Messages in this thread | | | Subject | Re: [PATCH] video: fbdev: via_aux_vt1632: remove VLA usage | From | "Gustavo A. R. Silva" <> | Date | Thu, 8 Mar 2018 11:27:25 -0600 |
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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
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