This would be a bit more verbose on calling, although you could define other member functions to hide the ugly code. You can then change the pointer to the table as necessary. Define a class with the required pointer-to-method-functions, then define a pointer in your class to one of these. It could also mess up deletes and exception handling.Ĭreate your own vtable. You'll have to use extreme caution to set this up. With newVtable defined with appropriate pointers-to-member-functions. Assuming the vtable is at the start of the class (which it is for simple classes in the WinAPI), you can replace that pointer with one to a table of your own. This is non-portable and has many ways to just go horribly wrong. The initial trace level is 0.Since the usual method of deriving another class won't work for you, there are three solutions I can think of.Ĭhange the vtable pointer. If positive, the trace hooksĪssociated with vm will be run. The trace level is restored to whatever it was once the hook That way the hooks don’t fire while you’re If the trace level is positive, hooks run įor convenience, when the VM fires a hook, it does so with the trap Getting an instance of the class may vary depending on the class we are trying to hook, sometimes we can create a fake and temporary object to traverse its VF table and find the real address of the function or another option could be to obtain a reference to an already. Guile exposes a single, heavy-handed knob to turn hooks on or off, the Basically, what we need to know are two things: an instance of the class and the offset of the method inside the VF table. The vm-next-hook has quite an impact, performance-wise. These hooks do impose a performance penalty, if they are on. Remove f from the corresponding VM hook for the current thread. Scheme Procedure: vm-remove-next-hook! f Scheme Procedure: vm-remove-apply-hook! f Scheme Procedure: vm-remove-return-hook! f Scheme Procedure: vm-remove-abort-hook! f Unfortunately, the values passed to the prompt handler are not easily In thatĬase, it corresponds to a non-local control flow jump, either because ofĪpplying a composable continuation or because of restoring a savedĪrrange to call f after aborting to a prompt. Not immediately proceeded by a call with that frame pointer. Note that it’s possible to return from an “inner” frame: one that was The frame will be the frame’s return values. Pointer compared the previous frame pointer.Īrrange to call f before returning from a frame. Respect to the frame previously in place, check the value of the frame To know whether a call is a tail call or not, with Note that procedure application is somewhat orthogonal to continuation Locals will be the callee, followed by the arguments to the call. The interface to hooks is provided by the (system vm vm) module:Īll of these functions implicitly act on the VM for the current threadĪrrange to call f when before an instruction is retired (andĪrrange to call f whenever a procedure is applied. The frame outside the extent of the hook, bad things will happen. The upshot here is that the frames are only valid within the dynamicĮxtent of the call to the hook. Since these hooks may be fired very frequently, Guileĭoes a terrible thing: it allocates the frames on the C stack instead of VM hooks are called with one argument: the current frame. For implementation reasons, these hooks are notĪctually implemented with first-class Scheme hooks (see Hooks) they To digress, Guile’s VM has 4 different hooks that can be fired atĭifferent times. Set-vm-engine! procedures to ensure that you are running in a VM When running your program, or otherwise use the call-with-vm and To ensure that you are running with hooks, pass -debug to Guile Hooks if you are running interactively, and otherwise they are disabled,Īs they do have some overhead (about 10 or 20 percent). Note that there are multiple VM “engines” for Guile. That defines a number of operations that Scheme programs can Examples might include intercepting keyboard or mouse event messages before they reach an application, or intercepting operating system calls in order to monitor behavior or. Hooking is used for many purposes, including debugging and extending functionality. Next: Trap Interface, Up: Traps Įverything that runs in Guile runs on its virtual machine, a C program Code that handles such intercepted function calls, events or messages is called a hook.
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