1 files changed, 119 insertions, 0 deletions
diff --git a/src/runtime/stack.h b/src/runtime/stack.h
new file mode 100644
index 000000000..7f8c43ee5
--- /dev/null
+++ b/src/runtime/stack.h
@@ -0,0 +1,119 @@
+// 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
+pointer against g->stackguard to check for overflow.  To cut one
+instruction from the check sequence for functions with tiny frames,
+the stack is allowed to protrude StackSmall bytes below the stack
+guard.  Functions with large frames don't bother with the check and
+always call morestack.  The sequences are (for amd64, others are
+similar):
+ 
+	guard = g->stackguard
+	frame = function's stack frame size
+	argsize = size of function arguments (call + return)
+
+	stack frame size <= StackSmall:
+		CMPQ guard, SP
+		JHI 3(PC)
+		MOVQ m->morearg, $(argsize << 32)
+		CALL morestack(SB)
+
+	stack frame size > StackSmall but < StackBig
+		LEAQ (frame-StackSmall)(SP), R0
+		CMPQ guard, R0
+		JHI 3(PC)
+		MOVQ m->morearg, $(argsize << 32)
+		CALL morestack(SB)
+
+	stack frame size >= StackBig:
+		MOVQ m->morearg, $((argsize << 32) | frame)
+		CALL morestack(SB)
+
+The bottom StackGuard - StackSmall bytes are important: there has
+to be enough room to execute functions that refuse to check for
+stack overflow, either because they need to be adjacent to the
+actual caller's frame (deferproc) or because they handle the imminent
+stack overflow (morestack).
+
+For example, deferproc might call malloc, which does one of the
+above checks (without allocating a full frame), which might trigger
+a call to morestack.  This sequence needs to fit in the bottom
+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 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 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 = 2048,
+
+	// The minimum stack segment size to allocate.
+	// If the amount needed for the splitting frame + StackExtra
+	// is less than this number, the stack will have this size instead.
+	StackMin = 8192,
+	StackSystemRounded = StackSystem + (-StackSystem & (StackMin-1)),
+	FixedStack = StackMin + StackSystemRounded,
+
+	// Functions that need frames bigger than this use an extra
+	// instruction to do the stack split check, to avoid overflow
+	// in case SP - framesize wraps below zero.
+	// This value can be no bigger than the size of the unmapped
+	// space at zero.
+	StackBig = 4096,
+
+	// The stack guard is a pointer this many bytes above the
+	// bottom of the stack.
+	StackGuard = 512 + StackSystem,
+
+	// After a stack split check the SP is allowed to be this
+	// many bytes below the stack guard.  This saves an instruction
+	// in the checking sequence for tiny frames.
+	StackSmall = 128,
+
+	// 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 = 88,
+};
+
+// Goroutine preemption request.
+// Stored into g->stackguard0 to cause split stack check failure.
+// Must be greater than any real sp.
+// 0xfffffade in hex.
+#define StackPreempt ((uint64)-1314)
+/*c2go
+enum
+{
+	StackPreempt = -1314,
+};
+*/