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To: "Mohammed, Moqtadir" <Moqtadir_Mohammed@reyrey.com>
Cc: <gdb@sourceware.org>
Subject: Re: Can this be happening?
References: <D8FBABA1EF6F2E4DBCC88903F60691F30A4401F9@houxchsvr.ucscorp.ucs.pvt>
From: Jim Blandy <jimb@codesourcery.com>
Date: Tue, 03 Jul 2007 21:38:00 -0000
In-Reply-To: <D8FBABA1EF6F2E4DBCC88903F60691F30A4401F9@houxchsvr.ucscorp.ucs.pvt> (Moqtadir Mohammed's message of "Fri, 29 Jun 2007 18:03:26 -0500")
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"Mohammed, Moqtadir" <Moqtadir_Mohammed@reyrey.com> writes:
> I was trying to look at a core dump of a program, and gdb displays the following result for
> #info registers
>
> eax            0xa0     160
> ecx            0x2      2
> edx            0xa      10
> ebx            0xa7e3de9c       -1478238564
> esp            0xa6babddc       0xa6babddc
> ebp            0xa6babe00       0xa6babe00
> esi            0xa7ef9d9a       -1477468774
> edi            0x838f44c        137950284
> eip            0xa7d85cec       0xa7d85cec <mempcpy+28>
> eflags         0x50203  [ CF IF RF AC ]
> cs             0x73     115
> ss             0x7b     123
> ds             0x7b     123
> es             0xb010007b       -1341128581
> fs             0x0      0
> gs             0x33     51
>
> Platform: IA32. (elf)
>
> My question is, how is the register 'es' being reported as a 32 bit value.
> I may be completely naive asking this question, but I have been trying to google for anything 
> related to it, but haven't found an answer. Is 'es' not supposed to be only 16bit.

Well, actually, GDB thinks they're all 32 bits long:

    static struct type *
    i386_register_type (struct gdbarch *gdbarch, int regnum)
    {
      if (regnum == I386_EIP_REGNUM)
        return builtin_type_void_func_ptr;

      if (regnum == I386_EFLAGS_REGNUM)
        return i386_eflags_type;

      if (regnum == I386_EBP_REGNUM || regnum == I386_ESP_REGNUM)
        return builtin_type_void_data_ptr;

      if (i386_fp_regnum_p (regnum))
        return builtin_type_i387_ext;

      if (i386_mmx_regnum_p (gdbarch, regnum))
        return i386_mmx_type (gdbarch);

      if (i386_sse_regnum_p (gdbarch, regnum))
        return i386_sse_type (gdbarch);

    #define I387_ST0_REGNUM I386_ST0_REGNUM
    #define I387_NUM_XMM_REGS (gdbarch_tdep (current_gdbarch)->num_xmm_regs)

      if (regnum == I387_MXCSR_REGNUM)
        return i386_mxcsr_type;

    #undef I387_ST0_REGNUM
    #undef I387_NUM_XMM_REGS

      return builtin_type_int;
    }

You can always check in GDB:

    (gdb) p sizeof ($cs)
    $1 = 4
    (gdb) ptype $cs
    type = int
    (gdb) 

I don't know why the upper bits would be set.  GDB may be
misinterpreting the information in the core file.