| Summary: | Inconsistency in between bfd and gold about -Wl,--as-needed | ||
|---|---|---|---|
| Product: | binutils | Reporter: | Martin Liska <mliska> |
| Component: | ld | Assignee: | Alan Modra <amodra> |
| Status: | RESOLVED FIXED | ||
| Severity: | normal | CC: | hjl.tools, matz |
| Priority: | P2 | ||
| Version: | 2.34 | ||
| Target Milestone: | 2.36 | ||
| Host: | Target: | ||
| Build: | Last reconfirmed: | 2020-08-25 00:00:00 | |
| Attachments: | A testcase | ||
FWIW, I think the gold behaviour is the correct one. The order of libraries on the cmdline is significant, and libfoo.so does fulfill the symbol request, so the object from libtest.a shouldn't be considered. No matter if LTO is or isn't involved. (In fact also bfd ld doesn't use the archive without LTO mode) Created attachment 12794 [details] A testcase $ make gcc -B./ -O2 -g -flto -c -o pr26530c.o pr26530c.c gcc -B./ -O2 -g -fPIC -c -o pr26530a.o pr26530a.c gcc -B./ -shared -o libpr26530.so pr26530a.o gcc -B./ -O2 -g -c -o pr26530b.o pr26530b.c ar rc -o libpr26530.a pr26530b.o gcc -B./ -Wl,--as-needed -o x pr26530c.o libpr26530.so libpr26530.a -Wl,-R,. ./x make: *** [Makefile:14: all] Aborted (core dumped) A patch is posted at https://sourceware.org/pipermail/binutils/2020-August/112996.html The master branch has been updated by Alan Modra <amodra@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=1e3b96fd6cf0c7d018083994ad951ccf92aba582 commit 1e3b96fd6cf0c7d018083994ad951ccf92aba582 Author: Alan Modra <amodra@gmail.com> Date: Fri Sep 4 13:54:21 2020 +0930 Allow plugin syms to mark as-needed shared libs needed We must tell LTO about symbols in all shared libraries loaded. That means we can't load extra shared libraries after LTO recompilation, at least, not those that affect the set of symbols that LTO cares about, the IR symbols. This change will likely result in complaints about --as-needed libraries being loaded unnecessarily, but being correct is more important than being optimal. One of the PR15146 tests regresses, and while that could be hidden by disabling the missing dso message by making it conditional on h->root.non_ir_ref_regular, that would just be sweeping a problem under the rug. bfd/ PR 15146 PR 26314 PR 26530 * elflink.c (elf_link_add_object_symbols): Do set def_regular and ref_regular for IR symbols. Don't clear dynsym, allowing IR symbols to load --as-needed shared libraries, but prevent IR symbols from becoming dynamic. ld/ * testsuite/ld-plugin/lto.exp: Don't run pr15146 tests. * testsuite/ld-plugin/pr15146.d: Delete. * testsuite/ld-plugin/pr15146a.c: Delete. * testsuite/ld-plugin/pr15146b.c: Delete. * testsuite/ld-plugin/pr15146c.c: Delete. * testsuite/ld-plugin/pr15146d.c: Delete. Fixed. The master branch has been updated by Alan Modra <amodra@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=b1a92c635c1ec10fd703302ce1fc4ab3a8515a04 commit b1a92c635c1ec10fd703302ce1fc4ab3a8515a04 Author: Alan Modra <amodra@gmail.com> Date: Fri Oct 30 14:56:35 2020 +1030 PR26806, Suspected linker bug with LTO This patch reverts most of git commit 1e3b96fd6cf, so IR symbols are again not marked def_regular or ref_regular. That should be enough to stop IR symbols from becoming dynamic. To mark as-needed shared libraries referenced by IR symbols, use the referencing BFD rather than the ref flags. bfd/ PR 15146 PR 26314 PR 26530 PR 26806 * elflink.c (elf_link_add_object_symbols): Don't set def/ref flags for plugin syms. Do allow plugin syms to mark as-needed libs. ld/ PR 26806 * testsuite/ld-plugin/lto-19.h, * testsuite/ld-plugin/lto-19a.c, * testsuite/ld-plugin/lto-19b.c, * testsuite/ld-plugin/lto-19c.c: New test. * testsuite/ld-plugin/pr26806.c, * testsuite/ld-plugin/pr26806.d: New test. * testsuite/ld-plugin/lto.exp: Run them. |
Let's consider the following example: $ cat foo.c const char *lrealpath(const char *a) { return a; } $ cat main.c const char *lrealpath(const char *a); int main(int argc, char **argv) { lrealpath (argv[0]); } $ gcc foo.c -fPIC -flto -c $ ar r libtest.a foo.o $ gcc -o libfoo.so foo.o -shared $ gcc main.o -Wl,--as-needed libfoo.so libtest.a --save-temps -fuse-ld=bfd -L. && cat libtest.res 2 main.o 2 200 6e870bd31e7efa23 PREVAILING_DEF main 206 6e870bd31e7efa23 RESOLVED_IR lrealpath libtest.a@0x92 1 199 76b392265247fa61 PREVAILING_DEF_IRONLY_EXP lrealpath while gold does: $ gcc main.o -Wl,--as-needed libfoo.so libtest.a --save-temps -fuse-ld=gold -L. && cat libtest.res 1 main.o 2 200 6e870bd31e7efa23 PREVAILING_DEF main 206 6e870bd31e7efa23 RESOLVED_DYN lrealpath So BFD takes symbols from LTO IR while GOLD takes them from the shared library.