It was incorrect to NULL out the pointer to our heap allocated buffer in
`reset`, because subsequent to framebuffer_reset, but while
the heap was still active, we could call `get_bufinfo` again,
leading to a fresh allocation on the heap that is about to be destroyed.
Typical stack trace:
```
#1 0x0006c368 in sharpdisplay_framebuffer_get_bufinfo
#2 0x0006ad6e in _refresh_display
#3 0x0006b168 in framebufferio_framebufferdisplay_background
#4 0x00069d22 in displayio_background
#5 0x00045496 in supervisor_background_tasks
#6 0x000446e8 in background_callback_run_all
#7 0x00045546 in supervisor_run_background_tasks_if_tick
#8 0x0005b042 in common_hal_neopixel_write
#9 0x00044c4c in clear_temp_status
#10 0x000497de in spi_flash_flush_keep_cache
#11 0x00049a66 in supervisor_external_flash_flush
#12 0x00044b22 in supervisor_flash_flush
#13 0x0004490e in filesystem_flush
#14 0x00043e18 in cleanup_after_vm
#15 0x0004414c in run_repl
#16 0x000441ce in main
```
When this happened -- which was inconsistent -- the display would keep
some heap allocation across reset which is exactly what we need to avoid.
NULLing the pointer in reconstruct follows what RGBMatrix does, and that
code is a bit more battle-tested anyway.
If I had a motivation for structuring the SharpMemory code differently,
I can no longer recall it.
Testing performed: Ran my complicated calculator program over multiple
iterations without observing signs of heap corruption.
Closes: #3473
As originally written, the TRANSLATE_SOURCES_EXC was incorrect. If
more than one build directory existed, "make translate"
(and make check-translate) would error.
I corrected the problem, commented it, and added a number of additional
exclude directives.
I reviewed the PR and should have caught this, but did not.
Having zero RGB pins may not have been caught, nor having a non-multiple-of-6
value. Generally, users will only have 6 RGB pins unless they are driving
multiple matrices in parallel. No existing breakouts exist to do this, and
there are probably not any efficient pinouts to be had anyway.
In #3482, @cwalther noted that, hypothetically, a zero byte allocation
could be made in the RGBMatrix constructor. Ensure that width is positive.
Height was already checked against the number of RGB pins if it was specified,
so zero is ruled out there as well.
I have a function where it should be impossible to reach the end, so I put in a safe-mode reset at the bottom:
```
int find_unused_slot(void) {
// precondition: you already verified that a slot was available
for (int i=0; i<NUM_SLOTS; i++) {
if( slot_free(i)) {
return i;
}
}
safe_mode_reset(MICROPY_FATAL_ERROR);
}
```
However, the compiler still gave a diagnostic, because safe_mode_reset was not declared NORETURN.
So I started by teaching the compiler that reset_into_safe_mode never returned. This leads at least one level deeper due to reset_cpu needing to be a NORETURN function. Each port is a little different in this area. I also marked reset_to_bootloader as NORETURN.
Additional notes:
* stm32's reset_to_bootloader was not implemented, but now does a bare reset. Most stm32s are not fitted with uf2 bootloaders anyway.
* ditto cxd56
* esp32s2 did not implement reset_cpu at all. I used esp_restart(). (not tested)
* litex did not implement reset_cpu at all. I used reboot_ctrl_write. But notably this is what reset_to_bootloader already did, so one or the other must be incorrect (not tested). reboot_ctrl_write cannot be declared NORETURN, as it returns unless the special value 0xac is written), so a new unreachable forever-loop is added.
* cxd56's reset is via a boardctl() call which can't generically be declared NORETURN, so a new unreacahble "for(;;)" forever-loop is added.
* In several places, NVIC_SystemReset is redeclared with NORETURN applied. This is accepted just fine by gcc. I chose this as preferable to editing the multiple copies of CMSIS headers where it is normally declared.
* the stub safe_mode reset simply aborts. This is used in mpy-cross.
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