On 12/4/2020 2:59 AM, Ferruh Yigit wrote:
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On 12/3/2020 1:59 PM, George Prekas wrote:
Insert a compiler barrier to make sure that the IP checksum calculation
happens after setting all the fields of the IP header.
Can you please provide the compiler details, and if there is any specific
instruction on how to reproduce this failure?
This happens with GCC 9 and GCC 10. It works fine on GCC 8.
Stephen was right that a compiler barrier here is not the right
solution. After spending some time on it, I realized that it is an
aliasing problem when casting the IP header to uint16_t*. As far as I
understand, this is not allowed by the C standard. As far as I know,
there are 3 ways to fix this problem: Use a union, use memcpy, or set
the compiler flag -fno-strict-aliasing. I assume that the last option is
the least intrusive. I've submitted a second version of the patch with it.
Let me know of your opinion.
Signed-off-by: George Prekas <preka...@amazon.com>
---
app/test-pmd/flowgen.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/app/test-pmd/flowgen.c b/app/test-pmd/flowgen.c
index acf3e2460..893b4b0b8 100644
--- a/app/test-pmd/flowgen.c
+++ b/app/test-pmd/flowgen.c
@@ -150,6 +150,7 @@ pkt_burst_flow_gen(struct fwd_stream *fs)
next_flow);
ip_hdr->total_length = RTE_CPU_TO_BE_16(pkt_size -
sizeof(*eth_hdr));
+ rte_compiler_barrier();
ip_hdr->hdr_checksum = ip_sum((unaligned_uint16_t
*)ip_hdr,
sizeof(*ip_hdr));
