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[Bug gdb/16062] New: stepi sometimes doesn't make progress


https://sourceware.org/bugzilla/show_bug.cgi?id=16062

            Bug ID: 16062
           Summary: stepi sometimes doesn't make progress
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: gdb
          Assignee: unassigned at sourceware dot org
          Reporter: palves at redhat dot com

I noticed something odd while doing "stepi" over a fork syscall:

 ...
 (gdb) set disassemble-next-line on
 ...
 (gdb) si
 0x000000323d4ba7c2      131       pid = ARCH_FORK ();
    0x000000323d4ba7a4 <__libc_fork+132>:        64 4c 8b 04 25 10 00 00 00    
 mov    %fs:0x10,%r8
    0x000000323d4ba7ad <__libc_fork+141>:        31 d2   xor    %edx,%edx
    0x000000323d4ba7af <__libc_fork+143>:        4d 8d 90 d0 02 00 00    lea   
0x2d0(%r8),%r10
    0x000000323d4ba7b6 <__libc_fork+150>:        31 f6   xor    %esi,%esi
    0x000000323d4ba7b8 <__libc_fork+152>:        bf 11 00 20 01  mov   
$0x1200011,%edi
    0x000000323d4ba7bd <__libc_fork+157>:        b8 38 00 00 00  mov   
$0x38,%eax
 => 0x000000323d4ba7c2 <__libc_fork+162>:        0f 05   syscall
    0x000000323d4ba7c4 <__libc_fork+164>:        48 3d 00 f0 ff ff       cmp   
$0xfffffffffffff000,%rax
    0x000000323d4ba7ca <__libc_fork+170>:        0f 87 2b 01 00 00       ja    
0x323d4ba8fb <__libc_fork+475>
 (gdb) si
 0x000000323d4ba7c4      131       pid = ARCH_FORK ();
    0x000000323d4ba7a4 <__libc_fork+132>:        64 4c 8b 04 25 10 00 00 00    
 mov    %fs:0x10,%r8
    0x000000323d4ba7ad <__libc_fork+141>:        31 d2   xor    %edx,%edx
    0x000000323d4ba7af <__libc_fork+143>:        4d 8d 90 d0 02 00 00    lea   
0x2d0(%r8),%r10
    0x000000323d4ba7b6 <__libc_fork+150>:        31 f6   xor    %esi,%esi
    0x000000323d4ba7b8 <__libc_fork+152>:        bf 11 00 20 01  mov   
$0x1200011,%edi
    0x000000323d4ba7bd <__libc_fork+157>:        b8 38 00 00 00  mov   
$0x38,%eax
    0x000000323d4ba7c2 <__libc_fork+162>:        0f 05   syscall
 => 0x000000323d4ba7c4 <__libc_fork+164>:        48 3d 00 f0 ff ff       cmp   
$0xfffffffffffff000,%rax
    0x000000323d4ba7ca <__libc_fork+170>:        0f 87 2b 01 00 00       ja    
0x323d4ba8fb <__libc_fork+475>
 (gdb) si
 0x000000323d4ba7c4      131       pid = ARCH_FORK ();
    0x000000323d4ba7a4 <__libc_fork+132>:        64 4c 8b 04 25 10 00 00 00    
 mov    %fs:0x10,%r8
    0x000000323d4ba7ad <__libc_fork+141>:        31 d2   xor    %edx,%edx
    0x000000323d4ba7af <__libc_fork+143>:        4d 8d 90 d0 02 00 00    lea   
0x2d0(%r8),%r10
    0x000000323d4ba7b6 <__libc_fork+150>:        31 f6   xor    %esi,%esi
    0x000000323d4ba7b8 <__libc_fork+152>:        bf 11 00 20 01  mov   
$0x1200011,%edi
    0x000000323d4ba7bd <__libc_fork+157>:        b8 38 00 00 00  mov   
$0x38,%eax
    0x000000323d4ba7c2 <__libc_fork+162>:        0f 05   syscall
 => 0x000000323d4ba7c4 <__libc_fork+164>:        48 3d 00 f0 ff ff       cmp   
$0xfffffffffffff000,%rax
    0x000000323d4ba7ca <__libc_fork+170>:        0f 87 2b 01 00 00       ja    
0x323d4ba8fb <__libc_fork+475>
 (gdb) si
 0x000000323d4ba7ca      131       pid = ARCH_FORK ();
    0x000000323d4ba7a4 <__libc_fork+132>:        64 4c 8b 04 25 10 00 00 00    
 mov    %fs:0x10,%r8
    0x000000323d4ba7ad <__libc_fork+141>:        31 d2   xor    %edx,%edx
    0x000000323d4ba7af <__libc_fork+143>:        4d 8d 90 d0 02 00 00    lea   
0x2d0(%r8),%r10
    0x000000323d4ba7b6 <__libc_fork+150>:        31 f6   xor    %esi,%esi
    0x000000323d4ba7b8 <__libc_fork+152>:        bf 11 00 20 01  mov   
$0x1200011,%edi
    0x000000323d4ba7bd <__libc_fork+157>:        b8 38 00 00 00  mov   
$0x38,%eax
    0x000000323d4ba7c2 <__libc_fork+162>:        0f 05   syscall
    0x000000323d4ba7c4 <__libc_fork+164>:        48 3d 00 f0 ff ff       cmp   
$0xfffffffffffff000,%rax
 => 0x000000323d4ba7ca <__libc_fork+170>:        0f 87 2b 01 00 00       ja    
0x323d4ba8fb <__libc_fork+475>

Notice how the third "si" didn't actually make progress.

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