Should the C++ constructor and destructor tables move into FLASH?

[metarutaiga]

Arduino/tools/sdk/ld/eagle.app.v6.common.ld.vtables.h

Lines 15 to 26 in fe451a8

	. = (. + 3) & ~ 3;
	/* C++ constructor and destructor tables, properly ordered: */
	__init_array_start = ABSOLUTE(.);
	KEEP (*crtbegin.o(.ctors))
	KEEP (*(EXCLUDE_FILE (*crtend.o) .ctors))
	KEEP (*(SORT(.ctors.*)))
	KEEP (*(.ctors))
	__init_array_end = ABSOLUTE(.);
	KEEP (*crtbegin.o(.dtors))
	KEEP (*(EXCLUDE_FILE (*crtend.o) .dtors))
	KEEP (*(SORT(.dtors.*)))
	KEEP (*(.dtors))

and

Arduino/tools/sdk/ld/eagle.app.v6.common.ld.vtables.h

Lines 35 to 39 in fe451a8

	. = ALIGN(4); /* this table MUST be 4-byte aligned */
	_bss_table_start = ABSOLUTE(.);
	LONG(_bss_start)
	LONG(_bss_end)
	_bss_table_end = ABSOLUTE(.);

These are all 32bit pointers.
It should move into flash to reduce memory usage.

I change it in my repo.
metarutaiga@3bc7ce4

[mcspr]

We could just copy-paste those .{c,d}tor entries from the vtables .h .rodata into the .irom0 one? No relation to vtables, just move those to flash at all times

[earlephilhower]

IIRC they're in RAM now because of IRQ safety. If any classes are used in IRQ handlers, you can't be sure the flash is accessible so risk crashes. There was a bug I can't find opened about this after the original memory map shuffling...

[mcspr]

Arent dtors & ctors (and the whole init array) are supposed to be used for global objects? IRQ code will inject ctor / dtor call when needed, where the actual section can be changed with the IRAM attr

[earlephilhower]

Good catch, that sounds right.

The __init_array_start/end are only used in the CRT initialization (now handled by us in main.cpp)

Arduino/cores/esp8266/core_esp8266_main.cpp

Lines 271 to 278 in fe451a8

	static void do_global_ctors(void) {
	static struct object ob;
	__register_frame_info( __eh_frame, &ob );
	void (**p)(void) = &__init_array_end;
	while (p != &__init_array_start)
	(*--p)();
	}

BSS start/end, I think is used by the ROM code to do the bzero but I can't find where we stuff it for the ROM to find right this morning.

I'd say move it at this point. We're not saving all that much space at this point, but every byte counts...