linux-kernel - [Question] for duplicate symbols, kallsyms and vmlinux may retain different symbol

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Date:	Tue, 19 Jul 2016 19:15:07 +0800
From:	Songshan Gong <gongss@...ux.vnet.ibm.com>
To:	acme@...nel.org, jolsa@...nel.org
Cc:	dsahern@...il.com, linux-kernel@...r.kernel.org
Subject: [Question] for duplicate symbols, kallsyms and vmlinux may retain
 different symbol

I try to fix the failure of testcase 'test__vmlinux_matches_kallsyms', 
and meet a kind of failure because of duplicate symbols.

For example,two functions:
kretprobe_trampoline_holder and kretprobe_trampoline

(1)They all start from the same addr,0x011b180;

(2)kretprobe_trampoline_holder is STB_LOCAL,
    kretprobe_trampoline is STB_GLOBAL;

(3) for kallsyms, because we cann't get the correct size of each symbol 
from /proc/kallsyms, before symbols__fixup_duplicate(), perf assumes 
each symbol's size is zero, so when choose_best_symbol(), we get 
kretprobe_trampoline because perf prefers 'a global symbol over a 
non-global one';

(4) for vmlinux, by readelf, I found that:
size of kretprobe_trampoline_holder is 4, not zero;
size of kretprobe_trampoline is zero;
So when choose_best_symbol(), we get pretprobe_trampoline_holder instead 
because perf prefers 'A symbol with non-zero length' and this condition 
is judged before 'prefer a global symbol';

I have a idea to fix this problem, but may be inappropriate:
Could we move the judge of symbol size to the bottom of the judge 
whether a symbol is global?

Anyone else have good idea?

Song Shan Gong