| Message ID | 20180307195415.GA666@embeddedgus (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
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
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
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)) return; printk(KERN_INFO "viafb: Found %s at address 0x%x\n", name, addr);
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 <gustavo@embeddedor.com> --- drivers/video/fbdev/via/via_aux_vt1632.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)