BochsDebug
| Bochs User Manual | ||
|---|---|---|
| Chapter 8. Tips and Techniques | ||
8.12. Using Bochs internal debugger
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 --enable-debugger and --enable-disasm flags. For example:
./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:
8.12.1. Execution Control
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
8.12.2. BreakPoints
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
8.12.3. Memory WatchPoints
watch read addr Insert a read watch point at physical addressaddrwatch r addr Insert a read watch point at physical addressaddrwatch write addr Insert a write watch point at physical addressaddrwatch w addr Insert a write watch point at physical addressaddrwatch 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
8.12.4. Manipulating Memory
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.
writemem dump a number of bytes of virtual memory starting from
the specified linear address into a file
crc addr1 addr2 Show CRC32 for physical memory range addr1..addr2
8.12.5. Info commands
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|xmm List of all SSE registers and their contents ymm List of all AVX 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 info device Show state of the specified device
8.12.6. Manipulating CPU Registers
set reg = expr Change a CPU register to value of expression.
Currently only general purpose registers and instruction pointer
are supported. You may not change eflags, segment registers,
floating point or SIMD registers.
Examples: set eax = 2+2/2
set esi = 2*eax+ebx
registers List of CPU registers and their contents
regs
reg
r
8.12.7. Disassembly commands
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'
8.12.8. Instruction tracing
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.
8.12.9. Instrumentation
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"
8.12.10. Instrumentation commands
instrument [command] calls BX_INSTR_DEBUG_CMD instrumentation callback with [command]
8.12.11. Other Commands
ptimePrint the current time (number of ticks since start of simulation).
sb delta Insert a time break point "delta" instructions into the future ("delta" is a 64-bit integer followed by "L", for example 1000L).
sba time Insert a time break point at "time" ("time" is a 64-bit integer followed by "L", for example 1000L).
print-stack [num words] Print the
num words top 16-bit words on the stack.
Num words defaults 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 filefilename[offset]
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
"%x %s".
show [string]
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