2009-07-19 15:30:31

by Julia Lawall

Subject: [PATCH 9/10] drivers/mmc: Move a dereference below a NULL test

From: Julia Lawall <[email protected]>

If the NULL test is necessary, then the dereference should be moved below
the NULL test.

The semantic patch that makes this change is as follows:
(http://www.emn.fr/x-info/coccinelle/)

// <smpl>
@@
type T;
expression E,E1;
identifier i,fld;
statement S;
@@

- T i = E->fld;
+ T i;
... when != E=E1
when != i
BUG_ON (E == NULL||
- i
+ E->fld
== NULL || ...);
+ i = E->fld;
// </smpl>

Signed-off-by: Julia Lawall <[email protected]>

---
drivers/mmc/host/omap.c | 5 +++--
1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/mmc/host/omap.c b/drivers/mmc/host/omap.c
index e7a331d..89281ab 100644
--- a/drivers/mmc/host/omap.c
+++ b/drivers/mmc/host/omap.c
@@ -255,11 +255,12 @@ static void mmc_omap_slot_release_work(struct work_struct *work)

static void mmc_omap_release_slot(struct mmc_omap_slot *slot, int clk_enabled)
{
- struct mmc_omap_host *host = slot->host;
+ struct mmc_omap_host *host;
unsigned long flags;
int i;

- BUG_ON(slot == NULL || host->mmc == NULL);
+ BUG_ON(slot == NULL || slot->host->mmc == NULL);
+ host = slot->host;

if (clk_enabled)
/* Keeps clock running for at least 8 cycles on valid freq */

2009-07-20 08:01:06

by Adrian Hunter

Subject: Re: [PATCH 9/10] drivers/mmc: Move a dereference below a NULL test

Julia Lawall wrote:
> From: Julia Lawall <[email protected]>
>
> If the NULL test is necessary, then the dereference should be moved below
> the NULL test.
>
> The semantic patch that makes this change is as follows:
> (http://www.emn.fr/x-info/coccinelle/)
>
> // <smpl>
> @@
> type T;
> expression E,E1;
> identifier i,fld;
> statement S;
> @@
>
> - T i = E->fld;
> + T i;
> ... when != E=E1
> when != i
> BUG_ON (E == NULL||
> - i
> + E->fld
> == NULL || ...);
> + i = E->fld;
> // </smpl>
>
> Signed-off-by: Julia Lawall <[email protected]>
>
> ---
> drivers/mmc/host/omap.c | 5 +++--
> 1 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/mmc/host/omap.c b/drivers/mmc/host/omap.c
> index e7a331d..89281ab 100644
> --- a/drivers/mmc/host/omap.c
> +++ b/drivers/mmc/host/omap.c
> @@ -255,11 +255,12 @@ static void mmc_omap_slot_release_work(struct work_struct *work)
>
> static void mmc_omap_release_slot(struct mmc_omap_slot *slot, int clk_enabled)
> {
> - struct mmc_omap_host *host = slot->host;
> + struct mmc_omap_host *host;
> unsigned long flags;
> int i;
>
> - BUG_ON(slot == NULL || host->mmc == NULL);
> + BUG_ON(slot == NULL || slot->host->mmc == NULL);
> + host = slot->host;
>
> if (clk_enabled)
> /* Keeps clock running for at least 8 cycles on valid freq */
> --

If slot is NULL it will oops anyway, so the following is better IMHO:

static void mmc_omap_release_slot(struct mmc_omap_slot *slot, int clk_enabled)
{
struct mmc_omap_host *host = slot->host;
unsigned long flags;
int i;

> - BUG_ON(slot == NULL || host->mmc == NULL);
> + BUG_ON(host->mmc == NULL);

if (clk_enabled)
/* Keeps clock running for at least 8 cycles on valid freq */

2009-07-20 12:33:43

by arun c

Subject: Re: [PATCH 9/10] drivers/mmc: Move a dereference below a NULL test

On Mon, Jul 20, 2009 at 1:31 PM, Adrian Hunter<[email protected]> wrote:
> Julia Lawall wrote:
>>
>> From: Julia Lawall <[email protected]>
>>
>> If the NULL test is necessary, then the dereference should be moved below
>> the NULL test.
>>
>> The semantic patch that makes this change is as follows:
>> (http://www.emn.fr/x-info/coccinelle/)
>>
>> // <smpl>
>> @@
>> type T;
>> expression E,E1;
>> identifier i,fld;
>> statement S;
>> @@
>>
>> - T i = E->fld;
>> + T i;
>> ?... when != E=E1
>> ? ? ?when != i
>> ?BUG_ON (E == NULL||
>> - ? ? i
>> + ? ? E->fld
>> ? ? ? == NULL || ...);
>> + i = E->fld;
>> // </smpl>
>>
>> Signed-off-by: Julia Lawall <[email protected]>
>>
>> ---
>> ?drivers/mmc/host/omap.c ? ? ? ? ? ? | ? ?5 +++--
>> ?1 files changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/mmc/host/omap.c b/drivers/mmc/host/omap.c
>> index e7a331d..89281ab 100644
>> --- a/drivers/mmc/host/omap.c
>> +++ b/drivers/mmc/host/omap.c
>> @@ -255,11 +255,12 @@ static void mmc_omap_slot_release_work(struct
>> work_struct *work)
>> ??static void mmc_omap_release_slot(struct mmc_omap_slot *slot, int
>> clk_enabled)
>> ?{
>> - ? ? ? struct mmc_omap_host *host = slot->host;
>> + ? ? ? struct mmc_omap_host *host;
>> ? ? ? ?unsigned long flags;
>> ? ? ? ?int i;
>> ?- ? ? ? BUG_ON(slot == NULL || host->mmc == NULL);
>> + ? ? ? BUG_ON(slot == NULL || slot->host->mmc == NULL);
>> + ? ? ? host = slot->host;
>> ? ? ? ? ?if (clk_enabled)
>> ? ? ? ? ? ? ? ?/* Keeps clock running for at least 8 cycles on valid freq
>> */
>> --
>
> If slot is NULL it will oops anyway, so the following is better IMHO:
>
> static void mmc_omap_release_slot(struct mmc_omap_slot *slot, int
> clk_enabled)
> {
> ? ? ? ?struct mmc_omap_host *host = slot->host;
> ? ? ? ?unsigned long flags;
> ? ? ? ?int i;
>
>> - ? ? ? BUG_ON(slot == NULL || host->mmc == NULL);
>> + ? ? ? BUG_ON(host->mmc == NULL);
>
> ? ? ? ?if (clk_enabled)
> ? ? ? ? ? ? ? ?/* Keeps clock running for at least 8 cycles on valid freq */
> --

According to http://isc.sans.org/diary.html?storyid=6820&rss "NULL check"
must be done before assigning the values. Does Julia Lawall's version
is the more correct one??

Arun

2009-07-20 12:42:40

by Adrian Hunter

Subject: Re: [PATCH 9/10] drivers/mmc: Move a dereference below a NULL test

arun c wrote:
> On Mon, Jul 20, 2009 at 1:31 PM, Adrian Hunter<[email protected]> wrote:
>> Julia Lawall wrote:
>>> From: Julia Lawall <[email protected]>
>>>
>>> If the NULL test is necessary, then the dereference should be moved below
>>> the NULL test.
>>>
>>> The semantic patch that makes this change is as follows:
>>> (http://www.emn.fr/x-info/coccinelle/)
>>>
>>> // <smpl>
>>> @@
>>> type T;
>>> expression E,E1;
>>> identifier i,fld;
>>> statement S;
>>> @@
>>>
>>> - T i = E->fld;
>>> + T i;
>>> ... when != E=E1
>>> when != i
>>> BUG_ON (E == NULL||
>>> - i
>>> + E->fld
>>> == NULL || ...);
>>> + i = E->fld;
>>> // </smpl>
>>>
>>> Signed-off-by: Julia Lawall <[email protected]>
>>>
>>> ---
>>> drivers/mmc/host/omap.c | 5 +++--
>>> 1 files changed, 3 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/mmc/host/omap.c b/drivers/mmc/host/omap.c
>>> index e7a331d..89281ab 100644
>>> --- a/drivers/mmc/host/omap.c
>>> +++ b/drivers/mmc/host/omap.c
>>> @@ -255,11 +255,12 @@ static void mmc_omap_slot_release_work(struct
>>> work_struct *work)
>>> static void mmc_omap_release_slot(struct mmc_omap_slot *slot, int
>>> clk_enabled)
>>> {
>>> - struct mmc_omap_host *host = slot->host;
>>> + struct mmc_omap_host *host;
>>> unsigned long flags;
>>> int i;
>>> - BUG_ON(slot == NULL || host->mmc == NULL);
>>> + BUG_ON(slot == NULL || slot->host->mmc == NULL);
>>> + host = slot->host;
>>> if (clk_enabled)
>>> /* Keeps clock running for at least 8 cycles on valid freq
>>> */
>>> --
>> If slot is NULL it will oops anyway, so the following is better IMHO:
>>
>> static void mmc_omap_release_slot(struct mmc_omap_slot *slot, int
>> clk_enabled)
>> {
>> struct mmc_omap_host *host = slot->host;
>> unsigned long flags;
>> int i;
>>
>>> - BUG_ON(slot == NULL || host->mmc == NULL);
>>> + BUG_ON(host->mmc == NULL);
>> if (clk_enabled)
>> /* Keeps clock running for at least 8 cycles on valid freq */
>> --
>
> According to http://isc.sans.org/diary.html?storyid=6820&rss "NULL check"
> must be done before assigning the values. Does Julia Lawall's version
> is the more correct one??
>
> Arun

It is not a "NULL check" it is an assertion, which can be compiled out.
On some platforms BUG is implemented as a null dereference anyway
e.g. on ARM it is *(int *)0 = 0;

2009-07-20 12:46:39

by Alan

Subject: Re: [PATCH 9/10] drivers/mmc: Move a dereference below a NULL test

> It is not a "NULL check" it is an assertion, which can be compiled out.
> On some platforms BUG is implemented as a null dereference anyway
> e.g. on ARM it is *(int *)0 = 0;

It's a bogus check because the

struct mmc_omap_host *host = slot->host;

has already been executed before you check for slot == NULL