Re: pthread_t ids of threads not showed by "thread info"

[Jan Kratochvil <jan dot kratochvil at redhat dot com>]

On Mon, 26 Apr 2010 10:38:09 +0200, Stefano Sabatini wrote:
> $ cd /usr/lib/debug/lib
> $ cd
> $ nm -S libpthread-2.10.2.so | grep __stack_user
> 00017160 00000008 b __GI___stack_user
> 00017160 00000008 b __stack_user
> $ nm -S libpthread-2.10.2.so | grep stack_used
> 0001511c 00000008 d stack_used

You should have DWARFs symbols.  The ELF symbols are not enough for structures
derefencing.

readelf -wi /usr/lib/debug/lib64/libpthread.so.0.debug
[ formatted a bit ]
 <1><9304>: Abbrev Number: 111 (DW_TAG_variable)
    <9305>   DW_AT_name        : (indirect string, offset: 0x300b): __stack_user
    <930f>   DW_AT_type        : <0x461b>
    <9313>   DW_AT_external    : 1
    <9314>   DW_AT_location    : 9 byte block: 3 80 b2 21 0 0 0 0 0     (DW_OP_addr: 21b280)
 <1><461b>: Abbrev Number: 3 (DW_TAG_typedef)
    <461c>   DW_AT_name        : (indirect string, offset: 0x7f8): list_t
    <4622>   DW_AT_type        : <0x45f0>
 <1><45f0>: Abbrev Number: 14 (DW_TAG_structure_type)
    <45f1>   DW_AT_name        : (indirect string, offset: 0x2469): list_head
    <45f5>   DW_AT_byte_size   : 16
 <2><45fc>: Abbrev Number: 11 (DW_TAG_member)
    <45fd>   DW_AT_name        : (indirect string, offset: 0x169d): next
    <4603>   DW_AT_type        : <0x4615>
    <4607>   DW_AT_data_member_location: 0
 <2><4608>: Abbrev Number: 11 (DW_TAG_member)
    <4609>   DW_AT_name        : (indirect string, offset: 0x1303): prev
    <460f>   DW_AT_type        : <0x4615>
    <4613>   DW_AT_data_member_location: 8

Anyway these symbols are not required for the right way of traversing this
list.  For that purpose (as being used for native non-core `info threads') GDB
just calls functions provided by /lib64/libthread_db.so.1 . You can check glibc
sources for nptl_db/td_ta_thr_iter.c . nptl_db uses simple ELF symbols not
requiring the debuginfo files, like this one:
$ gdb -q -ex 'p *(int *)_thread_db_pthread_list' -ex q /lib64/libpthread.so.0
$1 = 128


> I'm currently stucked with this, I really cannot say if it is a
> problem with what I'm doing or with some debian specific issue.

If Debian GDB cannot find the symbols guessing Debian probably has more light
(smaller) debug info packages.


Regards,
Jan