svn commit: r306319 - head/sys/i386/i386

[Bruce Evans]

Author: bde
Date: Sun Sep 25 18:39:24 2016
New Revision: 306319
URL: https://svnweb.freebsd.org/changeset/base/306319

Log:
  Minor fixes for 160-bit disassembly:
  
  (1) Print the default segment %ss before adresses relative to %bp.
      This is too cluttered for me, but so is printing some other default
      prefixes, and this is a reasonable reminder that %ss is quite
      likely to be different from %ds in 16-bit mode.
  
      db_disasm still handles prefixes poorly, by trying to discard
      redundant ones.  This loses information, and sometimes the result
      is wrong or misleading.
  
      Clean up nearby initializations and dead code.
  
  (2) Fix decoding of operand and address size prefixes in 16-bit mode.
      They reverse the default in all modes.
  
  Obtained from:            (1) is partly from r1.4 (2003/11/08) in DFlyBSD (?)

Modified:
  head/sys/i386/i386/db_disasm.c

Modified: head/sys/i386/i386/db_disasm.c
==============================================================================
--- head/sys/i386/i386/db_disasm.c	Sun Sep 25 18:29:02 2016	(r306318)
+++ head/sys/i386/i386/db_disasm.c	Sun Sep 25 18:39:24 2016	(r306319)
@@ -884,6 +884,7 @@ struct i_addr {
 	const char *	base;
 	const char *	index;
 	int		ss;
+	bool		defss;	/* set if %ss is the default segment */
 };
 
 static const char * const db_index_reg_16[8] = {
@@ -955,10 +956,12 @@ db_read_address(loc, short_addr, regmodr
 	}
 	addrp->is_reg = FALSE;
 	addrp->index = NULL;
+	addrp->ss = 0;
+	addrp->defss = FALSE;
 
 	if (short_addr) {
-	    addrp->index = NULL;
-	    addrp->ss = 0;
+	    if (rm == 2 || rm == 3 || (rm == 6 && mod != 0))
+		addrp->defss = TRUE;
 	    switch (mod) {
 		case 0:
 		    if (rm == 6) {
@@ -985,7 +988,7 @@ db_read_address(loc, short_addr, regmodr
 	    }
 	}
 	else {
-	    if (mod != 3 && rm == 4) {
+	    if (rm == 4) {
 		get_value_inc(sib, loc, 1, FALSE);
 		rm = sib_base(sib);
 		index = sib_index(sib);
@@ -1036,6 +1039,9 @@ db_print_address(seg, size, addrp)
 	if (seg) {
 	    db_printf("%s:", seg);
 	}
+	else if (addrp->defss) {
+	    db_printf("%%ss:");
+	}
 
 	db_printsym((db_addr_t)addrp->disp, DB_STGY_ANY);
 	if (addrp->base != NULL || addrp->index != NULL) {
@@ -1189,11 +1195,11 @@ db_disasm(db_addr_t loc, bool altfmt)
 	prefix = TRUE;
 	do {
 	    switch (inst) {
-		case 0x66:		/* data16 */
-		    size = WORD;
+		case 0x66:
+		    size = (altfmt ? LONG : WORD);
 		    break;
 		case 0x67:
-		    short_addr = TRUE;
+		    short_addr = !altfmt;
 		    break;
 		case 0x26:
 		    seg = "%es";