cmd/link: panic: runtime error: index out of range

[bradfitz]

Noticed during a trybot run on openbsd-386 at f09a660:

https://storage.googleapis.com/go-build-log/98a8c347/openbsd-386-gce56_e093cb69.log

...
?       cmd/pprof/internal/tempfile [no test files]
?       cmd/trace   [no test files]
?       cmd/yacc    [no test files]

##### GOMAXPROCS=2 runtime -cpu=1,2,4
--- FAIL: TestGcSys-4 (0.58s)
    crash_test.go:92: building source: exit status 2
        # _/tmp/go-build672872450
        panic: runtime error: index out of range

        goroutine 1 [running]:
        cmd/internal/ld.getvarint(0x192adda8, 0x6f)
            /tmp/buildlet-scatch822141721/go/src/cmd/internal/ld/pcln.go:46 +0x11b
        cmd/internal/ld.pciternext(0x192add9c)
            /tmp/buildlet-scatch822141721/go/src/cmd/internal/ld/pcln.go:81 +0xea
        cmd/internal/ld.stkcheck(0x1866a950, 0x0, 0x0)
            /tmp/buildlet-scatch822141721/go/src/cmd/internal/ld/lib.go:1456 +0x437
        cmd/internal/ld.dostkcheck()
            /tmp/buildlet-scatch822141721/go/src/cmd/internal/ld/lib.go:1400 +0x1b9
        cmd/internal/ld.Ldmain()
            /tmp/buildlet-scatch822141721/go/src/cmd/internal/ld/pobj.go:226 +0x17d2
        main.main()
            /tmp/buildlet-scatch822141721/go/src/cmd/8l/obj.go:44 +0x1d
FAIL
FAIL    runtime 109.404s
2015/05/06 09:50:46 Failed: exit status 1

Error: src/all.bash failed: exit status 1

[bradfitz]

/cc @ianlancetaylor

[rsc]

Unless this keeps happening, ascribing to fixed memory corruption.