From: "Wodkowski, PawelX" <pawelx.wodkowski@intel.com>
To: Thomas Monjalon <thomas.monjalon@6wind.com>,
"Qiu, Michael" <michael.qiu@intel.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>
Subject: Re: [dpdk-dev] error: value computed is not used
Date: Mon, 15 Dec 2014 11:27:35 +0000 [thread overview]
Message-ID: <F6F2A6264E145F47A18AB6DF8E87425D12B79ECF@IRSMSX102.ger.corp.intel.com> (raw)
In-Reply-To: <19703944.gAxOdpYSXo@xps13>
> -----Original Message-----
> From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com]
> Sent: Monday, December 15, 2014 11:55 AM
> To: Wodkowski, PawelX; Qiu, Michael
> Cc: dev@dpdk.org
> Subject: Re: [dpdk-dev] error: value computed is not used
>
> 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?
diff --git a/lib/librte_eal/common/include/arch/x86/rte_memcpy.h b/lib/librte_eal/common/include/arch/x86/rte_memcpy.h
index 290c5cd..906c911 100644
--- a/lib/librte_eal/common/include/arch/x86/rte_memcpy.h
+++ b/lib/librte_eal/common/include/arch/x86/rte_memcpy.h
@@ -168,10 +168,10 @@
rte_mov128(dst + 128, src + 128);
}
diff --git a/lib/librte_eal/common/include/arch/x86/rte_memcpy.h b/lib/librte_eal/common/include/arch/x86/rte_memcpy.h
index 290c5cd..c3e8b81 100644
--- a/lib/librte_eal/common/include/arch/x86/rte_memcpy.h
+++ b/lib/librte_eal/common/include/arch/x86/rte_memcpy.h
@@ -169,9 +169,9 @@
}
#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)); })
static inline void *
rte_memcpy_func(void *dst, const void *src, size_t n)
Thomas, can you check build with EXTRA_CFLAG='-Wunused-value'.
/home/pwodkowx/grizzly/dpdk_org_declan_v3_mode4_v2/lib/librte_pmd_ixgbe/ixgbe/ixgbe_common.c: In function 'ixgbe_host_interface_command':
/home/pwodkowx/grizzly/dpdk_org_declan_v3_mode4_v2/lib/librte_pmd_ixgbe/ixgbe/ixgbe_common.c:4429:3: error: statement with no effect [-Werror=unused-value]
/home/pwodkowx/grizzly/dpdk_org_declan_v3_mode4_v2/lib/librte_pmd_ixgbe/ixgbe/ixgbe_common.c:4448:3: error: statement with no effect [-Werror=unused-value]
next prev parent reply other threads:[~2014-12-15 11:27 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-12-08 9:05 Qiu, Michael
2014-12-08 11:00 ` Wodkowski, PawelX
2014-12-08 15:23 ` Qiu, Michael
2014-12-08 15:26 ` Wodkowski, PawelX
2014-12-15 10:54 ` Thomas Monjalon
2014-12-15 11:07 ` [dpdk-dev] [PATCH] enic: fix build on SUSE 11 Thomas Monjalon
2014-12-15 11:27 ` Wodkowski, PawelX [this message]
2014-12-15 13:26 ` [dpdk-dev] error: value computed is not used Thomas Monjalon
2014-12-15 13:47 ` Wodkowski, PawelX
2014-12-15 14:16 ` Thomas Monjalon
2014-12-15 15:44 ` Wodkowski, PawelX
2014-12-15 16:35 ` Ananyev, Konstantin
2014-12-15 16:00 ` Ananyev, Konstantin
2014-12-15 16:40 ` Thomas Monjalon
2014-12-15 17:03 ` Jastrzebski, MichalX K
2014-12-16 0:49 ` Qiu, Michael
2014-12-09 9:19 ` Qiu, Michael
2014-12-10 9:26 ` Qiu, Michael
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