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From: Geert Uytterhoeven <geert@linux-m68k.org>
To: Arnd Bergmann <arnd@kernel.org>
Cc: Linux-Arch <linux-arch@vger.kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Vineet Gupta <vgupta@synopsys.com>, Arnd Bergmann <arnd@arndb.de>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [RFC 12/12] asm-generic: simplify asm/unaligned.h
Date: Mon, 10 May 2021 08:39:35 +0200	[thread overview]
Message-ID: <CAMuHMdUuFPy8F8xwuZys7zdH_nRGQcrjgTSC0UTdcGMv+wEwRg@mail.gmail.com> (raw)
In-Reply-To: <20210507220813.365382-13-arnd@kernel.org>

Hi Arnd,

On Sat, May 8, 2021 at 12:12 AM Arnd Bergmann <arnd@kernel.org> wrote:
> The get_unaligned()/put_unaligned() implementations are much more complex
> than necessary, now that all architectures use the same code.
>
> Move everything into one file and use a much more compact way to express
> the same logic.
>
> I've compared the binary output using gcc-11 across defconfig builds for
> all architectures and found this patch to make no difference, except for
> a single function on powerpc that needs two additional register moves
> because of random differences in register allocation.
>
> There are a handful of callers of the low-level __get_unaligned_cpu32,
> so leave that in place for the time being even though the common code
> no longer uses it.
>
> This adds a warning for any caller of get_unaligned()/put_unaligned()
> that passes in a single-byte pointer, but I've sent patches for all
> instances that show up in x86 and randconfig builds. It would be nice
> to change the arguments of the endian-specific accessors to take the
> matching __be16/__be32/__be64/__le16/__le32/__le64 arguments instead of
> a void pointer, but that requires more changes to the rest of the kernel.
>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Thanks for your patch!

> @@ -6,20 +6,132 @@
>   * This is the most generic implementation of unaligned accesses
>   * and should work almost anywhere.
>   */
> +#include <linux/unaligned/packed_struct.h>
>  #include <asm/byteorder.h>
>
> -#if defined(__LITTLE_ENDIAN)
> -# include <linux/unaligned/le_struct.h>
> -# include <linux/unaligned/generic.h>
> -# define get_unaligned __get_unaligned_le
> -# define put_unaligned __put_unaligned_le
> -#elif defined(__BIG_ENDIAN)
> -# include <linux/unaligned/be_struct.h>
> -# include <linux/unaligned/generic.h>
> -# define get_unaligned __get_unaligned_be
> -# define put_unaligned __put_unaligned_be
> -#else
> -# error need to define endianess
> -#endif
> +#define __get_unaligned_t(type, ptr) ({                                                \
> +       const struct { type x; } __packed *__pptr = (typeof(__pptr))(ptr);      \
> +       __pptr->x;                                                              \

Space before tab (cfr. checkpatch).

> +})
> +
> +#define get_unaligned(ptr) ({                                                  \
> +       __auto_type __ptr = (ptr);                                              \
> +       __get_unaligned_t(typeof(*__ptr), __ptr);                               \
> +})
> +
> +#define __put_unaligned_t(type, val, ptr) ({                                   \
> +       struct { type x; } __packed *__pptr = (typeof(__pptr))(ptr);            \
> +       __pptr->x = (val);                                                      \

Likewise

> +})
>
Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

  parent reply	other threads:[~2021-05-10  6:39 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-07 22:07 [RFC 0/12] Unify asm/unaligned.h around struct helper Arnd Bergmann
2021-05-07 22:07 ` [RFC 01/12] asm-generic: use asm-generic/unaligned.h for most architectures Arnd Bergmann
2021-05-07 23:02   ` Thomas Gleixner
2021-05-10 10:16   ` Geert Uytterhoeven
2021-05-10 13:12     ` Arnd Bergmann
2021-05-07 22:07 ` [RFC 02/12] openrisc: always use unaligned-struct header Arnd Bergmann
2021-05-07 23:02   ` Stafford Horne
2021-05-08 11:42   ` David Laight
2021-05-07 22:07 ` [RFC 03/12] sh: remove unaligned access for sh4a Arnd Bergmann
2021-05-10 21:11   ` Rob Landley
2021-05-07 22:07 ` [RFC 04/12] m68k: select CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS Arnd Bergmann
2021-05-10 10:18   ` Geert Uytterhoeven
2021-05-07 22:07 ` [RFC 05/12] powerpc: use linux/unaligned/le_struct.h on LE power7 Arnd Bergmann
2021-05-07 22:07 ` [RFC 06/12] asm-generic: unaligned: remove byteshift helpers Arnd Bergmann
2021-05-08 11:38   ` Arnd Bergmann
2021-05-07 22:07 ` [RFC 07/12] asm-generic: unaligned always use struct helpers Arnd Bergmann
2021-05-07 22:07 ` [RFC 08/12] partitions: msdos: fix one-byte get_unaligned() Arnd Bergmann
2021-05-07 22:07 ` [RFC 09/12] apparmor: use get_unaligned() only for multi-byte words Arnd Bergmann
2021-05-10  8:17   ` John Johansen
2021-05-07 22:07 ` [RFC 10/12] mwifiex: re-fix for unaligned accesses Arnd Bergmann
2021-05-07 22:07 ` [RFC 11/12] netpoll: avoid put_unaligned() on single character Arnd Bergmann
2021-05-07 22:07 ` [RFC 12/12] asm-generic: simplify asm/unaligned.h Arnd Bergmann
2021-05-07 23:54   ` Linus Torvalds
2021-05-08  9:28     ` Arnd Bergmann
2021-05-08 15:23       ` Linus Torvalds
2021-05-08 11:03   ` David Laight
2021-05-08 14:18     ` David Laight
2021-05-10  6:39   ` Geert Uytterhoeven [this message]
2021-05-07 22:07 ` [RFC 0/12] Unify asm/unaligned.h around struct helper Arnd Bergmann

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