On 12/12/2014 11:51 AM, Florian Weimer wrote: > 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. Hmmm. That's probably possible today, but I don't think you can say anything about future calling conventions. I'd have to ask why this is so important. > (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. :-/) Yes. Andrew.
