* Re: [PATCH] video: fbdev: via_aux_vt1632: remove VLA usage
@ 2018-03-08 11:58 ` Emil Velikov
0 siblings, 0 replies; 7+ messages in thread
From: Emil Velikov @ 2018-03-08 11:58 UTC (permalink / raw)
To: Gustavo A. R. Silva
Cc: Florian Tobias Schandinat, Bartlomiej Zolnierkiewicz, linux-fbdev,
Gustavo A. R. Silva, Linux-Kernel@Vger. Kernel. Org, ML dri-devel
Hi Gustavo,
On 7 March 2018 at 19:54, Gustavo A. R. Silva <gustavo@embeddedor.com> 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 <gustavo@embeddedor.com>
> ---
> 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(&drv, 0x00, tmp, len) || memcmp(id, tmp, len))
> + if (!via_aux_read(&drv, 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
^ permalink raw reply [flat|nested] 7+ messages in thread* Re: [PATCH] video: fbdev: via_aux_vt1632: remove VLA usage
@ 2018-03-08 11:58 ` Emil Velikov
0 siblings, 0 replies; 7+ messages in thread
From: Emil Velikov @ 2018-03-08 11:58 UTC (permalink / raw)
To: Gustavo A. R. Silva
Cc: linux-fbdev, Bartlomiej Zolnierkiewicz, Florian Tobias Schandinat,
Linux-Kernel@Vger. Kernel. Org, ML dri-devel, Gustavo A. R. Silva
Hi Gustavo,
On 7 March 2018 at 19:54, Gustavo A. R. Silva <gustavo@embeddedor.com> 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 <gustavo@embeddedor.com>
> ---
> 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(&drv, 0x00, tmp, len) || memcmp(id, tmp, len))
> + if (!via_aux_read(&drv, 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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^ permalink raw reply [flat|nested] 7+ messages in thread* Re: [PATCH] video: fbdev: via_aux_vt1632: remove VLA usage
2018-03-08 11:58 ` Emil Velikov
@ 2018-03-08 17:27 ` Gustavo A. R. Silva
-1 siblings, 0 replies; 7+ messages in thread
From: Gustavo A. R. Silva @ 2018-03-08 17:27 UTC (permalink / raw)
To: Emil Velikov, Gustavo A. R. Silva
Cc: Florian Tobias Schandinat, Bartlomiej Zolnierkiewicz, linux-fbdev,
Linux-Kernel@Vger. Kernel. Org, ML dri-devel
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 <gustavo@embeddedor.com> 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 <gustavo@embeddedor.com>
>> ---
>> 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(&drv, 0x00, tmp, len) || memcmp(id, tmp, len))
>> + if (!via_aux_read(&drv, 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
^ permalink raw reply [flat|nested] 7+ messages in thread* Re: [PATCH] video: fbdev: via_aux_vt1632: remove VLA usage
@ 2018-03-08 17:27 ` Gustavo A. R. Silva
0 siblings, 0 replies; 7+ messages in thread
From: Gustavo A. R. Silva @ 2018-03-08 17:27 UTC (permalink / raw)
To: Emil Velikov, Gustavo A. R. Silva
Cc: Florian Tobias Schandinat, Bartlomiej Zolnierkiewicz, linux-fbdev,
Linux-Kernel@Vger. Kernel. Org, ML dri-devel
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 <gustavo@embeddedor.com> 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 <gustavo@embeddedor.com>
>> ---
>> 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(&drv, 0x00, tmp, len) || memcmp(id, tmp, len))
>> + if (!via_aux_read(&drv, 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
^ permalink raw reply [flat|nested] 7+ messages in thread