On 11/10/2018 16:23, Johannes Berg wrote:
Hi
On Thu, 2018-10-11 at 15:24 +0100, John Garry wrote:
+#define BUILD_BUG_ON_RET_ZERO(cond) (sizeof(char[1 - 2*!!(cond)]) - 1)
+#define BUILD_BUG_ON_NOT_POW2_RET_ZERO(n) BUILD_BUG_ON_RET_ZERO(((n) & ((n) - 1)) != 0)
Seems reasonable. However I did try this and was getting compiler
warnings about VLA, from a non-constant being fed into
BUILD_BUG_ON_RET_ZERO(), related to sizeof char[]:
drivers/iio/adc/meson_saradc.c:375:2: warning: ISO C90 forbids variable
length array [-Wvla]
regval = FIELD_PREP(MESON_SAR_ADC_CHAN_LIST_ENTRY_MASK(0),
Hmm, what's the code there?
Nothing special, it was just a sample. Here'e the code:
regval = FIELD_PREP(MESON_SAR_ADC_CHAN_LIST_ENTRY_MASK(0),
chan->address);
So val is a variable, and I find if remove both of the
BUILD_BUG_ON_RET_ZERO()' which use __bf_shf() then it goes away.
I don't see why the compiler should think it's a variable length?
Surely __NLA_ENSURE is getting a similar issue as it uses a similar
principle, no? I see that this is in -next now, but could not this macro
or derivatives being referenced.
Yeah, I have a patch now to reference it, but I don't see anything from
-Wvla with gcc 8.1?
I'm using a 7.3.1-based toolchain
See
https://git.kernel.org/pub/scm/linux/kernel/git/jberg/mac80211-next.git/commit/?id=3d7af878357acd9e37fc156928106f1a969c8942
and its parent.
Do you see -Wvla warnings there? Any idea how I could reproduce them?
I'll try it, thanks
John
johannes
.
