On Tue, Aug 27, 2019 at 10:43:27AM +0800, He Zhe wrote:

On 8/26/19 11:18 PM, Josh Poimboeuf wrote:

quoted

On Mon, Aug 26, 2019 at 10:42:53PM +0800, He Zhe wrote:

quoted

Hi All,

Since 3193c0836f20 ("bpf: Disable GCC -fgcse optimization for ___bpf_prog_run()"),
We have got the following warning,
kernel/bpf/core.o: warning: objtool: ___bpf_prog_run.cold()+0x7: call without frame pointer save/setup

If reverting the above commit, we will get the following warning,
kernel/bpf/core.o: warning: objtool: ___bpf_prog_run()+0x8b9: sibling call from callable instruction with modified stack frame
if CONFIG_RETPOLINE=n, and no warning if CONFIG_RETPOLINE=y

Can you please share the following:

- core.o file

Attached.

quoted

The following would also be helpful for me to try to recreate it:

- config file
- compiler version
- kernel version

I pasted them in the other reply.

Thanks.  I was able to recreate.  I reduced it to:

void a(b);
__attribute__((optimize(""))) c(void) { a(); }

Apparently '__attribute__((optimize()))' is overwriting GCC cmdline
flags, including -fno-omit-frame-pointer.  I had assumed it would append
instead of replace.

I'm guessing this is a GCC "feature" instead of a bug.  I'll need to
follow up.

-- 
Josh