From: gangchen@rdamicro•com (Chen Gang)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH 1/1] ARM : missing corrupted reg in __do_div_asm
Date: Mon, 08 Jun 2015 13:30:18 +0800 [thread overview]
Message-ID: <5575286A.1080002@rdamicro.com> (raw)
In-Reply-To: <1433225609-7148-1-git-send-email-gangchen@rdamicro.com>
Hi,
I tried to make a test program to illustrate the patch.
Without the patch, the log shows
"[250970.715392] remains1 is 2, remains2 is 0"
And the remains2 is wrong
With the patch, the log is
"[250977.724181] remains1 is 2, remains2 is 4".
now both remains1 and remains2 are correct.
I compared the output assembly and it showed in the faulty version,
r0 ( I am using little endian system) is not reload after the
first do_div and before the second do_div call in function mydiv64.
Br, Chen Gang
#include <asm/div64.h>
#include <linux/init.h>
#include <linux/printk.h>
typedef unsigned long long ull;
void mydiv64(ull tt, unsigned base1, unsigned base2,
unsigned *rems1, unsigned *rems2)
{
ull t = tt;
*rems1 = do_div(t, base1);
*rems2 = do_div(tt, base2);
return ;
}
static int __init div_test(void)
{
ull t;
unsigned int remains1;
unsigned int remains2;
unsigned base1, base2;
t = 100;
base1 = 7;
base2 = 8;
mydiv64(t, base1, base2, &remains1, &remains2);
printk(KERN_ERR"remains1 is %d, remains2 is %d\n",
remains1, remains2);
return -1;
}
static void __exit div_test_exit(void)
{
}
module_init(div_test);
module_exit(div_test_exit);
On 06/02/2015 02:13 PM, Chen Gang wrote:
> __xl (r0 in little endian system, or R1 in big endian system) is corrupted
> after calling __do_div64 and compiler is not informed about this in
> macro __do_div_asm. If n is used again afterwards, __xl won't be
> reloaded and n will contain incorrect value.
> ---
> arch/arm/include/asm/div64.h | 10 ++++++----
> 1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm/include/asm/div64.h b/arch/arm/include/asm/div64.h
> index 662c7bd..fa9489e 100644
> --- a/arch/arm/include/asm/div64.h
> +++ b/arch/arm/include/asm/div64.h
> @@ -34,12 +34,14 @@
> register unsigned long long __n asm("r0") = n; \
> register unsigned long long __res asm("r2"); \
> register unsigned int __rem asm(__xh); \
> + register unsigned int __clobber asm(__xl); \
> asm( __asmeq("%0", __xh) \
> - __asmeq("%1", "r2") \
> - __asmeq("%2", "r0") \
> - __asmeq("%3", "r4") \
> + __asmeq("%1", __xl) \
> + __asmeq("%2", "r2") \
> + __asmeq("%3", "r0") \
> + __asmeq("%4", "r4") \
> "bl __do_div64" \
> - : "=r" (__rem), "=r" (__res) \
> + : "=r" (__rem), "=r" (__clobber), "=r" (__res) \
> : "r" (__n), "r" (__base) \
> : "ip", "lr", "cc"); \
> n = __res; \
next prev parent reply other threads:[~2015-06-08 5:30 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] </home/gachen/Re: [PATCH 1_1] ARM:r0 is also corrupted after calling __do_div64..eml>
2015-06-02 6:13 ` [PATCH 1/1] ARM : missing corrupted reg in __do_div_asm Chen Gang
2015-06-08 5:30 ` Chen Gang [this message]
2015-06-09 13:09 ` Russell King - ARM Linux
2015-06-19 11:28 ` [PATCH v2 " Chen Gang
2015-06-28 11:29 ` [PATCH " Chen Gang
2016-03-28 4:19 Chen Gang
2016-03-29 10:19 ` Arnd Bergmann
2016-03-29 10:26 ` Dave Martin
2016-03-29 10:34 ` Russell King - ARM Linux
2016-03-29 10:56 ` Dave Martin
2016-03-30 3:27 ` 陈刚(Gangchen)
2016-03-30 14:07 ` Dave Martin
2016-03-31 7:56 ` 陈刚(Gangchen)
2016-03-31 10:30 ` Dave Martin
2016-03-31 11:20 ` 陈刚(Gangchen)
2016-03-31 11:41 ` Dave Martin
2016-03-29 10:58 ` 陈刚(Gangchen)
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