[PATCH v2] makefile: fix Clang link error when RSA_PUBLIC_KEY_PARSER is selected

[Tom Rini]

On Tue, Jun 03, 2025 at 07:42:55AM -0700, Raymond Mao wrote:

> MbedTLS bignum module needs '__udivti3' which is a 128-bit division
> function provided by the compiler runtime, typically libgcc for GCC or
> clang_rt.builtins for Clang.
> Thus 'clang_rt.builtins' library is required when building using Clang.
> 
> This patch supports the location layout of clang_rt.builtins libraries
> from both LLVM pre-15 pattern [1] and post-15(up to 20) pattern [2].
> 
> As a fact that starts from LLVM 20, no official prebuilt multi-targets
> are included and users might need to cross-built it from source. [3] is
> an example of instructions for building.
> 
> [1] <INST_DIR>/lib/clang/<REV>/lib/linux/libclang_rt.builtins-<ARCH>.a
> E.g.
> lib/clang/14.0.0/lib/linux/libclang_rt.builtins-aarch64.a
> lib/clang/14.0.0/lib/linux/libclang_rt.builtins-x86_64.a
> 
> [2] <INST_DIR>/lib/clang/<REV_MAJOR>/lib/<CROSSTOOL>/libclang_rt.builtins.a
> E.g.
> lib/clang/20/lib/aarch64-none-linux-gnu/libclang_rt.builtins.a
> lib/clang/20/lib/x86_64-unknown-linux-gnu/libclang_rt.builtins.a
> 
> [3]
> git clone https://github.com/llvm/llvm-project.git
> cd llvm-project
> git checkout -b llvmorg-20.1.6 llvmorg-20.1.6
> mkdir build-builtin && cd build-builtin
> cmake -G Ninja ../llvm \
>   -DCMAKE_BUILD_TYPE=Release \
>   -DCMAKE_C_COMPILER=clang \
>   -DLLVM_ENABLE_PROJECTS="clang" \
>   -DLLVM_ENABLE_RUNTIMES="compiler-rt" \
>   -DLLVM_TARGETS_TO_BUILD="X86;AArch64" \
>   -DLLVM_BUILTIN_TARGETS=\
>     "x86_64-unknown-linux-gnu;aarch64-none-linux-gnu" \
>   -DBUILTINS_aarch64-none-linux-gnu_CMAKE_SYSTEM_NAME=Linux \
>   -DBUILTINS_aarch64-none-linux-gnu_CMAKE_C_COMPILER=\
>     <YOUR_TOOLCHAIN_GCC> \
>   -DBUILTINS_aarch64-none-linux-gnu_CMAKE_ASM_COMPILER=\
>     <YOUR_TOOLCHAIN_GCC> \
>   -DBUILTINS_aarch64-none-linux-gnu_CMAKE_SYSROOT=\
>     <YOUR_TOOLCHAIN_LIBC_DIR> \
>   -DCOMPILER_RT_BUILD_BUILTINS=ON \
>   -DCOMPILER_RT_BUILD_SANITIZERS=OFF \
>   -DCOMPILER_RT_BUILD_XRAY=OFF \
>   -DCOMPILER_RT_BUILD_LIBFUZZER=OFF \
>   -DCOMPILER_RT_BUILD_PROFILE=OFF \
>   -DCMAKE_INSTALL_PREFIX=<INSTALL_DIR> \
>   -DLLVM_ENABLE_PER_TARGET_RUNTIME_DIR=OFF
> ninja builtins
> sudo ninja install
> 
> Fixes: 13de8483388c ("mbedtls: add mbedtls into the build system")
> Signed-off-by: Raymond Mao <raymond.mao at linaro.org>

I think that newer versions don't even ship this moves us further away
from a solution here as all of the logic. I think we need to look at the
suggestion of just importing the assembly version of the function.

-- 
Tom
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