rustc fails to link with clang (undefined reference to __muloti4)

[elichai]

Clang version: 9.0.0.

$ CC=clang CXX=clang++ make -f minicargo.mk

make -f Makefile all
make[1]: Entering directory '/home/elichai2/gits/mrustc'
make[1]: Nothing to be done for 'all'.
make[1]: Leaving directory '/home/elichai2/gits/mrustc'
test -e bin/mrustc
make -C tools/minicargo/
make[1]: Entering directory '/home/elichai2/gits/mrustc/tools/minicargo'
make[1]: Nothing to be done for 'all'.
make[1]: Leaving directory '/home/elichai2/gits/mrustc/tools/minicargo'
test -e tools/bin/minicargo
tools/bin/minicargo rustc-1.29.0-src/src/libstd --script-overrides script-overrides/stable-1.29.0-linux/ --output-dir output/ 
test -e output/libstd.rlib
tools/bin/minicargo rustc-1.29.0-src/src/libpanic_unwind --script-overrides script-overrides/stable-1.29.0-linux/ --output-dir output/ 
test -e output/libpanic_unwind.rlib
tools/bin/minicargo rustc-1.29.0-src/src/libtest --vendor-dir rustc-1.29.0-src/src/vendor --output-dir output/ 
test -e output/libtest.rlib
tools/bin/minicargo lib/libproc_macro --output-dir output/ 
test -e output/libproc_macro.rlib
mkdir -p output/rustc-build
CFG_COMPILER_HOST_TRIPLE=x86_64-unknown-linux-gnu LLVM_CONFIG=/home/elichai2/gits/mrustc/rustc-1.29.0-src/build/bin/llvm-config CFG_RELEASE= CFG_RELEASE_CHANNEL=stable CFG_VERSION=1.29.0-stable-mrustc CFG_PREFIX=mrustc CFG_LIBDIR_RELATIVE=lib LD_LIBRARY_PATH=/home/elichai
2/gits/mrustc/output tools/bin/minicargo rustc-1.29.0-src/src/rustc --vendor-dir rustc-1.29.0-src/src/vendor --output-dir output/rustc-build -L output/ 
BUILDING rustc_binary from rustc-main v0.0.0
> /home/elichai2/gits/mrustc/bin/mrustc rustc-1.29.0-src/src/rustc/rustc.rs -o output/rustc-build/rustc_binary --crate-name rustc_binary --crate-type bin -C emit-depfile=output/rustc-build/rustc_binary.d -g --cfg debug_assertions -O -L output -L output/rustc-build --exter
n rustc_target=output/rustc-build/librustc_target.rlib --extern rustc_driver=output/rustc-build/librustc_driver.rlib
/usr/bin/ld: output/rustc-build/librustc_mir.rlib.o: in function `ZRICj15overflowing_mul0g':
/home/elichai2/gits/mrustc/output/rustc-build/librustc_mir.rlib.c:1058314: undefined reference to `__muloti4'
clang-9: error: linker command failed with exit code 1 (use -v to see invocation)
C Compiler failed to execute - error code 256
Process exited with non-zero exit status 1
BUILD FAILED
make: *** [minicargo.mk:102: output/rustc] Error 1

[thepowersgang]

This appears to be a clang-level issue. mrustc emits __builtin_mul_overflow at that line, which clang has converted into a call to __muloti4, which doesn't exist in the default-linked libgcc (reportedly it's in compiler-builtins)

For reference, that mangled symbol is <i128>::overflowing_mul

[thepowersgang]

https://bugs.llvm.org/show_bug.cgi?id=16404
It appears that clang has an issue where it emits calls to helper methods, but doesn't add a link to compiler-rt to ensure that they're present.

You may need to force the use of compiler-rt somehow (since this is specific to using clang, I'm not sure how it could be handled in mrustc)