Hi,

currently on GNU/Linux running i386 inferior on x86_64 host you do not see some
of the debug info for the vDSO32 provided by the kernel.

Unpatched:
------------------------------------------------------------------------------
0xffffe410 in __kernel_vsyscall ()
(gdb) bt
#0  0xffffe410 in __kernel_vsyscall ()
#1  0x00c7a853 in __read_nocancel () from /lib/libc.so.6
#2  0x0804b263 in ?? ()
#3  0x0804941f in ?? ()
#4  0x00bcd3a0 in __libc_start_main () from /lib/libc.so.6
#5  0x08048c61 in ?? ()
(gdb) info line *0xffffe410
No line number information available for address 0xffffe410 <__kernel_vsyscall+16>
------------------------------------------------------------------------------

Patched:
------------------------------------------------------------------------------
__kernel_vsyscall () at arch/x86_64/ia32/vsyscall-sysenter.S:26
26              pop     %ebp
Current language:  auto; currently asm
(gdb) bt
#0  __kernel_vsyscall () at arch/x86_64/ia32/vsyscall-sysenter.S:26
#1  0x00c7a853 in __read_nocancel () from /lib/libc.so.6
#2  0x0804b263 in ?? ()
#3  0x0804941f in ?? ()
#4  0x00bcd3a0 in __libc_start_main () from /lib/libc.so.6
#5  0x08048c61 in ?? ()
(gdb) info line $eip
Convenience variables used in line specs must have integer values.
(gdb) info line $rip
Convenience variables used in line specs must have integer values.
(gdb) p/x $eip
$1 = 0xffffe410
(gdb) info line *0xffffe410
Line 26 of "arch/x86_64/ia32/vsyscall-sysenter.S" starts at address 0xffffe410 <__kernel_vsyscall+16>
   and ends at 0xffffe411 <__kernel_vsyscall+17>.
------------------------------------------------------------------------------

The problem is this vDSO is in assembly language, therefore its
 <0><b>: Abbrev Number: 1 (DW_TAG_compile_unit)
  < c>     DW_AT_stmt_list   : 0
  <10>     DW_AT_ranges      : 0
  <14>     DW_AT_name        : arch/x86_64/ia32/vsyscall-sysenter.S
  <39>     DW_AT_comp_dir    : /usr/src/debug////////kernel-2.6.22/linux-2.6.22.x86_64
  <71>     DW_AT_producer    : GNU AS 2.17.50.0.18
  <85>     DW_AT_language    : 32769    (MIPS assembler)

Contents of the .debug_ranges section:

    Offset   Begin    End
    00000000 ffffffff 00000000 (start > end)
    00000000 ffffe400 ffffe414
    00000000 ffffe500 ffffe508
    00000000 ffffe600 ffffe607
    00000000 <End of list>

DW_TAG_compile_unit has no children and it has neither DW_AT_low_pc nor
DW_AT_high_pc but it has DW_AT_ranges instead.  So far DW_AT_ranges was not
parsed into PSYMTABS and so this file was ignored during the debug info search
later.  Reasons for the discontinuous vDSO32 layout/hack are in the Linux
kernel sources.

Thanks to Roland McGrath for pointing out this .debug_info is not broken for
`.S'.


Regards,
Jan