Libclang_rt.builtins-x86_64.a missing for native clang-15

nitroglycerine · September 18, 2022, 2:46pm

Hello,

Yoe distribution-generated native clang-15 executable attempts to link to libclang_rt.builtins-x86_64.a and complains the file is missing. However, OpenBMC distribution-generated native clang-14 executable does not suffer from this issue. This issue is found for a pull request to meta-openembedded. A minimally working example noted in the pull request can be listed as follows:

$ cat a.cpp
#include <stdio.h>
int main() { printf("Hey!\n"); }

clang-15 in Yoe:

$ ~/yoe/build/tmp/work/x86_64-linux/clang-native/15.0.0-r0/build/bin/clang++ -nostdlib++ /tmp/a.cpp 
/usr/bin/ld: cannot find /usr/lib/clang/15.0.0/lib/linux/libclang_rt.builtins-x86_64.a: No such file or directory
/usr/bin/ld: cannot find -lunwind

clang-14 in OpenBMC:

$ /opt/evb-ast2500/tmp/work/x86_64-linux/clang-native/14.0.0-r0/build/bin/clang++ /tmp/a.cpp 
(successfully completes)

Is there anything else I need to check?
Thanks!

khem · September 19, 2022, 3:15am

Yoe distro uses clang defaulting to llvm runtime which perhaps OpenBMC is not doing. Its still defaulting to GCC runtime, this works unintended in native case because runtime default is gcc on linux sysems but does not work for yoe native clang compiler due to different defaults.

meta-clang now has a class which should be inherited to use it as a native compiler

github.com

kraj/meta-clang/blob/master/classes/clang-native.bbclass

# inherit this class if you would like to use clang to compile the native
# version of your recipes instead of system compiler ( which is normally gcc )
# on build machines
# to use it add
#
# inherit clang-native
#
# to the concerned recipe via a bbappend or directly to recipe file
#
DEPENDS:append:runtime-llvm = " clang-native compiler-rt-native libcxx-native"
# Use libcxx headers for native parts
CXXFLAGS:append:runtime-llvm = " -stdlib=libc++"
BUILD_CXXFLAGS:append:runtime-llvm = " -isysroot=${STAGING_DIR_NATIVE} -stdlib=libc++"
# Use libgcc for native parts
LDFLAGS:append:runtime-llvm = " -stdlib=libc++ -rtlib=libgcc -unwindlib=libgcc"
BUILD_LDFLAGS:append:runtime-llvm = " -stdlib=libc++ -rtlib=libgcc -unwindlib=libgcc"
BUILD_CC:runtime-llvm  = "${CCACHE}clang -isysroot=${STAGING_DIR_NATIVE}"
BUILD_CXX:runtime-llvm = "${CCACHE}clang++ -isysroot=${STAGING_DIR_NATIVE}"
BUILD_CPP:runtime-llvm = "${CCACHE}clang -isysroot=${STAGING_DIR_NATIVE} -E"
BUILD_CCLD:runtime-llvm = "${CCACHE}clang"

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Perhaps this is something you can use if you are using native clang during compiling perfetto

nitroglycerine · September 20, 2022, 10:50am

Thanks for the speedy reply, I was able to build perfetto by setting the compiler command to ${BUILD_CXX} ${BUILD_LDFLAGS} in the recipe as well as inheriting the clang-native class.

I’ve updated the pull request as well.

It seems to achieve the same effect as specifying the compiler command to ${RECIPE_SYSROOT_NATIVE}/usr/bin/clang++ --rtlib=libgcc --unwindlib=libgcc and not inheriting from clang-native, but I guess inheriting from clang-native makes it clear to the user of the recipe that the recipe makes use of clang as a native compiler, and makes it easier for the recipe to pick up any improvements in the clang-native class as meta-clang gets updated.

khem · September 20, 2022, 1:03pm

Since this recipe depends on clang compiler I think either it should be added to meta-clang or marked as clang only recipe

nitroglycerine · September 20, 2022, 8:30pm

This recipe (perfetto) is not clang-only, it has an is_clang switch that switches clang on or off.

Whether this recipe depends and inherits on clang-native depends on whether the user sets their Yocto toolchain to “clang”. (Yoe does this, but some other distributions like OpenBMC doesn’t.)

So I guess it probably doesn’t need to be marked as clang-only?

khem · September 20, 2022, 9:48pm

Yeah in that case we can manage it
With TOOLCHAIN flag