Re: [bpf-next:master 8/9] ld.lld: error: .tmp_vmlinux1.btf.o is incompatible with elf32lriscv

[Ihor Solodrai <ihor.solodrai@linux.dev>]

On 12/28/25 1:56 PM, Nathan Chancellor wrote:
> On Wed, Dec 24, 2025 at 06:02:31AM +0800, kernel test robot wrote:
>> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git master
>> head:   f14cdb1367b947d373215e36cfe9c69768dbafc9
>> commit: 522397d05e7d4a7c30b91841492360336b24f833 [8/9] resolve_btfids: Change in-place update with raw binary output
>> config: riscv-randconfig-002-20251224 (https://download.01.org/0day-ci/archive/20251224/202512240559.2M06DSX7-lkp@intel.com/config)
>> compiler: clang version 22.0.0git (https://github.com/llvm/llvm-project 4ef602d446057dabf5f61fb221669ecbeda49279)
>> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251224/202512240559.2M06DSX7-lkp@intel.com/reproduce)
>>
>> If you fix the issue in a separate patch/commit (i.e. not just a new version of
>> the same patch/commit), kindly add following tags
>> | Reported-by: kernel test robot <lkp@intel.com>
>> | Closes: https://lore.kernel.org/oe-kbuild-all/202512240559.2M06DSX7-lkp@intel.com/
>>
>> All errors (new ones prefixed by >>):
>>
>>>> ld.lld: error: .tmp_vmlinux1.btf.o is incompatible with elf32lriscv
> 
> While I have not verified this, I suspect this error occurs because the
> ${CC} command in gen_btf_o() in scripts/gen-btf.sh only includes
> CLANG_FLAGS for the target selection but not '-m32' or '-m64' from
> KBUILD_CFLAGS to control the word size (as documented in
> scripts/Makefile.clang).

Hi Nathan, thanks for the pointer.

I was able to reproduce this. Your suspicion is correct. 

The .o file generated by:

	echo "" | ${CC} ${CLANG_FLAGS} -c -x c -o ${btf_data} -

when cross-compiling to riscv is 64-bit, while vmlinux.o is 32-bit, hence the error.

This helps:

diff --git a/scripts/gen-btf.sh b/scripts/gen-btf.sh
index 06c6d8becaa2..12244dbe097c 100755
--- a/scripts/gen-btf.sh
+++ b/scripts/gen-btf.sh
@@ -96,7 +96,7 @@ gen_btf_o()
        # deletes all symbols including __start_BTF and __stop_BTF, which will
        # be redefined in the linker script.
        info OBJCOPY "${btf_data}"
-       echo "" | ${CC} ${CLANG_FLAGS} -c -x c -o ${btf_data} -
+       echo "" | ${CC} ${CLANG_FLAGS} ${KBUILD_CFLAGS} -c -x c -o ${btf_data} -
        ${OBJCOPY} --add-section .BTF=${ELF_FILE}.BTF \
                --set-section-flags .BTF=alloc,readonly ${btf_data}
        ${OBJCOPY} --only-section=.BTF --strip-all ${btf_data}

I'll send a proper patch later today. Have another bug report to check.

> 
> Cheers,
> Nathan