------- Comment #5 from ktietz at gcc dot gnu dot org 2009-08-08 08:43 ------- (In reply to comment #4) > -fno-builtin means more or less exactly that the compiler *should not* > assume anything special about a function from its name (unless the name > starts __builtin or some similar reserved-namespace cases such as __sync) > - that is, you declare alloca and because of -fno-builtin the compiler > assumes this is your own function with no special semantics whatever. By > -fno-builtin you are declaring that alloca, and all other normally > built-in functions, are normal functions with no special semantics the > compiler needs to know about. So of course it generates a call like it > would to any other random function you might have defined in another > translation unit. > > If you want to use alloca with its traditional memory allocation semantics > with -fno-builtin, you'll need to use a malloc-based emulation such as > that in libiberty, not something that uses the stack. >
Well, IMHO it is the same for alloca, as for setjmp, or longjmp. Even some code for detecting alloca semanices is present (in a slightly broken way), see calls.c (special_function_p). So, if it is really the intention that by -fno-builtin all function have standard calling convention, then this special cases in calls.c would be a bug. But well, I assume it isn't. I think the best thing to do here is, as written within this function commment, to have a function-declaration attribute, which indicated alloca behavior. Or, do I mis-read here something. Kai -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41001
