Support HTTP Traceparent header field reading in Go 1.24

[grcevski]

Swiss maps have been enabled by default in Go main, which means they will probably become the default in Go 1.24 and break the reading of the HTTP request maps. gRPC is not affected, since we read an array there.

https://go-review.googlesource.com/c/go/+/574516

Go 1.24 is scheduled for release in February (2nd week), we need a fix by then: https://docs.google.com/presentation/d/1jvc0RzrshOOjkeEnsyea2jwjs_zVOcyETG558pqPOK0/mobilepresent?slide=id.g840eaeb4b4_0_0

One possible fix for this is to write a version of the map lookup code which is meant for Swiss maps. Based on some quick code reading I did, this looks more complex now than it used to be.

Another possible solution we discussed at the Go Auto SIG today is potentially reading the Traceparent field while the headers are being parsed, although this will be slower since we will run a uprobe on every header field. The advantage of this approach is that this works for all Go versions.

[grcevski]

I also realized that maybe we simply need to figure out how to work with the swiss maps. To support manual spans we also read a Go map in fill_partial_tracer_id_from_tracers_map, which also reads a Go map.

[MrAlias]

We need to fully audit the existing probes to determine where we instrument using maps.

We should see if we can find short-term fixes for all these locations if we cannot get support for swiss maps working before their release.

[MrAlias]

@grcevski plans to contribute the code from Beyla they used to get a stop-gap solution working for HTTP

[MrAlias]

@MrAlias OTel global needs to be documented that it will not work with newer version of Go (if using the old versions of otel).

[MrAlias]

Doing a quick search for MAP_BUCKET_TYPE shows only two locations we are using that definition:

• opentelemetry-go-instrumentation/internal/pkg/instrumentation/bpf/net/http/server/bpf/probe.bpf.c

  Line 57 in d5869d5

  __uint(value_size, sizeof(MAP_BUCKET_TYPE(go_string_t, go_slice_t)));

• opentelemetry-go-instrumentation/internal/pkg/instrumentation/bpf/go.opentelemetry.io/otel/traceglobal/bpf/probe.bpf.c

  Line 120 in d5869d5

  __uint(value_size, sizeof(MAP_BUCKET_TYPE(go_tracer_with_scope_attributes_t, go_tracer_ptr)));

For completeness, it looks like the kafka header is read from a slice:

opentelemetry-go-instrumentation/internal/pkg/instrumentation/bpf/github.com/segmentio/kafka-go/consumer/bpf/probe.bpf.c

Lines 90 to 92 in d5869d5

	// Read the header
	struct kafka_header_t header = {0};
	bpf_probe_read(&header, sizeof(header), headers_slice.array + (i * sizeof(header)));

[MrAlias]

Plan for OTel global instrumentation support:

• Add package constraints to the uprobes that ensure they are not loaded for versions of Go >= 1.24
• Document in COMPATIBILITY.md that ...

  Versions of go.opentelemetry.io/otel < v1.33.0 are not supported when using Go >= 1.24.

[nikhil-thomas]

@MrAlias is this issue taken care of by #1573 completely.
let me know if i can contribute in any way docs/tests etc.

im new here and trying start contributing. 🧑‍💻

[MrAlias]

@nikhil-thomas: The work required for the traceglobal probe is complete.

@grcevski do you still plan to work on the net/http probe?

[grcevski]

Yes, I plan to work on the net/http probe. Sorry last week was quite busy being the first week back from the holidays, I'll make the PR this week.