On Fri, Aug 27, 2021 at 11:10:39PM +0800, kernel test robot wrote:

> All errors (new ones prefixed by >>):
> 
>    riscv32-linux-ld: kernel/bpf/trampoline.o: in function `.L57':
> >> trampoline.c:(.text+0x34c): undefined reference to `__SCK__perf_snapshot_branch_stack'
>    riscv32-linux-ld: kernel/bpf/trampoline.o: in function `.L61':
>    trampoline.c:(.text+0x360): undefined reference to `bpf_perf_branch_snapshot'
> 

This a build with PERF_EVENTS=n, I suppose you'd better make calling
perf_snapshot_branch_stack() dependent on having that :-)