Tahnks for your help, Matthias!
On Thu, Oct 17, 2019 at 02:37:11PM +0200, Matthias Pfaller wrote:
> Have a look at "arm-eabi-objdump -S -d main.elf". Sometimes this is
> quite revealing.
Yeah.
> Are you using openocd or something similar for debugging?
Yes. Openocd with gdb.
> You are compiling for a cortex-m0/3/4?
Cortex-m3
> Are you single stepping through the complete startup sequence or do set a
> break point ath the top of memset (i.e. are break points working at all)?
Breakpoints are working. But there is only a limited set of hardware
breakpoints (four, AFAIR).
> Interrupts are still disabled?
There are no interrupt sources enabled yet. But I wonder why the CPU is not
starting up with disabled IRQs? I am new to the ARM architecture, but every
other architecture I know of would come out from reset with disabled
interrupts... I'd expect BASEPRI and PRIMASK to be set to sane values before
the first instruction is executed?
Anyway, explicitly calling __set_PRIMASK(1) did also not help, although
primask ist still set when the processor crashes.
> Why is the stack pointer so low at this point of execution? Using
> 0x20018000-0x20017d20 == 0x2e0 bytes of stack seems a little excessive
> for just one call.
Ah!... Looks like you've spotted the problem! Actually, the SP is decremented
on every cycle of the loop:
(gdb) disass
Dump of assembler code for function memset:
0x08001008 <+0>: push {r4, lr}
0x0800100a <+2>: mov r4, r0
0x0800100c <+4>: cbz r2, 0x8001014 <memset+12>
=> 0x0800100e <+6>: uxtb r1, r1
0x08001010 <+8>: bl 0x8001008 <memset>
0x08001014 <+12>: mov r0, r4
0x08001016 <+14>: pop {r4, pc}
End of assembler dump.
This looks REALLY suspicous to me. Every cycle of the loop in memset() is
pushing something onto the stack?!?
Without the -ftree-loop-distribute-patterns option, the memset() function
looks entirely different:
cbz r2, <memset+18>
add r2, r0
subs r2, #1
uxtb r1, r1
subs r3, r0, #1
<+10>: strb.w r1, [r3, #1]!
cmp r3, r2
bne.n <memset+10>
<+18>: bx lr
> I usually start toggling output lines when I'm stuck like this...
?
--
Josef Wolf
jw@xxxxxxxxxxxxx
