Kernel Debugging: Difference between revisions

 

IMPORTANT NOTE #2: gcc thinks it is smarter than the programmer, so if you use "while(1);", then it will falsely assume that everything after that loop is not needed, and it will REMOVE all those code from the binary. You MUST use inline assembly so that gcc will keep your code as-is.

asm volatile ("1: jmp 1b");

 

== Use a virtual machine ==

 

Alternatively you can force a breakpoint in your code without knowing the name of the function or the address. Place an endless loop pseudo-breakpoint somewhere in your code

asm volatile ("1: jmp 1b");

 

Then on the terminal that's running gdb, when your VM hangs press Ctrl^C to stop execution and drop you at the debugger prompt. There

 

The easiest way to trigger a breakpoint in bochs is to place "xchg bx, bx" into your code. For example

asm volatile ("xchg %bx, %bx");

 

Then when you run the virtual machine, it will stop execution and drop you at debugger prompt. To single step from there, use

Unfortunately VirtualBox developers have removed the "--start-dbg" command line option, so there's no way to set up breakpoints before your VM starts execution.

But you can do a similar trick as with GDB, which is to place an endless loop pseudo-breakpoint in your code somewhere:

asm volatile ("1: jmp 1b");

 

Then when the execution hangs, access "Command line..." under "Debug" menu (if you don't have a Debug menu in the Machine window, you'll have to enable the debugger see below). In the debugger command line, the first thing to do is that you MUST stop the VM from running: