Re: [PATCH] video: fbdev: via_aux_vt1632: remove VLA usage

[Gustavo A. R. Silva]

Hi Emil,

On 03/08/2018 05:58 AM, Emil Velikov wrote:

Hi Gustavo,

On 7 March 2018 at 19:54, 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'.


What is the reason behind adding -Wvla? Is there a thread some that I
can read up on?



Sure. This is the thread: https://lkml.org/lkml/2018/3/7/621


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

Signed-off-by: Gustavo A. R. Silva 
---
  drivers/video/fbdev/via/via_aux_vt1632.c | 6 +++---
  1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/video/fbdev/via/via_aux_vt1632.c 
b/drivers/video/fbdev/via/via_aux_vt1632.c
index d24f4cd..0cd0d2a 100644
--- a/drivers/video/fbdev/via/via_aux_vt1632.c
+++ b/drivers/video/fbdev/via/via_aux_vt1632.c
@@ -35,10 +35,10 @@ static void probe(struct via_aux_bus *bus, u8 addr)
 .addr   =   addr,
 .name   =   name};
 /* check vendor id and device id */
-   const u8 id[] = {0x06, 0x11, 0x92, 0x31}, len = ARRAY_SIZE(id);
-   u8 tmp[len];
+   const u8 id[4] = {0x06, 0x11, 0x92, 0x31};
+   u8 tmp[4];

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


Generally, hard coding a bunch of numbers like that makes for
confusing and fragile code.



You are correct.


A lot simpler and more obvious solution is like the following.
It silences the compiler warning (-Wvla - pedantic) you while keeping
the original clarity.

 const u8 id[] = {0x06, 0x11, 0x92, 0x31}, len = ARRAY_SIZE(id);
-   u8 tmp[len];
+   u8 tmp[ARRAY_SIZE(id)]; // Using len causes a Wvla warning



Yeah, this works just fine.

There are a total of four instances of this same issue in other files 
for the VIA component. I'll fix them and send a single patch shortly.


Thanks for the feedback.
I appreciate it.
--
Gustavo
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Re: [PATCH] video: fbdev: via_aux_vt1632: remove VLA usage

[Emil Velikov]

Hi Gustavo,

On 7 March 2018 at 19:54, 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'.
>
What is the reason behind adding -Wvla? Is there a thread some that I
can read up on?

> Notice that no new IDs have been added in seven years.
>
> Signed-off-by: Gustavo A. R. Silva 
> ---
>  drivers/video/fbdev/via/via_aux_vt1632.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/video/fbdev/via/via_aux_vt1632.c 
> b/drivers/video/fbdev/via/via_aux_vt1632.c
> index d24f4cd..0cd0d2a 100644
> --- a/drivers/video/fbdev/via/via_aux_vt1632.c
> +++ b/drivers/video/fbdev/via/via_aux_vt1632.c
> @@ -35,10 +35,10 @@ static void probe(struct via_aux_bus *bus, u8 addr)
> .addr   =   addr,
> .name   =   name};
> /* check vendor id and device id */
> -   const u8 id[] = {0x06, 0x11, 0x92, 0x31}, len = ARRAY_SIZE(id);
> -   u8 tmp[len];
> +   const u8 id[4] = {0x06, 0x11, 0x92, 0x31};
> +   u8 tmp[4];
>
> -   if (!via_aux_read(, 0x00, tmp, len) || memcmp(id, tmp, len))
> +   if (!via_aux_read(, 0x00, tmp, 4) || memcmp(id, tmp, 4))

Generally, hard coding a bunch of numbers like that makes for
confusing and fragile code.

A lot simpler and more obvious solution is like the following.
It silences the compiler warning (-Wvla - pedantic) you while keeping
the original clarity.

const u8 id[] = {0x06, 0x11, 0x92, 0x31}, len = ARRAY_SIZE(id);
-   u8 tmp[len];
+   u8 tmp[ARRAY_SIZE(id)]; // Using len causes a Wvla warning

HTH
Emil
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[PATCH] video: fbdev: via_aux_vt1632: remove VLA usage

[Gustavo A. R. Silva]

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 
---
 drivers/video/fbdev/via/via_aux_vt1632.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/video/fbdev/via/via_aux_vt1632.c 
b/drivers/video/fbdev/via/via_aux_vt1632.c
index d24f4cd..0cd0d2a 100644
--- a/drivers/video/fbdev/via/via_aux_vt1632.c
+++ b/drivers/video/fbdev/via/via_aux_vt1632.c
@@ -35,10 +35,10 @@ static void probe(struct via_aux_bus *bus, u8 addr)
.addr   =   addr,
.name   =   name};
/* check vendor id and device id */
-   const u8 id[] = {0x06, 0x11, 0x92, 0x31}, len = ARRAY_SIZE(id);
-   u8 tmp[len];
+   const u8 id[4] = {0x06, 0x11, 0x92, 0x31};
+   u8 tmp[4];
 
-   if (!via_aux_read(, 0x00, tmp, len) || memcmp(id, tmp, len))
+   if (!via_aux_read(, 0x00, tmp, 4) || memcmp(id, tmp, 4))
return;
 
printk(KERN_INFO "viafb: Found %s at address 0x%x\n", name, addr);
-- 
2.7.4

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