Internal breakpoints

Internal breakpoints

[ankit thukral]

 hi all,
      i was debugging a program using GDB (in linux)
 and realized that GDB puts some breakpoints of it's
 own known as internal breakpoints.they are visible
 on
 issuing the following command :
 
 (gdb) maintainence info breakpoints
 
 -2  shlib events   keep y   0x4000c9c0
 <_dl_debug_state_internal>
         breakpoint already hit 3 times
 -7  longjmp        keep n   0x4000f870 <longjmp>
 -8  longjmp        keep n   0x42027240 <siglongjmp>
 -9  longjmp        keep n   0x42027240 <siglongjmp>
 -10 longjmp resume keep n   0x00000000
 
        can anyone explain to me in detail what are
 these for?
 
 thanks in advance,
 ankit.
 

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Re: Internal breakpoints

[Jim Blandy]

ankit thukral <ankit_plug@yahoo.com> writes:
>  -2  shlib events   keep y   0x4000c9c0
>  <_dl_debug_state_internal>
>          breakpoint already hit 3 times

The dynamic linker in the program being debugged calls this function
each time it loads or unloads a shared library.  GDB sets this
breakpoint so it can keep its copy of the shared library table up to
date.

>  -7  longjmp        keep n   0x4000f870 <longjmp>
>  -8  longjmp        keep n   0x42027240 <siglongjmp>
>  -9  longjmp        keep n   0x42027240 <siglongjmp>
>  -10 longjmp resume keep n   0x00000000

GDB needs to be able to recognize calls to longjmp, to avoid losing
control of the program, to make sure watchpoints on local variables in
frames popped by the longjmp are disabled, and so on.

You'll need to look at breakpoint.c for more detail.

Re: Internal breakpoints

[Eli Zaretskii]

> From: Jim Blandy <jimb@redhat.com>
> Date: 01 Oct 2003 01:40:51 -0500
> 
> You'll need to look at breakpoint.c for more detail.

I believe the node "Set Breaks" in the GDB manual has something about
this.