Austin Clements f6bff1d587 runtime: fix undead arguments in cgocall ... From the garbage collector's perspective, time can move backwards in cgocall. However, in the midst of this time warp, the pointer arguments to cgocall can go from dead back to live. If a stack growth happens while they're dead and then a GC happens when they become live again, GC can crash with a bad heap pointer. Specifically, the sequence that leads to a panic is: 1. cgocall calls entersyscall, which saves the PC and SP of its call site in cgocall. Call this PC/SP "X". At "X" both pointer arguments are live. 2. cgocall calls asmcgocall. Call the PC/SP of this call "Y". At "Y" neither pointer argument is live. 3. asmcgocall calls the C code, which eventually calls back into the Go code. 4. cgocallbackg remembers the saved PC/SP "X" in some local variables, calls exitsyscall, and then calls cgocallbackg1. 5. The Go code causes a stack growth. This stack unwind sees PC/SP "Y" in the cgocall frame. Since the arguments are dead at "Y", they are not adjusted. 6. The Go code returns to cgocallbackg1, which calls reentersyscall with the recorded saved PC/SP "X", so "X" gets stashed back into gp.syscallpc/sp. 7. GC scans the stack. It sees there's a saved syscall PC/SP, so it starts the traceback at PC/SP "X". At "X" the arguments are considered live, so it scans them, but since they weren't adjusted, the pointers are bad, so it panics. This issue started as of commit ca4089ad, when the compiler stopped marking arguments as live for the whole function. Since this is a variable liveness issue, fix it by adding KeepAlive calls that keep the arguments live across this whole time warp. The existing issue7978 test has all of the infrastructure for testing this except that it's currently up to chance whether a stack growth happens in the callback (it currently only happens on the linux-amd64-noopt builder, for example). Update this test to force a stack growth, which causes it to fail reliably without this fix. Fixes #17785. Change-Id: If706963819ee7814e6705693247bcb97a6f7adb8 Reviewed-on: https://go-review.googlesource.com/33710 Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org> Reviewed-by: Keith Randall <khr@golang.org>		2016-11-30 17:09:17 +00:00
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android	misc/android: make the exec wrapper exit code parsing more robust	2016-06-08 05:24:53 +00:00
arm	all: make copyright headers consistent with one space after period	2016-05-02 13:43:18 +00:00
cgo	runtime: fix undead arguments in cgocall	2016-11-30 17:09:17 +00:00
chrome/gophertool
git
ios
linkcheck
nacl	cmd/dist: use debug/pe directly for cmd/link	2016-10-17 15:22:17 +00:00
sortac
swig	all: make copyright headers consistent with one space after period	2016-05-02 13:43:18 +00:00
trace	misc/trace: disable trace resolution warning	2016-07-21 18:17:31 +00:00
benchcmp
editors