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Message-ID: <366548c1a0d9749e42c0d0c993414a353c9b0b02.camel@physik.fu-berlin.de>
Date: Fri, 21 Jun 2024 10:44:39 +0200
From: John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
To: Arnd Bergmann <arnd@...nel.org>, linux-arch@...r.kernel.org,
linux-kernel@...r.kernel.org
Cc: Arnd Bergmann <arnd@...db.de>, Thomas Bogendoerfer
<tsbogend@...ha.franken.de>, linux-mips@...r.kernel.org, Helge Deller
<deller@....de>, linux-parisc@...r.kernel.org, "David S. Miller"
<davem@...emloft.net>, Andreas Larsson <andreas@...sler.com>,
sparclinux@...r.kernel.org, Michael Ellerman <mpe@...erman.id.au>, Nicholas
Piggin <npiggin@...il.com>, Christophe Leroy <christophe.leroy@...roup.eu>,
"Naveen N . Rao" <naveen.n.rao@...ux.ibm.com>,
linuxppc-dev@...ts.ozlabs.org, Brian Cain <bcain@...cinc.com>,
linux-hexagon@...r.kernel.org, Guo Ren <guoren@...nel.org>,
linux-csky@...r.kernel.org, Heiko Carstens <hca@...ux.ibm.com>,
linux-s390@...r.kernel.org, Rich Felker <dalias@...c.org>,
linux-sh@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>, Alexander Viro
<viro@...iv.linux.org.uk>, Christian Brauner <brauner@...nel.org>,
linux-fsdevel@...r.kernel.org, libc-alpha@...rceware.org,
musl@...ts.openwall.com, ltp@...ts.linux.it, stable@...r.kernel.org
Subject: Re: [PATCH 09/15] sh: rework sync_file_range ABI
Hi Arnd,
thanks for your patch!
On Thu, 2024-06-20 at 18:23 +0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
>
> The unusual function calling conventions on superh ended up causing
^^^^^^
It's spelled SuperH
> sync_file_range to have the wrong argument order, with the 'flags'
> argument getting sorted before 'nbytes' by the compiler.
>
> In userspace, I found that musl, glibc, uclibc and strace all expect the
> normal calling conventions with 'nbytes' last, so changing the kernel
> to match them should make all of those work.
>
> In order to be able to also fix libc implementations to work with existing
> kernels, they need to be able to tell which ABI is used. An easy way
> to do this is to add yet another system call using the sync_file_range2
> ABI that works the same on all architectures.
>
> Old user binaries can now work on new kernels, and new binaries can
> try the new sync_file_range2() to work with new kernels or fall back
> to the old sync_file_range() version if that doesn't exist.
>
> Cc: stable@...r.kernel.org
> Fixes: 75c92acdd5b1 ("sh: Wire up new syscalls.")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
> arch/sh/kernel/sys_sh32.c | 11 +++++++++++
> arch/sh/kernel/syscalls/syscall.tbl | 3 ++-
> 2 files changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/arch/sh/kernel/sys_sh32.c b/arch/sh/kernel/sys_sh32.c
> index 9dca568509a5..d5a4f7c697d8 100644
> --- a/arch/sh/kernel/sys_sh32.c
> +++ b/arch/sh/kernel/sys_sh32.c
> @@ -59,3 +59,14 @@ asmlinkage int sys_fadvise64_64_wrapper(int fd, u32 offset0, u32 offset1,
> (u64)len0 << 32 | len1, advice);
> #endif
> }
> +
> +/*
> + * swap the arguments the way that libc wants it instead of
I think "swap the arguments to the order that libc wants them" would
be easier to understand here.
> + * moving flags ahead of the 64-bit nbytes argument
> + */
> +SYSCALL_DEFINE6(sh_sync_file_range6, int, fd, SC_ARG64(offset),
> + SC_ARG64(nbytes), unsigned int, flags)
> +{
> + return ksys_sync_file_range(fd, SC_VAL64(loff_t, offset),
> + SC_VAL64(loff_t, nbytes), flags);
> +}
> diff --git a/arch/sh/kernel/syscalls/syscall.tbl b/arch/sh/kernel/syscalls/syscall.tbl
> index bbf83a2db986..c55fd7696d40 100644
> --- a/arch/sh/kernel/syscalls/syscall.tbl
> +++ b/arch/sh/kernel/syscalls/syscall.tbl
> @@ -321,7 +321,7 @@
> 311 common set_robust_list sys_set_robust_list
> 312 common get_robust_list sys_get_robust_list
> 313 common splice sys_splice
> -314 common sync_file_range sys_sync_file_range
> +314 common sync_file_range sys_sh_sync_file_range6
^^^^^^ Why the suffix 6 here?
> 315 common tee sys_tee
> 316 common vmsplice sys_vmsplice
> 317 common move_pages sys_move_pages
> @@ -395,6 +395,7 @@
> 385 common pkey_alloc sys_pkey_alloc
> 386 common pkey_free sys_pkey_free
> 387 common rseq sys_rseq
> +388 common sync_file_range2 sys_sync_file_range2
> # room for arch specific syscalls
> 393 common semget sys_semget
> 394 common semctl sys_semctl
I wonder how you discovered this bug. Did you look up the calling convention on SuperH
and compare the argument order for the sys_sync_file_range system call documented there
with the order in the kernel?
Did you also check what order libc uses? I would expect libc on SuperH misordering the
arguments as well unless I am missing something. Or do we know that the code is actually
currently broken?
Thanks,
Adrian
--
.''`. John Paul Adrian Glaubitz
: :' : Debian Developer
`. `' Physicist
`- GPG: 62FF 8A75 84E0 2956 9546 0006 7426 3B37 F5B5 F913
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