code review 6569068: pkg/runtime: Plan 9: add support for recover() and pani...

src/pkg/runtime/stack.h

 // Copyright 2011 The Go Authors.  All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
 /*
 Stack layout parameters.
 Included both by runtime (compiled via 6c) and linkers (compiled via gcc).
 
 The per-goroutine g->stackguard is set to point StackGuard bytes
 above the bottom of the stack.  Each function compares its stack
@@ skipping 37 matching lines @@
 section of the stack.  On amd64, morestack's frame is 40 bytes, and
 deferproc's frame is 56 bytes.  That fits well within the
 StackGuard - StackSmall = 128 bytes at the bottom.··
 The linkers explore all possible call traces involving non-splitting
 functions to make sure that this limit cannot be violated.
  */
 
 enum {
         // StackSystem is a number of additional bytes to add
         // to each stack below the usual guard area for OS-specific
-        // purposes like signal handling. Used on Windows because
-        // it does not use a separate stack.
+        // purposes like signal handling. Used on Windows and on
+        // Plan 9 because they do not use a separate stack.
 #ifdef GOOS_windows
         StackSystem = 512 * sizeof(uintptr),
 #else
 #ifdef GOOS_plan9
+        // The size of the note handler frame varies among architectures,
+        // but 512 bytes should be enough for every implementation.
         StackSystem = 512,
 #else
         StackSystem = 0,
 #endif  // Plan 9
 #endif  // Windows
 
         // The amount of extra stack to allocate beyond the size
         // needed for the single frame that triggered the split.
         StackExtra = 1024,
 
@@ skipping 23 matching lines @@
 
         // The maximum number of bytes that a chain of NOSPLIT
         // functions can use.
         StackLimit = StackGuard - StackSystem - StackSmall,
 ········
         // The assumed size of the top-of-stack data block.
         // The actual size can be smaller than this but cannot be larger.
         // Checked in proc.c's runtime.malg.
         StackTop = 72,
 };