Command prologuer reports what fraction of samples from a profile are from IPs marked as function prologue in DWARF line tables.
In Go binaries (as of Go 1.12), this counts the stack bounds check up to and including the conditional branch to morestack. It does not the instructions that call morestack or the instructions that create a function's stack frame.
This is best used with precise profile samples, such as
perf record -e cycles:ppp -- <cmd>