd7a9c03cf8e396eb7ca/build/elf/ld.so] Error 1

See http://autobuild.buildroot.net/results/7df/7df2d0648dd666dd07845614b34f59d6afba96c1/build-end.log for a more complete build log.

The reason is that a number of functions in libgcc/unwind-dw2-fde.c call into C library functions. With an optimization level of -O1 at least, these functions get compiled out, and there is no problem. But at -O0, the code of those functions is kept, causing the above build failure.

To reproduce:

$ git clone https://gitlab.com/buildroot.org/buildroot.git
$ cd buildroot
$ cat > .config <<EOF
BR2_sh=y
BR2_sh4eb=y
BR2_KERNEL_HEADERS_4_14=y
BR2_GCC_VERSION_12_X=y
BR2_TOOLCHAIN_BUILDROOT_CXX=y
# BR2_STRIP_strip is not set
BR2_OPTIMIZE_0=y
EOF
$ make olddefconfig
$ make

(and wait)

Comment 1 Andrew Pinski 2022-11-16 21:54:53 UTC

This is not a GCC issue as __register_frame_table is declared as extern.
This is almost definitely a glibc issue really.
But I doubt glibc can be compiled at -O0 because of these issues.

Comment 2 Andrew Pinski 2022-11-16 22:09:18 UTC

Move over, the functions are not optimized out at -O2 but rather they don't get pulled in glibc building because another function is referenced.

Either libgcc should be built with -fdata-sections -ffunction-sections or glibc builds needs to be fixed such that it does not reference the function in the unwinder at -O0.  You need to look at the linker map to figure why the object file is being pulled into glibc at -O0 and not at -O2.
But it is still a bug in glibc's ld.so really.

Comment 3 Thomas Petazzoni 2022-11-16 22:51:30 UTC

Thanks for the super quick feedback. Could you clarify "Move over, the functions are not optimized out at -O2 but rather they don't get pulled in glibc building because another function is referenced." ?

For the record, we are able to work around this issue by passing -O1 in CFLAGS_FOR_TARGET/CXXFLAGS_FOR_TARGET when building the first stage gcc.

Comment 4 Arnout Vandecappelle 2022-11-24 16:49:14 UTC

This bug was already reported before at glibc: https://sourceware.org/bugzilla/show_bug.cgi?id=29621

There it was concluded that it is due to gcc stage1 being built with CFLAGS_FOR_TARGET="-O0". This is not something that is tested in glibc's testing infrastructure.

It's not clear to me whether the issue needs to be solved in GCC or in glibc.

Comment 5 Arnout Vandecappelle 2022-11-24 17:29:06 UTC

Based on

> glibc builds needs to be fixed such that it does not reference the function in the unwinder at -O0

I've traced through the map file why this symbol is pulled in:

/.../libgcc.a(unwind-dw2.o)
                              /.../libgcc.a(_umoddi3.o) (_Unwind_Resume)
/.../libgcc.a(unwind-dw2-fde-dip.o)
                              /.../libgcc.a(unwind-dw2.o) (_Unwind_Find_FDE)

In other words, _umoddi3.o is the one that pulls in the unwinder.

Comment 6 Andrew Pinski 2022-11-24 17:31:52 UTC

There still might not much to be done really.
But let's see ...