Re: [dpdk-dev] [PATCH 1/3] eal/x86: fix build with clang for old AVX

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

> Subject: [PATCH 1/3] eal/x86: fix build with clang for old AVX
> 
> When configuring RTE_MACHINE to "default", rte_memcpy implementation
> is the default one (old AVX).
> In this code, clang raises a warning thanks to -Wsometimes-uninitialized:
> 
> rte_memcpy.h:838:6: error:
> variable 'srcofs' is used uninitialized whenever 'if' condition is false
>         if (dstofss > 0) {
>             ^~~~~~~~~~~
> rte_memcpy.h:849:6: note: uninitialized use occurs here
>         if (srcofs == 0) {
>             ^~~~~~
> 
> It is fixed by initializing srcofs to 0.
> 
> Fixes: 1ae817f9f887 ("eal/x86: tune memcpy for platforms without AVX512")
> 
> Signed-off-by: Thomas Monjalon <thomas.monjalon@6wind.com>
> ---
>  lib/librte_eal/common/include/arch/x86/rte_memcpy.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)


Hi Thomas,

Thanks for pointing this out!
My last hasty modification on this is not correct.

The patch below will fix it. All modifications are tested.
Sorry for all the hassle! :'(

"srcofs" should be calculated based on source address anyway.


--- a/lib/librte_eal/common/include/arch/x86/rte_memcpy.h
+++ b/lib/librte_eal/common/include/arch/x86/rte_memcpy.h
@@ -512,8 +512,9 @@ COPY_BLOCK_64_BACK31:
 	/**
 	 * Make store aligned when copy size exceeds 512 bytes
 	 */
-	dstofss = 32 - ((uintptr_t)dst & 0x1F);
+	dstofss = (uintptr_t)dst & 0x1F;
 	if (dstofss > 0) {
+		dstofss = 32 - dstofss;
 		n -= dstofss;
 		rte_mov32((uint8_t *)dst, (const uint8_t *)src);
 		src = (const uint8_t *)src + dstofss;
@@ -834,14 +835,15 @@ COPY_BLOCK_64_BACK15:
 	 * unaligned copy functions require up to 15 bytes
 	 * backwards access.
 	 */
-	dstofss = 16 - ((uintptr_t)dst & 0x0F) + 16;
+	dstofss = (uintptr_t)dst & 0x0F;
 	if (dstofss > 0) {
+		dstofss = 16 - dstofss + 16;
 		n -= dstofss;
 		rte_mov32((uint8_t *)dst, (const uint8_t *)src);
 		src = (const uint8_t *)src + dstofss;
 		dst = (uint8_t *)dst + dstofss;
-		srcofs = ((uintptr_t)src & 0x0F);
 	}
+	srcofs = ((uintptr_t)src & 0x0F);
 
 	/**
 	 * For aligned copy