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Felix Geisendörfer 2021-03-30 14:54:47 +02:00
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stack-traces.md
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@ -125,10 +125,14 @@ The main downside to frame pointers is that they add some performance overhead t
Despite this Go used to omit frame pointers which caused interoperability issues with third party debuggers and profilers such as [Linux perf](http://www.brendangregg.com/perf.html). Fortunately the Go developers recognized the issue and since [Go 1.7](https://golang.org/doc/go1.7) frame pointers are always included for [64bit binaries ](https://sourcegraph.com/search?q=framepointer_enabled+repo:%5Egithub%5C.com/golang/go%24+&patternType=literal). And unlike `gcc`, the Go compiler offers no option to disable frame pointers, which is a good thing in my opinion.
Anyway, if all of this is too abstract for you, and you'd like to see some code, [here](https://github.com/felixge/gounwind/blob/5cc8505361807a22169595999689bd793ed6d391/gounwind.go) is an alternative `runtime.Callers()` implementation that uses frame pointer unwinding instead of [.gopclntab](#gopclntab). The simplicity should speak for itself when compared to the alternative methods described below.
Anyway, if all of this is too abstract for you, and you'd like to see some code, [here](https://github.com/felixge/gounwind/blob/5cc8505361807a22169595999689bd793ed6d391/gounwind.go) is an alternative `runtime.Callers()` implementation that uses frame pointer unwinding instead of [.gopclntab](#gopclntab). The simplicity should speak for itself when compared to the alternative methods described below. It should also be clear that frame pointer unwinding has `O(N)` time complexity where `N` is the number of stack frames that need to be traversed.
### .gopclntab
Since frame pointers are only available on 64bit platforms, Go has to use a more complicated approach to enable stack tracing in a cross-platform manner [for now](https://github.com/golang/go/issues/16638). The nitty-gritty of this has been described by Russ Cox in his [Go 1.2 Runtime Symbol Information](https://golang.org/s/go12symtab) document, but I'll try to summarize the key idea.
Simply speaking, the idea is to take the current program count (pc) of a goroutine and look it up in the sorted `<pc, func>` table in the `.gopclntab` section embedded in the binary. If you want, you can get access to this table using the [debug/elf](./examples/pclnttab/linux.go) or ([debug/macho](./examples/pclnttab/darwin.go)) package yourself.
### DWARF
> An unwinder that is several hundred lines long is simply not even *remotely* interesting to me.