/lib64/ld64.so.1 not being added to target sections list on ppc64

/lib64/ld64.so.1 not being added to target sections list on ppc64

[Paul Gilliam]

I am tracking down a bug where the inf. gets a segfault when the user sets 
a pointer variable to point to a string:

(gdb) set var ptr1="foo"

gdb "calls" 'malloc' in the inf.  It gets a function pointer to 'malloc', 
but fails to convert it to a function address because none of the sections 
of the object file with the .opd section corresponding to the function 
pointer  are loaded into the target sections table.  So 
'Convert_Function_Pointer_To_Address' (or whatever it's called) just 
returns the function pointer.  When gdb tries to 'call' that 
(non-executable) address, a segfault happens.

The .opd section corresponding to the function pointer is in the 
/lib64/ld64.so.1 object file.

But wait, there's more!

There is another table of sections that is used when the gdb command 'info 
symbol' is used.  If I go:
  (gdb) p &malloc
  (gdb) info symbol $1

gdb responds 'malloc is in the .opd section'

I don't understand:
 1) why are there two section tables?
 2) why aren't sections from /lib64/ld64.so.1 being loaded into the target 
sections table?
 3) why is the function pointer for 'malloc' pointing to a plt in the 
/lib64/ld64.so object and not one in the main executable?

I welcome any insight any of you might have.

Thanks in advance,

-=# Paul Gilliam #=-

PS:  I have changed jobs and don't work on GDB any more, but this one bug 
followed me to my new job.

Re: /lib64/ld64.so.1 not being added to target sections list on ppc64

[Daniel Jacobowitz]

On Mon, Feb 05, 2007 at 05:33:21PM -0800, Paul Gilliam wrote:
>  1) why are there two section tables?

History.  Hard to change, but probably advisable to change.  I believe
the problems will mostly deal with relocation and applying offsets to
sections.

-- 
Daniel Jacobowitz
CodeSourcery

Re: /lib64/ld64.so.1 not being added to target sections list on ppc64

[Andreas Schwab]

Paul Gilliam <gilliam@us.ibm.com> writes:

> There is another table of sections that is used when the gdb command 'info 
> symbol' is used.  If I go:
>   (gdb) p &malloc
>   (gdb) info symbol $1
>
> gdb responds 'malloc is in the .opd section'
>
> I don't understand:
>  1) why are there two section tables?
>  2) why aren't sections from /lib64/ld64.so.1 being loaded into the target 
> sections table?
>  3) why is the function pointer for 'malloc' pointing to a plt in the 
> /lib64/ld64.so object and not one in the main executable?

The problem is that there are two malloc implementation, the early one in
ld64.so and the real one in libc.so.  Unless you have debugging symbols
for libc.so the real one is never found.

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwab@suse.de
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
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