Re: [PATCH 07/15] parisc: use generic sys_fanotify_mark implementation

[Helge Deller]

On 6/20/24 18:23, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@xxxxxxxx>
>
> The sys_fanotify_mark() syscall on parisc uses the reverse word order
> for the two halves of the 64-bit argument compared to all syscalls on
> all 32-bit architectures. As far as I can tell, the problem is that
> the function arguments on parisc are sorted backwards (26, 25, 24, 23,
> ...) compared to everyone else,

r26 is arg0, r25 is arg1, and so on.
I'm not sure I would call this "sorted backwards".
I think the reason is simply that hppa is the only 32-bit big-endian
arch left...

> so the calling conventions of using an
> even/odd register pair in native word order result in the lower word
> coming first in function arguments, matching the expected behavior
> on little-endian architectures. The system call conventions however
> ended up matching what the other 32-bit architectures do.
>
> A glibc cleanup in 2020 changed the userspace behavior in a way that
> handles all architectures consistently, but this inadvertently broke
> parisc32 by changing to the same method as everyone else.

I appreciate such cleanups to make arches consistent.
But it's bad if breakages aren't noticed or reported then...

> The change made it into glibc-2.35 and subsequently into debian 12
> (bookworm), which is the latest stable release. This means we
> need to choose between reverting the glibc change or changing the
> kernel to match it again, but either hange will leave some systems
> broken.
>
> Pick the option that is more likely to help current and future
> users and change the kernel to match current glibc.

Agreed (assuming we have really a problem on parisc).

> This also
> means the behavior is now consistent across architectures, but
> it breaks running new kernels with old glibc builds before 2.35.
>
> Link: https://sourceware.org/git/?p=glibc.git;a=commitdiff;h=d150181d73d9
> Link: https://git.kernel.org/pub/scm/linux/kernel/git/history/history.git/commit/arch/parisc/kernel/sys_parisc.c?h=57b1dfbd5b4a39d
> Cc: Adhemerval Zanella <adhemerval.zanella@xxxxxxxxxx>
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---
> I found this through code inspection, please double-check to make
> sure I got the bug and the fix right.

The patch looks good at first sight.
I'll pick it up in my parisc git tree and will do some testing the
next few days and then push forward for 6.11 when it opens....

Thank you!!

Helge

> The alternative is to fix this by reverting glibc back to the
> unusual behavior.
> ---
>   arch/parisc/Kconfig                     | 1 +
>   arch/parisc/kernel/sys_parisc32.c       | 9 ---------
>   arch/parisc/kernel/syscalls/syscall.tbl | 2 +-
>   3 files changed, 2 insertions(+), 10 deletions(-)
>
> diff --git a/arch/parisc/Kconfig b/arch/parisc/Kconfig
> index daafeb20f993..dc9b902de8ea 100644
> --- a/arch/parisc/Kconfig
> +++ b/arch/parisc/Kconfig
> @@ -16,6 +16,7 @@ config PARISC
>   	select ARCH_HAS_UBSAN
>   	select ARCH_HAS_PTE_SPECIAL
>   	select ARCH_NO_SG_CHAIN
> +	select ARCH_SPLIT_ARG64 if !64BIT
>   	select ARCH_SUPPORTS_HUGETLBFS if PA20
>   	select ARCH_SUPPORTS_MEMORY_FAILURE
>   	select ARCH_STACKWALK
> diff --git a/arch/parisc/kernel/sys_parisc32.c b/arch/parisc/kernel/sys_parisc32.c
> index 2a12a547b447..826c8e51b585 100644
> --- a/arch/parisc/kernel/sys_parisc32.c
> +++ b/arch/parisc/kernel/sys_parisc32.c
> @@ -23,12 +23,3 @@ asmlinkage long sys32_unimplemented(int r26, int r25, int r24, int r23,
>       	current->comm, current->pid, r20);
>       return -ENOSYS;
>   }
> -
> -asmlinkage long sys32_fanotify_mark(compat_int_t fanotify_fd, compat_uint_t flags,
> -	compat_uint_t mask0, compat_uint_t mask1, compat_int_t dfd,
> -	const char  __user * pathname)
> -{
> -	return sys_fanotify_mark(fanotify_fd, flags,
> -			((__u64)mask1 << 32) | mask0,
> -			 dfd, pathname);
> -}
> diff --git a/arch/parisc/kernel/syscalls/syscall.tbl b/arch/parisc/kernel/syscalls/syscall.tbl
> index 39e67fab7515..66dc406b12e4 100644
> --- a/arch/parisc/kernel/syscalls/syscall.tbl
> +++ b/arch/parisc/kernel/syscalls/syscall.tbl
> @@ -364,7 +364,7 @@
>   320	common	accept4			sys_accept4
>   321	common	prlimit64		sys_prlimit64
>   322	common	fanotify_init		sys_fanotify_init
> -323	common	fanotify_mark		sys_fanotify_mark		sys32_fanotify_mark
> +323	common	fanotify_mark		sys_fanotify_mark		compat_sys_fanotify_mark
>   324	32	clock_adjtime		sys_clock_adjtime32
>   324	64	clock_adjtime		sys_clock_adjtime
>   325	common	name_to_handle_at	sys_name_to_handle_at