10000 Make struct used by digest in p4tc packed by vbnogueira · Pull Request #5329 · p4lang/p4c · GitHub
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Make struct used by digest in p4tc packed #5329

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Make struct used by digest in p4tc packed #5329

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@vbnogueira vbnogueira commented Jun 26, 2025 •
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The p4tc control path expects the digest message to be packed
For example, in testdata/p4tc_samples/digest.p4 we have the following
struct being sent throught digest pack:

struct mac_learn_digest_t {
    @tc_type("macaddr") bit<48> srcAddr;
    @tc_type("dev") PortId_t ingress_port;
};

As an eBPF C struct, this will be:

struct mac_learn_digest_t {
    u8 srcAddr[6]; /* bit<48> */
    u32 ingress_port; /* PortId_t */
};

Notice that this will create padding between srcAddr
and ingress_port. To avoid this we are making structs associated with
digest messages packed. So the previous struct will become:

struct __attribute__((__packed__)) mac_learn_digest_t {
    u8 srcAddr[6]; /* bit<48> */
    u32 ingress_port; /* PortId_t */
};

@vbnogueira
Make struct used by digest in p4tc packed
867f5d0 
The p4tc control path expects the digest message to be packed
For example, in testdata/p4tc_samples/digest.p4 we have the following
struct being sent throught digest pack:

struct mac_learn_digest_t {
    @tc_type("macaddr") bit<48> srcAddr;
    @tc_type("dev") PortId_t ingress_port;
};

As an eBPF C struct, this will be:

struct mac_learn_digest_t {
    u8 srcAddr[6]; /* bit<48> */
    u32 ingress_port; /* PortId_t */
};

Notice that this will create padding between srcAddr
and ingress_port. To avoid this we are making structs associated with
digest messages packed. So the previous struct will become:

struct __attribute__((__packed__)) mac_learn_digest_t {
    u8 srcAddr[6]; /* bit<48> */
    u32 ingress_port; /* PortId_t */
};

Signed-off-by: Victor Nogueira <victor@mojatatu.com>
@vbnogueira
Adapt digest examples for packed attribute
9e94135 
Signed-off-by: Victor Nogueira <victor@mojatatu.com>
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