nealef opened a new issue, #10898:
URL: https://github.com/apache/nuttx/issues/10898
I have been investigating signal handling in NuttX for SEGV/BUS/… for
armv7-m. I have got some PoC code written (for a backlevel NuttX) that, while
I’m in the interrupt handler, will schedule a signal handler. However, when it
returns from the interrupt in `exception_common` and the next instruction is
executed:
```
343 bx r14
/* And return */
(gdb) p $r14
$1 = 0xfffffffd
(gdb) stepi
up_sigdeliver () at armv7-m/up_sigdeliver.c:74
74 struct tcb_s *rtcb = this_task();
(gdb) bt
#0 up_sigdeliver () at armv7-m/up_sigdeliver.c:74
#1 <signal handler called>
```
I get a hardfault with a cfault of 0x1 (instruction access violation) and an
hfault of 0x40000000 (“FORCED”):
```
[ 9.439000] [12] up_hardfault: IRQ: 3 regs: 0xc0327078
[ 9.439000] [12] up_hardfault: BASEPRI: 00000080 PRIMASK: 00000000
IPSR: 00000003 CONTROL: 00000001
[ 9.439000] [12] up_hardfault: CFAULTS: 00000001 HFAULTS: 40000000
DFAULTS: 0000000b BFAULTADDR: 00000000 AFAULTS: 00000000
```
In the interrupt handler I thought I was clearing/acknowledging the
interrupt in the correct way in `up_memfault`:
```
uint32_t cfsr = getreg32(NVIC_CFAULTS);
uint32_t *mfsr = (uintptr_t) NVIC_CFAULTS;
:
*mfsr |= cfsr; /* Acknowledge interrupt */
```
I have looked through the ARM-7M Architecture Reference but I can’t work out
what the proper way of exiting the handler is (assuming this is the root cause
of the problem).
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