wasm-ld crash when LTO enabled: `__cxx_global_var_init.1` present in "init functions" but not defined

[sbc100]

We've seen certain situations where in LTO builds wasm-ld will crash during Writer::createCallCtorsFunction because one of the init function in the generted LTO object file ( __cxx_global_var_init.1) in undefined and does not get assigned a function index (so crashes in sym->getFunctionIndex()).

I'm still working on reducing the repro case as more.

This seems to have started with https://reviews.llvm.org/D135427, which I guess makes sense since that change explicitly calls out __cxx_global_var_init as being discarded.

[llvmbot]

@llvm/issue-subscribers-backend-webassembly

[llvmbot]

@llvm/issue-subscribers-lld-wasm

[jeremiahar]

Pasting this here as well for visibility from emscripten-core/emscripten#19774 . A potential repro is this:

CMakeLists.txt:

cmake_minimum_required(VERSION 3.13)

set(CMAKE_EXECUTABLE_SUFFIX_CXX .html)
set(CMAKE_CXX_STANDARD 17)

add_executable(lto_bug dummy.cpp)

add_library(main
  main.cpp
)

add_library(lib1
  lib1.cpp
)

target_link_libraries(lto_bug
  PRIVATE

  main
  lib1
)

main.cpp

int DoIt()
{
    return 0; 
}
inline int Unused0 = DoIt();

int GetUnused();

int main(int, char **)
{
    return GetUnused();
}

lib1.cpp:

int DoIt();
inline int Unused0 = DoIt();

int GetUnused()
{
    return Unused0;
}

dummy.cpp:

// Dummy file for cmake's add_executable

Compilation commands:

[jeremiah@jeremiah build]$ ~/emsdk/upstream/emscripten/emcmake cmake -DCMAKE_BUILD_TYPE=Release -DCMAKE_CXX_FLAGS="-flto" ../
configure: cmake -DCMAKE_BUILD_TYPE=Release -DCMAKE_CXX_FLAGS=-flto ../ -DCMAKE_TOOLCHAIN_FILE=/home/jeremiah/emsdk/upstream/emscripten/cmake/Modules/Platform/Emscripten.cmake -DCMAKE_CROSSCOMPILING_EMULATOR=/home/jeremiah/emsdk/node/16.20.0_64bit/bin/node
CMake Warning (dev) in CMakeLists.txt:
  No project() command is present.  The top-level CMakeLists.txt file must
  contain a literal, direct call to the project() command.  Add a line of
  code such as

    project(ProjectName)

  near the top of the file, but after cmake_minimum_required().

  CMake is pretending there is a "project(Project)" command on the first
  line.
This warning is for project developers.  Use -Wno-dev to suppress it.

CMake Warning (dev) in CMakeLists.txt:
  cmake_minimum_required() should be called prior to this top-level project()
  call.  Please see the cmake-commands(7) manual for usage documentation of
  both commands.
This warning is for project developers.  Use -Wno-dev to suppress it.

-- Configuring done (0.5s)
-- Generating done (0.0s)
-- Build files have been written to: /home/jeremiah/projects/emscripten_lto_bug/build
[jeremiah@jeremiah build]$ make -j64 VERBOSE=1
/usr/bin/cmake -S/home/jeremiah/projects/emscripten_lto_bug -B/home/jeremiah/projects/emscripten_lto_bug/build --check-build-system CMakeFiles/Makefile.cmake 0
/usr/bin/cmake -E cmake_progress_start /home/jeremiah/projects/emscripten_lto_bug/build/CMakeFiles /home/jeremiah/projects/emscripten_lto_bug/build//CMakeFiles/progress.marks
make  -f CMakeFiles/Makefile2 all
make[1]: Entering directory '/home/jeremiah/projects/emscripten_lto_bug/build'
make  -f CMakeFiles/lib1.dir/build.make CMakeFiles/lib1.dir/depend
make  -f CMakeFiles/main.dir/build.make CMakeFiles/main.dir/depend
make[2]: Entering directory '/home/jeremiah/projects/emscripten_lto_bug/build'
cd /home/jeremiah/projects/emscripten_lto_bug/build && /usr/bin/cmake -E cmake_depends "Unix Makefiles" /home/jeremiah/projects/emscripten_lto_bug /home/jeremiah/projects/emscripten_lto_bug /home/jeremiah/projects/emscripten_lto_bug/build /home/jeremiah/projects/emscripten_lto_bug/build /home/jeremiah/projects/emscripten_lto_bug/build/CMakeFiles/lib1.dir/DependInfo.cmake --color=
make[2]: Entering directory '/home/jeremiah/projects/emscripten_lto_bug/build'
cd /home/jeremiah/projects/emscripten_lto_bug/build && /usr/bin/cmake -E cmake_depends "Unix Makefiles" /home/jeremiah/projects/emscripten_lto_bug /home/jeremiah/projects/emscripten_lto_bug /home/jeremiah/projects/emscripten_lto_bug/build /home/jeremiah/projects/emscripten_lto_bug/build /home/jeremiah/projects/emscripten_lto_bug/build/CMakeFiles/main.dir/DependInfo.cmake --color=
Dependencies file "CMakeFiles/lib1.dir/lib1.cpp.o.d" is newer than depends file "/home/jeremiah/projects/emscripten_lto_bug/build/CMakeFiles/lib1.dir/compiler_depend.internal".
Consolidate compiler generated dependencies of target lib1
make[2]: Leaving directory '/home/jeremiah/projects/emscripten_lto_bug/build'
make  -f CMakeFiles/lib1.dir/build.make CMakeFiles/lib1.dir/build
Dependencies file "CMakeFiles/main.dir/main.cpp.o.d" is newer than depends file "/home/jeremiah/projects/emscripten_lto_bug/build/CMakeFiles/main.dir/compiler_depend.internal".
Consolidate compiler generated dependencies of target main
make[2]: Leaving directory '/home/jeremiah/projects/emscripten_lto_bug/build'
make  -f CMakeFiles/main.dir/build.make CMakeFiles/main.dir/build
make[2]: Entering directory '/home/jeremiah/projects/emscripten_lto_bug/build'
make[2]: Nothing to be done for 'CMakeFiles/lib1.dir/build'.
make[2]: Leaving directory '/home/jeremiah/projects/emscripten_lto_bug/build'
make[2]: Entering directory '/home/jeremiah/projects/emscripten_lto_bug/build'
make[2]: Nothing to be done for 'CMakeFiles/main.dir/build'.
make[2]: Leaving directory '/home/jeremiah/projects/emscripten_lto_bug/build'
[ 33%] Built target lib1
[ 66%] Built target main
make  -f CMakeFiles/lto_bug.dir/build.make CMakeFiles/lto_bug.dir/depend
make[2]: Entering directory '/home/jeremiah/projects/emscripten_lto_bug/build'
cd /home/jeremiah/projects/emscripten_lto_bug/build && /usr/bin/cmake -E cmake_depends "Unix Makefiles" /home/jeremiah/projects/emscripten_lto_bug /home/jeremiah/projects/emscripten_lto_bug /home/jeremiah/projects/emscripten_lto_bug/build /home/jeremiah/projects/emscripten_lto_bug/build /home/jeremiah/projects/emscripten_lto_bug/build/CMakeFiles/lto_bug.dir/DependInfo.cmake --color=
Dependencies file "CMakeFiles/lto_bug.dir/dummy.cpp.o.d" is newer than depends file "/home/jeremiah/projects/emscripten_lto_bug/build/CMakeFiles/lto_bug.dir/compiler_depend.internal".
Consolidate compiler generated dependencies of target lto_bug
make[2]: Leaving directory '/home/jeremiah/projects/emscripten_lto_bug/build'
make  -f CMakeFiles/lto_bug.dir/build.make CMakeFiles/lto_bug.dir/build
make[2]: Entering directory '/home/jeremiah/projects/emscripten_lto_bug/build'
[ 83%] Linking CXX executable lto_bug.html
/usr/bin/cmake -E cmake_link_script CMakeFiles/lto_bug.dir/link.txt --verbose=1
/home/jeremiah/emsdk/upstream/emscripten/em++ -flto -O3 -DNDEBUG @CMakeFiles/lto_bug.dir/objects1.rsp -o lto_bug.html @CMakeFiles/lto_bug.dir/linkLibs.rsp
wasm-ld: /b/s/w/ir/cache/builder/emscripten-releases/llvm-project/llvm/include/llvm/Support/Casting.h:578: decltype(auto) llvm::cast(From *) [To = lld::wasm::DefinedFunction, From = const lld::wasm::FunctionSymbol]: Assertion `isa<To>(Val) && "cast<Ty>() argument of incompatible type!"' failed.
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
Stack dump:
0.      Program arguments: /home/jeremiah/emsdk/upstream/bin/wasm-ld -o lto_bug.wasm CMakeFiles/lto_bug.dir/dummy.cpp.o libmain.a liblib1.a -L/home/jeremiah/emsdk/upstream/emscripten/cache/sysroot/lib/wasm32-emscripten/lto -lGL -lal -lhtml5 -lstubs -lnoexit -lc -ldlmalloc -lcompiler_rt -lc++-noexcept -lc++abi-noexcept -lsockets -mllvm -combiner-global-alias-analysis=false -mllvm -enable-emscripten-sjlj -mllvm -disable-lsr /tmp/tmp2ow3pfaelibemscripten_js_symbols.so --strip-debug --export-if-defined=main --export-if-defined=__start_em_asm --export-if-defined=__stop_em_asm --export-if-defined=__start_em_lib_deps --export-if-defined=__stop_em_lib_deps --export-if-defined=__start_em_js --export-if-defined=__stop_em_js --export-if-defined=__main_argc_argv --export=stackSave --export=stackRestore --export=stackAlloc --export=__errno_location --export=__get_temp_ret --export=__set_temp_ret --export=__wasm_call_ctors --export-table -z stack-size=65536 --initial-memory=16777216 --no-entry --max-memory=16777216 --global-base=1024
 #0 0x00007f58210121e8 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/home/jeremiah/emsdk/upstream/bin/../lib/libLLVM-17git.so+0x1c121e8)
 #1 0x00007f582100feae llvm::sys::RunSignalHandlers() (/home/jeremiah/emsdk/upstream/bin/../lib/libLLVM-17git.so+0x1c0feae)
 #2 0x00007f58210128c5 SignalHandler(int) Signals.cpp:0:0
 #3 0x00007f581f00cab0 (/usr/lib/libc.so.6+0x39ab0)
 #4 0x00007f581f05c26c (/usr/lib/libc.so.6+0x8926c)
 #5 0x00007f581f00ca08 raise (/usr/lib/libc.so.6+0x39a08)
 #6 0x00007f581eff5538 abort (/usr/lib/libc.so.6+0x22538)
 #7 0x00007f581eff545c (/usr/lib/libc.so.6+0x2245c)
 #8 0x00007f581f0053d6 (/usr/lib/libc.so.6+0x323d6)
 #9 0x0000561afea34177 (/home/jeremiah/emsdk/upstream/bin/wasm-ld+0x4f8177)
#10 0x0000561afea3d957 lld::wasm::(anonymous namespace)::Writer::run() Writer.cpp:0:0
#11 0x0000561afea35846 lld::wasm::writeResult() (/home/jeremiah/emsdk/upstream/bin/wasm-ld+0x4f9846)
#12 0x0000561afea0e185 lld::wasm::(anonymous namespace)::LinkerDriver::linkerMain(llvm::ArrayRef<char const*>) Driver.cpp:0:0
#13 0x0000561afea0b10a lld::wasm::link(llvm::ArrayRef<char const*>, llvm::raw_ostream&, llvm::raw_ostream&, bool, bool) (/home/jeremiah/emsdk/upstream/bin/wasm-ld+0x4cf10a)
#14 0x0000561afe6e7552 lld::unsafeLldMain(llvm::ArrayRef<char const*>, llvm::raw_ostream&, llvm::raw_ostream&, llvm::ArrayRef<lld::DriverDef>, bool) (/home/jeremiah/emsdk/upstream/bin/wasm-ld+0x1ab552)
#15 0x0000561afe6e6699 lld_main(int, char**, llvm::ToolContext const&) (/home/jeremiah/emsdk/upstream/bin/wasm-ld+0x1aa699)
#16 0x0000561afe6e6b71 main (/home/jeremiah/emsdk/upstream/bin/wasm-ld+0x1aab71)
#17 0x00007f581eff6850 (/usr/lib/libc.so.6+0x23850)
#18 0x00007f581eff690a __libc_start_main (/usr/lib/libc.so.6+0x2390a)
#19 0x0000561afe6e624a _start (/home/jeremiah/emsdk/upstream/bin/wasm-ld+0x1aa24a)
em++: error: '/home/jeremiah/emsdk/upstream/bin/wasm-ld -o lto_bug.wasm CMakeFiles/lto_bug.dir/dummy.cpp.o libmain.a liblib1.a -L/home/jeremiah/emsdk/upstream/emscripten/cache/sysroot/lib/wasm32-emscripten/lto -lGL -lal -lhtml5 -lstubs -lnoexit -lc -ldlmalloc -lcompiler_rt -lc++-noexcept -lc++abi-noexcept -lsockets -mllvm -combiner-global-alias-analysis=false -mllvm -enable-emscripten-sjlj -mllvm -disable-lsr /tmp/tmp2ow3pfaelibemscripten_js_symbols.so --strip-debug --export-if-defined=main --export-if-defined=__start_em_asm --export-if-defined=__stop_em_asm --export-if-defined=__start_em_lib_deps --export-if-defined=__stop_em_lib_deps --export-if-defined=__start_em_js --export-if-defined=__stop_em_js --export-if-defined=__main_argc_argv --export=stackSave --export=stackRestore --export=stackAlloc --export=__errno_location --export=__get_temp_ret --export=__set_temp_ret --export=__wasm_call_ctors --export-table -z stack-size=65536 --initial-memory=16777216 --no-entry --max-memory=16777216 --global-base=1024' failed (received SIGABRT (-6))
make[2]: *** [CMakeFiles/lto_bug.dir/build.make:101: lto_bug.html] Error 1
make[2]: Leaving directory '/home/jeremiah/projects/emscripten_lto_bug/build'
make[1]: *** [CMakeFiles/Makefile2:88: CMakeFiles/lto_bug.dir/all] Error 2
make[1]: Leaving directory '/home/jeremiah/projects/emscripten_lto_bug/build'
make: *** [Makefile:91: all] Error 2
[jeremiah@jeremiah build]$ 

[Mintyboi]

hi @EugeneZelenko, it's great that there is now a simple reproducer for this issue!
Do you think this issue can be relooked into and see if we can find a way to resolve this? 🙏

cc @MaskRay

[kleisauke]

Here's another reproducer:

cat <<EOT > foo.h
int foo();
inline int unused = foo(); // FIXME: Remove to fix the build
EOT
cat <<EOT > foo.cc
#include "foo.h"

int foo() {
  return 42;
}
EOT
cat <<EOT > main.cc
#include "foo.h"

int main() {
  return foo();
}
EOT
em++ -c -flto foo.cc -o foo.o
em++ -c -flto main.cc -o main.o
emar rcsT libfoo.a foo.o
emar rcsT libmain.a main.o
em++ libmain.a libfoo.a