On 3/11/20 1:39 AM, Alexei Starovoitov wrote:
fmod_ret progs are emitted as:
start = __bpf_prog_enter();
call fmod_ret
*(u64 *)(rbp - 8) = rax
__bpf_prog_exit(, start);
test eax, eax
jne do_fexit
That 'test eax, eax' is working by accident. The compiler is free to use rax
inside __bpf_prog_exit() or inside functions that __bpf_prog_exit() is calling.
Which caused "test_progs -t modify_return" to sporadically fail depending on
compiler version and kconfig. Fix it by using 'cmp [rbp - 8], 0' instead of
'test eax, eax'.
Fixes: ae24082331d9 ("bpf: Introduce BPF_MODIFY_RETURN")
Reported-by: Andrii Nakryiko <andriin@xxxxxx>
Acked-by: Andrii Nakryiko <andriin@xxxxxx>
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Applied, thanks!
