image/draw: linux/arm64 segfault

[crawshaw]

The builder has little to say:

signal: segmentation fault (core dumped)
FAIL    image/draw  0.367s

Appears to be independent of other failures, will investigate tomorrow.

[crawshaw]

@4ad are you planning on looking at this? If so, I'll avoid duplicating your work. :-)

[4ad]

I can take a look, but only on Saturday, so if you want to look into it sooner, go ahead.

[crawshaw]

This is the simplest reproduction I could come up with without digging into compiler diagnostics. It prints signal: segmentation fault on linux/arm64, running from tip.

package main

var ch  = make(chan bool)

func main() {
    f()
    go g()
    <-ch
}

func g() {
    defer func() {
        r := recover()
        if r != nil {
            panic(r)
        }
        close(ch)
    }()
    f()
}

func f() {
    i1 := 8
    srcb := make([]byte, i1)
    dstb := make([]byte, i1)
    d0 := 0
    s0 := 0
    ddelta := 1
    sdelta := 1
    idelta := 1
    i0 := 0
    for dy := 1; dy > 0; dy-- {
        dpix := dstb[d0:]
        spix := srcb[s0:]
        for i := i0; i != i1; i += idelta {
            var sr, sg, sb, sa byte

            var dr, dg, db, da byte

            _ = spix[i]
            _ = dpix[i]
            _ = sa
            _ = dr
            _ = sr
            _ = dg
            _ = sg
            _ = db
            _ = sb
            _ = da
            _ = sa
        }
    }

    _ = ddelta
    _ = sdelta
}