Date: Fri, 12 Apr 2019 07:48:45 -0400 From: Rich Felker <dalias@...c.org> To: musl@...ts.openwall.com Subject: Re: Re: use of varargs in open and various functions On Thu, Apr 11, 2019 at 06:36:31PM +0200, Norbert Lange wrote: > > On Thu, Apr 11, 2019 at 04:25:50PM +0200, Norbert Lange wrote: > > > Hello, > > > > > > I had some dealings with software that forwards arguments from vararg functions, > > > the kind with optional but known fixed type. > > > open, fcntl, ioctl are some examples. > > > > > > What happens in musl is that the optional argument is optionally or > > > always retrieved (fcntl). > > > I think this is pretty much pointless, > > Tough. The interfaces are just defined this way. In case of fcntl, it > > is merely a convenience of circumstance that allows musl to do what it > > does. fcntl()'s third argument can be a pointer to various structures, > > or an unsigned long. Linux requires a C implementation where pointers > > can be losslessly converted to long and back, but that is the only > > reason this call to va_arg() works. > > Those are C interfaces, they can be implemented in any language you > you see fit. > if you write asm, you can just pick the registers or pull the values from > the stack. > declaration can and should stay the same, no point stressing this further. I think what you're not understanding is that the goal of musl is not to provide C that translates into asm/machine code that matches a particular ABI. It's to provide C that's valid as C, which makes it useful and interesting in a much larger context and relevant to the future, where C very well may be consumed mainly in some kind of memory-safe abstract machine that has little to do with our current conceptions of machine ABIs, rather than just the present. Naturally, the C library can't be implemented entirely in C, so this goal is always incomplete. The adapted version of this goal then becomes minimizing the amount of code that's not portable C (i.e. asm source files, inline asm, C extensions, code that's C but that assumes particular addressing/stack/etc. models, ...) to what's strictly necessary. Rich
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