linux-kernel - Stack trace of csum_partial_copy

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Date:	Fri, 13 May 2016 14:07:47 +0300
From:	Nikolay Borisov <kernel@...p.com>
To:	Josh Poimboeuf <jpoimboe@...hat.com>
Cc:	"Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>
Subject: Stack trace of csum_partial_copy_generic

Hello Josh, 

I'd like to ask you whether objtool is supposed to produce a 
warning when arch/x86/lib/csum-copy_64.o (produced from 
arch/x86/lib/csum-copy_64.S). Since I cannot see any specific 
usage of rbp for defining a stackframe. I'm chasing against 
poor performance of a network benchmark and this is what perf produces: 

# Overhead          Command          Shared Object                                         Symbol
# ........  ...............  .....................  .............................................
#
    37.30%            iperf  [kernel.kallsyms]      [k] csum_partial_copy_generic                
                      |
                      --- csum_partial_copy_generic
                         |          
                         |--99.98%-- 0x7f809108b7cd
                         |          |          
                         |          |--69.72%-- 0x20000
                         |          |          
                         |           --30.28%-- 0x7f809108b7c2
                         |                     0x20000
                          --0.02%-- [...]

So this is not very helpful in tracing where this is being 
called from. Presumably somewhere from the networking layer. So 
should objtool catch this or since csum_partial_copy_generic is a leaf
function reliable stack trace isn't needed? Furthermore this function 
is called from C wrapper in csum-wrappers_64.c - shouldn't at least
they be present in the callstack?

This is on 4.6 master from linus and CONFIG_FRAME_POINTER being enabled. 

Regards, 
Nikolay