linux-kernel - Re: [PATCH 1/6] ARM: fix memset size error

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Message-ID: <472EA59F.3060800@cn.fujitsu.com>
Date:	Mon, 05 Nov 2007 13:09:51 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	"Robert P. J. Day" <rpjday@...shcourse.ca>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, buytenh@...tstofly.org
Subject: Re: [PATCH 1/6] ARM: fix memset size error

Robert P. J. Day wrote:
> On Mon, 5 Nov 2007, Li Zefan wrote:
> 
>> The size passing to memset is wrong. And here we can replace
>> kmalloc with kzalloc.
>>
>> Signed-off-by Li Zefan <lizf@...fujitsu.com>
>>
>> ---
>>  arch/arm/common/uengine.c |    6 ++----
>>  1 files changed, 2 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/arm/common/uengine.c b/arch/arm/common/uengine.c
>> index 95c8508..117cab3 100644
>> --- a/arch/arm/common/uengine.c
>> +++ b/arch/arm/common/uengine.c
>> @@ -374,8 +374,8 @@ static int set_initial_registers(int uengine, struct ixp2000_uengine_code *c)
>>  	u8 *ucode;
>>  	int i;
>>
>> -	gpr_a = kmalloc(128 * sizeof(u32), GFP_KERNEL);
>> -	gpr_b = kmalloc(128 * sizeof(u32), GFP_KERNEL);
>> +	gpr_a = kzalloc(128 * sizeof(u32), GFP_KERNEL);
>> +	gpr_b = kzalloc(128 * sizeof(u32), GFP_KERNEL);
>>  	ucode = kmalloc(513 * 5, GFP_KERNEL);
>>  	if (gpr_a == NULL || gpr_b == NULL || ucode == NULL) {
>>  		kfree(ucode);
>> @@ -388,8 +388,6 @@ static int set_initial_registers(int uengine, struct ixp2000_uengine_code *c)
>>  	if (c->uengine_parameters & IXP2000_UENGINE_4_CONTEXTS)
>>  		per_ctx_regs = 32;
>>
>> -	memset(gpr_a, 0, sizeof(gpr_a));
>> -	memset(gpr_b, 0, sizeof(gpr_b));
>>  	for (i = 0; i < 256; i++) {
>>  		struct ixp2000_reg_value *r = c->initial_reg_values + i;
>>  		u32 *bank;
>>
>   it's unlikely that patch will cause any trouble whatsoever, but
> notice that it *is* changing the underlying logic.  those original
> memsets should probably have been written initially as
> "sizeof(*gpr_a)" so they would previously have zeroed only memory the
>         ^
> size of a pointer, no?
> 
>   now, i'm guessing the logic is correct but i figured it's worth
> noting what the code *used* to do.  unless i'm misreading something
> horribly.
> 

In the for loop, some elems of gpr_a and gpr_b will be assigned with a value,
but not all elems. So those unassigned elems should be filled with 0.

I think it happens now and then to mistake to regard a pointer as a static
array, and I guess this is what sizeof(gpr_a) means.

Li Zefan
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