This is the mail archive of the
systemtap@sourceware.org
mailing list for the systemtap project.
RE: Stap is translating to functions in __exit sections...and later module load fails
- From: "Keshavamurthy, Anil S" <anil dot s dot keshavamurthy at intel dot com>
- To: "Mao, Bibo" <bibo dot mao at intel dot com>, "Eugeniy Meshcheryakov" <eugeniy dot meshcheryakov at googlemail dot com>
- Cc: "Stone, Joshua I" <joshua dot i dot stone at intel dot com>, "Systemtap" <systemtap at sources dot redhat dot com>
- Date: Tue, 17 Oct 2006 17:52:03 -0700
- Subject: RE: Stap is translating to functions in __exit sections...and later module load fails
After commenting (i.e not discarding) *(.exit.text)
from arch/ia64/kernel/vmlinux.lds.S file and booting with this new kernel,
stap ignores functions in __exit sections and elaborates and
translates functions properly.
Can someone tell me why this section is not discarded on Ia32?
Thanks,
-Anil Keshavamurthy
-----Original Message-----
From: Mao, Bibo
Sent: Monday, October 16, 2006 4:27 AM
To: Eugeniy Meshcheryakov
Cc: Stone, Joshua I; Keshavamurthy, Anil S; Systemtap
Subject: Re: Stap is translating to functions in __exit sections...and later module load fails
I do not think it is gcc bug, I think it depends on ld script, this
is part of IA64 linux 2.6.19-rc2 vmlinux.lds.S,
SECTIONS
{
/* Sections to be discarded */
/DISCARD/ : {
*(.exit.text)
*(.exit.data)
*(.exitcall.exit)
*(.IA_64.unwind.exit.text)
*(.IA_64.unwind_info.exit.text)
}
.......
it seems that .exit.text is discarded when vmlinux image is linked, and
on IA32 .exit.text segment is not discarded, the script
stap -e 'probe kernel.function("*") { print(".") }' can run on IA32
platform.
it is strange that when exit_pfm_fs is probe there is one such line
probe exit_pfm_fs@arch/ia64/kernel/perfmon.c:1507 pc=0x0
I do not how function probe-point is parsed, I am not familiar with
Elfutils package :(
And powerpc has the same ld link script, it should has the same problem.
thanks
bibo,mao
Eugeniy Meshcheryakov wrote:
> 13 жовÑ'нÑ? 2006 о 15:28 -0700 Stone, Joshua I напиÑ?ав(-ла):
>> This seems to support the notion that the linker elided that function.
>>
>> So, as Eugeniy wondered, why did the translator pick up that function at
>> all? I'm also curious what IP it chose for the kprobe, if the function
>> no longer exists... Please try this command:
>>
>> $ stap -p2 -vv -e 'probe kernel.function("exit_pfm_fs"){}' 2>&1 | grep
>> 'pc='
>>
>> I suspect that either elfutils is giving 'stale' debug information, or
>> the translator is misinterpreting its results.
> It loks like a bug in some version of gcc. I tried to compile the
> following program with version from Debian stable and unstable on ia64:
>
> $ cat test.c
> static void __attribute__((section(".exit.text"))) exit_pfm_fs(void)
> {
> return;
> }
> $
>
> With gcc 3.3.5:
>
> $ readelf -a test.o | grep exit_
> 9: 0000000000000000 16 FUNC LOCAL DEFAULT 9 exit_pfm_fs
> $ objdump -W test.o
> ...
> The section .debug_info contains:
>
> Compilation Unit @ offset 0x0:
> Length: 52
> Version: 2
> Abbrev Offset: 0
> Pointer Size: 8
> <0><b>: Abbrev Number: 1 (DW_TAG_compile_unit)
> DW_AT_stmt_list : 0
> DW_AT_name : (indirect string, offset: 0x38): test.c
> DW_AT_comp_dir : (indirect string, offset: 0x0): /home/eugen
> DW_AT_producer : (indirect string, offset: 0xc): GNU C 3.3.5
> (Debian 1:3.3.5-13)
> DW_AT_language : 1 (ANSI C)
> <1><1d>: Abbrev Number: 2 (DW_TAG_subprogram)
> DW_AT_name : (indirect string, offset: 0x2c): exit_pfm_fs
> DW_AT_decl_file : 1
> DW_AT_decl_line : 2
> DW_AT_prototyped : 1
> DW_AT_low_pc : 0
> DW_AT_high_pc : 0x10
> DW_AT_frame_base : 1 byte block: 5c (DW_OP_reg12)
> ...
> $
>
> With gcc 4.1.2:
>
> $ readelf -a t.o | grep exit_
> $ objdump -W t.o | grep exit_
> objdump: Error: No comp units in .debug_info section ?objdump: Error: No
> comp units in .debug_info section ?$
>
>