Awesome, thanks for the answer. That makes sense to just leave indexing the stack up to the user. Same with letting the user do some legwork to find the address of the function.
Have you considered the (sort of edge) case when arguments are passed in registers? For example (in the VC compiler, as far as I remember) the "this" pointer is generally passed in the register ECX instead of being pushed onto the stack. In those cases it might be useful to have access to the register contents inside the JS callback.
Along a similar line, the EAX register is generally used for return values. It might be useful to provide access to that as well (through another callback?), although that would probably require changing how your trampoline works so that it replaces the return address in the stack... (i miss working with low level things sometimes).
Ahh yes, exposing registers is planned and very trivial to implement, as it's available at the C code level, just needs to be exposed to the script runtime (V8). Future versions may also allow specifying an ABI, so args[0] maps to ecx for thiscall in 32-bit mode.
My explanation of the hooking was a bit oversimplified, there is indeed support for hooking the return. Just implement onLeave(retval) in addition to onEnter(args), and you'll have access to the return value (coming from EAX/RAX).
Feedback is most appreciated, so please let me know if there's any issues. :)
Have you considered the (sort of edge) case when arguments are passed in registers? For example (in the VC compiler, as far as I remember) the "this" pointer is generally passed in the register ECX instead of being pushed onto the stack. In those cases it might be useful to have access to the register contents inside the JS callback.
Along a similar line, the EAX register is generally used for return values. It might be useful to provide access to that as well (through another callback?), although that would probably require changing how your trampoline works so that it replaces the return address in the stack... (i miss working with low level things sometimes).
Keep up the awesome work :D