Re: single stepping mips remote programs built with gcc 4.0

[Daniel Jacobowitz <drow at false dot org>]

On Thu, Nov 17, 2005 at 12:13:48PM -0800, Newman, Sarah R wrote:
> Hi, I have a version of gdb from CVS on 8/29/2005.  I have configured with the target as mips-elf and the host as cygwin and I am using it to connect to a remote mips system.  All of my programs I am trying to run remotely have been built with GCC 4+.  I am single stepping through code where part of it consists of something like the following in the disassembly listing:
> 
> 00003dac <initialize()>:
> 00003dac:	24040001 	li	a0,1
> 00003db0:	08000deb 	j	000037ac <setArraySize(int, int)>
> 00003db4:	24050001 	li	a1,1
> 
> 00003db8 <getCurrentBuffer2(int&)>:
> 00003db8:	3c02bd00 	lui	v0,0xbd00
> 
> When stopped at the beginning of the function, I can tell by looking
> at the remote protocol debug output that a breakpoint is being set in
> memory at the location of getCurrentBuffer2, not setArraySize.  We
> suspect that this may have to do with GCC 4+ doing straight jumps to
> other functions and not jump and link followed by jump register to
> leave the function.  Has anyone else encountered this or found a
> solution?

Could you please build a debuggable GDB binary, and trace through
mips32_next_pc?  It looks like it should handle the 'j' instruction
just fine:

        case 2:         /* J */
        case 3:         /* JAL */
          {
            unsigned long reg;
            reg = jtype_target (inst) << 2;
            /* Upper four bits get never changed... */
            pc = reg + ((pc + 4) & 0xf0000000);
          }
          break;

J and JAL share a format, so this should be correct.  It's as if the
value GDB is extracting for the instruction is incorrect.

-- 
Daniel Jacobowitz
CodeSourcery, LLC