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SubjectRE: [PATCH V7 03/20] compat: consolidate the compat_flock{,64} definition
Date
From: guoren@kernel.org
> Sent: 27 February 2022 16:28
>
> From: Christoph Hellwig <hch@lst.de>
>
> Provide a single common definition for the compat_flock and
> compat_flock64 structures using the same tricks as for the native
> variants. Another extra define is added for the packing required on
> x86.
...
> diff --git a/arch/x86/include/asm/compat.h b/arch/x86/include/asm/compat.h
...
> /*
> - * IA32 uses 4 byte alignment for 64 bit quantities,
> - * so we need to pack this structure.
> + * IA32 uses 4 byte alignment for 64 bit quantities, so we need to pack the
> + * compat flock64 structure.
> */
...
> +#define __ARCH_NEED_COMPAT_FLOCK64_PACKED
>
> struct compat_statfs {
> int f_type;
> diff --git a/include/linux/compat.h b/include/linux/compat.h
> index 1c758b0e0359..a0481fe6c5d5 100644
> --- a/include/linux/compat.h
> +++ b/include/linux/compat.h
> @@ -258,6 +258,37 @@ struct compat_rlimit {
> compat_ulong_t rlim_max;
> };
>
> +#ifdef __ARCH_NEED_COMPAT_FLOCK64_PACKED
> +#define __ARCH_COMPAT_FLOCK64_PACK __attribute__((packed))
> +#else
> +#define __ARCH_COMPAT_FLOCK64_PACK
> +#endif
...
> +struct compat_flock64 {
> + short l_type;
> + short l_whence;
> + compat_loff_t l_start;
> + compat_loff_t l_len;
> + compat_pid_t l_pid;
> +#ifdef __ARCH_COMPAT_FLOCK64_PAD
> + __ARCH_COMPAT_FLOCK64_PAD
> +#endif
> +} __ARCH_COMPAT_FLOCK64_PACK;
> +

Provided compat_loff_t are correctly defined with __aligned__(4)
marking the structure packed isn't needed.
I believe compat_u64 and compat_s64 both have aligned(4).
It is also wrong, consider:

struct foo {
char x;
struct compat_flock64 fl64;
};

There should be 3 bytes of padding after 'x'.
But you've removed it.

David

-
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