From: Alexei Starovoitov
Date: Wed, 9 Mar 2016 18:56:49 -0800
> 0-day bot reported build error:
> kernel/built-in.o: In function `map_lookup_elem':
>>> kernel/bpf/.tmp_syscall.o:(.text+0x329b3c): undefined reference to
>>> `bpf_stackmap_copy'
> when CONFIG_BPF_SYSCALL is set and CONFIG_PERF_EVEN
0-day bot reported build error:
kernel/built-in.o: In function `map_lookup_elem':
>> kernel/bpf/.tmp_syscall.o:(.text+0x329b3c): undefined reference to
>> `bpf_stackmap_copy'
when CONFIG_BPF_SYSCALL is set and CONFIG_PERF_EVENTS is not.
Add weak definition to resolve it.
This code path in map_look
