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

[Tom Rini]

On Wed, May 28, 2025 at 10:25:06AM +0200, Jerome Forissier wrote:
> Hi Rayond,
> 
> On 5/27/25 23:05, 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.
> 
> How do you reproduce the problem? Can you give the config and build
> command you are using?
> 
> > 
> > Fixes: 13de8483388c ("mbedtls: add mbedtls into the build system")
> > Signed-off-by: Raymond Mao <raymond.mao at linaro.org>
> > ---
> >  Makefile | 6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> > 
> > diff --git a/Makefile b/Makefile
> > index f88684947ee..16506dcaec6 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -37,7 +37,6 @@ else ifeq ("riscv32", $(MK_ARCH))
> >  else ifeq ("riscv64", $(MK_ARCH))
> >    export HOST_ARCH=$(HOST_ARCH_RISCV64)
> >  endif
> > -undefine MK_ARCH
> >  
> >  # Avoid funny character set dependencies
> >  unexport LC_ALL
> > @@ -915,8 +914,13 @@ PLATFORM_LIBGCC = arch/$(ARCH)/lib/lib.a
> >  else
> >  ifndef CONFIG_CC_IS_CLANG
> >  PLATFORM_LIBGCC := -L $(shell dirname `$(CC) $(c_flags) -print-libgcc-file-name`) -lgcc
> > +else ifeq ($(CONFIG_RSA_PUBLIC_KEY_PARSER_MBEDTLS),y)
> > +# mbedtls bignum needs '__udivti3' - a 128-bit division function that's provided by clang-rt.
> > +CLANG_RT_DIR := $(shell $(CC) --print-resource-dir)/lib/linux
> > +PLATFORM_LIBGCC := -L$(CLANG_RT_DIR) -lclang_rt.builtins-$(MK_ARCH)
> 
> I'm afraid this won't work when cross-compiling because the compiler-rt
> builtins libraries are usually not installed with the compiler.
> For example on my Ubuntu 24.04 machine:
> 
> $ clang --version
> Ubuntu clang version 18.1.3 (1ubuntu1)
> Target: x86_64-pc-linux-gnu
> Thread model: posix
> InstalledDir: /usr/bin

How about if you use the llvm.org packages?

-- 
Tom
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