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Re: SH breakpoint problem
- To: Jonathan Larmour <jlarmour at redhat dot com>
- Subject: Re: SH breakpoint problem
- From: Elena Zannoni <ezannoni at cygnus dot com>
- Date: Tue, 7 Aug 2001 10:34:46 -0400
- Cc: gdb at sources dot redhat dot com
- References: <3B6F5625.ADBD6F53@redhat.com>
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?
Elena