[Bug ld/25618] New: use of gcc lto breaks --exclude-libs

[sergeev917 at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=25618

            Bug ID: 25618
           Summary: use of gcc lto breaks --exclude-libs
           Product: binutils
           Version: 2.34
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: ld
          Assignee: unassigned at sourceware dot org
          Reporter: sergeev917 at gmail dot com
  Target Milestone: ---

Created attachment 12329
  --> https://sourceware.org/bugzilla/attachment.cgi?id=12329&action=edit
source files and shell validation script

(Originally reported to GCC bug tracker:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93980)

The apparent issue is that with LTO disabled -Wl,--exclude-libs,ALL flag works
as intended, but with -flto -- symbols from linked archives are not hidden
anymore.

The issue is easily reproduced with about 10 lines of code with no std libs
involved. The reproducer consists of a static library "foo" and a shared
library "bar" that links with "foo" (and we would like to hide "foo" symbols in
"bar").

foo.h:
#pragma once
__attribute__((visibility("default"))) int foo();

foo.cc:
#include "foo.h"
int foo() { return 100; }

bar.h:
#pragma once
__attribute__((visibility("default"))) int bar();

bar.cc:
#include "bar.h"
#include "foo.h"
int bar() { return foo(); }

Build commands:
g++ -fPIC -fvisibility=hidden -fvisibility-inlines-hidden -flto -c foo.cc -o
.foo.o
ar qc .foo.a .foo.o
g++ -fPIC -fvisibility=hidden -fvisibility-inlines-hidden -flto -c bar.cc -o
.bar.o
g++ -Wl,--exclude-libs,ALL -flto -shared -o libbar.so .bar.o .foo.a
readelf --dyn-syms --wide libbar.so | c++filt

The last command produces both bar() and foo() -- that is, foo() is not hidden.
Replacing -flto with -fno-lto gives only bar(), which is the expected result.
The issue is present when using both ld.bfd and ld.gold (ie -fuse-ld=gold).

--

$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-pc-linux-gnu/9.2.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with:
/var/tmp/portage/sys-devel/gcc-9.2.0-r4/work/gcc-9.2.0/configure
--host=x86_64-pc-linux-gnu --build=x86_64-pc-linux-gnu --prefix=/usr
--bindir=/usr/x86_64-pc-linux-gnu/gcc-bin/9.2.0
--includedir=/usr/lib/gcc/x86_64-pc-linux-gnu/9.2.0/include
--datadir=/usr/share/gcc-data/x86_64-pc-linux-gnu/9.2.0
--mandir=/usr/share/gcc-data/x86_64-pc-linux-gnu/9.2.0/man
--infodir=/usr/share/gcc-data/x86_64-pc-linux-gnu/9.2.0/info
--with-gxx-include-dir=/usr/lib/gcc/x86_64-pc-linux-gnu/9.2.0/include/g++-v9
--with-python-dir=/share/gcc-data/x86_64-pc-linux-gnu/9.2.0/python
--enable-languages=c,c++,go,fortran --enable-obsolete --enable-secureplt
--disable-werror --with-system-zlib --disable-nls --enable-checking=release
--with-bugurl=https://bugs.gentoo.org/ --with-pkgversion='Gentoo 9.2.0-r4 p5'
--disable-esp --enable-libstdcxx-time --with-build-config=bootstrap-lto
--disable-libstdcxx-pch --enable-shared --enable-threads=posix
--enable-__cxa_atexit --enable-clocale=gnu --disable-multilib
--with-multilib-list=m64 --disable-altivec --disable-fixed-point
--enable-targets=all --enable-libgomp --disable-libmudflap --disable-libssp
--disable-systemtap --enable-vtable-verify --enable-lto --without-isl
--enable-default-pie --enable-default-ssp
Thread model: posix
gcc version 9.2.0 (Gentoo 9.2.0-r4 p5)

$ ld -v
GNU ld (Gentoo 2.34 p1) 2.34.0

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