linux-kernel - vmlinux symtab matching kallsyms fails: dso__find_symbol_by

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Message-ID: <CAJ_BOiC=nLyaYW9RGFH2xCpEUv6w4tQEHRG9DCc+7bGXDz_stw@mail.gmail.com>
Date:	Tue, 25 Jun 2013 11:03:14 +0530
From:	Prabhat Kumar Ravi <prabhatravi09@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: vmlinux symtab matching kallsyms fails: dso__find_symbol_by_name ----
 end ----

Hi All,

On 3.4-rc49, I got following failure running `perf test`:

/ # perf test -v 1
 1: vmlinux symtab matches kallsyms:
--- start ---
dso__find_symbol_by_name ---- end ----
vmlinux symtab matches kallsyms: FAILED!

Perf test is failing at dsofind_symbol_by_name

where

        kallsyms_map = machine__kernel_map(&kallsyms, type);

     sym = map__find_symbol_by_name(kallsyms_map, ref_reloc_sym.name, NULL);
     if (sym == NULL) {
                pr_debug("dso__find_symbol_by_name ");
                goto out;
        }

Here sym is search for "_stext" which is NULL here so perf test fails
here only.

On investigation found that _stext having same address as asm_do_IRQ
and exception_text_start,

c00081c0 T asm_do_IRQ
c00081c0 T _stext
c00081c0 T __exception_text_start

so being deleted by symbolsfixup_duplicate in

if (choose_best_symbol(curr, next) == SYMBOL_A) {

                        rb_erase(&next->rb_node, symbols); --> symbole
getting erase here.
                        goto again;
                } else {


My doubt is, Is we really need this commit??:

commit 3f5a42722b9e78a434d5a4ee5e607dc33c69ac80
Author: Anton Blanchard <anton@...ba.org>
Date:   Wed Aug 24 16:40:15 2011 +1000

    perf symbols: /proc/kallsyms does not sort module symbols

    kallsyms__parse assumes that /proc/kallsyms is sorted and sets the end
    of the previous symbol to the start of the current one.

    Unfortunately module symbols are not sorted, eg:

    ffffffffa0081f30 t e1000_clean_rx_irq   [e1000e]
    ffffffffa00817a0 t e1000_alloc_rx_buffers       [e1000e]

    Some symbols end up with a negative length and others have a length
    larger than they should. This results in confusing perf output.

    We already have a function to fixup the end of zero length symbols so
    use that instead.

Or we can search or other string.??
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