On Wed, Sep 23, 2020 at 12:39 PM Al Viro [off-list ref] wrote:

On Wed, Sep 23, 2020 at 03:59:01PM +0100, Al Viro wrote:

quoted

quoted

That's a very good question.  But it does not just compile but actually
works.  Probably because all the syscall wrappers mean that we don't
actually generate the normal names.  I just tried this:

--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h

@@ -468,7 +468,7 @@ asmlinkage long sys_lseek(unsigned int fd, off_t offset,
 asmlinkage long sys_read(unsigned int fd, char __user *buf, size_t count);
 asmlinkage long sys_write(unsigned int fd, const char __user *buf,
                            size_t count);
-asmlinkage long sys_readv(unsigned long fd,
+asmlinkage long sys_readv(void *fd,

for fun, and the compiler doesn't care either..

Try to build it for sparc or ppc...

FWIW, declarations in syscalls.h used to serve 4 purposes:
        1) syscall table initializers needed symbols declared
        2) direct calls needed the same
        3) catching mismatches between the declarations and definitions
        4) centralized list of all syscalls

(2) has been (thankfully) reduced for some time; in any case, ksys_... is
used for the remaining ones.

(1) and (3) are served by syscalls.h in architectures other than x86, arm64
and s390.  On those 3 (1) is done otherwise (near the syscall table initializer)
and (3) is not done at all.

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 think this would be a good idea.  I have been working on a patchset
to clean up the conditional syscall handling (sys_ni.c), and conflicts
with the prototypes in syscalls.h have been getting in the way.
Having the prototypes use SYSCALL_DECLAREx(...) would solve that
issue.

--
Brian Gerst