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

[Tom Rini]

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).
So hopefully we just need some temporary workaround until things get
fixed upstream.

-- 
Tom
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