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

[Jerome Forissier]

On 6/6/25 00:10, Raymond Mao wrote:
> Hi Tom,
> 
> On Thu, 5 Jun 2025 at 17:46, Tom Rini <trini at konsulko.com> wrote:
>>
>> On Thu, Jun 05, 2025 at 04:52:20PM -0400, Raymond Mao wrote:
>>> Hi Tom,
>>>
>>> On Thu, 5 Jun 2025 at 16:01, Tom Rini <trini at konsulko.com> wrote:
>>>>
>>>> On Thu, Jun 05, 2025 at 03:45:00PM -0400, Raymond Mao wrote:
>>>>> Hi Tom,
>>>>>
>>>>> On Thu, 5 Jun 2025 at 13:15, Tom Rini <trini at konsulko.com> wrote:
>>>>>>
>>>>>> 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.
>>>>>
>>>>> But, the assembly versions are architecture-specific, do you want a
>>>>> portable C code for it?
>>>>
>>>> Is it easily done in C? If not, we can just try and make it clear what
>>>> needs to be pulled out of LLVM sources if/when another platform
>>>> encounters the problem.
>>>>
>>> But maybe we can ask the LLVM project owner why they removed the
>>> prebuilt multi-targets since 20.0.0.
>>> May current patch can support multiple target layouts of pre-15 and
>>> post-15 patterns (I believe they will keep the one of post-15 for the
>>> future), if they can provide the prebuilt multi-targets via package
>>> managers or release tarballs then it is the best solution.
>>> In the future we might need other functions from those libraries and
>>> implementing it in U-Boot is not a good choice IMO.
>>
>> I think adding all of that logic to the Makefile is taking us down the
>> wrong path. Looking at the kernel, they're working with LLVM to be able
>> to disable these 128bit intrinsics currently (as part of rust support).

Good to know.

>> So hopefully we just need some temporary workaround until things get
>> fixed upstream.
>>
> I will try to implement a C code function as a temporary solution and
> be back shortly.

To solve a similar issue in OP-TEE we decided to import a few files
unmodified from the LLVM compiler-rt tree, and that's plain C [1]. OTOH if
it's only a temporary solution, maybe a single C file can be put together.

[1] https://github.com/OP-TEE/optee_os/commit/48952fd403d867dbf13675e062cd8a7d2e5260a9

HTH,
-- 
Jerome