runtime: add precise stack scan support

    
    This CL adds support of precise stack scan using stack maps to
    the runtime. The stack maps are generated by the compiler (if
    supported). Each safepoint is associated with a (real or dummy)
    landing pad, and its "type info" in the exception table is a
    pointer to the stack map. When a stack is scanned, the stack map
    is found by the stack unwinding code by inspecting the exception
    table (LSDA).
    
    For precise stack scan we need to unwind the stack. There are
    three cases:
    
    - If a goroutine is scanning its own stack, it can unwind the
      stack and scan the frames.
    
    - If a goroutine is scanning another, stopped, goroutine, it
      cannot directly unwind the target stack. We handle this by
      switching (runtime.gogo) to the target g, letting it unwind
      and scan the stack, and switch back.
    
    - If we are scanning a goroutine that is blocked in a syscall,
      we send a signal to the target goroutine's thread, and let the
      signal handler unwind and scan the stack. Extra care is needed
      as this races with enter/exit syscall.
    
    Currently this is only implemented on linux.
    
    Reviewed-on: https://go-review.googlesource.com/c/140518

From-SVN: r266832

1 files changed, 5 insertions, 0 deletions

diff --git a/libgo/go/runtime/runtime2.go b/libgo/go/runtime/runtime2.go
index e12e832..6eb9491 100644
--- a/libgo/go/runtime/runtime2.go
+++ b/libgo/go/runtime/runtime2.go
@@ -430,6 +430,9 @@ type g struct {
 
 	scanningself bool // whether goroutine is scanning its own stack
 
+	scang   uintptr // the g that wants to scan this g's stack (uintptr to avoid write barrier)
+	scangcw uintptr // gc worker for scanning stack (uintptr to avoid write barrier)
+
 	isSystemGoroutine bool // whether goroutine is a "system" goroutine
 
 	traceback uintptr // stack traceback buffer
@@ -514,6 +517,8 @@ type m struct {
 	exiting    bool // thread is exiting
 
 	gcing int32
+
+	scannote note // synchonization for signal-based stack scanning
 }
 
 type p struct {