search for: patchable_ret

...with the iterator. > > So you mean I should insert a pseudo instruction in the machinefunction pass, then replace it when function call lowering? (Like segemented stack implementation?) > Yes, inserting pseudo instructions in the MachineFunctionPass -- you might want to have a look at PATCHABLE_RET and how we handle this in XRay. Essentially the idea (which I saw Sanjoy Das do first) is to wrap the actual instruction (in this case, CALL or LEA, or something specific in the platform you're targeting) in a pseudo instruction that just lowers to the correct sequence. This gives you complete...

...> > Do you have any example for this? I would like have a look at how you handle this in XRay if it is possible. > Yes, this is all upstream -- if you look in lib/CodeGen/XRayInstrument.cpp and the associated lowering code for X86 in lib/Target/X86/X86MCInstLower.cpp and/or search for PATCHABLE_RET in include/... and lib/... then that should give you a better idea of how this works. :) Cheers -- Dean

...dd thresholds for some heuristics. 3. *LLVM:* Add new LLVM pseudo instructions for indicating where the instrumentation sleds should be placed, and what kind of sleds these are. For entry sleds, we can use the `PATCHABLE_OP` instruction, and a new instruction for patching exits (`PATCHABLE_RET`?) that get handled by the assembly printer per platform. Currently only implemented for x86_64. 4. *LLVM:* Use a separate section to map the instrumentation sled locations. This will work even in non-debug builds and the sections will be merged by the linker. 5. *compiler-rt...

...============= XRay relies on statically inserted instrumentation points (implemented as nop-sleds) and a dynamic enable/disable mechanism implemented in a runtime library. As of this writing the implementation of the XRay prototype involves adding two pseudo-instructions (PATCHABLE_FUNCTION_ENTER, PATCHABLE_RET) that serve as placeholders for where the nop-sleds are to be emitted when lowering. PATCHABLE_FUNCTION_ENTER is an instruction that takes no operands and serves as a pure placeholder. PATCHABLE_RET effectively behaves as a return instruction (isReturn = true) and wraps whatever the return instruct...

We do something very similar here for XRay, and I would think the approach would be similar. What XRay does are the following: - Find the machine instructions in a MachineFunctionPass that look interesting from the XRay perspective. Theses turn out to be: the beginning of the function (not really an instruction but a location), tail calls, and returns. I suspect you can very simply find the call