add more magic breakpoints fix #55 #56

therealdreg · 2023-07-24T11:34:12Z

This PR was moved to #58

Implemented support for various types of magic breakpoints, along with the ability to modify them at runtime from within the debugger. So, the Windows XP NTLDR will no longer be a problem.

fix #55

windows xp ntldr have code like this:

0000000000020252: (                    ): mov cr0, eax              ; 0f22c0
0000000000020255: (                    ): xchg bx, bx               ; 87db
0000000000020257: (                    ): nop                       ; 90

And this code is called a lot of times!

ring3 code CANT execute OUT instruction (0x8AE0)

So the ring3-dev cant use magic breakpoints on Bochs debugger (on first instance)

with this PR, the user can select what register should breaks:

#=======================================================================
# MAGIC_BREAK:
# This enables the "magic breakpoint" feature when using the debugger.
# The useless cpu instructions XCHG %REGW, %REGW causes Bochs to enter the
# debugger mode. This might be useful for software development.
#
# %cx %dx %bx %sp %bp %si %di
#
# Example for breaking on "XCHGW %DI, %DI" or "CHGW %SP, %SP" execution
#   magic_break: enabled=1 %di %sp
#
# Example for breaking on "XCHG %BX, %BX" execution (Windows XP ntldr can cause problems with %BX)
#   magic_break: enabled=1
#=======================================================================
magic_break: enabled=1 %di %sp

This PR is 100% backward compatibility

Added a new command to change from debugger the mask of registers, example adding XCHGW %DI, %DI or XCHGW %BX, %BX

setmagicbps "%di %bx"

@stlintel @vruppert do you like it?

stlintel · 2023-08-19T07:37:17Z

bochs/.bochsrc

 # debugger mode. This might be useful for software development.
 #
-# Example:
+# Register number id:
+#   0: DISABLE MAGIC_BREAK


Hi,

I haven't even notice these pull requests.
For some reason I didn't receive a notification from github,
This one is fine (with small adjustments to make to match general Bochs coding style).
How about adding capability to control/toggle them from inside the debugger interface ?
How about enabling more than one together ?
I think it should be a bitmask of 8 bits instead of bool in bx_dbg.magic_break and checking smth like
((1<dst()) & bx_dbg.magic_break)

awesome idea! I will do it :-)

therealdreg · 2023-08-19T13:23:08Z

Done, @stlintel take a look

This PR is 100% backward compatibility,

btw @stlintel who upload the new parser and lexer files? me or you?

bochs/.bochsrc

bochs/bx_debug/dbg_main.cc

stlintel · 2023-08-19T16:07:45Z

bochs/bx_debug/dbg_main.cc

+    {
+      new_mask |= 1 << 1;
+    }
+  if (strstr(str, "%sp") != NULL)


why do you think strstr is better than strcmp ?
in your case %spd will be catched too as well as %sp

bochs/bx_debug/parser.y

bochs/cpu/data_xfer16.cc

bochs/doc/docbook/user/user.dbk

therealdreg · 2023-08-19T17:09:02Z

@stlintel take a look! more suggestions?

bochs/bx_debug/dbg_main.cc

stlintel · 2023-08-19T17:38:34Z

bochs/bx_debug/dbg_main.cc

+    {
+      new_mask |= 1 << MBP_CX;
+    }
+  if (strstr(str, "dx") != NULL)


still - why strstr ?

bochs/bx_debug/dbg_main.cc

bochs/bx_debug/debug.h

stlintel · 2023-08-19T17:41:10Z

bochs/bx_debug/dbg_main.cc

@@ -3791,7 +3840,7 @@ void bx_dbg_print_help(void)
  dbg_printf("h|help command - show short command description\n");
  dbg_printf("-*- Debugger control -*-\n");
  dbg_printf("    help, q|quit|exit, set, instrument, show, trace, trace-reg,\n");
-  dbg_printf("    trace-mem, u|disasm, ldsym, slist, addlyt, remlyt, lyt, source\n");
+  dbg_printf("    trace-mem, u|disasm, ldsym, setmagicbps, slist, addlyt, remlyt, lyt, source\n");


how about clearmagicbps ?

bochs/config.cc

bochs/cpu/data_xfer16.cc

bochs/bx_debug/dbg_main.cc

stlintel · 2023-08-20T04:10:06Z

di is the 7 register id, so I store it in 7nth position in mask
for a xchg di, di --> src() = 7
I need check the 7-nth bit in mask: 1 X X X X X X
to generate 1000000b I need do: 1 << 6

Bits are counted from 0:
#define AX 0 mask = 1
#define CX 1 mask = 2
#define DX 2 mask = 4
#define BX 3 mask = 8
#define SP 4 mask = 0x10 or mask = (1<<regnum)
#define BP 5 mask = 0x20
#define SI 6 mask = 0x40
#define DI 7 mask = 0x80

why -1 ?
AX will be never in use

BTW, to generate 1000000 you need 1<<7

stlintel · 2023-08-20T04:10:46Z

Please also pay attention on indentation requirements

therealdreg · 2023-08-20T05:47:25Z

@stlintel I fix my coding style and I remove -1 and checking 0. do you like in this way?

Tested and working 100%

bochs/bx_debug/debug.h

bochs/bx_debug/dbg_main.cc

bochs/doc/docbook/user/user.dbk

therealdreg · 2023-08-20T07:07:09Z

done! @stlintel

stlintel · 2023-08-20T07:12:58Z

bochs/bx_debug/dbg_main.cc

+{
+  dbg_printf("magic breakpoint mask: 0x%x ", mask);
+
+  if (mask & MBP_CX) {


static const char *regs = { "ax" /* not accessible */, "cx", "dx", "bx", "sp", "bp", "si", "di" }; for (int i=1;i<8;i++) if (mask & (1<<i)) dbg_printf("%s ", regs[i]);

stlintel · 2023-08-20T07:17:31Z

bochs/bx_debug/dbg_main.cc

+
+Bit8u bx_dbg_get_magic_bp_mask_from_str(const char *str)
+{
+  Bit8u new_mask = 0;


same here for (int i=1; i<8;i++) if (strstr(str, regs[i]) new_mask |= (1<<i) // bx for backward compatilibility if (new_mask == 0) new_mask = (1<<BX_16BIT_REG_BX);

stlintel · 2023-08-20T07:18:48Z

bochs/bx_debug/debug.h

@@ -204,6 +208,16 @@ int bx_dbg_lbreakpoint_symbol_command(const char *Symbol, const char *condition)
 bx_address bx_dbg_get_symbol_value(const char *Symbol);
 const char* bx_dbg_disasm_symbolic_address(bx_address eip, bx_address base);

+typedef enum {


and without that enum

therealdreg · 2023-08-20T07:52:01Z

@stlintel I'm closing this PR because it has become a mess; let's continue in #58

therealdreg mentioned this pull request Jul 24, 2023

magic breakpoints problem on XP ntldr #55

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therealdreg changed the title ~~add more magic breakpoint types fix #55~~ add more magic breakpoints fix #55 Jul 24, 2023

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add more magic breakpoints fix #55 #56

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