Re: [Libunwind-devel] src/os-linux.h:maps_init and threads

[Philippe De Muyter]

On Thu, Aug 31, 2017 at 11:54:14AM +0200, Philippe De Muyter wrote:
> Hi all
> 
> I try to use libunwind (on arm linux) and I need a clarification.
> 
> I use libunwind to get call stacks of a running multithreaded process.
> 
> Do I need to call 'UPT_create' for each thread pid, as the documentation
> of unw_init_remote() seems to imply, or only once for the process pid ?
> 
> I looked at libunwind sources and /proc on my current linux machine,
> and see that 'maps_init' in src/os-linux.h opens /proc/pid/maps,
> while on my machine that file exists only with the pid of a process,
> but not for any of its threads, so _UPT_get_proc_info, as called by
> unw_step often fails, IIRC.
> 
> Do I need to create my own find_proc_info accessor that will call
>  _UPT_find_proc_info replacing the thread (void *arg) by one
> created for the process ?

I have tried that, and it shows no progress : libunwind retrieves some
infos but misses also other ones, that gdb can retrieve on the same
running process or core file :

using libunwind :
_UPT_find_proc_info(0x73bd48d4) ret = -10
_UPT_find_proc_info(0x73bd48e0) ret = -10
_UPT_find_proc_info(0x73b58644) ret = -10
_UPT_find_proc_info(0x6e0540bc) ret = -10
_UPT_find_proc_info(0x6e050868) ret = -10
_UPT_find_proc_info(0x6e050720) ret = -10
_UPT_find_proc_info(0x6e0580ac) ret = -10

gdb on the core file
(gdb) x /i 0x6e0580ac
   0x6e0580ac <convert_image_to_from+272>:      subs    r11, r0, #0
(gdb) x /i 0x6e050720
   0x6e050720 <single_line_file_read+40>:       subs    r5, r0, #0
(gdb) x /i 0x6e050868
   0x6e050868 <single_line_file_update+32>:     subs    r5, r0, #0
(gdb) x /i 0x6e0540bc
   0x6e0540bc <put_header+332>: mov     r4, r0
(gdb) x /i 0x73b58644
   0x73b58644 <melpiResultGetPlateAttr+128>:    str     r0, [r6]
(gdb) x /i 0x73bd48e0
   0x73bd48e0 <gst_melpi_com+424>:                      ; <UNDEFINED> 
instruction: 0xe7f001f0
(gdb) x /i 0x73bd48d4
   0x73bd48d4 <gst_melpi_com+412>:                      ; <UNDEFINED> 
instruction: 0xe7f001f0
(gdb)

-- 
Philippe De Muyter +32 2 6101532 Macq SA rue de l'Aeronef 2 B-1140 Bruxelles