Messages in this thread | | | Date | Fri, 03 Apr 2009 16:40:13 +0300 | From | Avi Kivity <> | Subject | Re: [PATCH -tip 0/6 V4] tracing: kprobe-based event tracer |
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Vegard Nossum wrote: > For the record, kmemcheck requirements for an instruction decoder are these: > > For any instruction with memory operands, we need to know which are > the operands (so for movl %eax, (%ebx) we need to combine the > instruction with a struct pt_regs to get the actual address > dereferenced, i.e. the contents of %ebx), and their sizes (for movzbl, > the source operand is 8 bits, destination operand is 32 bits). For > things like movsb, we need to be able to get both %esi and %edi. > >
The kvm emulator does all of this.
> mmiotrace additionally needs to know what the actual values > read/written were, for instructions that read/write to memory (again, > combined with a struct pt_regs). >
And this.
> Maybe this doesn't really say much, since this is what a generic > instruction decoder would be able to do anyway. But kmemcheck and > mmiotrace both have very special-purpose decoders. I don't really know > what other decoders look like, but what I would wish for is this: Some > macros for iterating the operands, where each operand has a type (e.g. > input (for reads), output (for writes), target (for jumps), immediate > address, immediate value, etc.), a size (in bits), and a way to > evaluate the operand. So eval(op, regs) for op=%eax, it will return > regs->eax; for op=4(%eax), it will return regs->eax + 4; for op=4 it > will return 4, etc. >
You can do something like this by executing the instruction and observing what memory is touches through the callbacks.
-- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.
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