Set ba (break on access) breakpoint in managed code programmatically

Question

For investigating managed heap corruption I would like to use ba (break on access) breakpoints. Can I use them in managed code? If yes, how can I set them programmatically?

UPDATE: It would also be okay so set them in WinDbg (-> set ba for every object of type XY)

Answer 1

Breakpoints set by 'ba' command are called processor or hardware breakpoints.

First the good news

It is easy to set hardware breakpoint. You will need to set one of the processor's debug registers (DR0, DR1, DR2 or DR3) with the address of the data and set debug control register DR7 with fields to set size of memory and type of access. The instruction (in x64 assembler) looks like:

MOV rax, DR0

Obviously you will have to somehow execute this assembler instruction from your language of choice, or use interop to C++ and inline assembly, but this is easier than for example setting software breakpoint.

Now the bad news

First of all, on SMP machines you will have to do this for all processors that can touch your code. This is probably solvable if you configure processor affinity for you process, or do debugging on single-proc machine. Second, there are only 4 debug processors on Intel architecture. If you try setting processor breakpoints with WinDbg, after 4th it will complain Too many data breakpoints for thread N after you hit g.

I assume the whole purpose you are asking about automation is because there are too many objects to set breakpoints by hand. Since you are limited to 4 ba breakpoints anyways, there is not much point in automating this.