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cmd/compile: incorrect stack trace for nil dereference in inlined function #27201

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robfig opened this Issue Aug 24, 2018 · 1 comment

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@robfig
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robfig commented Aug 24, 2018

I believe that the stack trace for panics that occur when computing arguments to an inlined function are incorrectly attributed to the inlined function. I'm not sure if this is a known / expected consequence of inlining, but it caused a lot of confusion to see a line identified where a nil dereference is impossible.

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

Go 1.10.3

Does this issue reproduce with the latest release?

Yes, it still exists in Go 1.11rc1

What did you do?

https://play.golang.org/p/V5EzYYYSDjz

What did you expect to see?

A panic with this stack trace, identifying the line of the nil dereference:

goroutine 1 [running]:
main.main()
	/tmp/sandbox722989325/main.go:10 +0x1a

What did you see instead?

Incorrect attribution to an innocent function.

goroutine 1 [running]:
main.helperCall(...)
	/tmp/sandbox722989325/main.go:14
main.main()
	/tmp/sandbox722989325/main.go:10 +0x1a

@ianlancetaylor ianlancetaylor changed the title from Incorrect Stack Trace to cmd/compile: incorrect stack trace for nil dereference in inlined function Aug 24, 2018

@ianlancetaylor ianlancetaylor added this to the Go1.12 milestone Aug 24, 2018

@randall77

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randall77 commented Aug 24, 2018

Not sure what's going on here. Something with the inlining records, presumably.
The assembly instruction that does the nil dereference has the correct line number:

	0x001f 00031 (/Users/khr/gowork/issue27201.go:10)	MOVLQSX	(AX), AX

@davidlazar

@odeke-em odeke-em self-assigned this Oct 18, 2018

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