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

[Raymond Mao]

Hi Jerome,

On Fri, 6 Jun 2025 at 02:58, Jerome Forissier
<jerome.forissier at linaro.org> wrote:
>
>
>
> 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.
>
Sounds good. I can put the same stuff under
'<u-boot>/lib/mbedtls/port/compiler-rt'.
Thanks for sharing.

Raymond

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