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cmd/cover: coverage instrumentation causes diff in gcflags=-m output #56475

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thanm opened this issue Oct 28, 2022 · 1 comment
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cmd/cover: coverage instrumentation causes diff in gcflags=-m output #56475

thanm opened this issue Oct 28, 2022 · 1 comment
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@thanm
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thanm commented Oct 28, 2022

What version of Go are you using (go version)?

$ go version
go version devel go1.20-d398025345 Fri Oct 28 11:18:38 2022 -0400 linux/amd64

Does this issue reproduce with the latest release?

Yes.

What operating system and processor architecture are you using (go env)?

linux/amd64

What did you do?

With this package:

package tiny

func Simple(x int) int {
	if x != 42 {
		return 42
	}
	return 42
}

func CallSimple() int {
	return Simple(42)
}

Do a build with "go build -gcflags=-m tiny" and then with "go build -gcflags=-m -cover tiny"

What did you expect to see?

Same "-m" output

What did you see instead?

The addition of "-cover" perturbs some of the output.

Here's the baseline (no "-cover"):

# cov.example/tiny
./tiny.go:3:6: can inline Simple
./tiny.go:10:6: can inline CallSimple
./tiny.go:11:15: inlining call to Simple

and here is with "-cover":

# cov.example/tiny
./tiny.go:3: can inline Simple
./tiny.go:10: can inline CallSimple
./tiny.go:11: inlining call to Simple

Note that we've lost the column information.

FWIW, this same problem seems to exist for "go test -cover" in previous versions of Go, so this doesn't appear to be a regression.

@thanm thanm added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Oct 28, 2022
@thanm thanm self-assigned this Oct 28, 2022
@thanm thanm added this to the Go1.20 milestone Oct 28, 2022
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Change https://go.dev/cl/446259 mentions this issue: cmd/cover: fix buglet causing differences in -m output

romaindoumenc pushed a commit to TroutSoftware/go that referenced this issue Nov 3, 2022
Use a slightly different line number pragma when emitting instrumented
code, so as to ensure that we don't get any changes in the
"-gcflags=-m" output for coverage vs non-coverage.

Fixes golang#56475.

Change-Id: I3079171fdf83c0434ed6ea0ce3eb2797c2280c55
Reviewed-on: https://go-review.googlesource.com/c/go/+/446259
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Than McIntosh <thanm@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
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