Note, if you are looking for a graphical front-end for the bochs debugger, you may want to check out BFE. This is a package written by a Bochs user which can interface with the text based Bochs debugger. No linking is necessary. It's not part of Bochs, but you may find it useful.
You can now conditionally compile in a GDB like command line debugger, that allows you to set breakpoints, step through instructions, and other useful functions. If there isn't a command for something you believe is generally useful for the debugger, let me know and I'll implement it if possible.
To use the debugger, you must configure Bochs with the
./configure --enable-debugger --enable-disasm
Note: You must use flex version 2.5.4 or greater. I have heard that version 2.5.2 will not work.
When you first start up Bochs, you will see the command line prompt
bochs:1>From here, you may use the following commands:
c continue executing cont continue s [count] execute count instructions, default is 1 step [count] s [cpu] [count] for SMP simulation, execute count instructions on cpu, default is 1 step [cpu] [count] s all [count] for SMP simulation, execute count instructions on all cpus step all [count] Ctrl-C stop execution, and return to command line prompt Ctrl-D if at empty line on command line, exit q quit debugger and execution quit exit
NOTE: The format of 'seg', 'off', and 'addr' in these descriptions, are as follows. I don't have any way to set the current radix. hexidecimal: 0xcdef0123 decimal: 123456789 octal: 01234567 vbreak seg:off Set a virtual address instruction breakpoint vb seg:off lbreak addr Set a linear address instruction breakpoint lb addr pbreak [*] addr Set a physical address instruction breakpoint pb [*] addr (the '*' is optional for GDB compatibility) break [*] addr b [*] addr info break Display state of all current breakpoints bpe n Enable a breakpoint bpd n Disable a breakpoint delete n Delete a breakpoint del n d n
watch read addr Insert a read watch point at physical address
addrwatch r addr Insert a read watch point at physical address
addrwatch write addr Insert a write watch point at physical address
addrwatch w addr Insert a write watch point at physical address
addrwatch Display state of current memory watchpoints watch stop Stop simulation when a watchpoint is encountered (default) watch continue Do not stop simulation when a watchpoint is encountered unwatch addr Remove watchpoint to specific physical address unwatch Remove all watch points trace-mem on/off Enable/Disable memory access tracing
x /nuf addr Examine memory at linear address addr xp /nuf addr Examine memory at physical address addr n Count of how many units to display u Unit size; one of b Individual bytes h Halfwords (2 bytes) w Words (4 bytes) g Giant words (8 bytes) NOTE: these are *not* typical Intel nomenclature sizes, but they are consistent with GDB convention. f Printing format. one of x Print in hexadecimal d Print in decimal u Print in unsigned decimal o Print in octal t Print in binary n, f, and u are optional parameters. u and f default to the last values you used, or to w(words) and x(hex) if none have been supplied. n currently defaults to 1. If none of these optional parameters are used, no slash should be typed. addr is also optional. If you don't specify it, it will be the value the next address (as if you had specified n+1 in the last x command). setpmem addr datasize val Set physical memory location of size datasize to value val. crc addr1 addr2 Show CRC32 for physical memory range addr1..addr2
r|reg|regs|registers List of CPU integer registers and their contents fp|fpu List of all FPU registers and their contents mmx List of all MMX registers and their contents sse List of all SSE registers and their contents sreg Show segment registers and their contents dreg Show debug registers and their contents creg Show control registers and their contents info cpu List of all CPU registers and their contents info eflags Show decoded EFLAGS register info break Information about current breakpoint status info tab Show paging address translation set $cpu = N Cause debugger to use cpu number "N". For example, "regs" will now print the registers of cpuN.
set reg = expr Change a CPU register to value of expression. Currently only general purpose registers are supported, you may not change: eflags, eip, cs, ss, ds, es, fs, gs. Examples: set eax = 2+2/2 set esi = 2*eax+ebx registers List of CPU registers and their contents regs reg r
disassemble start end Disassemble instructions in given linear address range, inclusive of start, exclusive of end. Use "set $disassemble_size =" to tell debugger desired segment size. Use a value for end of less than start (or zero) if you only want the first instruction disassembled. disassemble switch-mode Switch between Intel and AT&T disassebly styles for debugger disassembler. disassemble size = n Tell debugger what segment size to use when the "disassemble" command is used. Use values of 0, 16 or 32 for n. Value of 0 means "use segment size specified by current CS segment". Default is 0. set $auto_disassemble = n Cause debugger to disassemble current instruction every time execution stops if n=1. Default is 0. Segment size of current CPU context is used for disassembly, so the "disassemble size" variable is ignored. set disassemble on The same as 'set $auto_disassemble = 1' set disassemble off The same as 'set $auto_disassemble = 0'
trace on Disassemble every executed instruction. Note that instructions which caused exceptions are not really executed, and therefore not traced. trace off Disable instruction tracing.
To use instrumentation features in bochs, you must compile in support for it. You should build a custom instrumentation library in a separate directory in the "instrument/" directory. To tell configure which instrumentation library you want to use, use the "--enable-instrumentation" option. The default library consists of a set of stubs, and the following are equivalent:
./configure [...] --enable-instrumentation ./configure [...] --enable-instrumentation="instrument/stubs"You could make a separate directory with your custom library, for example "instrument/myinstrument", copy the contents of the "instrument/stubs" directory to it, then customize it. Use:
./configure [...] --enable-instrumentation="instrument/myinstrument"
instrument [command] calls BX_INSTR_DEBUG_CMD instrumentation callback with [command]
ptimePrint the current time (number of ticks since start of simulation).
sbInsert a time break point "delta" instructions into the future ("delta" is a 64-bit integer followed by "L", for example 1000L).
sbaInsert a time break point at "time" ("time" is a 64-bit integer followed by "L", for example 1000L).
recordRecord console input to file
filename. The file consists of zero or more lines of the form "%s %d %x", where the first word is the event type, the second is a time stamp and the third is event specific data.
playbackPlayback console input from file
filename. Additional input can be given directly in the console window. Events in the file will be played back at times relative to the time when the playback command was executed.
print-stack [Print the
num wordstop 16-bit words on the stack.
Num wordsdefaults to 16. Only works reliably in protected mode when the base address of the stack segment is zero.
modebpToggles CPU mode switch breakpoint.
ldsym [global]Load symbols from file
filename. If the global keyword is added, then the the symbols will be visible in all contexts for which symbols have not been loaded.
Offset(default is 0) is added to every symbol entry. The symbols are loaded in the current (executing) context.
The symbol file consists of zero or more lines of the format
Toggles show symbolic info (calls to begin with). show - shows current show mode show mode - show, when processor switch mode show int - show, when interrupt is happens show call - show, when call is happens show ret - show, when iret is happens show off - toggles off symbolic info show dbg-all - turn on all show flags show dbg-none - turn off all show flags