Re: SH breakpoint problem

[Elena Zannoni <ezannoni at cygnus dot com>]

Jonathan Larmour writes:
 > Elena Zannoni wrote:
 > > 
 > > Jonathan Larmour writes:
 > >  > I've been sanity checking both the GCC 3.0.1 candidate and the GDB 5.1
 > >  > candidate, and I've found an issue on the SH, which I'm debugging remotely.
 > >  > Setting a breakpoint on this simple function:
 > >  >
 > >  > void
 > >  > cyg_test_exit(void)
 > >  > {
 > >  >     for(;;);
 > >  > }
 > >  >
 > >  > fails - it reports a SIGILL. I believe this is probably a watchdog timer.
 > >  > The problem is that, given the disassembly:
 > >  >
 > >  > Dump of assembler code for function cyg_test_exit:
 > >  > 0x800b130 <cyg_test_exit>:   mov.l   r14,@-r15
 > >  > 0x800b132 <cyg_test_exit+2>: mov     r15,r14
 > >  > 0x800b134 <cyg_test_exit+4>: bra     0x800b134 <cyg_test_exit+4>
 > >  > 0x800b136 <cyg_test_exit+6>: nop
 > >  >
 > >  > GDB sets the breakpoint at 0x800b136, rather than 0x800b134. Tracing
 > >  > through GDB, I found after_prologue() in sh-tdep.c does:
 > >  >
 > >  >   /* Get the line associated with FUNC_ADDR.  */
 > >  >   sal = find_pc_line (func_addr, 0);
 > >  >
 > >  >   /* There are only two cases to consider.  First, the end of the source
 > >  > line
 > >  >      is within the function bounds.  In that case we return the end of the
 > >  >      source line.  Second is the end of the source line extends beyond the
 > >  >      bounds of the current function.  We need to use the slow code to
 > >  >      examine instructions in that case.  */
 > >  >   if (sal.end < func_end)
 > >  >     return sal.end;
 > >  >
 > >  > The problem is, I believe, that the debug info is probably right and the
 > >  > end of the source line is indeed 0x800b136 (as is returned from
 > >  > find_pc_line) since the nop is in a delay slot, but it is mistaken to
 > >  > assume that is where the breakpoint should be set.
 > >  >
 > >  > But I don't know what way I should try to fix it. Matching instructions
 > >  > with delay slots like branches explicitly by reading from the target is my
 > >  > first thought but it seems awfully wasteful, and I'm sure there is received
 > >  > knowledge on this subject. So, what is it :-).
 > > 
 > > I should know, but I don't (I am the gdb sh person). :-(
 > > What does gdb do with the same program against the simulator?
 > 
 > It has the same failing:
 > 
 > (gdb) disass cyg_test_exit
 > Dump of assembler code for function cyg_test_exit:
 > 0x10e4 <cyg_test_exit>:	mov.l	r14,@-r15
 > 0x10e6 <cyg_test_exit+2>:	mov	r15,r14
 > 0x10e8 <cyg_test_exit+4>:	bra	0x10e8 <cyg_test_exit+4>
 > 0x10ea <cyg_test_exit+6>:	nop	
 > End of assembler dump.
 > (gdb) b cyg_test_exit
 > Breakpoint 1 at 0x10ea: file foo.c, line 3.
 > (gdb) run
 > Starting program: /export/pot/ecc-obj/sh/edk/foo 
 > 
 > Program received signal SIGTRAP, Trace/breakpoint trap.
 > 0x000010e8 in cyg_test_exit () at foo.c:2
 > 2	{
 > (gdb) 

Ok, I guess we'll (or I) have to cook up something similar to what mips does
for delay slots.

Elena


 > 
 > Jifl
 > -- 
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