void __builtin_return_address (unsigned int level);

void __builtin_return_address (unsigned int level);
    Returns the return address of the current function, or of one of its callers. Where level argument is a constant literal indicating the number of frames to scan up the call stack. The level must range from 0 to 63. A value of 0 yields the return address of the current function, a value of 1 yields the return address of the caller of the current function and so on.

Notes:

1. When the top of the stack is reached, the function will return 0.
2. The level must range from 0 to 63, otherwise a warning message will be issued and the compilation will halt.
3. When functions are inlined, the return address corresponds to that of the function that is returned to.
4. Compiler optimization may affect expected return value due to introducing extra stack frames or fewer stack frames than expected due to optimizations such as inlining.

    __builtin_return_address(0) yields the address to which the current function will return. __builtin_return_address(1) yields the address to which the caller will return, and so on up the stack.
    Return probes operates by replacing the return address in the stack (or in a known register, such as the lr register for ppc - what else can you do with a system with 100's of registers :) ). This may cause __builtin_return_address(0), when invoked from return-probed function, to return the address of the return-probes trampoline. There has been concern that this will break something.
    __builtin_return_address is used entirely for tracing, profiling, and error reporting.