add comments

From-SVN: r50805

gcc/unwind-dw2.c

@@ -48,7 +48,9 @@
 #define PRE_GCC3_DWARF_FRAME_REGISTERS DWARF_FRAME_REGISTERS
 #endif
 
-/* This is the register and unwind state for a particular frame.  */
+/* This is the register and unwind state for a particular frame.  This
+   provides the information necessary to unwind up past a frame and return
+   to its caller.  */
 struct _Unwind_Context
 {
   void *reg[DWARF_FRAME_REGISTERS+1];
@@ -889,6 +891,11 @@ execute_cfa_program (const unsigned char *insn_ptr,
     }
 }
 
+/* Given the _Unwind_Context CONTEXT for a stack frame, look up the FDE for
+   its caller and decode it into FS.  This function also sets the
+   args_size and lsda members of CONTEXT, as they are really information
+   about the caller's frame.  */
+
 static _Unwind_Reason_Code
 uw_frame_state_for (struct _Unwind_Context *context, _Unwind_FrameState *fs)
 {
@@ -1083,6 +1090,11 @@ uw_update_context_1 (struct _Unwind_Context *context, _Unwind_FrameState *fs)
       }
 }
 
+/* CONTEXT describes the unwind state for a frame, and FS describes the FDE
+   of its caller.  Update CONTEXT to refer to the caller as well.  Note
+   that the args_size and lsda members are not updated here, but later in
+   uw_frame_state_for.  */
+
 static void
 uw_update_context (struct _Unwind_Context *context, _Unwind_FrameState *fs)
 {

gcc/unwind.inc

@@ -72,7 +72,6 @@ _Unwind_RaiseException_Phase2(struct _Unwind_Exception *exc,
   return code;
 }
 
-
 /* Raise an exception, passing along the given exception object.  */
 
 _Unwind_Reason_Code
@@ -81,6 +80,7 @@ _Unwind_RaiseException(struct _Unwind_Exception *exc)
   struct _Unwind_Context this_context, cur_context;
   _Unwind_Reason_Code code;
 
+  /* Set up this_context to describe the current stack frame.  */
   uw_init_context (&this_context);
   cur_context = this_context;
 
@@ -90,6 +90,8 @@ _Unwind_RaiseException(struct _Unwind_Exception *exc)
     {
       _Unwind_FrameState fs;
 
+      /* Set up fs to describe the FDE for the caller of cur_context.  The
+	 first time through the loop, that means __cxa_throw.  */
       code = uw_frame_state_for (&cur_context, &fs);
 
       if (code == _URC_END_OF_STACK)
@@ -112,6 +114,7 @@ _Unwind_RaiseException(struct _Unwind_Exception *exc)
 	    return _URC_FATAL_PHASE1_ERROR;
 	}
 
+      /* Update cur_context to describe the same frame as fs.  */
       uw_update_context (&cur_context, &fs);
     }
 
@@ -144,6 +147,7 @@ _Unwind_ForcedUnwind_Phase2(struct _Unwind_Exception *exc,
       _Unwind_FrameState fs;
       int action;
 
+      /* Set up fs to describe the FDE for the caller of cur_context.  */
       code = uw_frame_state_for (context, &fs);
       if (code != _URC_NO_REASON && code != _URC_END_OF_STACK)
 	return _URC_FATAL_PHASE2_ERROR;
@@ -172,6 +176,7 @@ _Unwind_ForcedUnwind_Phase2(struct _Unwind_Exception *exc,
 	    return _URC_FATAL_PHASE2_ERROR;
 	}
 
+      /* Update cur_context to describe the same frame as fs.  */
       uw_update_context (context, &fs);
     }