linux-kernel - Re: [Question] How to print size

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Message-ID: <CAMuHMdWOAWr40YOoOVRvV-gPUU+ioSnShzHYcMoGpvhUO6chXw@mail.gmail.com>
Date:	Mon, 15 Dec 2014 10:38:23 +0100
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Masahiro Yamada <yamada.m@...panasonic.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Randy Dunlap <rdunlap@...radead.org>,
	Andrew Murray <amurray@...-data.co.uk>,
	linux-m68k <linux-m68k@...ts.linux-m68k.org>
Subject: Re: [Question] How to print size_t type variable?

Hi Yamada-san,


On Mon, Dec 15, 2014 at 10:32 AM, Masahiro Yamada
<yamada.m@...panasonic.com> wrote:
> I read through Documentation/printk-formats.txt
>
> It clearly says to use "%zu" or "%zx" to print size_t variables,
> but I still have a question.
>
>
> Assume we have code something like:
>
>     printk("%zx", (size_t)10);
>
>
> I think this code works fine as long as it includes
> the compiler-provided <stddef.h>.
>
> In the kernel space, however, <stddef.h> is never included.
> Instead, size_t is defined by include/linux/types.h
> and include/uapi/asm-generic/posix_types.h.
>
>
> That is, size_t is defined independently from the compiler you are using,
> although the compiler still decides which variable type is expected for the "%zx" format.

That's correct.

> This causes compiler warnings for some compilers.
>
> On bare-metal m68k toolchains, for example, size_t is "unsignd long",
> whearas it is "unsigned int" on kernel.org m68k toolchains.
>
>
> I see such warnings when I built the kernel with bare-metal m68k toolchains.
>
>
> $ git describe
> v3.18
> $ make ARCH=m68k  CROSS_COMPILE=m68k-elf-  defconfig all
>   HOSTCC  scripts/basic/fixdep
>   HOSTCC  scripts/kconfig/conf.o
>   SHIPPED scripts/kconfig/zconf.tab.c
>   SHIPPED scripts/kconfig/zconf.lex.c
>   SHIPPED scripts/kconfig/zconf.hash.c
>   HOSTCC  scripts/kconfig/zconf.tab.o
>   HOSTLD  scripts/kconfig/conf
> *** Default configuration is based on 'multi_defconfig'
> kernel/time/Kconfig:163:warning: range is invalid
> #
> # configuration written to .config
> #
>
>   [ snip ]
>
>   LD      init/mounts.o
>   CC      init/initramfs.o
> init/initramfs.c: In function 'populate_rootfs':
> init/initramfs.c:635:5: warning: format '%zd' expects argument of type 'signed size_t', but argument 2 has type 'ssize_t' [-Wformat]

Please use a compiler configured for Linux, i.e. m68k-linux-*.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-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
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