Re: [dpdk-dev] [PATCH] A fix to work around strict-aliasing rules breaking

["Wang, Zhihong" <zhihong.wang@intel.com>]

> -----Original Message-----
> From: Richardson, Bruce
> Sent: Monday, March 02, 2015 6:32 PM
> To: Wang, Zhihong
> Cc: dev@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH] A fix to work around strict-aliasing rules
> breaking
> 
> On Mon, Mar 02, 2015 at 05:03:50PM +0800, zhihong.wang@intel.com wrote:
> > Fixed strict-aliasing rules breaking errors for some GCC version.
> >
> 
> This looks messy. Also, I believe the definition of memcpy should include the
> "restrict" keyword to indicate that source and dest can't overlap. Might that
> help fix the issue?

It's actually caused by casting void * to multiple other pointer types.

> 
> /Bruce
> 
> > Signed-off-by: Zhihong Wang <zhihong.wang@intel.com>
> > ---
> >  .../common/include/arch/x86/rte_memcpy.h           | 44 ++++++++++++----
> ------
> >  1 file changed, 24 insertions(+), 20 deletions(-)
> >
> > 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 69a5c6f..f412099 100644
> > --- a/lib/librte_eal/common/include/arch/x86/rte_memcpy.h
> > +++ b/lib/librte_eal/common/include/arch/x86/rte_memcpy.h
> > @@ -195,6 +195,8 @@ rte_mov256blocks(uint8_t *dst, const uint8_t *src,
> > size_t n)  static inline void *  rte_memcpy(void *dst, const void
> > *src, size_t n)  {
> > +	uintptr_t dstu = (uintptr_t)dst;
> > +	uintptr_t srcu = (uintptr_t)src;
> >  	void *ret = dst;
> >  	int dstofss;
> >  	int bits;
> > @@ -204,22 +206,22 @@ rte_memcpy(void *dst, const void *src, size_t n)
> >  	 */
> >  	if (n < 16) {
> >  		if (n & 0x01) {
> > -			*(uint8_t *)dst = *(const uint8_t *)src;
> > -			src = (const uint8_t *)src + 1;
> > -			dst = (uint8_t *)dst + 1;
> > +			*(uint8_t *)dstu = *(const uint8_t *)srcu;
> > +			srcu = (uintptr_t)((const uint8_t *)srcu + 1);
> > +			dstu = (uintptr_t)((uint8_t *)dstu + 1);
> >  		}
> >  		if (n & 0x02) {
> > -			*(uint16_t *)dst = *(const uint16_t *)src;
> > -			src = (const uint16_t *)src + 1;
> > -			dst = (uint16_t *)dst + 1;
> > +			*(uint16_t *)dstu = *(const uint16_t *)srcu;
> > +			srcu = (uintptr_t)((const uint16_t *)srcu + 1);
> > +			dstu = (uintptr_t)((uint16_t *)dstu + 1);
> >  		}
> >  		if (n & 0x04) {
> > -			*(uint32_t *)dst = *(const uint32_t *)src;
> > -			src = (const uint32_t *)src + 1;
> > -			dst = (uint32_t *)dst + 1;
> > +			*(uint32_t *)dstu = *(const uint32_t *)srcu;
> > +			srcu = (uintptr_t)((const uint32_t *)srcu + 1);
> > +			dstu = (uintptr_t)((uint32_t *)dstu + 1);
> >  		}
> >  		if (n & 0x08) {
> > -			*(uint64_t *)dst = *(const uint64_t *)src;
> > +			*(uint64_t *)dstu = *(const uint64_t *)srcu;
> >  		}
> >  		return ret;
> >  	}
> > @@ -458,6 +460,8 @@ static inline void *  rte_memcpy(void *dst, const
> > void *src, size_t n)  {
> >  	__m128i xmm0, xmm1, xmm2, xmm3, xmm4, xmm5, xmm6, xmm7,
> xmm8;
> > +	uintptr_t dstu = (uintptr_t)dst;
> > +	uintptr_t srcu = (uintptr_t)src;
> >  	void *ret = dst;
> >  	int dstofss;
> >  	int srcofs;
> > @@ -467,22 +471,22 @@ rte_memcpy(void *dst, const void *src, size_t n)
> >  	 */
> >  	if (n < 16) {
> >  		if (n & 0x01) {
> > -			*(uint8_t *)dst = *(const uint8_t *)src;
> > -			src = (const uint8_t *)src + 1;
> > -			dst = (uint8_t *)dst + 1;
> > +			*(uint8_t *)dstu = *(const uint8_t *)srcu;
> > +			srcu = (uintptr_t)((const uint8_t *)srcu + 1);
> > +			dstu = (uintptr_t)((uint8_t *)dstu + 1);
> >  		}
> >  		if (n & 0x02) {
> > -			*(uint16_t *)dst = *(const uint16_t *)src;
> > -			src = (const uint16_t *)src + 1;
> > -			dst = (uint16_t *)dst + 1;
> > +			*(uint16_t *)dstu = *(const uint16_t *)srcu;
> > +			srcu = (uintptr_t)((const uint16_t *)srcu + 1);
> > +			dstu = (uintptr_t)((uint16_t *)dstu + 1);
> >  		}
> >  		if (n & 0x04) {
> > -			*(uint32_t *)dst = *(const uint32_t *)src;
> > -			src = (const uint32_t *)src + 1;
> > -			dst = (uint32_t *)dst + 1;
> > +			*(uint32_t *)dstu = *(const uint32_t *)srcu;
> > +			srcu = (uintptr_t)((const uint32_t *)srcu + 1);
> > +			dstu = (uintptr_t)((uint32_t *)dstu + 1);
> >  		}
> >  		if (n & 0x08) {
> > -			*(uint64_t *)dst = *(const uint64_t *)src;
> > +			*(uint64_t *)dstu = *(const uint64_t *)srcu;
> >  		}
> >  		return ret;
> >  	}
> > --
> > 1.9.3
> >