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    SubjectRe: [PATCH -tip 0/6 V4] tracing: kprobe-based event tracer
    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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      Last update: 2009-04-03 15:43    [W:0.022 / U:6.988 seconds]
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