Issue 1:
linux-amd64 trybot crash here, with git parent 7837418:

https://storage.googleapis.com/go-build-log/ea276538/linux-amd64_e00cadd4.log

...
ok crypto/subtle 0.006s
unexpected fault address 0x0
fatal error: fault
[signal 0x7 code=0x80 addr=0x0 pc=0x55c755]

goroutine 36 [running]:
runtime.throw(0x70f852, 0x5)
/tmp/workdir/go/src/runtime/panic.go:566 +0x8c fp=0xc8201ed2b0 sp=0xc8201ed298
runtime.sigpanic()
/tmp/workdir/go/src/runtime/sigpanic_unix.go:21 +0xe8 fp=0xc8201ed300 sp=0xc8201ed2b0
math/big.nat.cmp(0xdeaddeaddeaddead, 0x9, 0x1e, 0xc82007a410, 0x9, 0xa, 0x9)
/tmp/workdir/go/src/math/big/nat.go:162 +0x45 fp=0xc8201ed308 sp=0xc8201ed300
math/big.nat.div(0x0, 0x0, 0x0, 0xdeaddeaddeaddead, 0x9, 0x1e, 0xdeaddeaddeaddead, 0x9, 0x1e, 0xc82007a410, ...)
/tmp/workdir/go/src/math/big/nat.go:525 +0x7b fp=0xc8201ed3c8 sp=0xc8201ed308
math/big.(*Int).QuoRem(0xc8201ed4b0, 0xc8203ac200, 0xc82000e920, 0xc8203ac200, 0xc820012840, 0xc82039c920)
/tmp/workdir/go/src/math/big/int.go:227 +0xaf fp=0xc8201ed478 sp=0xc8201ed3c8
math/big.(*Int).Mod(0xc8203ac200, 0xc8203ac200, 0xc82000e920, 0xc82039c8a0)
/tmp/workdir/go/src/math/big/int.go:258 +0xcf fp=0xc8201ed4f8 sp=0xc8201ed478
crypto/ecdsa.Verify(0xc8201b1900, 0xc8201b1de0, 0x14, 0x20, 0xc8201b1e00, 0xc8201b1e20, 0x0)
/tmp/workdir/go/src/crypto/ecdsa/ecdsa.go:259 +0x405 fp=0xc8201ed608 sp=0xc8201ed4f8
crypto/tls.(*ecdheKeyAgreement).processServerKeyExchange(0xc8201aebc0, 0xc820080280, 0xc8201b23c0, 0xc8201de580, 0xc8201f0480, 0xc8201b6c30, 0x0, 0xc8201cec00)
/tmp/workdir/go/src/crypto/tls/key_agreement.go:366 +0x796 fp=0xc8201ed738 sp=0xc8201ed608
crypto/tls.(*clientHandshakeState).doFullHandshake(0xc8201edc50, 0xc8201cec60, 0x59)
/tmp/workdir/go/src/crypto/tls/handshake_client.go:318 +0x416 fp=0xc8201edaa0 sp=0xc8201ed738
crypto/tls.(*Conn).clientHandshake(0xc8201cc600, 0x72a778, 0xc8201cc614)
/tmp/workdir/go/src/crypto/tls/handshake_client.go:209 +0xec9 fp=0xc8201edd00 sp=0xc8201edaa0
crypto/tls.(*Conn).Handshake(0xc8201cc600, 0x0, 0x0)
/tmp/workdir/go/src/crypto/tls/conn.go:1031 +0x9f fp=0xc8201edd28 sp=0xc8201edd00
crypto/tls.(*Conn).Write(0xc8201cc600, 0xc8201ede70, 0x6, 0x6, 0x0, 0x0, 0x0)
/tmp/workdir/go/src/crypto/tls/conn.go:878 +0xdd fp=0xc8201eddb0 sp=0xc8201edd28
crypto/tls.(*clientTest).run.func1(0xc8201cc600, 0xc82013ecf0, 0xc8201c6b80, 0x7fc10778e7e0, 0xc8201b49a0, 0xc8201ceae0)
/tmp/workdir/go/src/crypto/tls/handshake_client_test.go:212 +0x8a fp=0xc8201edf60 sp=0xc8201eddb0
runtime.goexit()
/tmp/workdir/go/src/runtime/asm_amd64.s:2006 +0x1 fp=0xc8201edf68 sp=0xc8201edf60
created by crypto/tls.(*clientTest).run
/tmp/workdir/go/src/crypto/tls/handshake_client_test.go:223 +0x210

goroutine 1 [chan receive]:
testing.RunTests(0x72a0e8, 0x83d3e0, 0x41, 0x41, 0xc820080201)
/tmp/workdir/go/src/testing/testing.go:582 +0x359
testing.(*M).Run(0xc820031f08, 0x404cda)
/tmp/workdir/go/src/testing/testing.go:515 +0x79
main.main()
crypto/tls/_test/_testmain.go:184 +0xb4

goroutine 17 [syscall, locked to thread]:
runtime.goexit()
/tmp/workdir/go/src/runtime/asm_amd64.s:2006 +0x1

goroutine 35 [semacquire]:
sync.runtime_Syncsemacquire(0xc8201c84c0)
/tmp/workdir/go/src/runtime/sema.go:241 +0x1a0
sync.(*Cond).Wait(0xc8201c84b0)
/tmp/workdir/go/src/sync/cond.go:63 +0x69
io.(*pipe).read(0xc8201c8480, 0xc8201055f0, 0x86, 0x86, 0x0, 0x0, 0x0)
/tmp/workdir/go/src/io/pipe.go:52 +0xdc
io.(*PipeReader).Read(0xc8201ca040, 0xc8201055f0, 0x86, 0x86, 0x0, 0x0, 0x0)
/tmp/workdir/go/src/io/pipe.go:134 +0x42
io.ReadAtLeast(0x7fc10778e840, 0xc8201b49b0, 0xc8201055f0, 0x86, 0x86, 0x86, 0x0, 0x0, 0x7fc10778e840)
/tmp/workdir/go/src/io/io.go:297 +0xa3
io.ReadFull(0x7fc10778e840, 0xc8201b49b0, 0xc8201055f0, 0x86, 0x86, 0x86, 0x0, 0x0)
/tmp/workdir/go/src/io/io.go:315 +0x4e
crypto/tls.(*clientTest).run(0xc8201c6b80, 0xc82013ecf0, 0x0)
/tmp/workdir/go/src/crypto/tls/handshake_client_test.go:236 +0x7f0
crypto/tls.runClientTestForVersion(0xc82013ecf0, 0xc820033f00, 0x6f0ee0, 0x7, 0x6f0ce1, 0x5)
/tmp/workdir/go/src/crypto/tls/handshake_client_test.go:277 +0x245
crypto/tls.runClientTestTLS10(0xc82013ecf0, 0xc820033f00)
/tmp/workdir/go/src/crypto/tls/handshake_client_test.go:281 +0x55
crypto/tls.TestHandshakeClientECDHEECDSAAES(0xc82013ecf0)
/tmp/workdir/go/src/crypto/tls/handshake_client_test.go:335 +0xf1
testing.tRunner(0xc82013ecf0, 0x83d488)
/tmp/workdir/go/src/testing/testing.go:473 +0x7e
created by testing.RunTests
/tmp/workdir/go/src/testing/testing.go:581 +0x313
FAIL crypto/tls 0.155s
ok crypto/x509 1.621s
...

Issue 2:
See http://build.golang.org/log/1b98f2faca78eb97adbd218ad62fb20d3b62d8e8. But it happened only once on the freebsd-race buildbot.

unexpected fault address 0x5ec7a6
fatal error: fault
[signal 0xa code=0x3 addr=0x5ec7a6 pc=0x5ec7a6]

goroutine 23 [running]:
runtime.throw(0x7df110, 0x5)
/tmp/workdir/go/src/runtime/panic.go:549 +0x8c fp=0xc820098cf0 sp=0xc820098cd8
runtime.sigpanic()
/tmp/workdir/go/src/runtime/sigpanic_unix.go:21 +0x1ce fp=0xc820098d40 sp=0xc820098cf0
math/big.mulAddVWW(0xc8201b8070, 0x9, 0xe, 0xdeaddeaddeaddead, 0x9, 0x1e, 0x1, 0x0, 0xe, 0x9, ...)
/tmp/workdir/go/src/math/big/arith_amd64.s:331 +0x26 fp=0xc820098d48 sp=0xc820098d40
math/big.nat.mulAddWW(0x0, 0x0, 0x0, 0xdeaddeaddeaddead, 0x9, 0x1e, 0x1, 0x0, 0x9, 0xe, ...)
/tmp/workdir/go/src/math/big/nat.go:183 +0x184 fp=0xc820098db8 sp=0xc820098d48
math/big.nat.mul(0x0, 0x0, 0x0, 0xdeaddeaddeaddead, 0x9, 0x1e, 0xc8201d4060, 0x1, 0x6, 0x0, ...)
/tmp/workdir/go/src/math/big/nat.go:408 +0xac8 fp=0xc820098ea8 sp=0xc820098db8
math/big.(*Int).Mul(0xc8200990d0, 0xc8202f8580, 0xc820099130, 0xc8200990f0)
/tmp/workdir/go/src/math/big/int.go:156 +0xdf fp=0xc820098f30 sp=0xc820098ea8
crypto/elliptic.(*CurveParams).addJacobian(0xc820052800, 0xc82025dee0, 0xc82025df00, 0xc82025c000, 0xc8202f8580, 0xc8202f85a0, 0xc82025c020, 0x0, 0xc8201d5d70, 0x1)
/tmp/workdir/go/src/crypto/elliptic/elliptic.go:133 +0x420 fp=0xc820099158 sp=0xc820098f30
crypto/elliptic.(*CurveParams).Add(0xc820052800, 0xc82025dee0, 0xc82025df00, 0xc8202f8580, 0xc8202f85a0, 0x42, 0xc8202f8580)
/tmp/workdir/go/src/crypto/elliptic/elliptic.go:105 +0xaf fp=0xc8200991b8 sp=0xc820099158
crypto/ecdsa.Verify(0xc8201e90a0, 0xc8201e9580, 0x14, 0x20, 0xc8201e95a0, 0xc8201e95c0, 0x0)
/tmp/workdir/go/src/crypto/ecdsa/ecdsa.go:253 +0x73b fp=0xc8200992e8 sp=0xc8200991b8
crypto/tls.(*ecdheKeyAgreement).processServerKeyExchange(0xc8200f1d40, 0xc820084280, 0xc820085680, 0xc820089e40, 0xc8201f6000, 0xc8201d4ff0, 0x0, 0x715360)
/tmp/workdir/go/src/crypto/tls/key_agreement.go:366 +0xe82 fp=0xc8200994a0 sp=0xc8200992e8
crypto/tls.(*clientHandshakeState).doFullHandshake(0xc820099c10, 0xc8201d78c0, 0x59)
/tmp/workdir/go/src/crypto/tls/handshake_client.go:316 +0x2569 fp=0xc820099928 sp=0xc8200994a0
crypto/tls.(*Conn).clientHandshake(0xc8201dc600, 0x8508c8, 0xc8201dc614)
/tmp/workdir/go/src/crypto/tls/handshake_client.go:207 +0x19cc fp=0xc820099cc0 sp=0xc820099928
crypto/tls.(*Conn).Handshake(0xc8201dc600, 0x0, 0x0)
/tmp/workdir/go/src/crypto/tls/conn.go:1033 +0x123 fp=0xc820099d00 sp=0xc820099cc0
crypto/tls.(*Conn).Write(0xc8201dc600, 0xc820099e50, 0x6, 0x6, 0x0, 0x0, 0x0)
/tmp/workdir/go/src/crypto/tls/conn.go:880 +0xfc fp=0xc820099d90 sp=0xc820099d00
crypto/tls.(*clientTest).run.func1(0xc8201dc600, 0xc8201ea1b0, 0xc820103400, 0x800aae7b8, 0xc82010dc20, 0xc8201d7740)
/tmp/workdir/go/src/crypto/tls/handshake_client_test.go:211 +0x9b fp=0xc820099f60 sp=0xc820099d90
runtime.goexit()
/tmp/workdir/go/src/runtime/asm_amd64.s:2006 +0x1 fp=0xc820099f68 sp=0xc820099f60
created by crypto/tls.(*clientTest).run
/tmp/workdir/go/src/crypto/tls/handshake_client_test.go:222 +0x298