[PowerPC] Pointers

//Tutorial by Bad Luck Brian

Pointers



This lesson will be short but it is very important to understand what is a pointer !

A pointer is an address containing an address as bytes.

I know it sounds weird at first but lets make an example.

we can't use 'strings' in registers so we need to use pointers to use strings !
Code:
0x12340000 = my string
0x55550000 = pointer
in the memory:

Code:
*ADDRESS  |                               *BYTES*                                  |  ASCII
0x12340000: 55 55 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
...
0x55550000: 42 61 64 20 4C 75 63 6B 20 42 72 69 61 6E 00 00  Bad Luck Brian..

here is how i would load the pointer in powerpc

Code:
lis r3, 0x1234
lwz r3, 0x12340000(r3)
the lis will set r3 to: 12 34 00 00 (0x12340000)
and the lwz will read the memory at 0x12340000(pointer) and store it in r3

so r3 = 0x55550000 (55 55 00 00)

now r3 will contain the address of the string , of course in this case we could just use lis r3, 0x5500
but sometimes we have to use pointers like in RPC where the address of the function to call will be stored as bytes at our address

example of rpc:
Code:
//0x2100000 = pointer to call

//read memory to get your arguments using lwz
lis r9, 0x210   (0x2100000)   //time to load the address
mtctr r9  //this will save the address in a special register (count register), will talk about it in the next lesson
bctrl  //this will call the address in the count register, will talk about it in the next lesson
that's why pointers are important !