[Bug target/28854] New: unwinder reports sentinel frame.

[Bug target/28854] New: unwinder reports sentinel frame.

[pluto at agmk dot net]

on alpha-linux target the unwinder reports sentinel frame.
imho it has no sense.

$ gcc testcase.c -O2; ./a.out
ip = 0x120000768
ip = 0x20000076860
ip = 0x120000668
ip = (nil)
a.out: testcase.c:10: helper: Assertion `ip != 0' failed.

$ cat testcase.c
#include <dlfcn.h>
#include <unwind.h>
#include <assert.h>
#include <stdio.h>
_Unwind_Reason_Code helper( struct _Unwind_Context* ctx, void* arg )
{
        _Unwind_Ptr ip = _Unwind_GetIP( ctx );
        printf( "ip = %p\n", (void*)ip );
        assert( ip != 0 );
        return _URC_NO_REASON;
}
int main()
{
        _Unwind_Backtrace( helper, 0 );
        return 0;
}


-- 
           Summary: unwinder reports sentinel frame.
           Product: gcc
           Version: 4.1.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: pluto at agmk dot net
GCC target triplet: alpha-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28854

[Bug target/28854] unwinder reports sentinel frame.

[pluto at agmk dot net]

------- Comment #1 from pluto at agmk dot net  2006-08-25 23:28 -------
the 0x120000668 is a last valid return point.

0x0000000120000630 <_start+0>:  br      gp,0x120000634 <_start+4>
0x0000000120000634 <_start+4>:  ldah    gp,2(gp)
0x0000000120000638 <_start+8>:  lda     gp,-31092(gp)
0x000000012000063c <_start+12>: subq    sp,0x10,sp
0x0000000120000640 <_start+16>: mov     0,fp
0x0000000120000644 <_start+20>: ldq     a0,-32728(gp)
0x0000000120000648 <_start+24>: ldl     a1,16(sp)
0x000000012000064c <_start+28>: lda     a2,24(sp)
0x0000000120000650 <_start+32>: ldq     a3,-32736(gp)
0x0000000120000654 <_start+36>: ldq     a4,-32752(gp)
0x0000000120000658 <_start+40>: mov     v0,a5
0x000000012000065c <_start+44>: stq     sp,0(sp)
0x0000000120000660 <_start+48>: ldq     t12,-32720(gp)
0x0000000120000664 <_start+52>: jsr     ra,(t12),0x120000668 <_start+56>
0x0000000120000668 <_start+56>: halt
0x000000012000066c <_start+60>: unop


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28854

[Bug target/28854] unwinder reports sentinel frame.

[pluto at agmk dot net]

------- Comment #2 from pluto at agmk dot net  2006-11-07 14:14 -------
ping, please update status.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28854

[Bug target/28854] unwinder reports sentinel frame.

[ubizjak at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28854

--- Comment #5 from Uros Bizjak <ubizjak at gmail dot com> 2011-10-24 14:44:49 UTC ---
Just FYI, this is due to the fact that _start from /usr/crt1.o has a FDE:

$ objdump --dwarf  /usr/lib/crt1.o 

/usr/lib/crt1.o:     file format elf64-alpha

Contents of the .eh_frame section:

00000000 00000010 00000000 CIE
  Version:               1
  Augmentation:          "zR"
  Code alignment factor: 4
  Data alignment factor: -8
  Return address column: 15
  Augmentation data:     1b

  DW_CFA_def_cfa_register: r30
  DW_CFA_nop

00000014 00000010 00000018 FDE cie=00000000 pc=00000000..0000003c
  DW_CFA_advance_loc: 20 to 00000014
  DW_CFA_def_cfa_register: r15

This FDE of _start function is discovered by uw_frame_state_for, and only after
this recursion

  if (context->ra == 0)
    return _URC_END_OF_STACK;

is triggered.

So if there is a bug at all, it is in glibc - perhaps_start should not set FDE.

[Bug target/28854] unwinder reports sentinel frame.

[ubizjak at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28854

Uros Bizjak <ubizjak at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |WONTFIX

--- Comment #4 from Uros Bizjak <ubizjak at gmail dot com> 2011-06-22 22:15:25 UTC ---
(In reply to comment #3)
> please close this issue, my last alpha hardware died.

Wontfix.

[Bug target/28854] unwinder reports sentinel frame.

[pluto at agmk dot net]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28854

Pawel Sikora <pluto at agmk dot net> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|                            |

--- Comment #3 from Pawel Sikora <pluto at agmk dot net> 2011-06-22 21:48:28 UTC ---
please close this issue, my last alpha hardware died.