> -----Original Message----- > From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Thomas Monjalon > Sent: Monday, December 15, 2014 2:17 PM > To: Wodkowski, PawelX > Cc: dev at dpdk.org > Subject: Re: [dpdk-dev] error: value computed is not used > > 2014-12-15 13:47, Wodkowski, PawelX: > > From: Thomas Monjalon [mailto:thomas.monjalon at 6wind.com] > > > 2014-12-15 11:27, Wodkowski, PawelX: > > > > From: Thomas Monjalon [mailto:thomas.monjalon at 6wind.com] > > > > > 2014-12-08 15:26, Wodkowski, PawelX: > > > > > > From: Qiu, Michael > > > > > > > On 2014/12/8 19:00, Wodkowski, PawelX wrote: > > > > > > > >> lib/librte_pmd_enic/enic_main.c: In function 'enic_set_rsskey': > > > > > > > >> lib/librte_pmd_enic/enic_main.c:862:2: error: value computed > > > > > > > >> is not > > > used > > > > > > > >> > > > > > > > >> I dig out that, it was ome issue of the macros rte_memcpy() > > > > > > > >> #define rte_memcpy(dst, src, n) \ > > > > > > > >> ((__builtin_constant_p(n)) ? \ > > > > > > > >> memcpy((dst), (src), (n)) : \ > > > > > > > >> rte_memcpy_func((dst), (src), (n))) > > > > > > > >> > > > > > > > >> When I use only (n) instead of (__builtin_constant_p(n), it > > > > > > > >> will pass( I > > > > > > > >> know that it was incorrect, just a experiment). > > > > > > > >> > > > > > > > >> But I try to use inline function instead of macros: > > > > > > > >> static inline void * rte_memcpy(void *dst, const void *src, > > > > > > > >> size_t n) > > > > > > > >> { > > > > > > > >> return __builtin_constant_p(n) ? memcpy(dst, src, n) : > > > > > > > >> rte_memcpy_func(dst, > > > > > > > >> src, n); > > > > > > > >> } > > > > > > > >> > > > > > > > >> It will pass:), and works, this could be one potential > > > > > > > >> workaround fix. > > > > > > > >> > > > > > > > >> Who knows why? The root cause is what? > > > > > > > >> > > > > > > > >> I've no idea about this. > > > > > > > >> > > > > > > > > I got the same issue while ago. I don't remember exactly > > > > > > > > everything > > > > > > > > but my conclusion was that there was some bug in compiler. I > > > > > > > > think, > > > > > > > > when 'n' I constant and/or small compiler is inlining memcpy and > > > throwing > > > > > > > > everything else (including returned value). In that case error > > > > > > > > is not > > > > > > > > produced (I think this is a bug in compiler). In other case it > > > > > > > > is computing > > > > > > > > some value calling memcpy or rte_ memcpy and you should at least > > > > > > > > explicitly throw it away by casting to void. I like solution > > > > > > > > with static > > > > > > > > > > > > > > Actually, I try to pass "n" as a Int value like 4, it still > > > > > > > report this > > > > > > > error :) > > > > > > > > > > > > My workaround was: > > > > > > (void) rte_memcpy(...); > > > > > > > > > > > > But this is only a workaround. > > > > > > > > > > It's not so bad. > > > > > > > > > > > > > inline but someone else should spoke about possible side > > > > > > > > effects. > > > > > > > > > > > > > > Yes, but as I know inline is better than macros. > > > > > > > > > > From the GCC manual: > > > > > " > > > > > You may use this built-in function in either a macro or an inline > > > > > function. > > > > > However, if you use it in an inlined function and pass an argument of > > > > > the > > > > > function as the argument to the built-in, GCC never returns 1 when > > > > > you call > > > > > the inline function with a string constant or compound literal and > > > > > does not > > > > > return 1 when you pass a constant numeric value to the inline > > > > > function unless > > > > > you specify the -O option. > > > > > " > > > > > > > > > > It seems the "inline fix" cannot be used. > > > > > > > > > > I'm going to send a patch with Pawel's workaround. > > > > > > > > And something like this? > > > > > > > > #define rte_memcpy(dst, src, n) \ > > > > - ((__builtin_constant_p(n)) ? \ > > > > + ({ (__builtin_constant_p(n)) ? \ > > > > memcpy((dst), (src), (n)) : \ > > > > - rte_memcpy_func((dst), (src), (n))) > > > > + rte_memcpy_func((dst), (src), (n)); }) > > > > > > What happens to the returned value after this change? > > > ptr = rte_memcpy(dst, src, n) + offset: > > > > > https://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html#Statement-Exprs > > > > Whole expression should be 'void *' type (like *memcpy()) and it should work > > as usual (see maxint() example in above link). It is GCC extension. > > OK nice. > I didn't test it on SUSE 11 SP3. I assume you did it? > Please Pawel, could you send a proper patch quickly? > If nobody disagree, it'll be merged in RC5 today. > > > > > Thomas, can you check build with EXTRA_CFLAG='-Wunused-value'. > > > > > > You mean EXTRA_CFLAGS (with a S). > > > It fails in many locations. > > > What's your point? > > > > I am just asking if this is an typo, error or intend to do statements with > > no effects like bellow. > > > > ixgbe_common.c:4429:3: error: statement with no effect > > [-Werror=unused-value] > > > > 4426: /* first pull in the header so we know the buffer length */ > > 4427: for (bi = 0; bi < dword_len; bi++) { > > 4428: buffer[bi] = IXGBE_READ_REG_ARRAY(hw, IXGBE_FLEX_MNG, > > bi); > > 4429: IXGBE_LE32_TO_CPUS(&buffer[bi]); // <------ here > > 4430 } > > It's an intent. On big endian CPU, this has an effect.
Hmm, I think there is a bug in lib/librte_pmd_ixgbe/ixgbe/ixgbe_osdep.h: #define IXGBE_LE32_TO_CPUS(_i) rte_le_to_cpu_32(_i) It probably should be: #define IXGBE_LE32_TO_CPUS(_i) rte_le_to_cpu_32(*(_i)) Not much point to do byte swapping for the pointer. And that what ixgbe BSD driver is doing. Though I still not sure why it is needed here, as the computed value is not used anyway. What the author probably meant to do: buffer[bi] = rte_le_to_cpu_32 (buffer[bi]); To achieve that we need: #define IXGBE_LE32_TO_CPUS(x) (*(x) = rte_le_to_cpu_32(*(x))) Correct? Konstantin > > > > Do you to support -Wunused-value? > > > > No, I just turned this on to check above change and was surprised what > > happened. > > Honestly, I don't know if there is a good fix for this warning. > > -- > Thomas
