Before, the mheap structure was in the bss,
but it's quite large (today, 256 MB, much of
which is never actually paged in), and it makes
Go binaries run afoul of exec-time bss size
limits on some BSD systems.
Fixes#4447.
R=golang-dev, dave, minux.ma, remyoudompheng, iant
CC=golang-dev
https://golang.org/cl/7307122
* Separate internal and external LockOSThread, for cgo safety.
* Show goroutine that made faulting cgo call.
* Never start a panic due to a signal caused by a cgo call.
Fixes#3774.
Fixes#3775.
Fixes#3797.
R=golang-dev, iant
CC=golang-dev
https://golang.org/cl/7228081
Useful for debugging of runtime bugs.
+ Do not print "stack segment boundary" unless GOTRACEBACK>1.
+ Do not traceback system goroutines unless GOTRACEBACK>1.
R=rsc, minux.ma
CC=golang-dev
https://golang.org/cl/7098050