Hi Yamada-san,
On Tue, Dec 16, 2014 at 4:05 AM, Masahiro Yamada
<yamada.m@xxxxxxxxxxxxxxxx> wrote:
On Mon, 15 Dec 2014 12:00:25 +0100
Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote:
On Mon, Dec 15, 2014 at 11:51 AM, Masahiro Yamada
<yamada.m@xxxxxxxxxxxxxxxx> wrote:
Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote:
On Mon, Dec 15, 2014 at 10:32 AM, Masahiro Yamada
<yamada.m@xxxxxxxxxxxxxxxx> 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-*.
Yes, I can use it, but I am still curious.
Do we have a good reason to keep this limitation?
(All the problem I could see for using GCC that was not configured for Linux
was just the printk-related warnings.)
Instead of hard-coding the size_t type,
can we use compiler-provided __SIZE_TYPE__ (or include <stddef.h>) ??
Note that cris and s390 used __SIZE_TYPE__ in kernel headers before,
but it caused other compiler warnings due to a mismatch in the base types
for size_t and ssize_t, cfr. https://lkml.org/lkml/2012/8/12/36.
AFAIK, there's no __SSIZE_TYPE__.
I notice __kernel_(s)size_t has the same width as "long".
(The kernel does not support LLP64. We just have to take LP64 into account.)
On 64-bit, __kernel_(s)size_t are indeed (unsigned) long
On 32-bit, __kernel_(s)size_t is usually (unsigned) int for historical
reasons.
Cfr. include/uapi/asm-generic/posix_types.h:
/*
* Most 32 bit architectures use "unsigned int" size_t,
* and all 64 bit architectures use "unsigned long" size_t.
*/
#ifndef __kernel_size_t
#if __BITS_PER_LONG != 64
typedef unsigned int __kernel_size_t;
typedef int __kernel_ssize_t;
typedef int __kernel_ptrdiff_t;
#else
typedef __kernel_ulong_t __kernel_size_t;
typedef __kernel_long_t __kernel_ssize_t;
typedef __kernel_long_t __kernel_ptrdiff_t;
#endif
#endif
The are a few exceptions (e.g. avr32 and blackfin)
Perhaps, we should have hard-coded
typedef __kernel_ulong_t __kernel_size_t;
typedef __kernel_long_t __kernel_ssize_t;
and used "%lx" to print (s)size_t type variables.
I think we do not have a good reason to use "%zx",
although it might be too late.
In hindsight, it would have been better for (s)size_t to match (unsigned) long,
removing the need for %z.
However, that was realized only after 64-bit architectures were introduced.
It's definitely to late to change this for existing 32-bit architectures.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
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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