https://sourceware.org/bugzilla/show_bug.cgi?id=20090
Bug ID: 20090
Summary: [Fix] clang fail on LTO phase with BFD linker (+patch)
Product: binutils
Version: 2.27 (HEAD)
Status: NEW
Severity: normal
Priority: P2
Component: ld
Assignee: unassigned at sourceware dot org
Reporter: igor.venevtsev at gmail dot com
Target Milestone: ---
Created attachment 9256
--> https://sourceware.org/bugzilla/attachment.cgi?id=9256&action=edit
reproducer
Reproducer is just trying to make an executable using one object and two
archives with LTO info inside. First arch, live.a, contains live() function
which is called from main(). The second one, dead.a, contains never called
function dead(). During linking phase, clang comply on 'Unexpected resolution'
and terminates with UNREACHABLE.
bash-4.3$ make
[...skip...]
Unexpected resolution
UNREACHABLE executed at
/users/ivvenevt/llvm/llvm/tools/gold/gold-plugin.cpp:759!
clang-3.9: error: unable to execute command: Aborted (core dumped)
clang-3.9: error: linker command failed due to signal (use -v to see
invocation)
Makefile:26: recipe for target 'test' failed
The reason is wrong resolution reported by ld.bfd for dead (never included to
link) symbols. When LTO plugin asks for dead symbol resolution via
get_symbols() callback, ld.bfd is trying to find BFD entry for this symbol. But
there is no BFD entry for dead symbol despite the symbol itself is defined
(sym.def != LDPK_UNDEF). As a result ld.bfd set resolution to LDPR_UNKNOWN and
confuses the LLVMgold.so plugin. Opposite, GOLD linker reports
LDPR_PREEMPTED_REG for dead symbols. (gold/plugin.cc:959)
Please find reproducer and patch in attachments.
To run reproducer you should specify locations for clang and bfd.ld via
CLANG_BIN and BINUTILS_BIN vars.
Thanks, Igor
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