startup.c broken with large BSS areas

[fenugrec]

candle-usb/candleLight_fw#135 (comment)

hardfault on a F042. Description copied from the comment linked above :

I think I have an idea of the issue causing the hardfault.

in startup.c :

typedef struct _zero_table_t
{
	uint32_t* dest;
	uint32_t wlen;
} zero_table_t;


void Reset_Handler(void)
{
....

	for (zero_table_t const* table = &__zero_table_start__; table < &__zero_table_end__; ++table)
	{
		for (size_t i=0; i<table->wlen; ++i)
		{
			table->dest[i] = 0u;
		}
	}

the for loop runs wlen times, but it writes a u32 every loop. Perfect, but the ldscripts calculate wlen with LONG (__data_end__ - __data_start__) , i.e. a value in bytes !

So the hardfault occurs on a build here with wlen=0x930 , at i=0x601 (thus trying to write at 0x2000 1804 - right outside an F042 's 6kB of RAM !)

[marckleinebudde]

The __copy_table code triggers the same problem. Once length in a copy or zero table entry reaches 1/4 of the total RAM size this code will hard fault the system. Before this it will only overwrite the memory....