improvement of the magic breakpoints fix #55 (#58)

bochs-emu · Aug 20, 2023 · 244033e · 244033e
1 parent b7d4445
commit 244033e
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Showing 9 changed files with 152 additions and 19 deletions.
diff --git a/bochs/.bochsrc b/bochs/.bochsrc
@@ -1271,13 +1271,22 @@ speaker: enabled=1, mode=sound, volume=15
 #=======================================================================
 # MAGIC_BREAK:
 # This enables the "magic breakpoint" feature when using the debugger.
-# The useless cpu instruction XCHG BX, BX causes Bochs to enter the
+# The useless cpu instructions XCHG %REGW, %REGW causes Bochs to enter the
 # debugger mode. This might be useful for software development.
 #
-# Example:
+# You can specify multiple at once:
+#
+# cx dx bx sp bp si di
+#
+# Example for breaking on "XCHGW %DI, %DI" or "XCHG %SP, %SP" execution
+#   magic_break: enabled=1 di sp
+#
+# If nothing is specified, the default will be used: XCHGW %BX, %BX 
 #   magic_break: enabled=1
+#
+# Note: Windows XP ntldr can cause problems with XCHGW %BX, %BX
 #=======================================================================
-#magic_break: enabled=1
+# magic_break: enabled=1
 
 #=======================================================================
 # DEBUG_SYMBOLS:

diff --git a/bochs/bochs.h b/bochs/bochs.h
@@ -287,7 +287,7 @@ typedef struct {
   bool exceptions;
   bool print_timestamps;
 #if BX_DEBUGGER
-  bool magic_break_enabled;
+  Bit8u magic_break;
 #endif
 #if BX_GDBSTUB
   bool gdbstub_enabled;

diff --git a/bochs/bx_debug/dbg_main.cc b/bochs/bx_debug/dbg_main.cc
@@ -2283,6 +2283,50 @@ void bx_dbg_lyt(void)
   bx_nest_infile(layoutpath);
 }
 
+void bx_dbg_set_magic_bp_mask(Bit8u new_mask)
+{
+  bx_dbg.magic_break = new_mask;
+  bx_dbg_print_magic_bp_mask_from_str(bx_dbg.magic_break);
+}
+
+void bx_dbg_clr_magic_bp_mask(Bit8u mask)
+{
+  bx_dbg.magic_break &= ~mask;
+  bx_dbg_print_magic_bp_mask_from_str(bx_dbg.magic_break);
+}
+
+static const char* const magic_bp_regs[] = { "ax" /* not accessible */, "cx", "dx", "bx", "sp", "bp", "si", "di" };
+
+void bx_dbg_print_magic_bp_mask_from_str(Bit8u mask)
+{
+  dbg_printf("magic breakpoint mask: 0x%x ", mask);
+
+  for (int i = 1; i < 8; i++) {
+    if (mask & (1 << i)) {
+      dbg_printf("%s ", magic_bp_regs[i]);
+    }
+  }
+
+  dbg_printf("\n");
+}
+
+Bit8u bx_dbg_get_magic_bp_mask_from_str(const char *str)
+{
+  Bit8u new_mask = 0;
+
+  if (NULL == str) {
+    return 0;
+  }
+
+  for (int i = 1; i < 8; i++) {
+    if (strstr(str, magic_bp_regs[i]) != NULL) {
+      new_mask |= (1 << i);
+    }
+  }
+
+  return new_mask;
+}
+
 void bx_dbg_print_guard_results(void)
 {
   unsigned cpu, i;
@@ -3796,7 +3840,7 @@ void bx_dbg_print_help(void)
   dbg_printf("    c|cont|continue, s|step, p|n|next, modebp, vmexitbp\n");
   dbg_printf("-*- Breakpoint management -*-\n");
   dbg_printf("    vb|vbreak, lb|lbreak, pb|pbreak|b|break, sb, sba, blist,\n");
-  dbg_printf("    bpe, bpd, d|del|delete, watch, unwatch\n");
+  dbg_printf("    bpe, bpd, d|del|delete, watch, unwatch, setmagicbps, clrmagicbps\n");
   dbg_printf("-*- CPU and memory contents -*-\n");
   dbg_printf("    x, xp, setpmem, writemem, loadmem, crc, info, deref,\n");
   dbg_printf("    r|reg|regs|registers, fp|fpu, mmx, sse, sreg, dreg, creg,\n");

diff --git a/bochs/bx_debug/debug.h b/bochs/bx_debug/debug.h
@@ -76,6 +76,10 @@ bool bx_dbg_register_debug_info(const char *devname, void *dev);
 void bx_dbg_addlyt(const char* new_layoutpath);
 void bx_dbg_remlyt(void);
 void bx_dbg_lyt(void);
+void bx_dbg_set_magic_bp_mask(Bit8u new_mask);
+void bx_dbg_clr_magic_bp_mask(Bit8u mask);
+Bit8u bx_dbg_get_magic_bp_mask_from_str(const char *str);
+void bx_dbg_print_magic_bp_mask_from_str(Bit8u mask);
 bool bx_dbg_read_linear(unsigned which_cpu, bx_address laddr, unsigned len, Bit8u *buf);
 bool bx_dbg_write_linear(unsigned which_cpu, bx_address laddr, unsigned len, Bit8u *buf);
 Bit16u bx_dbg_get_selector_value(unsigned int seg_no);

diff --git a/bochs/bx_debug/lexer.l b/bochs/bx_debug/lexer.l
@@ -146,6 +146,8 @@ read            { bxlval.sval = strdup(bxtext); return(BX_TOKEN_READ); }
 w|write         { bxlval.sval = strdup(bxtext); return(BX_TOKEN_WRITE); }
 show            { bxlval.sval = strdup(bxtext); return(BX_TOKEN_SHOW); }
 ldsym           { bxlval.sval = strdup(bxtext); return(BX_TOKEN_LOAD_SYMBOLS); }
+setmagicbps     { bxlval.sval = strdup(bxtext); return(BX_TOKEN_SET_MAGIC_BREAK_POINTS); }
+clrmagicbps     { bxlval.sval = strdup(bxtext); return(BX_TOKEN_CLEAR_MAGIC_BREAK_POINTS); }
 symbols         { bxlval.sval = strdup(bxtext); return(BX_TOKEN_SYMBOLS); }
 slist           { bxlval.sval = strdup(bxtext); return(BX_TOKEN_LIST_SYMBOLS); }
 global          { bxlval.sval = strdup(bxtext); return(BX_TOKEN_GLOBAL); }

diff --git a/bochs/bx_debug/parser.y b/bochs/bx_debug/parser.y
@@ -113,6 +113,8 @@ Bit64u eval_value;
 %token <sval> BX_TOKEN_WRITE
 %token <sval> BX_TOKEN_SHOW
 %token <sval> BX_TOKEN_LOAD_SYMBOLS
+%token <sval> BX_TOKEN_SET_MAGIC_BREAK_POINTS
+%token <sval> BX_TOKEN_CLEAR_MAGIC_BREAK_POINTS
 %token <sval> BX_TOKEN_SYMBOLS
 %token <sval> BX_TOKEN_LIST_SYMBOLS
 %token <sval> BX_TOKEN_GLOBAL
@@ -200,6 +202,8 @@ command:
     | vmexitbp_command
     | print_stack_command
     | backtrace_command
+    | set_magic_break_points_command
+    | clr_magic_break_points_command
     | watch_point_command
     | page_command
     | tlb_command
@@ -459,6 +463,32 @@ symbol_command:
       }
     ;
 
+set_magic_break_points_command:
+      BX_TOKEN_SET_MAGIC_BREAK_POINTS '\n'
+      {
+        bx_dbg_set_magic_bp_mask(0);
+        free($1);
+      }
+    | BX_TOKEN_SET_MAGIC_BREAK_POINTS BX_TOKEN_STRING '\n'
+      {
+        bx_dbg_set_magic_bp_mask(bx_dbg_get_magic_bp_mask_from_str($2));
+        free($1); free($2);
+      }
+    ;
+
+clr_magic_break_points_command:
+      BX_TOKEN_CLEAR_MAGIC_BREAK_POINTS '\n'
+      {
+        bx_dbg_set_magic_bp_mask(0);
+        free($1);
+      }
+    | BX_TOKEN_CLEAR_MAGIC_BREAK_POINTS BX_TOKEN_STRING '\n'
+      {
+        bx_dbg_clr_magic_bp_mask(bx_dbg_get_magic_bp_mask_from_str($2));
+        free($1); free($2);
+      }
+    ;
+
 where_command:
       BX_TOKEN_WHERE '\n'
       {
@@ -1158,6 +1188,16 @@ help_command:
          dbg_printf("ldsym [global] <filename> [offset] - load symbols from file\n");
          free($1);free($2);
        }
+     | BX_TOKEN_HELP BX_TOKEN_SET_MAGIC_BREAK_POINTS '\n'
+       {
+         dbg_printf("setmagicbps \"cx dx bx sp bp si di\" - set new magic breakpoints. You can specify multiple at once. Using the setmagicbps command without any arguments will disable all of them\n");
+         free($1);free($2);
+       }
+     | BX_TOKEN_HELP BX_TOKEN_CLEAR_MAGIC_BREAK_POINTS '\n'
+       {
+         dbg_printf("clrmagicbps \"cx dx bx sp bp si di\" - clear magic breakpoints. You can specify multiple at once. Using the clrmagicbps command without any arguments will disable all of them\n");
+         free($1);free($2);
+       }
      | BX_TOKEN_HELP BX_TOKEN_LIST_SYMBOLS '\n'
        {
          dbg_printf("slist [string] - list symbols whose preffix is string (same as 'info symbols')\n");

diff --git a/bochs/config.cc b/bochs/config.cc
@@ -3147,6 +3147,7 @@ static int parse_line_formatted(const char *context, int num_params, char *param
 #endif
   } else if (!strcmp(params[0], "magic_break")) {
 #if BX_DEBUGGER
+    bx_dbg.magic_break = 0;
     if (num_params != 2) {
       PARSE_ERR(("%s: magic_break directive: wrong # args.", context));
     }
@@ -3155,14 +3156,14 @@ static int parse_line_formatted(const char *context, int num_params, char *param
     }
     if (params[1][8] == '0') {
       BX_INFO(("Ignoring magic break points"));
-      bx_dbg.magic_break_enabled = 0;
-    }
-    else if (params[1][8] == '1') {
-      BX_INFO(("Stopping on magic break points"));
-      bx_dbg.magic_break_enabled = 1;
-    }
-    else {
-      PARSE_ERR(("%s: magic_break directive malformed.", context));
+    } else if (params[1][8] == '1') {
+      bx_dbg_set_magic_bp_mask(bx_dbg_get_magic_bp_mask_from_str(params[1]));
+      if (0 == bx_dbg.magic_break) {
+        // bx if not specified for backward compatibility
+        bx_dbg_set_magic_bp_mask(bx_dbg_get_magic_bp_mask_from_str("bx"));
+      }
+    } else {
+      PARSE_ERR(("%s: magic_break directive malformed", context));
     }
 #else
     PARSE_WARN(("%s: Bochs is not compiled with internal debugger support", context));
@@ -3406,7 +3407,7 @@ int bx_write_debugger_options(FILE *fp)
 {
 #if BX_DEBUGGER
   fprintf(fp, "debugger_log: %s\n", SIM->get_param_string(BXPN_DEBUGGER_LOG_FILENAME)->getptr());
-  fprintf(fp, "magic_break: enabled=%d\n", bx_dbg.magic_break_enabled);
+  fprintf(fp, "magic_break: enabled=1 0x%x\n", bx_dbg.magic_break);
   // TODO: debug symbols
 #endif
 #if BX_GDBSTUB

diff --git a/bochs/cpu/data_xfer16.cc b/bochs/cpu/data_xfer16.cc
@@ -219,9 +219,16 @@ void BX_CPP_AttrRegparmN(1) BX_CPU_C::XCHG_EwGwR(bxInstruction_c *i)
   Bit16u op1_16, op2_16;
 
 #if BX_DEBUGGER
-  // Note for mortals: the instruction to trigger this is "xchgw %bx,%bx"
-  if (bx_dbg.magic_break_enabled && (i->src() == 3) && (i->dst() == 3))
-  {
+  /* Note for mortals: the instruction to trigger this is "xchgw %regw,%regw"
+    66:87C9  | xchg cx,cx  | 1000011111 001 001 -> 1
+    66:87D2  | xchg dx,dx  | 1000011111 010 010 -> 2
+    66:87DB  | xchg bx,bx  | 1000011111 011 011 -> 3
+    66:87E4  | xchg sp,sp  | 1000011111 100 100 -> 4
+    66:87ED  | xchg bp,bp  | 1000011111 101 101 -> 5
+    66:87F6  | xchg si,si  | 1000011111 110 110 -> 6
+    66:87FF  | xchg di,di  | 1000011111 111 111 -> 7
+  */
+  if (bx_dbg.magic_break && i->src() == i->dst() && (bx_dbg.magic_break & (1 << (i->src())))) {
     BX_CPU_THIS_PTR magic_break = 1;
     BX_NEXT_INSTR(i);
   }

diff --git a/bochs/doc/docbook/user/user.dbk b/bochs/doc/docbook/user/user.dbk
@@ -5167,13 +5167,21 @@ This enables the GDB stub. See <xref linkend="debugging-with-gdb">.
 
 <section><title>magic_break</title>
 <para>
-Example:
+Example for breaking on "XCHGW %DI, %DI" or "XCHGW %SP, %SP" execution
+<screen>
+  magic_break: enabled=1 di sp
+</screen>
+If nothing is specified, the default will be used: XCHGW %BX, %BX 
+Note: Windows XP ntldr can cause problems with XCHGW %BX, %BX
 <screen>
   magic_break: enabled=1
 </screen>
 This enables the "magic breakpoint" feature when using the debugger.
-The useless cpu instruction XCHG BX, BX causes Bochs to enter the
+The useless cpu instruction XCHGW REGW, REGW causes Bochs to enter the
 debugger mode. This might be useful for software development.
+<screen>
+  cx dx bx sp bp si di
+</screen>
 </para>
 </section>
 
@@ -7391,6 +7399,24 @@ context.
 <para>
 The symbol file consists of zero or more lines of the format <screen>"%x %s"</screen>.
 
+<screen>setmagicbps "cx dx bx sp bp si di"</screen>
+
+Set new magic breakpoints. You can specify multiple at once. Using the setmagicbps command without any arguments will disable all of them
+
+Example for breaking on "XCHGW %DI, %DI" or "XCHGW %SP, %SP" execution
+<screen>
+  setmagicbps "di sp"
+</screen>
+
+<screen>clrmagicbps "cx dx bx sp bp si di"</screen>
+
+Clear magic breakpoints. You can specify multiple at once. Using the clrmagicbps command without any arguments will disable all of them
+
+Example for clearing "XCHGW %DI, %DI" and "XCHGW %SP, %SP"
+<screen>
+  clrmagicbps "di sp"
+</screen>
+
 <screen>show [<varname>string</varname>]</screen>
 
 <screen>