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x/tools/cmd/godoc: incomplete list of callers #13235

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mdempsky opened this issue Nov 13, 2015 · 2 comments

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commented Nov 13, 2015

At head (f762d0d, golang/tools@d94e6fe), if I run

GOPATH= godoc -http=:6060 -analysis=type,pointer

and go to http://localhost:6060/src/runtime/runtime2.go, and click "func" in

81  func efaceOf(ep *interface{}) *eface {

it lists only two callers:

Callers of runtime.efaceOf:
getgcmask at line 1640
BenchSetType at line 134

But there's at least several more:

$ grep efaceOf *.go
error.go:   e := efaceOf(&x)
export_test.go: e := *efaceOf(&x)
heapdump.go:        eface := efaceOf(&p.arg)
mbitmap.go: typ := (*ptrtype)(unsafe.Pointer(efaceOf(&x)._type)).elem
mbitmap.go: e := *efaceOf(&ep)
mfinal.go:  e := efaceOf(&obj)
mfinal.go:  f := efaceOf(&finalizer)
mfinal.go:      if assertE2I2(ityp, *efaceOf(&obj), nil) {
runtime2.go:func efaceOf(ep *interface{}) *eface {

CC @alandonovan

@mdempsky mdempsky added this to the Unreleased milestone Nov 13, 2015

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commented Nov 13, 2015

The pointer analysis treats calls to exported functions in the runtime package specially because when the analysis was written, the package was mostly C code so there wasn't much to analyze. Instead of looking at the source for that package, the analysis has built-in knowledge of the aliasing and callgraph effects of the important functions, which are few.

Even though the runtime package is now in Go, I would not revisit this decision because the package makes such extensive use of unsafe.Pointer conversions, which the pointer analysis handles unsoundly: it treats a conversion from unsafe.Pointer to T just like new(T).

You can see the list of PTA intrinsics in golang.org/x/tools/go/pointer/intrinsics.go.

So, working as intended, and tough luck if you work on the runtime. :(

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commented Nov 13, 2015

Hm, I'm having trouble understanding how PTA and package runtime instrinsics would be relevant to the particular issue I pointed out. All of the efaceOf calls are direct calls via the function's name, so it's odd to me that it finds a couple of them, but not all?

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