2009-11-12 07:48:37

by Julia Lawall

Subject: [PATCH 1/4] drivers/net/enic: decrement sizeof size in strncmp

From: Julia Lawall <[email protected]>

As observed by Joe Perches, sizeof of a constant string includes the
trailing 0. If what is wanted is to check the initial characters of
another string, this trailing 0 should not be taken into account. If an
exact match is wanted, strcmp should be used instead.

The semantic patch that makes this change is as follows:
(http://coccinelle.lip6.fr/)

// <smpl>
@@
expression foo;
constant char *abc;
@@

strncmp(foo, abc,
- sizeof(abc)
+ sizeof(abc)-1
)
// </smpl>

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

---
drivers/net/enic/vnic_dev.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff -u -p a/drivers/net/enic/vnic_dev.c b/drivers/net/enic/vnic_dev.c
--- a/drivers/net/enic/vnic_dev.c
+++ b/drivers/net/enic/vnic_dev.c
@@ -358,9 +358,9 @@ int vnic_dev_hw_version(struct vnic_dev
if (err)
return err;

- if (strncmp(fw_info->hw_version, "A1", sizeof("A1")) == 0)
+ if (strncmp(fw_info->hw_version, "A1", sizeof("A1") - 1) == 0)
*hw_ver = VNIC_DEV_HW_VER_A1;
- else if (strncmp(fw_info->hw_version, "A2", sizeof("A2")) == 0)
+ else if (strncmp(fw_info->hw_version, "A2", sizeof("A2") - 1) == 0)
*hw_ver = VNIC_DEV_HW_VER_A2;
else
*hw_ver = VNIC_DEV_HW_VER_UNKNOWN;

2009-11-12 10:07:57

by Jörg-Volker Peetz

Subject: Re: [PATCH 1/4] drivers/net/enic: decrement sizeof size in strncmp

Julia Lawall wrote:
<snip>
> strncmp(foo, abc,
> - sizeof(abc)
> + sizeof(abc)-1
> )
<snip>
> - if (strncmp(fw_info->hw_version, "A1", sizeof("A1")) == 0)
> + if (strncmp(fw_info->hw_version, "A1", sizeof("A1") - 1) == 0)
> *hw_ver = VNIC_DEV_HW_VER_A1;
> - else if (strncmp(fw_info->hw_version, "A2", sizeof("A2")) == 0)
> + else if (strncmp(fw_info->hw_version, "A2", sizeof("A2") - 1) == 0)
<snip>
Why not use strlen(abc) instead of sizeof(abc) - 1 ?
--
Regards,
J?rg-Volker.

2009-11-12 10:17:34

by Jörg-Volker Peetz

Subject: Re: [PATCH 1/4] drivers/net/enic: decrement sizeof size in strncmp

Julia Lawall wrote:
> From: Julia Law all <[email protected]>
>
> As observed by Joe Perches, sizeof of a constant string includes the
> trailing 0. If what is wanted is to check the initial characters of
> another string, this trailing 0 should not be taken into account. If an
> exact match is wanted, strcmp should be used instead.
>
> The semantic patch that makes this change is as follows:
> (http://coccinelle.lip6.fr/)
>
> // <smpl>
> @@
> expression foo;
> constant char *abc;
> @@
>
> strncmp(foo, abc,
> - sizeof(abc)
> + sizeof(abc)-1
> )
> // </smpl>
>
<snip>
How about this pattern (uses length of first argument):

strncmp(foo, abc,
- sizeof(foo)

?
--
Best regards,
J?rg-Volker.

2009-11-16 23:46:24

by Scott Feldman

Subject: Re: [PATCH 1/4] drivers/net/enic: decrement sizeof size in strncmp

Thanks Julia/Jorg. We'll pick up change in next enic patch series.

-scott


On 11/11/09 11:48 PM, "Julia Lawall" <[email protected]> wrote:

> From: Julia Lawall <[email protected]>
>
> As observed by Joe Perches, sizeof of a constant string includes the
> trailing 0. If what is wanted is to check the initial characters of
> another string, this trailing 0 should not be taken into account. If an
> exact match is wanted, strcmp should be used instead.
>
> The semantic patch that makes this change is as follows:
> (http://coccinelle.lip6.fr/)
>
> // <smpl>
> @@
> expression foo;
> constant char *abc;
> @@
>
> strncmp(foo, abc,
> - sizeof(abc)
> + sizeof(abc)-1
> )
> // </smpl>
>
> Signed-off-by: Julia Lawall <[email protected]>
>
> ---
> drivers/net/enic/vnic_dev.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff -u -p a/drivers/net/enic/vnic_dev.c b/drivers/net/enic/vnic_dev.c
> --- a/drivers/net/enic/vnic_dev.c
> +++ b/drivers/net/enic/vnic_dev.c
> @@ -358,9 +358,9 @@ int vnic_dev_hw_version(struct vnic_dev
> if (err)
> return err;
>
> - if (strncmp(fw_info->hw_version, "A1", sizeof("A1")) == 0)
> + if (strncmp(fw_info->hw_version, "A1", sizeof("A1") - 1) == 0)
> *hw_ver = VNIC_DEV_HW_VER_A1;
> - else if (strncmp(fw_info->hw_version, "A2", sizeof("A2")) == 0)
> + else if (strncmp(fw_info->hw_version, "A2", sizeof("A2") - 1) == 0)
> *hw_ver = VNIC_DEV_HW_VER_A2;
> else
> *hw_ver = VNIC_DEV_HW_VER_UNKNOWN;