meson.bbclass builds the bindgen arguments as:
def bindgen_args(d):
args = '${HOST_CC_ARCH}${TOOLCHAIN_OPTIONS} --target=${TARGET_SYS}'
TOOLCHAIN_OPTIONS carries --sysroot, which is enough for C headers. It is not
enough for C++: when clang cross-compiles against a GCC sysroot it does not
infer the libstdc++ include directories from --sysroot alone, so any recipe
running bindgen over a C++ header fails to find the standard library.
mesa hits this with PACKAGECONFIG opencl, which turns on gallium-rusticl and
runs bindgen over rusticl_llvm_bindings.hpp with -x c++ -std=c++17:
FAILED: src/gallium/frontends/rusticl/rusticl_llvm_bindings.rs
.../recipe-sysroot/usr/include/llvm/ADT/DenseMapInfo.h:17:10:
fatal error: 'cassert' file not found
Unable to generate bindings: clang diagnosed error
Seen on mesa 26.0.5 with oe-core wrynose, aarch64 target, LLVM 22.1.3.
The missing arguments are the staged C++ headers:
-I${STAGING_INCDIR}/c++/<version>
-I${STAGING_INCDIR}/c++/<version>/${TARGET_SYS}
Our downstream workaround appends them to bindgen_clang_arguments in
meson.cross from a mesa bbappend, which works but is recipe-specific and
hardcodes a realpath glob over the staged header directory. It also has to run
after do_prepare_recipe_sysroot, since the glob is empty on a clean build.
Reporting rather than sending a patch because the right fix is a design call:
bindgen_args() is generic, so this affects any meson recipe doing C++ bindgen,
not just mesa. Options seem to be teaching bindgen_args() about the C++ include
paths unconditionally, gating it on whether the recipe does C++ bindgen, or
having clang-native resolve the GCC sysroot properly. A maintainer is better
placed to pick.
Happy to test a proposed fix on aarch64.
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