cmd/compile: DW_AT_decl_line ignores //line directives

[heschi]

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

go version devel +4558321eb2 Mon Feb 5 18:37:02 2018 +0000 linux/amd64

Does this issue reproduce with the latest release?

No, 1.9 doesn't have DW_AT_decl_line

What did you do?

$ cat > linedir.go
package main

func main() {
//line /foobar.go:200
	s := "hi world"
	println(s)
}

$ go build -gcflags="-N -l" linedir.go
$ readelf --debug-dump=info linedir

What did you expect to see?

DW_AT_decl_line 200

What did you see instead?

 <2><31721>: Abbrev Number: 9 (DW_TAG_variable)
    <31722>   DW_AT_name        : s
    <31724>   DW_AT_decl_line   : 5
    <31725>   DW_AT_type        : <0x23901>
    <31729>   DW_AT_location    : 2 byte block: 91 60   (DW_OP_fbreg: -32)

I verified that if I introduce a syntax error the compiler reports it at 200:

# command-line-arguments
/foobar.go:200: syntax error: unexpected ! at end of statement

@thanm Presumably this boils down to

go/src/cmd/compile/internal/gc/pgen.go

Line 422 in 4558321

declpos := Ctxt.InnermostPos(n.Pos)

returning the wrong thing somehow; any ideas how to fix it?

[thanm]

I'd be happy to poke and it and see what I can find out. Off the top of my head I am not sure what the issue is (the code on line 422 is just picking the pos off the autom).

[heschi]

I was mostly just hoping you knew more about the way position information works than I did. Maybe @griesemer or @mdempsky can help?

[thanm]

It looks as though perhaps the DWARF code should be using

			DeclFile:      declpos.RelFilename(),
			DeclLine:      declpos.RelLine(),

instead of the existing

			DeclFile:      declpos.Base().SymFilename(),
			DeclLine:      declpos.Line(),

?

[heschi]

Good call. I looked at DW_AT_decl_file for functions, and it seems that's already correct, though I don't see how it happens exactly. You want to send the CL or shall I?

[gopherbot]

Change https://golang.org/cl/92255 mentions this issue: compiler: honor //line directives in DWARF variable file/line attrs