doc: use "high address/low address" instead of "top/bottom"

The current document uses the "top" and "bottom" when talking
about the address within a frame, which may easily lead to
misunderstandings. This patch directly uses "high address"
and "low address" to make the expression clearer.

Change-Id: I7469330bbdc158672d7f0314fe6680ebdd9ab79a
Reviewed-on: https://go-review.googlesource.com/c/go/+/339369
Trust: fannie zhang <Fannie.Zhang@arm.com>
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>

doc/asm.html

@@ -166,7 +166,7 @@ <h3 id="symbols">Symbols</h3>
 </li>
 
 <li>
-<code>SP</code>: Stack pointer: top of stack.
+<code>SP</code>: Stack pointer: the highest address within the local stack frame.
 </li>
 
 </ul>
@@ -216,7 +216,7 @@ <h3 id="symbols">Symbols</h3>
 The <code>SP</code> pseudo-register is a virtual stack pointer
 used to refer to frame-local variables and the arguments being
 prepared for function calls.
-It points to the top of the local stack frame, so references should use negative offsets
+It points to the highest address within the local stack frame, so references should use negative offsets
 in the range [−framesize, 0):
 <code>x-8(SP)</code>, <code>y-4(SP)</code>, and so on.
 </p>
@@ -409,7 +409,7 @@ <h3 id="directives">Directives</h3>
 (For <code>TEXT</code> items.)
 Don't insert the preamble to check if the stack must be split.
 The frame for the routine, plus anything it calls, must fit in the
-spare space at the top of the stack segment.
+spare space remaining in the current stack segment.
 Used to protect routines such as the stack splitting code itself.
 </li>
 <li>
@@ -460,7 +460,7 @@ <h3 id="directives">Directives</h3>
 <code>TOPFRAME</code> = 2048
 <br>
 (For <code>TEXT</code> items.)
-Function is the top of the call stack. Traceback should stop at this function.
+Function is the outermost frame of the call stack. Traceback should stop at this function.
 </li>
 </ul>
 

src/cmd/internal/obj/textflag.go

@@ -49,8 +49,8 @@ const (
 	// Function can call reflect.Type.Method or reflect.Type.MethodByName.
 	REFLECTMETHOD = 1024
 
-	// Function is the top of the call stack. Call stack unwinders should stop
-	// at this function.
+	// Function is the outermost frame of the call stack. Call stack unwinders
+	// should stop at this function.
 	TOPFRAME = 2048
 
 	// Function is an ABI wrapper.

src/runtime/textflag.h

@@ -32,8 +32,8 @@
 #define NOFRAME 512
 // Function can call reflect.Type.Method or reflect.Type.MethodByName.
 #define REFLECTMETHOD 1024
-// Function is the top of the call stack. Call stack unwinders should stop
-// at this function.
+// Function is the outermost frame of the call stack. Call stack unwinders
+// should stop at this function.
 #define TOPFRAME 2048
 // Function is an ABI wrapper.
 #define ABIWRAPPER 4096