Re: back into the thread....

[Pedro Alves <palves@redhat.com>]

On 11/12/2013 10:54 PM, Mark Manning wrote:
> 
> Also, the "can not access addres zero" error is totally bogus, there
> is no attempted access to address zero by my code.  What i believe is
> happening is GDB is accessing some structure related to debug info for
> the code it is about to execute and the pointer it is trying to use is
> null (this is pure guesswork).
> 
> The exact address that is in question here is 0xc000 which due to my
> ye-olde C64 days is very easy to remember :).  After hitting my break
> point i jump to this address, i know the program counter is at this
> address because i can do a dump of the disassembly from $pc but
> someone somewhere is attempting to access address zero immediately
> after i single step that branch (actally a mov pc, lr).

"mov pc, lr" moves the contents of $lr to $pc.  IOW, it's a jump.
ARM has no hardware single-step support.  This means that to single-step
one instruction, GDB has to figure out where the instruction might
land (by disassembling the instruction and being aware of the instruction
set), place a breakpoint there, and then let execution continue.

It just sounds like $lr is 0, and GDB is then trying to set
the breakpoint there, which of course fails.  That would be a
bug in your code, not GDB.

-- 
Pedro Alves