backends/tc: Fix issues reported in #4327 (#4484)

* tc: Fix ingress pipeline not restoring header pointer from metadata. Issue reported in #4327. * tc: Fix lookahead not restoring offsetVar. Issue reported in #4327. * Update p4tc golden outputs.
p4lang · Feb 29, 2024 · dcae42a · dcae42a
1 parent 24ecde7
commit dcae42a
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Showing 33 changed files with 69 additions and 1 deletion.
diff --git a/backends/ebpf/ebpfParser.h b/backends/ebpf/ebpfParser.h
@@ -39,7 +39,7 @@ class StateTranslationVisitor : public CodeGenInspector {
     virtual void compileExtractField(const IR::Expression *expr, const IR::StructField *field,
                                      unsigned hdrOffsetBits, EBPFType *type);
     virtual void compileExtract(const IR::Expression *destination);
-    void compileLookahead(const IR::Expression *destination);
+    virtual void compileLookahead(const IR::Expression *destination);
     void compileAdvance(const P4::ExternMethod *ext);
     void compileVerify(const IR::MethodCallExpression *expression);
 

diff --git a/backends/tc/ebpfCodeGen.cpp b/backends/tc/ebpfCodeGen.cpp
@@ -268,6 +268,10 @@ void TCIngressPipelinePNA::emit(EBPF::CodeBuilder *builder) {
         builder->newline();
         builder->emitIndent();
         builder->appendFormat("unsigned %s = hdrMd->%s;", offsetVar.c_str(), offsetVar.c_str());
+        builder->newline();
+        builder->emitIndent();
+        builder->appendFormat("%s = %s + BYTES(%s);", headerStartVar.c_str(),
+                              packetStartVar.c_str(), offsetVar.c_str());
     }
     builder->newline();
     emitHeadersFromCPUMAP(builder);
@@ -705,6 +709,34 @@ void PnaStateTranslationVisitor::compileExtractField(const IR::Expression *expr,
     builder->newline();
 }
 
+void PnaStateTranslationVisitor::compileLookahead(const IR::Expression *destination) {
+    cstring msgStr = Util::printf_format("Parser: lookahead for %s %s",
+                                         state->parser->typeMap->getType(destination)->toString(),
+                                         destination->toString());
+    builder->target->emitTraceMessage(builder, msgStr.c_str());
+
+    builder->emitIndent();
+    builder->blockStart();
+    builder->emitIndent();
+    builder->appendFormat("u8* %s_save = %s", state->parser->program->headerStartVar.c_str(),
+                          state->parser->program->headerStartVar.c_str());
+    builder->endOfStatement(true);
+    builder->emitIndent();
+    builder->appendFormat("unsigned %s_save = %s", state->parser->program->offsetVar.c_str(),
+                          state->parser->program->offsetVar.c_str());
+    builder->endOfStatement(true);
+    compileExtract(destination);
+    builder->emitIndent();
+    builder->appendFormat("%s = %s_save", state->parser->program->headerStartVar.c_str(),
+                          state->parser->program->headerStartVar.c_str());
+    builder->endOfStatement(true);
+    builder->emitIndent();
+    builder->appendFormat("%s = %s_save", state->parser->program->offsetVar.c_str(),
+                          state->parser->program->offsetVar.c_str());
+    builder->endOfStatement(true);
+    builder->blockEnd(true);
+}
+
 // =====================EBPFTablePNA=============================
 void EBPFTablePNA::emitKeyType(EBPF::CodeBuilder *builder) {
     builder->emitIndent();

diff --git a/backends/tc/ebpfCodeGen.h b/backends/tc/ebpfCodeGen.h
@@ -121,6 +121,7 @@ class PnaStateTranslationVisitor : public EBPF::PsaStateTranslationVisitor {
  protected:
     void compileExtractField(const IR::Expression *expr, const IR::StructField *field,
                              unsigned hdrOffsetBits, EBPF::EBPFType *type) override;
+    void compileLookahead(const IR::Expression *destination) override;
 };
 
 class EBPFPnaParser : public EBPF::EBPFPsaParser {

diff --git a/testdata/p4tc_samples_outputs/calculator_control_blocks.c b/testdata/p4tc_samples_outputs/calculator_control_blocks.c
@@ -56,6 +56,7 @@ static __always_inline int process(struct __sk_buff *skb, struct headers_t *hdr,
     if (!hdrMd)
         return TC_ACT_SHOT;
     unsigned ebpf_packetOffsetInBits = hdrMd->ebpf_packetOffsetInBits;
+    hdr_start = pkt + BYTES(ebpf_packetOffsetInBits);
     hdr = &(hdrMd->cpumap_hdr);
     meta = &(hdrMd->cpumap_usermeta);
 {

diff --git a/testdata/p4tc_samples_outputs/calculator_parser.c b/testdata/p4tc_samples_outputs/calculator_parser.c
@@ -34,6 +34,7 @@ static __always_inline int run_parser(struct __sk_buff *skb, struct headers_t *h
         check_p4calc: {
             {
                 u8* hdr_start_save = hdr_start;
+                unsigned ebpf_packetOffsetInBits_save = ebpf_packetOffsetInBits;
                 if ((u8*)ebpf_packetEnd < hdr_start + BYTES(128 + 0)) {
                     ebpf_errorCode = PacketTooShort;
                     goto reject;
@@ -65,9 +66,11 @@ static __always_inline int run_parser(struct __sk_buff *skb, struct headers_t *h
                 hdr_start += BYTES(128);
 
                 hdr_start = hdr_start_save;
+                ebpf_packetOffsetInBits = ebpf_packetOffsetInBits_save;
             }
             {
                 u8* hdr_start_save = hdr_start;
+                unsigned ebpf_packetOffsetInBits_save = ebpf_packetOffsetInBits;
                 if ((u8*)ebpf_packetEnd < hdr_start + BYTES(128 + 0)) {
                     ebpf_errorCode = PacketTooShort;
                     goto reject;
@@ -99,9 +102,11 @@ static __always_inline int run_parser(struct __sk_buff *skb, struct headers_t *h
                 hdr_start += BYTES(128);
 
                 hdr_start = hdr_start_save;
+                ebpf_packetOffsetInBits = ebpf_packetOffsetInBits_save;
             }
             {
                 u8* hdr_start_save = hdr_start;
+                unsigned ebpf_packetOffsetInBits_save = ebpf_packetOffsetInBits;
                 if ((u8*)ebpf_packetEnd < hdr_start + BYTES(128 + 0)) {
                     ebpf_errorCode = PacketTooShort;
                     goto reject;
@@ -133,6 +138,7 @@ static __always_inline int run_parser(struct __sk_buff *skb, struct headers_t *h
                 hdr_start += BYTES(128);
 
                 hdr_start = hdr_start_save;
+                ebpf_packetOffsetInBits = ebpf_packetOffsetInBits_save;
             }
             u32 select_0;
             select_0 = (((((u32)(((u16)tmp_0.p << 8) | ((u16)tmp_2.four & 0xff)) << 8) & ((1 << 24) - 1)) | (((u32)tmp_4.ver & 0xff) & ((1 << 24) - 1))) & ((1 << 24) - 1));

diff --git a/testdata/p4tc_samples_outputs/checksum_control_blocks.c b/testdata/p4tc_samples_outputs/checksum_control_blocks.c
@@ -47,6 +47,7 @@ static __always_inline int process(struct __sk_buff *skb, struct my_ingress_head
     if (!hdrMd)
         return TC_ACT_SHOT;
     unsigned ebpf_packetOffsetInBits = hdrMd->ebpf_packetOffsetInBits;
+    hdr_start = pkt + BYTES(ebpf_packetOffsetInBits);
     hdr = &(hdrMd->cpumap_hdr);
     meta = &(hdrMd->cpumap_usermeta);
 {

diff --git a/testdata/p4tc_samples_outputs/const_entries_range_mask_control_blocks.c b/testdata/p4tc_samples_outputs/const_entries_range_mask_control_blocks.c
@@ -45,6 +45,7 @@ static __always_inline int process(struct __sk_buff *skb, struct Header_t *h, st
     if (!hdrMd)
         return TC_ACT_SHOT;
     unsigned ebpf_packetOffsetInBits = hdrMd->ebpf_packetOffsetInBits;
+    hdr_start = pkt + BYTES(ebpf_packetOffsetInBits);
     h = &(hdrMd->cpumap_hdr);
     m = &(hdrMd->cpumap_usermeta);
 {

diff --git a/testdata/p4tc_samples_outputs/default_action_example_control_blocks.c b/testdata/p4tc_samples_outputs/default_action_example_control_blocks.c
@@ -68,6 +68,7 @@ static __always_inline int process(struct __sk_buff *skb, struct headers_t *hdr,
     if (!hdrMd)
         return TC_ACT_SHOT;
     unsigned ebpf_packetOffsetInBits = hdrMd->ebpf_packetOffsetInBits;
+    hdr_start = pkt + BYTES(ebpf_packetOffsetInBits);
     hdr = &(hdrMd->cpumap_hdr);
     user_meta = &(hdrMd->cpumap_usermeta);
 {

diff --git a/testdata/p4tc_samples_outputs/default_action_with_param_01_control_blocks.c b/testdata/p4tc_samples_outputs/default_action_with_param_01_control_blocks.c
@@ -66,6 +66,7 @@ static __always_inline int process(struct __sk_buff *skb, struct headers_t *hdr,
     if (!hdrMd)
         return TC_ACT_SHOT;
     unsigned ebpf_packetOffsetInBits = hdrMd->ebpf_packetOffsetInBits;
+    hdr_start = pkt + BYTES(ebpf_packetOffsetInBits);
     hdr = &(hdrMd->cpumap_hdr);
     user_meta = &(hdrMd->cpumap_usermeta);
 {

diff --git a/testdata/p4tc_samples_outputs/default_action_with_param_control_blocks.c b/testdata/p4tc_samples_outputs/default_action_with_param_control_blocks.c
@@ -68,6 +68,7 @@ static __always_inline int process(struct __sk_buff *skb, struct headers_t *hdr,
     if (!hdrMd)
         return TC_ACT_SHOT;
     unsigned ebpf_packetOffsetInBits = hdrMd->ebpf_packetOffsetInBits;
+    hdr_start = pkt + BYTES(ebpf_packetOffsetInBits);
     hdr = &(hdrMd->cpumap_hdr);
     user_meta = &(hdrMd->cpumap_usermeta);
 {

diff --git a/testdata/p4tc_samples_outputs/default_hit_const_example_control_blocks.c b/testdata/p4tc_samples_outputs/default_hit_const_example_control_blocks.c
@@ -52,6 +52,7 @@ static __always_inline int process(struct __sk_buff *skb, struct headers_t *hdr,
     if (!hdrMd)
         return TC_ACT_SHOT;
     unsigned ebpf_packetOffsetInBits = hdrMd->ebpf_packetOffsetInBits;
+    hdr_start = pkt + BYTES(ebpf_packetOffsetInBits);
     hdr = &(hdrMd->cpumap_hdr);
     meta = &(hdrMd->cpumap_usermeta);
 {

diff --git a/testdata/p4tc_samples_outputs/drop_packet_example_control_blocks.c b/testdata/p4tc_samples_outputs/drop_packet_example_control_blocks.c
@@ -45,6 +45,7 @@ static __always_inline int process(struct __sk_buff *skb, struct headers_t *hdr,
     if (!hdrMd)
         return TC_ACT_SHOT;
     unsigned ebpf_packetOffsetInBits = hdrMd->ebpf_packetOffsetInBits;
+    hdr_start = pkt + BYTES(ebpf_packetOffsetInBits);
     hdr = &(hdrMd->cpumap_hdr);
     user_meta = &(hdrMd->cpumap_usermeta);
 {

diff --git a/testdata/p4tc_samples_outputs/global_action_example_01_control_blocks.c b/testdata/p4tc_samples_outputs/global_action_example_01_control_blocks.c
@@ -68,6 +68,7 @@ static __always_inline int process(struct __sk_buff *skb, struct my_ingress_head
     if (!hdrMd)
         return TC_ACT_SHOT;
     unsigned ebpf_packetOffsetInBits = hdrMd->ebpf_packetOffsetInBits;
+    hdr_start = pkt + BYTES(ebpf_packetOffsetInBits);
     hdr = &(hdrMd->cpumap_hdr);
     meta = &(hdrMd->cpumap_usermeta);
 {

diff --git a/testdata/p4tc_samples_outputs/global_action_example_02_control_blocks.c b/testdata/p4tc_samples_outputs/global_action_example_02_control_blocks.c
@@ -69,6 +69,7 @@ static __always_inline int process(struct __sk_buff *skb, struct my_ingress_head
     if (!hdrMd)
         return TC_ACT_SHOT;
     unsigned ebpf_packetOffsetInBits = hdrMd->ebpf_packetOffsetInBits;
+    hdr_start = pkt + BYTES(ebpf_packetOffsetInBits);
     hdr = &(hdrMd->cpumap_hdr);
     meta = &(hdrMd->cpumap_usermeta);
 {

diff --git a/testdata/p4tc_samples_outputs/hash1_control_blocks.c b/testdata/p4tc_samples_outputs/hash1_control_blocks.c
@@ -25,6 +25,7 @@ static __always_inline int process(struct __sk_buff *skb, struct my_ingress_head
     if (!hdrMd)
         return TC_ACT_SHOT;
     unsigned ebpf_packetOffsetInBits = hdrMd->ebpf_packetOffsetInBits;
+    hdr_start = pkt + BYTES(ebpf_packetOffsetInBits);
     hdr = &(hdrMd->cpumap_hdr);
     meta = &(hdrMd->cpumap_usermeta);
 {

diff --git a/testdata/p4tc_samples_outputs/ipip_control_blocks.c b/testdata/p4tc_samples_outputs/ipip_control_blocks.c
@@ -52,6 +52,7 @@ static __always_inline int process(struct __sk_buff *skb, struct headers_t *hdr,
     if (!hdrMd)
         return TC_ACT_SHOT;
     unsigned ebpf_packetOffsetInBits = hdrMd->ebpf_packetOffsetInBits;
+    hdr_start = pkt + BYTES(ebpf_packetOffsetInBits);
     hdr = &(hdrMd->cpumap_hdr);
     meta = &(hdrMd->cpumap_usermeta);
 {

diff --git a/testdata/p4tc_samples_outputs/matchtype_control_blocks.c b/testdata/p4tc_samples_outputs/matchtype_control_blocks.c
@@ -114,6 +114,7 @@ static __always_inline int process(struct __sk_buff *skb, struct headers_t *hdr,
     if (!hdrMd)
         return TC_ACT_SHOT;
     unsigned ebpf_packetOffsetInBits = hdrMd->ebpf_packetOffsetInBits;
+    hdr_start = pkt + BYTES(ebpf_packetOffsetInBits);
     hdr = &(hdrMd->cpumap_hdr);
     user_meta = &(hdrMd->cpumap_usermeta);
 {

diff --git a/testdata/p4tc_samples_outputs/mix_matchtype_example_control_blocks.c b/testdata/p4tc_samples_outputs/mix_matchtype_example_control_blocks.c
@@ -120,6 +120,7 @@ static __always_inline int process(struct __sk_buff *skb, struct headers_t *hdr,
     if (!hdrMd)
         return TC_ACT_SHOT;
     unsigned ebpf_packetOffsetInBits = hdrMd->ebpf_packetOffsetInBits;
+    hdr_start = pkt + BYTES(ebpf_packetOffsetInBits);
     hdr = &(hdrMd->cpumap_hdr);
     user_meta = &(hdrMd->cpumap_usermeta);
 {

diff --git a/testdata/p4tc_samples_outputs/multiple_tables_example_01_control_blocks.c b/testdata/p4tc_samples_outputs/multiple_tables_example_01_control_blocks.c
@@ -190,6 +190,7 @@ static __always_inline int process(struct __sk_buff *skb, struct headers_t *hdr,
     if (!hdrMd)
         return TC_ACT_SHOT;
     unsigned ebpf_packetOffsetInBits = hdrMd->ebpf_packetOffsetInBits;
+    hdr_start = pkt + BYTES(ebpf_packetOffsetInBits);
     hdr = &(hdrMd->cpumap_hdr);
     user_meta = &(hdrMd->cpumap_usermeta);
 {

diff --git a/testdata/p4tc_samples_outputs/multiple_tables_example_02_control_blocks.c b/testdata/p4tc_samples_outputs/multiple_tables_example_02_control_blocks.c
@@ -187,6 +187,7 @@ static __always_inline int process(struct __sk_buff *skb, struct headers_t *hdr,
     if (!hdrMd)
         return TC_ACT_SHOT;
     unsigned ebpf_packetOffsetInBits = hdrMd->ebpf_packetOffsetInBits;
+    hdr_start = pkt + BYTES(ebpf_packetOffsetInBits);
     hdr = &(hdrMd->cpumap_hdr);
     user_meta = &(hdrMd->cpumap_usermeta);
 {

diff --git a/testdata/p4tc_samples_outputs/name_annotation_example_control_blocks.c b/testdata/p4tc_samples_outputs/name_annotation_example_control_blocks.c
@@ -67,6 +67,7 @@ static __always_inline int process(struct __sk_buff *skb, struct headers_t *hdr,
     if (!hdrMd)
         return TC_ACT_SHOT;
     unsigned ebpf_packetOffsetInBits = hdrMd->ebpf_packetOffsetInBits;
+    hdr_start = pkt + BYTES(ebpf_packetOffsetInBits);
     hdr = &(hdrMd->cpumap_hdr);
     user_meta = &(hdrMd->cpumap_usermeta);
 {

diff --git a/testdata/p4tc_samples_outputs/no_table_example_control_blocks.c b/testdata/p4tc_samples_outputs/no_table_example_control_blocks.c
@@ -25,6 +25,7 @@ static __always_inline int process(struct __sk_buff *skb, struct headers_t *hdr,
     if (!hdrMd)
         return TC_ACT_SHOT;
     unsigned ebpf_packetOffsetInBits = hdrMd->ebpf_packetOffsetInBits;
+    hdr_start = pkt + BYTES(ebpf_packetOffsetInBits);
     hdr = &(hdrMd->cpumap_hdr);
     user_meta = &(hdrMd->cpumap_usermeta);
 {

diff --git a/testdata/p4tc_samples_outputs/noaction_example_01_control_blocks.c b/testdata/p4tc_samples_outputs/noaction_example_01_control_blocks.c
@@ -67,6 +67,7 @@ static __always_inline int process(struct __sk_buff *skb, struct headers_t *hdr,
     if (!hdrMd)
         return TC_ACT_SHOT;
     unsigned ebpf_packetOffsetInBits = hdrMd->ebpf_packetOffsetInBits;
+    hdr_start = pkt + BYTES(ebpf_packetOffsetInBits);
     hdr = &(hdrMd->cpumap_hdr);
     user_meta = &(hdrMd->cpumap_usermeta);
 {

diff --git a/testdata/p4tc_samples_outputs/noaction_example_02_control_blocks.c b/testdata/p4tc_samples_outputs/noaction_example_02_control_blocks.c
@@ -58,6 +58,7 @@ static __always_inline int process(struct __sk_buff *skb, struct headers_t *hdr,
     if (!hdrMd)
         return TC_ACT_SHOT;
     unsigned ebpf_packetOffsetInBits = hdrMd->ebpf_packetOffsetInBits;
+    hdr_start = pkt + BYTES(ebpf_packetOffsetInBits);
     hdr = &(hdrMd->cpumap_hdr);
     user_meta = &(hdrMd->cpumap_usermeta);
 {

diff --git a/testdata/p4tc_samples_outputs/nummask_annotation_example_control_blocks.c b/testdata/p4tc_samples_outputs/nummask_annotation_example_control_blocks.c
@@ -47,6 +47,7 @@ static __always_inline int process(struct __sk_buff *skb, struct headers_t *hdr,
     if (!hdrMd)
         return TC_ACT_SHOT;
     unsigned ebpf_packetOffsetInBits = hdrMd->ebpf_packetOffsetInBits;
+    hdr_start = pkt + BYTES(ebpf_packetOffsetInBits);
     hdr = &(hdrMd->cpumap_hdr);
     meta = &(hdrMd->cpumap_usermeta);
 {

diff --git a/testdata/p4tc_samples_outputs/send_to_port_example_control_blocks.c b/testdata/p4tc_samples_outputs/send_to_port_example_control_blocks.c
@@ -47,6 +47,7 @@ static __always_inline int process(struct __sk_buff *skb, struct headers_t *hdr,
     if (!hdrMd)
         return TC_ACT_SHOT;
     unsigned ebpf_packetOffsetInBits = hdrMd->ebpf_packetOffsetInBits;
+    hdr_start = pkt + BYTES(ebpf_packetOffsetInBits);
     hdr = &(hdrMd->cpumap_hdr);
     user_meta = &(hdrMd->cpumap_usermeta);
 {

diff --git a/testdata/p4tc_samples_outputs/set_entry_timer_example_control_blocks.c b/testdata/p4tc_samples_outputs/set_entry_timer_example_control_blocks.c
@@ -66,6 +66,7 @@ static __always_inline int process(struct __sk_buff *skb, struct headers_t *hdr,
     if (!hdrMd)
         return TC_ACT_SHOT;
     unsigned ebpf_packetOffsetInBits = hdrMd->ebpf_packetOffsetInBits;
+    hdr_start = pkt + BYTES(ebpf_packetOffsetInBits);
     hdr = &(hdrMd->cpumap_hdr);
     user_meta = &(hdrMd->cpumap_usermeta);
 {

diff --git a/testdata/p4tc_samples_outputs/simple_exact_example_control_blocks.c b/testdata/p4tc_samples_outputs/simple_exact_example_control_blocks.c
@@ -47,6 +47,7 @@ static __always_inline int process(struct __sk_buff *skb, struct my_ingress_head
     if (!hdrMd)
         return TC_ACT_SHOT;
     unsigned ebpf_packetOffsetInBits = hdrMd->ebpf_packetOffsetInBits;
+    hdr_start = pkt + BYTES(ebpf_packetOffsetInBits);
     hdr = &(hdrMd->cpumap_hdr);
     meta = &(hdrMd->cpumap_usermeta);
 {

diff --git a/testdata/p4tc_samples_outputs/simple_lpm_example_control_blocks.c b/testdata/p4tc_samples_outputs/simple_lpm_example_control_blocks.c
@@ -47,6 +47,7 @@ static __always_inline int process(struct __sk_buff *skb, struct my_ingress_head
     if (!hdrMd)
         return TC_ACT_SHOT;
     unsigned ebpf_packetOffsetInBits = hdrMd->ebpf_packetOffsetInBits;
+    hdr_start = pkt + BYTES(ebpf_packetOffsetInBits);
     hdr = &(hdrMd->cpumap_hdr);
     meta = &(hdrMd->cpumap_usermeta);
 {

diff --git a/testdata/p4tc_samples_outputs/simple_ternary_example_control_blocks.c b/testdata/p4tc_samples_outputs/simple_ternary_example_control_blocks.c
@@ -53,6 +53,7 @@ static __always_inline int process(struct __sk_buff *skb, struct my_ingress_head
     if (!hdrMd)
         return TC_ACT_SHOT;
     unsigned ebpf_packetOffsetInBits = hdrMd->ebpf_packetOffsetInBits;
+    hdr_start = pkt + BYTES(ebpf_packetOffsetInBits);
     hdr = &(hdrMd->cpumap_hdr);
     meta = &(hdrMd->cpumap_usermeta);
 {

diff --git a/testdata/p4tc_samples_outputs/size_param_example_control_blocks.c b/testdata/p4tc_samples_outputs/size_param_example_control_blocks.c
@@ -67,6 +67,7 @@ static __always_inline int process(struct __sk_buff *skb, struct headers_t *hdr,
     if (!hdrMd)
         return TC_ACT_SHOT;
     unsigned ebpf_packetOffsetInBits = hdrMd->ebpf_packetOffsetInBits;
+    hdr_start = pkt + BYTES(ebpf_packetOffsetInBits);
     hdr = &(hdrMd->cpumap_hdr);
     user_meta = &(hdrMd->cpumap_usermeta);
 {

diff --git a/testdata/p4tc_samples_outputs/tc_type_annotation_example_control_blocks.c b/testdata/p4tc_samples_outputs/tc_type_annotation_example_control_blocks.c
@@ -59,6 +59,7 @@ static __always_inline int process(struct __sk_buff *skb, struct headers_t *hdr,
     if (!hdrMd)
         return TC_ACT_SHOT;
     unsigned ebpf_packetOffsetInBits = hdrMd->ebpf_packetOffsetInBits;
+    hdr_start = pkt + BYTES(ebpf_packetOffsetInBits);
     hdr = &(hdrMd->cpumap_hdr);
     user_meta = &(hdrMd->cpumap_usermeta);
 {

diff --git a/testdata/p4tc_samples_outputs/test_ipv6_example_control_blocks.c b/testdata/p4tc_samples_outputs/test_ipv6_example_control_blocks.c
@@ -42,6 +42,7 @@ static __always_inline int process(struct __sk_buff *skb, struct headers_t *hdr,
     if (!hdrMd)
         return TC_ACT_SHOT;
     unsigned ebpf_packetOffsetInBits = hdrMd->ebpf_packetOffsetInBits;
+    hdr_start = pkt + BYTES(ebpf_packetOffsetInBits);
     hdr = &(hdrMd->cpumap_hdr);
     user_meta = &(hdrMd->cpumap_usermeta);
 {