* mn10300-tdep.c (mn10300_analyze_prologue): Doc fixes.

1 files changed, 55 insertions, 11 deletions

diff --git a/gdb/mn10300-tdep.c b/gdb/mn10300-tdep.c
index 472e260..1e684f8 100644
--- a/gdb/mn10300-tdep.c
+++ b/gdb/mn10300-tdep.c
@@ -291,16 +291,59 @@ set_movm_offsets (struct frame_info *fi, int movm_args)
 /* The main purpose of this file is dealing with prologues to extract
    information about stack frames and saved registers.
 
-   For reference here's how prologues look on the mn10300:
+   In gcc/config/mn13000/mn10300.c, the expand_prologue prologue
+   function is pretty readable, and has a nice explanation of how the
+   prologue is generated.  The prologues generated by that code will
+   have the following form:
 
-   With frame pointer:
-   movm [d2,d3,a2,a3],sp
-   mov sp,a3
-   add <size>,sp
+   + If this is an old-style varargs function, then its arguments
+     need to be flushed back to the stack:
+     
+        mov d0,(4,sp)
+        mov d1,(4,sp)
 
-   Without frame pointer:
-   movm [d2,d3,a2,a3],sp (if needed)
-   add <size>,sp
+   + If we use any of the callee-saved registers, save them now.
+     
+        movm [some callee-saved registers],(sp)
+
+   + If we have any floating-point registers to save:
+
+     - Decrement the stack pointer to reserve space for the registers.
+       If the function doesn't need a frame pointer, we may combine
+       this with the adjustment that reserves space for the frame.
+
+        add -SIZE, sp
+
+     - Save the floating-point registers.  We have two possible
+       strategies:
+
+       . Save them at fixed offset from the SP:
+
+        fmov fsN,(OFFSETN,sp)
+        fmov fsM,(OFFSETM,sp)
+        ...
+
+       . Or, set a0 to the start of the save area, and then use
+       post-increment addressing to save the FP registers.
+
+        mov sp, a0
+        add SIZE, a0
+        fmov fsN,(a0+)
+        fmov fsM,(a0+)
+        ...
+
+   + If the function needs a frame pointer, we set it here.
+
+        mov sp, a3
+
+   + Now we reserve space for the stack frame proper.  This could be
+     merged into the `add -SIZE, sp' instruction for FP saves up
+     above, unless we needed to set the frame pointer in the previous
+     step, or the frame is so large that allocating the whole thing at
+     once would put the FP register save slots out of reach of the
+     addressing mode (128 bytes).
+      
+        add -SIZE, sp        
 
    One day we might keep the stack pointer constant, that won't
    change the code for prologues, but it will make the frame
@@ -330,7 +373,7 @@ set_movm_offsets (struct frame_info *fi, int movm_args)
    save instructions.
 
    MY_FRAME_IN_FP: The base of the current frame is in the
-   frame pointer register ($a2).
+   frame pointer register ($a3).
 
    NO_MORE_FRAMES: Set this if the current frame is "start" or
    if the first instruction looks like mov <imm>,sp.  This tells
@@ -416,8 +459,9 @@ mn10300_analyze_prologue (struct frame_info *fi, CORE_ADDR pc)
       return addr;
     }
 
-  /* First see if this insn sets the stack pointer; if so, it's something
-     we won't understand, so quit now.   */
+  /* First see if this insn sets the stack pointer from a register; if
+     so, it's probably the initialization of the stack pointer in _start,
+     so mark this as the bottom-most frame.  */
   if (buf[0] == 0xf2 && (buf[1] & 0xf3) == 0xf0)
     {
       if (fi)