On Wed, Sep 23, 2020 at 08:45:51PM +0200, Arnd Bergmann wrote: > On Wed, Sep 23, 2020 at 6:38 PM Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote: > > > > I wonder if we should do something like > > > > SYSCALL_DECLARE3(readv, unsigned long, fd, const struct iovec __user *, vec, > > unsigned long, vlen); > > in syscalls.h instead, and not under that ifdef. > > > > Let it expand to declaration of sys_...() in generic case and, on x86, into > > __do_sys_...() and __ia32_sys_...()/__x64_sys_...(), with types matching > > what SYSCALL_DEFINE ends up using. > > > > Similar macro would cover compat_sys_...() declarations. That would > > restore mismatch checking for x86 and friends. AFAICS, the cost wouldn't > > be terribly high - cpp would have more to chew through in syscalls.h, > > but it shouldn't be all that costly. Famous last words, of course... > > > > Does anybody see fundamental problems with that? > > I've had some ideas along those lines in the past and I think it should work. > > As a variation of this, the SYSCALL_DEFINEx() macros could go away > entirely, leaving only the macro instantiations from the header to > require that syntax. It would require first changing the remaining > architectures to build the syscall table from C code instead of > assembler though. > > Regardless of that, another advantage of having the SYSCALL_DECLAREx() > would be the ability to include that header file from elsewhere with a different > macro definition to create a machine-readable version of the interface when > combined with the syscall.tbl files. This could be used to create a user > space stub for calling into the low-level syscall regardless of the > libc interfaces, > or for synchronizing the interfaces with strace, qemu-user, or anything that > needs to deal with the low-level interface. FWIW, after playing with that for a while... Do we really want the compat_sys_...() declarations to live in linux/compat.h? Most of the users of that file don't want those; why not move them to linux/syscalls.h? Reason: there's a lot more users of linux/compat.h than those of linux/syscalls.h - it's pulled by everything in the networking stack, for starters...
