On 12/12/2014 12:30 PM, Andrew Haley wrote:
On 12/12/2014 10:20 AM, Florian Weimer wrote:open is declared as: int open(const char *pathname, int flags, ...); The intent is to have two overloaded variants: int open(const char *pathname, int flags); int open(const char *pathname, int flags, mode_t mode); The presence of the mode argument depends on the flags specified. The set of such flags is known by the kernel. I wish to avoid to maintain this implementation detail in libc as well, so I want to always read the mode argument, possibly passing a garbage value to the kernel. Is there GCC-portable way to achieve this?You're assuming that for all targets the varargs calling convention is the same as the non-varargs calling convention, at least for integer registers. I don't think this is true for all targets, although it might be true for the targets GCC supports today.
No, I would be perfectly satisfied with calling va_arg unconditionally to read a garbage argument if that can be made GCC-portable in some way. The implementation can still be vararg.
(And I think we had a related conversation about this in the context of the ppc64le bring-up, with the result that we practically need matching calling conventions. :-/)
-- Florian Weimer / Red Hat Product Security
