Why does gcc return 0 instead of the address of a stack allocated variable?

Question

As part of an experiment using custom stacks, I wanted a function to return the address of a stack allocated char buffer.

// return pointer to stack variabl         


        

Answer 1

GCC deliberately returns NULL in this case as can be seen from the code:

tree zero = build_zero_cst (TREE_TYPE (val));
gimple_return_set_retval (return_stmt, zero);
update_stmt (stmt);

Newer versions of GCC and Clang exploit undefined behavior more aggressively so this check is not suprising. It also makes code fail fast which is a good thing in most cases (not yours, apparently).