On 27 December 2016 at 21:45, Adeel Mujahid <adee...@outlook.com> wrote: > For instance, consider a C/C++ project with couple of .asm/.S files > containing Intel or ATT flavored assembly code for AMD64, and the > aim is to port to AARCH64 -- is it even a deterministic problem > to transpile precise and bug free AARCH64 assembly code, given the > full usage context and all code paths at our disposal?
I don't think this approach is likely to produce useful results. Generally the reason for some code being in assembly is because it is a critical path for the program and has to execute as fast as possible. If you try to automatedly translate that to a different instruction set (with QEMU or otherwise) you will produce output which is slower than it should be, because it has to reproduce all the effects of the original code (like setting flags correctly, getting the right floating point results, etc). If you want something that will work on any host architecture (at the cost of being slightly slow) you should write a C language version of the assembly code as a fallback path, or even as the only code path. The C code can then correctly express what the code actually requires (with no unwanted side effects like having to set flags, etc) and the compiler can produce good native code. (This is useful anyway for testing whether the native assembly version is broken.) If the codepath is sufficiently hot that a native assembly version is absolutely needed, then there is no substitute for a real human doing the work, possibly starting from what the C compiler produced. The oddities of different architecture instruction sets (like how their SIMD works, whether they have custom instructions for particular operations, etc) are not something that's really possible for automatic code generation to make full use of. (If it were possible, you could just do that in the C compiler back end and write the code in C in the first place.) TLDR: doing C -> asm (with the C compiler) will get you much better quality code than trying to do asm -> asm with any kind of JIT/emulator like QEMU. thanks -- PMM
