cmd/link: runtime error: index out of range

[bradfitz]

Seen at http://build.golang.org/log/9c020399c951339481c3f765bc35974c7dacf548 for openbsd-amd64-gce56 at 0d0ce8a

The linker crashed?

##### Testing packages.
ok      archive/tar 0.035s
ok      archive/zip 0.976s
ok      bufio   0.183s
ok      bytes   0.154s
ok      compress/bzip2  0.088s
ok      compress/flate  1.234s
ok      compress/gzip   0.014s
ok      compress/lzw    0.105s
ok      compress/zlib   2.157s
ok      container/heap  0.008s
ok      container/list  0.008s
ok      container/ring  0.020s
ok      crypto/aes  0.046s
ok      crypto/cipher   0.010s
ok      crypto/des  0.043s
ok      crypto/dsa  0.010s
ok      crypto/ecdsa    0.052s
ok      crypto/elliptic 0.084s
ok      crypto/hmac 0.009s
ok      crypto/md5  0.010s
ok      crypto/rand 0.045s
ok      crypto/rc4  0.172s
# testmain
panic: runtime error: index out of range

goroutine 1 [running]:
cmd/link/internal/ld.genasmsym(0x6d2cc0)
    /tmp/workdir/go/src/cmd/link/internal/ld/lib.go:1752 +0xe0e
cmd/link/internal/ld.Asmelfsym()
    /tmp/workdir/go/src/cmd/link/internal/ld/symtab.go:200 +0x71
cmd/link/internal/amd64.asmb()
    /tmp/workdir/go/src/cmd/link/internal/amd64/asm.go:735 +0x10ed
cmd/link/internal/ld.Ldmain()
    /tmp/workdir/go/src/cmd/link/internal/ld/pobj.go:245 +0x1ed1
cmd/link/internal/amd64.Main()
    /tmp/workdir/go/src/cmd/link/internal/amd64/obj.go:44 +0x19
main.main()
    /tmp/workdir/go/src/cmd/link/main.go:26 +0x189
ok      crypto/rsa  0.229s
FAIL    crypto/sha1 [build failed]
ok      crypto/sha256   0.009s
ok      crypto/sha512   0.041s
ok      crypto/subtle   0.019s
ok      crypto/tls  2.075s
ok      crypto/x509 2.003s
ok      database/sql    0.342s
ok      database/sql/driver 0.058s
ok      debug/dwarf 0.027s
ok      debug/elf   0.025s
ok      debug/gosym 0.376s
2015/06/12 06:27:45 Failed: exit status 2

/cc @rsc

[bradfitz]

Line 1752 is the second line here:

        for s := Ctxt.Allsym; s != nil; s = s.Allsym {  
                if s.Hide != 0 || (s.Name[0] == '.' && s.Version == 0 && s.Name != ".rathole") {  
                        continue  
                }  

So s.Name is the empty string?

[bradfitz]

@aclements, memory corruption in the GC?

[aclements]

@bradfitz, not impossible, but that's also an easy conclusion to jump to. :) Unfortunately, it looks like this is the only time this has happened, so there's not much data to go by. Are there any goroutines or potential sources of non-determinism in the linker itself?

[bradfitz]

The compiler and linker are both still single-threaded programs as far as I know, and I've never seen this before (and it was a random occurrence in the middle of other unrelated commits where the build passed), which makes me suspect memory corruption.

[rsc]

Going to close unless we can reproduce. We have plenty of memory corruption bugs, many of them fixed.