crypto/cipher: panic on s390x when len(src) == 0

[mundaym]

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

go version go1.7.1 linux/s390x

What did you do?

Encrypt an empty plaintext using AES in CBC mode.

c := cipher.NewCBCEncrypter(b, iv[:])
pt := make([]byte, 0)
c.CryptBlocks(pt, pt)
fmt.Println("ok!")

https://play.golang.org/p/InSmIcI_MT

What did you expect to see?

ok!

What did you see instead?

panic: runtime error: index out of range

goroutine 1 [running]:
panic(0xb2c00, 0x1245f0)
    /localbox/munday/go/src/runtime/panic.go:527 +0x190
crypto/aes.(*cbc).CryptBlocks(0xc42000e220, 0x14fad8, 0x0, 0x0, 0x14fad8, 0x0, 0x0)
    /localbox/munday/go/src/crypto/aes/cbc_s390x.go:51 +0xd8
main.main()
    /localbox/munday/main.go:18 +0x122
exit status 2

Will send a CL to fix (I'm working on a test now). If there is still time I'd like to get this fix into 1.7.2.

[gopherbot]

CL https://golang.org/cl/31070 mentions this issue.

[gopherbot]

CL https://golang.org/cl/31291 mentions this issue.