2018-03-07 19:59:47

by Gustavo A. R. Silva

Subject: [PATCH] video: fbdev: via_aux_vt1636: remove VLA usage

In preparation to enabling -Wvla, remove VLA and replace it
with a fixed-length array instead. Also, remove variable 'len'.

Notice that no new IDs have been added in seven years.

Signed-off-by: Gustavo A. R. Silva <[email protected]>
---
drivers/video/fbdev/via/via_aux_vt1636.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/video/fbdev/via/via_aux_vt1636.c b/drivers/video/fbdev/via/via_aux_vt1636.c
index 9e015c1..d6273a4 100644
--- a/drivers/video/fbdev/via/via_aux_vt1636.c
+++ b/drivers/video/fbdev/via/via_aux_vt1636.c
@@ -35,10 +35,10 @@ void via_aux_vt1636_probe(struct via_aux_bus *bus)
.addr = 0x40,
.name = name};
/* check vendor id and device id */
- const u8 id[] = {0x06, 0x11, 0x45, 0x33}, len = ARRAY_SIZE(id);
- u8 tmp[len];
+ const u8 id[4] = {0x06, 0x11, 0x45, 0x33};
+ u8 tmp[4];

- if (!via_aux_read(&drv, 0x00, tmp, len) || memcmp(id, tmp, len))
+ if (!via_aux_read(&drv, 0x00, tmp, 4) || memcmp(id, tmp, 4))
return;

printk(KERN_INFO "viafb: Found %s\n", name);
--
2.7.4

2018-03-09 10:13:39

by Eric Engestrom

Subject: Re: [PATCH] video: fbdev: via_aux_vt1636: remove VLA usage

On Wednesday, 2018-03-07 13:47:03 -0600, Gustavo A. R. Silva wrote:
> In preparation to enabling -Wvla, remove VLA and replace it
> with a fixed-length array instead. Also, remove variable 'len'.
>
> Notice that no new IDs have been added in seven years.
>
> Signed-off-by: Gustavo A. R. Silva <[email protected]>
> ---
> drivers/video/fbdev/via/via_aux_vt1636.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/video/fbdev/via/via_aux_vt1636.c b/drivers/video/fbdev/via/via_aux_vt1636.c
> index 9e015c1..d6273a4 100644
> --- a/drivers/video/fbdev/via/via_aux_vt1636.c
> +++ b/drivers/video/fbdev/via/via_aux_vt1636.c
> @@ -35,10 +35,10 @@ void via_aux_vt1636_probe(struct via_aux_bus *bus)
> .addr = 0x40,
> .name = name};
> /* check vendor id and device id */
> - const u8 id[] = {0x06, 0x11, 0x45, 0x33}, len = ARRAY_SIZE(id);
> - u8 tmp[len];
> + const u8 id[4] = {0x06, 0x11, 0x45, 0x33};
> + u8 tmp[4];
>
> - if (!via_aux_read(&drv, 0x00, tmp, len) || memcmp(id, tmp, len))
> + if (!via_aux_read(&drv, 0x00, tmp, 4) || memcmp(id, tmp, 4))

I would recommend keeping ARRAY_SIZE(); even if nothing's been added in
a while, it's still clearer in the code if we can see where these `4`
come from.

Something like this instead?
----8<----
@@ -35,10 +35,10 @@ void via_aux_vt1636_probe(struct via_aux_bus *bus)
.addr = 0x40,
.name = name};
/* check vendor id and device id */
- const u8 id[] = {0x06, 0x11, 0x45, 0x33}, len = ARRAY_SIZE(id);
- u8 tmp[len];
+ const u8 id[] = {0x06, 0x11, 0x45, 0x33};
+ u8 tmp[ARRAY_SIZE(id)];

- if (!via_aux_read(&drv, 0x00, tmp, len) || memcmp(id, tmp, len))
+ if (!via_aux_read(&drv, 0x00, tmp, ARRAY_SIZE(id)) || memcmp(id, tmp, ARRAY_SIZE(id)))
return;

printk(KERN_INFO "viafb: Found %s\n", name);
---->8----

Note that sizeof is evaluated a compile time, so `u8 tmp[ARRAY_SIZE(id)]`
is *not* a VLA. All that's needed was to remove `len` :)

> return;
>
> printk(KERN_INFO "viafb: Found %s\n", name);
> --
> 2.7.4
>
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