From: gang.chen@asianux•com (Chen Gang)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH] arch: configuration, deleting 'CONFIG_BUG' since always need it.
Date: Thu, 23 May 2013 18:05:10 +0800 [thread overview]
Message-ID: <519DE9D6.8000707@asianux.com> (raw)
In-Reply-To: <CAMuHMdWez-j1Maa3BD7ucmzv0_zFJnChERQiHFmkCaZUzG0_AA@mail.gmail.com>
On 05/23/2013 05:12 PM, Geert Uytterhoeven wrote:
> On Thu, May 23, 2013 at 11:05 AM, Russell King - ARM Linux
> <linux@arm•linux.org.uk> wrote:
>> > On Thu, May 23, 2013 at 10:40:29AM +0200, Geert Uytterhoeven wrote:
>>> >> On Thu, May 23, 2013 at 9:57 AM, Chen Gang <gang.chen@asianux•com> wrote:
>>>> >> > -config BUG
>>>> >> > - bool "BUG() support" if EXPERT
>>>> >> > - default y
>>>> >> > - help
>>>> >> > - Disabling this option eliminates support for BUG and WARN, reducing
>>>> >> > - the size of your kernel image and potentially quietly ignoring
>>>> >> > - numerous fatal conditions. You should only consider disabling this
>>>> >> > - option for embedded systems with no facilities for reporting errors.
>>>> >> > - Just say Y.
>>> >>
>>> >> ... It's about reducing memory size on devices where you can't show bug or
>>> >> warning messages.
>> >
>> > And turning off CONFIG_BUG causes lots of warning messages at compile time
>> > about functions which are returning nothing which shouldn't.
>> >
>> > The problem is: trying to fix that _will_ mean the result is a larger
>> > kernel than if you just do the usual arch-implemented thing of placing
>> > an defined faulting instruction at the BUG() site - which defeats the
>> > purpose of turning off CONFIG_BUG.
> Is __builtin_unreachable() working well these days?
In fact, using __builtin_unreachable() is a standard way for
architectures to implemented their own BUG() (e.g. x86, s390, powerpc,
arm ...)
Before __builtin_unreachable(), must need an inline asm instruction
which architecture specific.
I have test using __builtin_unreachable() without an related asm
instruction before, it prints many unexpected things (please see the
attachment).
So I think, it is not suitable to use it in "asm-generic/bug.h"
Thanks.
--
Chen Gang
Asianux Corporation
-------------- next part --------------
#include <stdio.h>
#include <sys/types.h>
#include <error.h>
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/stat.h>
int main()
{
int file;
int ret;
char buf[0x100];
file = open("/tmp/work.c", O_RDONLY);
if (file == -1) {
printf("\nopen file failed. errno = %d\n", errno);
goto err;
} else
printf("\nopen file succeed.\n");
printf("before unreachable\n");
__builtin_unreachable();
printf("after unreachable\n");
if (lseek(file, 10, SEEK_END) < 0) {
printf("\nlseek file failed. errno = %d\n", errno);
goto err;
}
ret = read(file, buf, 0x100);
if (ret < 0) {
printf("\n1st read file failed. errno = %d, ret = %d\n", errno, ret);
goto err;
} else
printf("\n1st read file succeed. errno = %d, ret = %d\n", errno, ret);
ret = read(file, buf, 0x100);
if (ret < 0) {
printf("\n2nd read file failed. errno = %d, ret = %d\n", errno, ret);
goto err;
} else
printf("\n2nd read file succeed. errno = %d, ret = %d\n", errno, ret);
ret = read(file, buf, 0x100);
if (ret < 0) {
printf("\n2rd read file failed. errno = %d, ret = %d\n", errno, ret);
goto err;
} else
printf("\n3rd read file succeed. errno = %d, ret = %d\n", errno, ret);
return 0;
err:
return -1;
}
next prev parent reply other threads:[~2013-05-23 10:05 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-05-23 7:57 [PATCH] arch: configuration, deleting 'CONFIG_BUG' since always need it Chen Gang
2013-05-23 8:40 ` Geert Uytterhoeven
2013-05-23 8:54 ` Arnd Bergmann
2013-05-23 9:05 ` Russell King - ARM Linux
2013-05-23 9:12 ` Geert Uytterhoeven
2013-05-23 9:39 ` Arnd Bergmann
2013-05-23 10:04 ` Russell King - ARM Linux
2013-05-23 10:41 ` Chen Gang
2013-05-23 10:59 ` Arnd Bergmann
2013-05-23 11:19 ` Chen Gang
2013-05-23 11:24 ` Russell King - ARM Linux
2013-05-23 12:09 ` Arnd Bergmann
2013-05-23 12:50 ` Russell King - ARM Linux
2013-05-23 14:10 ` Geert Uytterhoeven
2013-05-24 2:13 ` Chen Gang
2013-05-24 4:17 ` Chen Gang
2013-05-26 4:43 ` [PATCH v2] arch: configuration issue, random return value when disable 'CONFIG_BUG' Chen Gang
2013-05-28 8:19 ` [PATCH] arch: configuration, deleting 'CONFIG_BUG' since always need it Ingo Molnar
2013-05-28 10:25 ` Chen Gang
2013-05-28 14:49 ` Arnd Bergmann
2013-05-28 14:55 ` H. Peter Anvin
2013-05-28 15:43 ` Arnd Bergmann
2013-05-28 16:06 ` H. Peter Anvin
2013-05-28 17:20 ` Arnd Bergmann
2013-05-23 10:09 ` Eric W. Biederman
2013-05-23 10:29 ` Russell King - ARM Linux
2013-05-23 10:05 ` Chen Gang [this message]
2013-05-24 5:59 ` Eric W. Biederman
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