x86_64 gdb and objdump

x86_64 gdb and objdump

[Srinivas Murthy]

From a core dump file, I see that with gdb I get a "Cannot access
memory at address xx" msg but using objdump, I can see the contents of
the memory location on the core file.

Any ideas what is going wrong?

Thanks.

# gdb test core_dir/core.test.30235
GNU gdb 6.6
Copyright (C) 2006 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB.  Type "show warranty" for details.
This GDB was configured as "x86_64-unknown-linux-gnu"...
Using host libthread_db library "/lib64/libthread_db.so.1".
Core was generated by `./test'.
Program terminated with signal 11, Segmentation fault.
#0  0x00000000004004f5 in bar () at test.c:10
10      test.c: No such file or directory.
        in test.c
(gdb) bt
#0  0x00000000004004f5 in bar () at test.c:10
Cannot access memory at address 0x7fbfffee98


However, objdump shows that there is some valid content at the location:

# objdump -D /tmp/core.test.30235 |less |grep 7fbfffee98
  7fbfffe95f:   00 08                   add    %cl,(%rax)

Re: x86_64 gdb and objdump

[Daniel Jacobowitz]

On Mon, Jul 02, 2007 at 12:14:43PM -0700, Srinivas Murthy wrote:
> #0  0x00000000004004f5 in bar () at test.c:10
> 10      test.c: No such file or directory.
>        in test.c
> (gdb) bt
> #0  0x00000000004004f5 in bar () at test.c:10
> Cannot access memory at address 0x7fbfffee98

Does x/x 0x7fbfffee98 work?

> However, objdump shows that there is some valid content at the location:
> 
> # objdump -D /tmp/core.test.30235 |less |grep 7fbfffee98
>  7fbfffe95f:   00 08                   add    %cl,(%rax)

That's not the same address...

-- 
Daniel Jacobowitz
CodeSourcery

Re: x86_64 gdb and objdump

[Srinivas Murthy]

I did try "x ..." at a bunch of memory locations and it outputs the
same error msg.

It seems like its not able to access any memory location in the core file.

Thanks.


On 7/2/07, Daniel Jacobowitz <drow@false.org> wrote:
> On Mon, Jul 02, 2007 at 12:14:43PM -0700, Srinivas Murthy wrote:
> > #0  0x00000000004004f5 in bar () at test.c:10
> > 10      test.c: No such file or directory.
> >        in test.c
> > (gdb) bt
> > #0  0x00000000004004f5 in bar () at test.c:10
> > Cannot access memory at address 0x7fbfffee98
>
> Does x/x 0x7fbfffee98 work?
>
> > However, objdump shows that there is some valid content at the location:
> >
> > # objdump -D /tmp/core.test.30235 |less |grep 7fbfffee98
> >  7fbfffe95f:   00 08                   add    %cl,(%rax)
>
> That's not the same address...
>
> --
> Daniel Jacobowitz
> CodeSourcery
>

Re: x86_64 gdb and objdump

[Daniel Jacobowitz]

On Mon, Jul 02, 2007 at 01:39:05PM -0700, Srinivas Murthy wrote:
> I did try "x ..." at a bunch of memory locations and it outputs the
> same error msg.
> 
> It seems like its not able to access any memory location in the core file.

This works fine for me.  Can you provide a test case?

-- 
Daniel Jacobowitz
CodeSourcery

Re: x86_64 gdb and objdump

[Srinivas Murthy]

[-- Attachment #1: Type: text/plain, Size: 747 bytes --]

I've attached the core dump, the executable and the source is listed below:

void bar() {

char *p = 0;
printf("%s %d \n", __FUNCTION__, __LINE__);
 *p = 0;
 return;
}
void foo() {

 printf("%s %d \n", __FUNCTION__, __LINE__);

 bar();

return;
}
int main() {

foo();

return 0;
}


On 7/2/07, Daniel Jacobowitz <drow@false.org> wrote:
On Mon, Jul 02, 2007 at 01:39:05PM -0700, Srinivas Murthy wrote:
> I did try "x ..." at a bunch of memory locations and it outputs the
> same error msg.
>
> It seems like its not able to access any memory location in the core file.
This works fine for me.  Can you provide a test case?

--
Daniel Jacobowitz
CodeSourcery
Attachment:
core.temp
Description: Binary data
Attachment:
temp
Description: Binary data


[-- Attachment #2: temp --]
[-- Type: application/x-executable, Size: 10109 bytes --]