crypto/rsa: fix out-of-bound access with short session keys.

Thanks to Cedric Staub for noting that a short session key would lead
to an out-of-bounds access when conditionally copying the too short
buffer over the random session key.

LGTM=davidben, bradfitz
R=davidben, bradfitz
CC=golang-codereviews
https://codereview.appspot.com/102670044
archive/tar: reuse temporary buffer in writeHeader

A temporary 512 bytes buffer is allocated for every call to
writeHeader. This buffer could be reused the lower the number
of memory allocations.

benchmark                   old ns/op     new ns/op     delta
BenchmarkWriteFiles100k     634622051     583810847     -8.01%

benchmark                   old allocs     new allocs     delta
BenchmarkWriteFiles100k     2701920        2602621        -3.68%

benchmark                   old bytes     new bytes     delta
BenchmarkWriteFiles100k     115383884     64349922      -44.23%

This change is very important if your code has to write a lot of
tarballs with a lot of files.

LGTM=dsymonds
R=golang-codereviews, dave, dsymonds
CC=golang-codereviews
https://codereview.appspot.com/107440043

Committer: David Symonds <dsymonds@golang.org>
archive/tar: reuse temporary buffer in readHeader

A temporary 512 bytes buffer is allocated for every call to
readHeader. This buffer isn't returned to the caller and it could
be reused to lower the number of memory allocations.

This CL improves it by using a pool and zeroing out the buffer before
putting it back into the pool.

benchmark                  old ns/op     new ns/op     delta
BenchmarkListFiles100k     545249903     538832687     -1.18%

benchmark                  old allocs    new allocs    delta
BenchmarkListFiles100k     2105167       2005692       -4.73%

benchmark                  old bytes     new bytes     delta
BenchmarkListFiles100k     105903472     54831527      -48.22%

This improvement is very important if your code has to deal with a lot
of tarballs which contain a lot of files.

LGTM=dsymonds
R=golang-codereviews, dave, dsymonds, bradfitz
CC=golang-codereviews
https://codereview.appspot.com/108240044

Committer: David Symonds <dsymonds@golang.org>
runtime: make runtime·usleep and runtime·osyield callable from cgo callback

runtime·usleep and runtime·osyield fall back to calling an
assembly wrapper for the libc functions in the absence of a m,
so they can be called in cgo callback context.

LGTM=rsc
R=minux.ma, rsc
CC=dave, golang-codereviews
https://codereview.appspot.com/102620044

Committer: Dave Cheney <dave@cheney.net>
crypto/x509: fix format strings in test
Currently it says:
--- PASS: TestDecrypt-2 (0.11s)
pem_decrypt_test.go:17: test 0. %!s(x509.PEMCipher=1)
--- PASS: TestEncrypt-2 (0.00s)
pem_decrypt_test.go:42: test 0. %!s(x509.PEMCipher=1)

LGTM=alex.brainman
R=golang-codereviews, alex.brainman
CC=golang-codereviews
https://codereview.appspot.com/108400044
runtime: delete unnecessary confusing code
The code in GC that handles gp->gobuf.ctxt is wrong,
because it does not mark the ctxt object itself,
if just queues the ctxt object for scanning.
So the ctxt object can be collected as garbage.
However, Gobuf.ctxt is void*, so it's always marked and
scanned through G.

LGTM=khr
R=golang-codereviews, khr
CC=golang-codereviews, khr, rsc
https://codereview.appspot.com/105490044
cmd/go, cmd/ld, runtime, os/user: TLS emulation for android

Based on cl/69170045 by Elias Naur.

There are currently several schemes for acquiring a TLS
slot to save the g register. None of them appear to work
for android. The closest are linux and darwin.

Linux uses a linker TLS relocation. This is not supported
by the android linker.

Darwin uses a fixed offset, and calls pthread_key_create
until it gets the slot it wants. As the runtime loads
late in the android process lifecycle, after an
arbitrary number of other libraries, we cannot rely on
any particular slot being available.

So we call pthread_key_create, take the first slot we are
given, and put it in runtime.tlsg, which we turn into a
regular variable in cmd/ld.

Makes android/arm cgo binaries work.

LGTM=minux
R=elias.naur, minux, dave, josharian
CC=golang-codereviews
https://codereview.appspot.com/106380043
runtime/cgo: revert use of undefined logging function

It snuck into cl/106380043. Too many active clients.

LGTM=ruiu
R=golang-codereviews, ruiu
CC=golang-codereviews
https://codereview.appspot.com/110830045
doc/contribute: reorder documented steps to match normal workflow.

LGTM=adg
R=golang-codereviews, bradfitz, adg
CC=golang-codereviews
https://codereview.appspot.com/109970043

Committer: Shenghou Ma <minux@golang.org>
runtime/cgo: replace fprintf(stderr, ...) with fatalf(...) for linux/android

Both stdout and stderr are sent to /dev/null in android
apps. Introducing fatalf allows android to implement its
own copy that sends fatal errors to __android_log_print.

LGTM=minux, dave
R=minux, dave
CC=golang-codereviews
https://codereview.appspot.com/108400045