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Decode function entry mask on VAXen


Hi!

An entry point of a function on a VAX is a bit different compared to
those of other CPUs: at the address of the entry point the CPU won't
find the first instruction to execute, but a 2 byte long bit mask
indicating the registers to be pushed onto the stack prior function
execution (basically, this is all registers used in that function,
except registers 0+1, which are used for the return value, as well
as stack/frame/argument pointer and PC).

Unfortunately, objdump didn't honor the entry mask, disassembling it
as regular instructions. In some cases, the first (two) bytes won't
make one two-byte (or two one-byte) instructions, thus mixing up the
remaining functional part of the function.

I'd like to see a patch like this installed, please comment on it.
(A changelog entry is however missing...):

diff -Nurp ../cvs-repos/binutils/binutils-upstream-HEAD/binutils/objdump.c src/binutils/objdump.c
--- ../cvs-repos/binutils/binutils-upstream-HEAD/binutils/objdump.c	2005-03-01 16:18:42.000000000 +0100
+++ src/binutils/objdump.c	2005-03-08 02:53:26.000000000 +0100
@@ -1379,7 +1379,11 @@ disassemble_bytes (struct disassemble_in
 	      info->stream = (FILE *) &sfile;
 	      info->bytes_per_line = 0;
 	      info->bytes_per_chunk = 0;
-	      info->flags = 0;
+	      info->last_symbol_address = section->vma + start_offset;
+	      if (disassemble && disassemble_all)
+		info->flags = FORCE_DISASSEMBLE;
+	      else
+		info->flags = 0;
 
 #ifdef DISASSEMBLER_NEEDS_RELOCS
 	      if (*relppp < relppend)
diff -Nurp ../cvs-repos/binutils/binutils-upstream-HEAD/include/dis-asm.h src/include/dis-asm.h
--- ../cvs-repos/binutils/binutils-upstream-HEAD/include/dis-asm.h	2005-03-03 12:58:01.000000000 +0100
+++ src/include/dis-asm.h	2005-03-08 01:26:23.000000000 +0100
@@ -98,7 +98,11 @@ typedef struct disassemble_info {
      The top 16 bits are reserved for public use (and are documented here).
      The bottom 16 bits are for the internal use of the disassembler.  */
   unsigned long flags;
-#define INSN_HAS_RELOC	0x80000000
+#define INSN_HAS_RELOC		0x80000000
+#define FORCE_DISASSEMBLE	0x40000000	/* Force disassembly of the
+						   address, even if it was
+						   probably better handled in
+						   a different way  */
   void *private_data;
 
   /* Function used to get bytes to disassemble.  MEMADDR is the
@@ -187,6 +191,7 @@ typedef struct disassemble_info {
   bfd_vma target;		/* Target address of branch or dref, if known;
 				   zero if unknown.  */
   bfd_vma target2;		/* Second target address for dref2 */
+  bfd_vma last_symbol_address;	/* Address of last symbol or section start  */
 
   /* Command line options specific to the target disassembler.  */
   char * disassembler_options;
diff -Nurp ../cvs-repos/binutils/binutils-upstream-HEAD/opcodes/vax-dis.c src/opcodes/vax-dis.c
--- ../cvs-repos/binutils/binutils-upstream-HEAD/opcodes/vax-dis.c	2002-05-10 01:11:30.000000000 +0200
+++ src/opcodes/vax-dis.c	2005-03-08 03:01:48.000000000 +0100
@@ -1,5 +1,5 @@
 /* Print VAX instructions.
-   Copyright 1995, 1998, 2000, 2001, 2002 Free Software Foundation, Inc.
+   Copyright 1995, 1998, 2000-2002, 2005 Free Software Foundation, Inc.
    Contributed by Pauline Middelink <middelin@polyware.iaf.nl>
 
 This program is free software; you can redistribute it and/or modify
@@ -34,6 +34,21 @@ static char *reg_names[] =
   "r8", "r9", "r10", "r11", "ap", "fp", "sp", "pc"
 };
 
+/* Definitions for the function entry mask bits.  */
+static char *entry_mask_bit[] =
+{
+  /* Registers 0 and 1 shall not be saved, since they're used to pass back
+     a function's result to it's caller...  */
+  "~r0~", "~r1~",
+  /* Registers 2 .. 11 are normal registers.  */
+  "r2", "r3", "r4", "r5", "r6", "r7", "r8", "r9", "r10", "r11",
+  /* Registers 12 and 13 are argument and frame pointer and must not
+     be saved by using the entry mask.  */
+  "~ap~", "~fp~",
+  /* Bits 14 and 15 control integer and decimal overflow.  */
+  "IntOvfl", "DecOvfl",
+};
+
 /* Sign-extend an (unsigned char). */
 #if __STDC__ == 1
 #define COERCE_SIGNED_CHAR(ch) ((signed char)(ch))
@@ -140,6 +155,26 @@ print_insn_vax (memaddr, info)
       buffer[1] = 0;
     }
 
+  /* Decode function entry mask.  */
+  if (memaddr - info->last_symbol_address < 2 &&
+		  !(info->flags & FORCE_DISASSEMBLE))
+    {
+      int i = 0;
+      int register_mask = buffer[1] << 8 | buffer[0];
+
+      (*info->fprintf_func) (info->stream, "Entry mask 0x%04x = <",
+			     register_mask);
+
+      for (i = 15; i >= 0; i--)
+	if (register_mask & (1 << i))
+          (*info->fprintf_func) (info->stream, " %s",
+			entry_mask_bit[i]);
+
+      (*info->fprintf_func) (info->stream, " >");
+
+      return 2;
+    }
+
   for (votp = &votstrs[0]; votp->name[0]; votp++)
     {
       register vax_opcodeT opcode = votp->detail.code;


My goal is to do further cleanups of the VAX code (starting with the
simple parts like converting K&R-style function heads, ...).

MfG, JBG
-- 
Look hard: my ~/.signature is well hidden! You won't find it :-)


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