Bug 883451

Summary:	sys-libs/compiler-rt[clang] sys-libs/compiler-rt-sanitizers[clang] sys-libs/libcxx[clang] sys-libs/libcxxabi[clang] sys-libs/llvm-libunwind[clang] strips -unwindlib=libunwind
Product:	Gentoo Linux	Reporter:	unhappy-ending <unhappy-ending>
Component:	Current packages	Assignee:	LLVM support project <llvm>
Status:	UNCONFIRMED ---
Severity:	normal
Priority:	Normal
Version:	unspecified
Hardware:	AMD64
OS:	Linux
See Also:	https://bugs.gentoo.org/show_bug.cgi?id=881579
Whiteboard:
Package list:		Runtime testing required:	---
Attachments:	libcxxabi example stripping flags libcxxabi example bypassing flag stripping

Description unhappy-ending 2022-11-28 18:41:39 UTC

When using the clang USE flag, portage will strip out -unwindlib=libunwind which causes linking error ld.lld: error: undefined symbol: _Unwind_Resume.

Default behavior outputs the following in the build log:

-- <<< Gentoo configuration >>>
Build type      RelWithDebInfo
Install path    /usr
Compiler flags:
C               -march=native -O2 -pipe -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wmissing-field-initializers -Wimplicit-fallthrough -Wcovered-switch-default -Wno-comment -Wstring-conversion -Wmisleading-indentation -fdiagnostics-color -ffunction-sections -fdata-sections
C++             -march=native -O2 -pipe -stdlib=libc++ -fvisibility-inlines-hidden -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wno-comment -fdiagnostics-color
Linker flags:
Executable      -fuse-ld=lld -rtlib=compiler-rt -Wl,--color-diagnostics
Module          -fuse-ld=lld -rtlib=compiler-rt -Wl,-z,nodelete -Wl,--color-diagnostics
Shared          -fuse-ld=lld -rtlib=compiler-rt -Wl,-z,defs -Wl,-z,nodelete -Wl,--color-diagnostics

Adding _FLAG_O_MATIC_ECLASS=1 to workaround the issue shows:

-- <<< Gentoo configuration >>>
Build type      RelWithDebInfo
Install path    /usr
Compiler flags:
C               -march=native -O2 -pipe -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wmissing-field-initializers -Wimplicit-fallthrough -Wcovered-switch-default -Wno-comment -Wstring-conversion -Wmisleading-indentation -fdiagnostics-color -ffunction-sections -fdata-sections
C++             -march=native -O2 -pipe -stdlib=libc++ -fvisibility-inlines-hidden -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wno-comment -fdiagnostics-color
Linker flags:
Executable      -fuse-ld=lld -rtlib=compiler-rt -unwindlib=libunwind -Wl,--color-diagnostics
Module          -fuse-ld=lld -rtlib=compiler-rt -unwindlib=libunwind -Wl,-z,nodelete -Wl,--color-diagnostics
Shared          -fuse-ld=lld -rtlib=compiler-rt -unwindlib=libunwind -Wl,-z,defs -Wl,-z,nodelete -Wl,--color-diagnostics


Reproducible: Always

Steps to Reproduce:
1. Compile the LLVM toolchain
2. Build libcxxabi with the clang USE flag and LDFLAGS="-rtlib=compiler-rt -unwindlib=libunwind"
3. Portage strips -unwindlib=libunwind
Actual Results:  
In LLVM 15.0.2 resulted in failure with unresolved symbols to GCC's unwinder but I can't reproduce the failure since I bootstrapped the toolchain circa 15.0.2.

Expected Results:  
Success with resolved symbols to LLVM's unwinder

Behavior still persists, but no build failures since bootstrapping. I'm assuming an initial LLVM built by GCC and then attempt to bootstrap would retain the link time failure.

Comment 1 unhappy-ending 2022-11-28 18:42:53 UTC

Created attachment 838007 [details]
libcxxabi example stripping flags

Portage strips -unwindlib=libunwind and libcxxabi fails to build.

Comment 2 unhappy-ending 2022-11-28 18:44:33 UTC

Created attachment 838009 [details]
libcxxabi example bypassing flag stripping

Bypassing the stripping results in a proper build with -unwindlib=libunwind intact.