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Re: 64bit pointer
- From: freindlyuser at hushmail dot com
- To: "Jan Kratochvil" <jan dot kratochvil at redhat dot com>
- Cc: gdb at sourceware dot org
- Date: Thu, 03 Sep 2009 13:27:18 +0000
- Subject: Re: 64bit pointer
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On Thu, 03 Sep 2009 12:33:25 +0000 Jan Kratochvil
<jan.kratochvil@redhat.com> wrote:
>On Thu, 03 Sep 2009 14:21:41 +0200, freindlyuser@hushmail.com
>wrote:
>> (gdb) x/s *($rdi+0x8)
>> 0x4210a9b7: <Address 0x4210a9b7 out of bounds>
>
>This syntax is not much recommended, it means the same as:
>
>(gdb) x/s *(int *) ($rdi+0x8)
>0x4210a9b7: <Address 0x4210a9b7 out of bounds>
>
>On 64bit arch sizeof (int) == 4 but sizeof (void *) == 8 so you
>will not fetch
>the whole address.
>
>
>> (gdb) x/x $rdi+0x8
>> 0x3a9b4210b7a4: 0x00003a9b4210a9b7
>> (gdb) x/s 0x00003a9b4210a9b7
>> 0x3a9b4210a9b7: "The string it points to"
>
>Therefore you want one indirection there.
>
>> Should this be happening?
>
>Yes. Until GDB forbids dereferencing numeric arguments as `int *'
>which IMHO
>is more confusing than convenient. [Would a patch be approved?]
>
>
>> Is there a work around where I can read the data in
>> 0x00003a9b4210a9b7 without having to manually copy and paste
>(ie:
>> in the commands that are executed on a breakpoint).
>
>This way it should work:
>
>(gdb) x/s *(void **) ($rdi+0x8)
>OR
>(gdb) p *(char **) ($rdi+0x8)
>
>
>Regards,
>Jan
The work around works perfectly.
Thank you.
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