https://bugs.llvm.org/show_bug.cgi?id=41692
Bug ID: 41692
Summary: -z combreloc sorts only by symbol index, not address
Product: lld
Version: unspecified
Hardware: All
URL: https://storage.googleapis.com/fuchsia-build/reproduce
r/lld-combreloc+comdat.tar.gz
OS: other
Status: NEW
Severity: normal
Priority: P
Component: ELF
Assignee: unassignedb...@nondot.org
Reporter: rol...@hack.frob.com
CC: jakehehrl...@google.com, llvm-bugs@lists.llvm.org,
peter.sm...@linaro.org, pho...@chromium.org
The --reproduce tarball at
https://storage.googleapis.com/fuchsia-build/reproducer/lld-combreloc+comdat.tar.gz
demonstrates the issue
with ld.lld from monorepo rev 2efd30571bcc53003376410d4221f7e4dd19f4c3.
In the `readelf -Wr libc.so.debug` output see e.g.:
0000000000385f80 0000026700000001 R_X86_64_64 00000000001a8880
__execvpe + 0
00000000002924f0 0000026700000006 R_X86_64_GLOB_DAT 00000000001a8880
__execvpe + 0
These two relocs have the same symbol index and so are adjacent. But the one
with the lower r_offset is after the one with the higher offset.
lld sorts only on symbol index (see SyntheticSections.cpp::compRelocations).
The GNU linkers sort for on symbol index, then on reloc address (r_offset).
Gold finally sorts on reloc type, though BFD doesn't. The comment in Gold's
code seems to suggest that this is just meant to stand in for a stable sort.
(I don't know why it doesn't just use a stable sort instead.) Probably that
bit doesn't matter if the sort is stable, and lld uses std::stable_sort for
this already.
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