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From: Al Viro <viro@zeniv.linux.org.uk>
To: Christoph Hellwig <hch@lst.de>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Jens Axboe <axboe@kernel.dk>, Arnd Bergmann <arnd@arndb.de>,
	David Howells <dhowells@redhat.com>,
	David Laight <David.Laight@aculab.com>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org,
	linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
	linux-s390@vger.kernel.org, sparclinux@vger.kernel.org,
	linux-block@vger.kernel.org, linux-scsi@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, linux-aio@kvack.org,
	io-uring@vger.kernel.org, linux-arch@vger.kernel.org,
	linux-mm@kvack.org, netdev@vger.kernel.org,
	keyrings@vger.kernel.org, linux-security-module@vger.kernel.org
Subject: Re: [PATCH 5/9] fs: remove various compat readv/writev helpers
Date: Wed, 23 Sep 2020 17:38:31 +0100
Message-ID: <20200923163831.GO3421308@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20200923145901.GN3421308@ZenIV.linux.org.uk>

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

> > 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?

  reply index

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-23  6:05 let import_iovec deal with compat_iovecs as well v3 Christoph Hellwig
2020-09-23  6:05 ` [PATCH 1/9] compat.h: fix a spelling error in <linux/compat.h> Christoph Hellwig
2020-09-23  6:05 ` [PATCH 2/9] iov_iter: move rw_copy_check_uvector() into lib/iov_iter.c Christoph Hellwig
2020-09-23  6:05 ` [PATCH 3/9] iov_iter: refactor rw_copy_check_uvector and import_iovec Christoph Hellwig
2020-09-23 14:16   ` Al Viro
2020-09-23 14:38     ` David Laight
2020-09-23 14:49       ` Al Viro
2020-09-23 14:40     ` Al Viro
2020-09-23  6:05 ` [PATCH 4/9] iov_iter: transparently handle compat iovecs in import_iovec Christoph Hellwig
2020-09-23  6:05 ` [PATCH 5/9] fs: remove various compat readv/writev helpers Christoph Hellwig
2020-09-23 14:25   ` Al Viro
2020-09-23 14:32     ` Christoph Hellwig
2020-09-23 14:59       ` Al Viro
2020-09-23 16:38         ` Al Viro [this message]
2020-09-23 17:05           ` Al Viro
2020-09-23 17:46             ` Christoph Hellwig
2020-09-23 17:08           ` Brian Gerst
2020-09-23 18:45           ` Arnd Bergmann
2020-09-23 19:47             ` Al Viro
2020-09-23 19:52               ` Arnd Bergmann
2020-09-23 21:30             ` David Laight
2020-09-23  6:05 ` [PATCH 6/9] fs: remove the compat readv/writev syscalls Christoph Hellwig
2020-09-23  6:05 ` [PATCH 7/9] fs: remove compat_sys_vmsplice Christoph Hellwig
2020-09-23  6:05 ` [PATCH 8/9] mm: remove compat_process_vm_{readv,writev} Christoph Hellwig
2020-09-23  6:05 ` [PATCH 9/9] security/keys: remove compat_keyctl_instantiate_key_iov Christoph Hellwig
  -- strict thread matches above, loose matches on Subject: below --
2020-09-25  4:51 let import_iovec deal with compat_iovecs as well v4 Christoph Hellwig
2020-09-25  4:51 ` [PATCH 5/9] fs: remove various compat readv/writev helpers Christoph Hellwig
2020-09-18 12:45 let import_iovec deal with compat_iovecs as well Christoph Hellwig
2020-09-18 12:45 ` [PATCH 5/9] fs: remove various compat readv/writev helpers Christoph Hellwig

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