cmd/gc: closure variables have invalid offset in debug info

[DanielMorsing]

Compile the following program

package main

func main() {
        var y int
        var foo = func(){
                y = 10
        }
        foo()
}

which turns into

--- prog list "func·001" ---
0014 (a.go:5) TEXT    func·001+0(SB),$0-0
0015 (a.go:5) LOCALS  ,$0
0016 (a.go:5) TYPE    &y+-1000000000(SP){*int},$8
0017 (a.go:5) MOVQ    8(DX),BX
0018 (a.go:6) MOVQ    $10,(BX)
0019 (a.go:5) RET     ,

The offset from the type instruction makes it into the debug info, causing a segfault
when doing "info locals" in gdb

[rsc]

Comment 1:

All yours if you want to fix it. :-)

[DanielMorsing]

Comment 2:

After some late night hacking, I've found out that this is a bigger job than anticipated.
There's some work involved in both telling the linker which closure variables there are
and how to put out the right DWARF code to dereference the context register.

[DanielMorsing]

Comment 3:

The closure part of this bug is actually irrelevant. For any function where all locals
are optimized away, their type instructions would stay in the stream.
I have a fix at https://golang.org/cl/7385055

Status changed to Started.

[DanielMorsing]

Comment 4:

This issue was closed by revision 43c04ba.

Status changed to Fixed.