On 5/19/05, Paul Brook <[EMAIL PROTECTED]> wrote: > No. The problem is to turn machine code into (a different form of) machine > code. A lot of the complexity in a compiler is involved with with turning the > high-level language constructs into simple low-level machine operations.
I see your point. I did write a Z80 emulator on an early x86 once. The flags where extremely close, and most commands have a direct correspondency. You just have to decide on a register mapping, and you can start. I wrote short assembler sequences for each command, very much like the targets in qemu. But this is a special case: mapping one architecture on a similar architecture. Qemu is special an that it avoid both the problem in "papering over the differences", and it avoids the combinatorial explosion of n targets on m hosts. And it does this exactly because it uses C to express machine commands, and not some other machine language. I think you cannot take this away without changing the very nature of qemu. The reason I care about this is that qemu has achived a lot more than all other similar open source projects together. Look at bochs, or plex86 or valgrind: they are nowhere near the performance of qemu, and they only support x86 targets. So there must be something very ingenious about the design of qemu, and I think it is the combination of gcc and dyngen. I certainly welcome every possible improvement, but I want to stress how good qemu alread is. > With qemu we're just translating from one simple form to another, so I'd argue > that all you really need is a clever way of papering over the differences > between the host and the guest. So many projects have failed in this direction that I am tempted to assume that this is a flawed approach. Apart from kqemu and VMware, there is not one convincing solution even for the supposedly trivial x86 on x86 case. > What we have now (dyngen) is basically just an assembler. It maps qemu micro > ops directly into blocks host code. The only reason dyngen uses gcc is to > avoid having to hand write host encodings for all the ops. It as also because C avoids the n by m problem. Thomas _______________________________________________ Qemu-devel mailing list Qemu-devel@nongnu.org http://lists.nongnu.org/mailman/listinfo/qemu-devel
