From: Michal Nazarewicz <mina86@mina86.com>
To: Andrew Morton <akpm@linux-foundation.org>, Tejun Heo <tj@kernel.org>
Cc: John Stultz <john.stultz@linaro.org>,
LKML <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>,
"Steven Rostedt \(Red Hat\)" <rostedt@goodmis.org>,
Peter Zijlstra <peterz@infradead.org>,
Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
Prarit Bhargava <prarit@redhat.com>,
Richard Cochran <richardcochran@gmail.com>,
Thomas Gleixner <tglx@linutronix.de>,
"Theodore Ts'o" <tytso@mit.edu>,
Andreas Dilger <adilger.kernel@dilger.ca>,
Dave Chinner <dchinner@redhat.com>, Joe Perches <joe@perches.com>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [RFC][PATCH 0/5] Fixes for abs() usage on 64bit values
Date: Wed, 16 Sep 2015 00:54:09 +0200 [thread overview]
Message-ID: <xa1tmvwnfg4u.fsf@mina86.com> (raw)
In-Reply-To: <20150915142120.7a2f7ac90b2d69b4879b68d7@linux-foundation.org>
On Tue, Sep 15 2015, Andrew Morton wrote:
> On Mon, 14 Sep 2015 23:46:32 -0400 Tejun Heo <tj@kernel.org> wrote:
>
>> Anyways, let's please get abs() working for all types, one way or the
>> other.
>
> That would be by far the best solution, of course.
>
> This seems to work OK:
>
> --- a/include/linux/kernel.h~a
> +++ a/include/linux/kernel.h
> @@ -207,8 +207,11 @@ extern int _cond_resched(void);
> * for those.
> */
> #define abs(x) ({ \
> - long ret; \
> - if (sizeof(x) == sizeof(long)) { \
> + s64 ret; \
> + if (sizeof(x) == sizeof(s64)) { \
> + s64 __x = (x); \
> + ret = (__x < 0) ? -__x : __x; \
> + } else if (sizeof(x) == sizeof(long)) { \
> long __x = (x); \
> ret = (__x < 0) ? -__x : __x; \
> } else { \
If the return type is an issue, we can use __builtin_choose_expr, no?
#define abs(x) __builtin_choose_expr(sizeof(x) == sizeof(s64), abs64(x), ({ \
long ret; \
if (sizeof(x) == sizeof(long)) { \
long __x = (x); \
ret = (__x < 0) ? -__x : __x; \
} else { \
int __x = (x); \
ret = (__x < 0) ? -__x : __x; \
} \
ret; \
}))
This is awkward but will make even printk happy.
>
> Test case:
>
> --- /dev/null
> +++ a/lib/xx.c
> @@ -0,0 +1,33 @@
> +#include <linux/kernel.h>
> +
> +#define newabs(x) ({ \
> + s64 ret; \
> + if (sizeof(x) == sizeof(s64)) { \
> + s64 __x = (x); \
> + ret = (__x < 0) ? -__x : __x; \
> + } else if (sizeof(x) == sizeof(long)) { \
> + long __x = (x); \
> + ret = (__x < 0) ? -__x : __x; \
> + } else { \
> + int __x = (x); \
> + ret = (__x < 0) ? -__x : __x; \
> + } \
> + ret; \
> + })
> +
> +#define oldabs(x) ({ \
> + long ret; \
> + if (sizeof(x) == sizeof(long)) { \
> + long __x = (x); \
> + ret = (__x < 0) ? -__x : __x; \
> + } else { \
> + int __x = (x); \
> + ret = (__x < 0) ? -__x : __x; \
> + } \
> + ret; \
> + })
> +
> +int foo(int x)
> +{
> + return oldabs(x);
> +}
> diff -puN lib/Makefile~b lib/Makefile
> --- a/lib/Makefile~b
> +++ a/lib/Makefile
> @@ -13,7 +13,7 @@ lib-y := ctype.o string.o vsprintf.o cmd
> sha1.o md5.o irq_regs.o argv_split.o \
> proportions.o flex_proportions.o ratelimit.o show_mem.o \
> is_single_threaded.o plist.o decompress.o kobject_uevent.o \
> - earlycpio.o seq_buf.o nmi_backtrace.o
> + earlycpio.o seq_buf.o nmi_backtrace.o xx.o
>
> obj-$(CONFIG_ARCH_HAS_DEBUG_STRICT_USER_COPY_CHECKS) += usercopy.o
> lib-$(CONFIG_MMU) += ioremap.o
>
>
> on i386, xx.o's text is 68 bytes with either newabs() or oldabs().
>
>
> lib/percpu_counter.o's text does get larger with newabs(). That's
> because __percpu_counter_compare() is doing abs() on an s64, doh.
>
--
Best regards, _ _
.o. | Liege of Serenely Enlightened Majesty of o' \,=./ `o
..o | Computer Science, ミハウ “mina86” ナザレヴイツ (o o)
ooo +--<mpn@google.com>--<xmpp:mina86@jabber.org>-----ooO--(_)--Ooo--
next prev parent reply other threads:[~2015-09-15 22:54 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-15 1:05 [RFC][PATCH 0/5] Fixes for abs() usage on 64bit values John Stultz
2015-09-15 1:05 ` [RFC][PATCH 1/5] clocksource: Fix abs() usage w/ " John Stultz
2015-10-02 20:57 ` [tip:timers/urgent] " tip-bot for John Stultz
2015-09-15 1:05 ` [RFC][PATCH 2/5] time: Fix abs() usage with 64-bit values John Stultz
2015-09-15 1:05 ` [RFC][PATCH 3/5] ext4: Fix abs() usage in ext4_mb_check_group_pa John Stultz
2015-09-15 1:05 ` [RFC][PATCH 4/5] percpu: Fix abs() usage in percpu_counter_compare() John Stultz
2015-09-15 1:05 ` [RFC][PATCH 5/5] abs(): Provide build error on passing 64bit value to abs() John Stultz
2015-09-15 5:22 ` Ingo Molnar
2015-09-15 23:52 ` Linus Torvalds
2015-09-16 12:57 ` [PATCH] kernel.h: make abs() work with 64-bit types Michal Nazarewicz
2015-09-18 3:12 ` John Stultz
2015-09-15 1:49 ` [RFC][PATCH 0/5] Fixes for abs() usage on 64bit values Tejun Heo
2015-09-15 3:27 ` John Stultz
2015-09-15 3:46 ` Tejun Heo
2015-09-15 12:09 ` Jeff Epler
2015-09-15 21:21 ` Andrew Morton
2015-09-15 22:54 ` Michal Nazarewicz [this message]
2015-09-15 5:20 ` Ingo Molnar
2015-09-15 23:43 ` Linus Torvalds
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