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[dpdk-dev] error: value computed is not used

Message ID F6F2A6264E145F47A18AB6DF8E87425D12B79ECF@IRSMSX102.ger.corp.intel.com (mailing list archive)
State Not Applicable, archived
Headers show

Commit Message

Wodkowski, PawelX Dec. 15, 2014, 11:27 a.m. UTC
> -----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?

-	((__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]

Comments

Thomas Monjalon Dec. 15, 2014, 1:26 p.m. UTC | #1
2014-12-15 11:27, Wodkowski, PawelX:
> From: Thomas Monjalon [mailto:thomas.monjalon@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:

> 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? Do you to support -Wunused-value?
Wodkowski, PawelX Dec. 15, 2014, 1:47 p.m. UTC | #2
> -----Original Message-----
> From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com]
> Sent: Monday, December 15, 2014 2:27 PM
> To: Wodkowski, PawelX
> Cc: Qiu, Michael; dev@dpdk.org
> Subject: Re: [dpdk-dev] error: value computed is not used
> 
> 2014-12-15 11:27, Wodkowski, PawelX:
> > From: Thomas Monjalon [mailto:thomas.monjalon@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. 

> > 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	}


> Do you to support -Wunused-value?
No, I just turned this on to check above change and was surprised what happened.
Thomas Monjalon Dec. 15, 2014, 2:16 p.m. UTC | #3
2014-12-15 13:47, Wodkowski, PawelX:
> From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com]
> > 2014-12-15 11:27, Wodkowski, PawelX:
> > > From: Thomas Monjalon [mailto:thomas.monjalon@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.

> > 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.
Wodkowski, PawelX Dec. 15, 2014, 3:44 p.m. UTC | #4
> > > > 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?
I did not tested this, as this was only proposal. I only run build process and it pass.
Patch proposal will be sent in a while.

> 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.
> 

If you see something what I am not, please ignore this part but for me this looks like it should be:
tmp = IXGBE_READ_REG_ARRAY(hw, IXGBE_FLEX_MNG,
buffer[bi] = IXGBE_LE32_TO_CPUS (tmp);

Pawel
Ananyev, Konstantin Dec. 15, 2014, 4 p.m. UTC | #5
> -----Original Message-----
> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Thomas Monjalon
> Sent: Monday, December 15, 2014 2:17 PM
> To: Wodkowski, PawelX
> Cc: dev@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@6wind.com]
> > > 2014-12-15 11:27, Wodkowski, PawelX:
> > > > From: Thomas Monjalon [mailto:thomas.monjalon@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
Ananyev, Konstantin Dec. 15, 2014, 4:35 p.m. UTC | #6
> -----Original Message-----
> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Wodkowski, PawelX
> Sent: Monday, December 15, 2014 3:44 PM
> To: Thomas Monjalon
> Cc: dev@dpdk.org
> Subject: Re: [dpdk-dev] error: value computed is not used
> 
> > > > > 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?
> I did not tested this, as this was only proposal. I only run build process and it pass.
> Patch proposal will be sent in a while.
> 
> > 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.
> >
> 
> If you see something what I am not, please ignore this part but for me this looks like it should be:
> tmp = IXGBE_READ_REG_ARRAY(hw, IXGBE_FLEX_MNG,
> buffer[bi] = IXGBE_LE32_TO_CPUS (tmp);

Yep, same thought here, see my other mail on that subject.
Konstantin

> 
> Pawel
Thomas Monjalon Dec. 15, 2014, 4:40 p.m. UTC | #7
2014-12-15 16:00, Ananyev, Konstantin:
> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Thomas Monjalon
> > 2014-12-15 13:47, Wodkowski, PawelX:
> > > From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com]
> > > > 2014-12-15 11:27, Wodkowski, PawelX:
> > > > > 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?

Oh yes, you and Pawel are probably right.
I was focusing on definition of IXGBE_LE32_TO_CPUS and have not seen the bug.

> > > > 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.
Michal Jastrzebski Dec. 15, 2014, 5:03 p.m. UTC | #8
> -----Original Message-----
> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Thomas Monjalon
> Sent: Monday, December 15, 2014 3:17 PM
> To: Wodkowski, PawelX
> Cc: dev@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@6wind.com]
> > > 2014-12-15 11:27, Wodkowski, PawelX:
> > > > From: Thomas Monjalon [mailto:thomas.monjalon@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.
Hi Thomas,
I sent this patch on behalf of Pawel. It is:
[PATCH] fix rte_memcpy() macro: avoid unused value	warning

Michal
> 
> > > > 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.
> 
> > > 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
diff mbox

Patch

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)              \