add startline to function when symbolizing elf

[albertlockett]

Adds the StartLine to the profile Function during symbolization. This is needed to support pgo https://go.dev/doc/pgo#alternative-sources

Function.start_line must be set. This is the line number of the start of the function. i.e., the line containing the func keyword. The Go compiler uses this field to compute line offsets of samples (Location.Line.line - Function.start_line). Note that many existing pprof converters omit this field.

Tested using pprof that was collected by parca-agent & downloaded from pacra UI.

Before:

$ go build  -gcflags="all=-N -l" -o bin/ -pgo ~/Downloads/profile_before.pb ./my/test
# internal/coverage/rtcov
compile: /home/albertlockett/Downloads/profile(1).pb: PGO error: profile missing Function.start_line data (Go version of profiled application too old? Go 1.20+ automatically adds this to profiles)
# internal/goos
compile: /home/albertlockett/Downloads/profile(1).pb: PGO error: profile missing Function.start_line data (Go version of profiled application too old? Go 1.20+ automatically adds this to profiles)
# internal/goarch
compile: /home/albertlockett/Downloads/profile(1).pb: PGO error: profile missing Function.start_line data (Go version of profiled application too old? Go 1.20+ automatically adds this to profiles)
# internal/goexperiment

After:

$ go build  -gcflags="all=-N -l" -o bin/ -pgo ~/Downloads/profile_after ./my/test
# no problems

[CLAassistant]

All committers have signed the CLA.

[brancz]

Looks a test needs to be adapted, otherwise lgtm!

[albertlockett]

Looks a test needs to be adapted, otherwise lgtm!

thanks! fixed test 👍

[manojVivek]

@all-contributors Please add @albertlockett for code.

[allcontributors]

@manojVivek

I've put up a pull request to add @albertlockett! 🎉