BOLT triggers assert with mold's synthetic $plt symbol

[ishitatsuyuki]

We're trying out BOLT compatibility at rui314/mold#789. During testing we discovered the following assert:

llvm-bolt: /home/ishitatsuyuki/llvm-project/bolt/lib/Core/BinaryContext.cpp:753: llvm::bolt::BinaryFunction *llvm::bolt::BinaryContext::createBinaryFunction(const std::string &, llvm::bolt::BinarySection &, uint64_t, uint64_t, uint64_t, uint16_t): Assertion `Result.second == true && "unexpected duplicate function"' failed.
 #0 0x000055839b75737a llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) /home/ishitatsuyuki/llvm-project/llvm/lib/Support/Unix/Signals.inc:569:11
 #1 0x000055839b75752b PrintStackTraceSignalHandler(void*) /home/ishitatsuyuki/llvm-project/llvm/lib/Support/Unix/Signals.inc:636:1
 #2 0x000055839b755b76 llvm::sys::RunSignalHandlers() /home/ishitatsuyuki/llvm-project/llvm/lib/Support/Signals.cpp:104:5
 #3 0x000055839b757c55 SignalHandler(int) /home/ishitatsuyuki/llvm-project/llvm/lib/Support/Unix/Signals.inc:407:1
 #4 0x00007fded65a2520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
 #5 0x00007fded65f6a7c __pthread_kill_implementation ./nptl/pthread_kill.c:44:76
 #6 0x00007fded65f6a7c __pthread_kill_internal ./nptl/pthread_kill.c:78:10
 #7 0x00007fded65f6a7c pthread_kill ./nptl/pthread_kill.c:89:10
 #8 0x00007fded65a2476 gsignal ./signal/../sysdeps/posix/raise.c:27:6
 #9 0x00007fded65887f3 abort ./stdlib/abort.c:81:7
#10 0x00007fded658871b _nl_load_domain ./intl/loadmsgcat.c:1177:9
#11 0x00007fded6599e96 (/lib/x86_64-linux-gnu/libc.so.6+0x39e96)
#12 0x000055839d0e9105 llvm::bolt::BinaryContext::createBinaryFunction(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>> const&, llvm::bolt::BinarySection&, unsigned long, unsigned long, unsigned long, unsigned short) /home/ishitatsuyuki/llvm-project/bolt/lib/Core/BinaryContext.cpp:754:32
#13 0x000055839b872746 llvm::bolt::RewriteInstance::createPLTBinaryFunction(unsigned long, unsigned long, unsigned long) /home/ishitatsuyuki/llvm-project/bolt/lib/Rewrite/RewriteInstance.cpp:1268:6
#14 0x000055839b873002 llvm::bolt::RewriteInstance::disassemblePLTSectionX86(llvm::bolt::BinarySection&, unsigned long) /home/ishitatsuyuki/llvm-project/bolt/lib/Rewrite/RewriteInstance.cpp:1386:3
#15 0x000055839b873220 llvm::bolt::RewriteInstance::disassemblePLT()::$_9::operator()(llvm::bolt::BinarySection&, unsigned long) const /home/ishitatsuyuki/llvm-project/bolt/lib/Rewrite/RewriteInstance.cpp:1394:3
#16 0x000055839b871838 llvm::bolt::RewriteInstance::disassemblePLT() /home/ishitatsuyuki/llvm-project/bolt/lib/Rewrite/RewriteInstance.cpp:1401:5
#17 0x000055839b86c4dc llvm::bolt::RewriteInstance::discoverFileObjects() /home/ishitatsuyuki/llvm-project/bolt/lib/Rewrite/RewriteInstance.cpp:1173:3
#18 0x000055839b868952 llvm::bolt::RewriteInstance::run() /home/ishitatsuyuki/llvm-project/bolt/lib/Rewrite/RewriteInstance.cpp:720:3
#19 0x000055839ac9b76b main /home/ishitatsuyuki/llvm-project/bolt/tools/driver/llvm-bolt.cpp:244:17
#20 0x00007fded6589d90 __libc_start_call_main ./csu/../sysdeps/nptl/libc_start_call_main.h:58:16
#21 0x00007fded6589e40 call_init ./csu/../csu/libc-start.c:128:20
#22 0x00007fded6589e40 __libc_start_main ./csu/../csu/libc-start.c:379:5
#23 0x000055839ac9a6d5 _start (./build/bin/llvm-bolt+0x2326d5)
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
Stack dump:
0.      Program arguments: ./build/bin/llvm-bolt -instrument /home/ishitatsuyuki/rust/obj/build/x86_64-unknown-linux-gnu/llvm/build/lib/libLLVM-15-rust-1.66.0-nightly.so -o /tmp/out.so

It looks like BOLT apparently doesn't like the synthetic PLT symbols mold creates (rui314/mold@a7f1e20 for implementation). The symbols are synthesized to ease looking at the disassembly, and looks like this:

    29: 0000000000001540     0 FUNC    LOCAL  DEFAULT   15 puts$plt
    30: 0000000000001550     0 FUNC    LOCAL  DEFAULT   16 __cxa_finalize$pltgot
    31: 0000000000002890     0 OBJECT  LOCAL  DEFAULT   23 __gmon_start__$got
    32: 0000000000002898     0 OBJECT  LOCAL  DEFAULT   23 _ITM_deregisterTMCloneTable$got
    33: 00000000000028a0     0 OBJECT  LOCAL  DEFAULT   23 _ITM_registerTMCloneTable$got
    34: 00000000000028a8     0 OBJECT  LOCAL  DEFAULT   23 __cxa_finalize$got
    35: 00000000000028b0     0 OBJECT  LOCAL  DEFAULT   23 __libc_start_main$got

To my understanding the mere existence of these local symbols should not prevent BOLT from functioning correctly, so we would like to get this fixed on BOLT side. However, if there's a legitimate reason that these symbols might affect BOLT's operation, we would be more than happy to consider other options to work around this in mold.

(cc @rui314)

[ishitatsuyuki]

emit-relocs.zip

Here's a small binary generated from mold's test suite that should reproduce the issue (you can run it to produce the binary by yourself too). Note that we have pending fixes for bugs on the mold side (rui314/mold#798, now merged) but this small scale test case is not affected by that.

[llvmbot]

@llvm/issue-subscribers-bolt

[maksfb]

Thanks for letting know. I'll take a look.