Bochs: Difference between revisions

The CPU didn't manage to invoke an exception handler and would normally [[Triple Fault|triple fault]]. This is probably due to a bad [[Interrupt Descriptor Table|IDT]] register content, or a bad IDT descriptor. Sometimes (but less likely), it can also be due to a severe bug in your exception handler code. Check your exception works with "illegal" asm instructions like <tt>idiv 0</tt>, or

 

push 0xf001

pop ds ; 0xf001 is no valid segment,

mov ax, ~[ds:0x12345678] ; let's see if we get the GPF

 

In several cases, there are other error messages prior to this one which can provide more details in the error. Some common messages that might be displayed:

Some useful macros when Bochs is compiled with the I/O debug ports enabled (<tt>port_e9_hack: enabled=1</tt> if Bochs 2.4 or newer, <tt>configure --port-e9-hack</tt> if not):

 

//outputs a character to the debug console

#define BochsConsolePrintChar(c) outportb(0xe9, c)

//stops simulation and breaks into the debug console

#define BochsBreak() outportw(0x8A00,0x8A00); outportw(0x8A00,0x08AE0);

 

===Magic Breakpoint===

Bochs has many compile-time configuration options, some of which conflict, and therefore a binary distribution of Bochs may not be suitable for your purposes. I found it was best to compile my own copy of Bochs to be sure I had the features that I needed. Also, you should consider using the CVS snapshot version of Bochs if the released version is old and not working for you. I found this was necessary up until version 2.4 was released, for example. On Ubuntu, you may have to run

 

sudo apt-get install libgtk2.0-dev

 

and enter your password. On other linux distros, try the equivalent.

The array of Bochs configuration options can be confusing, and you cannot assume the defaults are going to be sensible. These are the options I use, this can get you started:

 

./configure --enable-smp \

--enable-cpu-level=6 \

--disable-docbook \

--with-x --with-x11 --with-term --with-sdl2

 

A few notes:

* The default compile does not support x86-64, --enable-x86-64 will turn it on

* On many Linux distributions it is possible to install Bochs via a package manager. For example, on distributions that use apt-get we can do

sudo apt-get install bochs

sudo apt-get install bochs-x

to install Bochs and the X11 plugin (which may crash on ubuntu/linux mint: install the sdl plugin and use sdl instead of x as the display library in this case). Note that there is a big chance that the graphical debugger is not enabled in the binaries from the package manager.

 

===External Links===

*[http://bochs.sourceforge.net Bochs Homepage]

*[http://www.codeproject.com/system/MakingOS_2.asp CodeProject article on using Bochs]