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.
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