Bas van Dijk Bas van Dijk - 1 year ago 100
C Question

How to place a variable at a given absolute address in memory (with GCC)

The RealView ARM C Compiler supports placing a variable at a given memory address using the variable attribute


int var __attribute__((at(0x40001000)));
var = 4; // changes the memory located at 0x40001000

Does GCC have a similar variable attribute?

Answer Source

I don't know, but you can easily create a workaround like this:

int *var = (int*)0x40001000;
*var = 4;

It's not exactly the same thing, but in most situations a perfect substitute.

If you use GCC, i assume you also use GNU ld (although it is not a certainty, of course) and ld has support for placing variables wherever you want them.

I imagine letting the linker do that job is pretty common.

Inspired by answer by @rib, I'll add that if the absolute address is for some control register, I'd add volatile to the pointer definition. If it is just RAM, it doesn't matter.