1TCG Interpreter (TCI) - Copyright (c) 2011 Stefan Weil. 2 3This file is released under the BSD license. 4 51) Introduction 6 7TCG (Tiny Code Generator) is a code generator which translates 8code fragments ("basic blocks") from target code (any of the 9targets supported by QEMU) to a code representation which 10can be run on a host. 11 12QEMU can create native code for some hosts (arm, i386, ia64, ppc, ppc64, 13s390, sparc, x86_64). For others, unofficial host support was written. 14 15By adding a code generator for a virtual machine and using an 16interpreter for the generated bytecode, it is possible to 17support (almost) any host. 18 19This is what TCI (Tiny Code Interpreter) does. 20 212) Implementation 22 23Like each TCG host frontend, TCI implements the code generator in 24tcg-target.c.inc, tcg-target.h. Both files are in directory tcg/tci. 25 26The additional file tcg/tci.c adds the interpreter. 27 28The bytecode consists of opcodes (same numeric values as those used by 29TCG), command length and arguments of variable size and number. 30 313) Usage 32 33For hosts without native TCG, the interpreter TCI must be enabled by 34 35 configure --enable-tcg-interpreter 36 37If configure is called without --enable-tcg-interpreter, it will 38suggest using this option. Setting it automatically would need 39additional code in configure which must be fixed when new native TCG 40implementations are added. 41 42System emulation should work on any 32 or 64 bit host. 43User mode emulation might work. Maybe a new linker script (*.ld) 44is needed. Byte order might be wrong (on big endian hosts) 45and need fixes in configure. 46 47For hosts with native TCG, the interpreter TCI can be enabled by 48 49 configure --enable-tcg-interpreter 50 51The only difference from running QEMU with TCI to running without TCI 52should be speed. Especially during development of TCI, it was very 53useful to compare runs with and without TCI. Create /tmp/qemu.log by 54 55 qemu-system-i386 -d in_asm,op_opt,cpu -D /tmp/qemu.log -singlestep 56 57once with interpreter and once without interpreter and compare the resulting 58qemu.log files. This is also useful to see the effects of additional 59registers or additional opcodes (it is easy to modify the virtual machine). 60It can also be used to verify native TCGs. 61 62Hosts with native TCG can also enable TCI by claiming to be unsupported: 63 64 configure --cpu=unknown --enable-tcg-interpreter 65 66configure then no longer uses the native linker script (*.ld) for 67user mode emulation. 68 69 704) Status 71 72TCI needs special implementation for 32 and 64 bit host, 32 and 64 bit target, 73host and target with same or different endianness. 74 75 | host (le) host (be) 76 | 32 64 32 64 77------------+------------------------------------------------------------ 78target (le) | s0, u0 s1, u1 s?, u? s?, u? 7932 bit | 80 | 81target (le) | sc, uc s1, u1 s?, u? s?, u? 8264 bit | 83 | 84target (be) | sc, u0 sc, uc s?, u? s?, u? 8532 bit | 86 | 87target (be) | sc, uc sc, uc s?, u? s?, u? 8864 bit | 89 | 90 91System emulation 92s? = untested 93sc = compiles 94s0 = bios works 95s1 = grub works 96s2 = Linux boots 97 98Linux user mode emulation 99u? = untested 100uc = compiles 101u0 = static hello works 102u1 = linux-user-test works 103 1045) Todo list 105 106* TCI is not widely tested. It was written and tested on a x86_64 host 107 running i386 and x86_64 system emulation and Linux user mode. 108 A cross compiled QEMU for i386 host also works with the same basic tests. 109 A cross compiled QEMU for mipsel host works, too. It is terribly slow 110 because I run it in a mips malta emulation, so it is an interpreted 111 emulation in an emulation. 112 A cross compiled QEMU for arm host works (tested with pc bios). 113 A cross compiled QEMU for ppc host works at least partially: 114 i386-linux-user/qemu-i386 can run a simple hello-world program 115 (tested in a ppc emulation). 116 117* Some TCG opcodes are either missing in the code generator and/or 118 in the interpreter. These opcodes raise a runtime exception, so it is 119 possible to see where code must be added. 120 121* The pseudo code is not optimized and still ugly. For hosts with special 122 alignment requirements, it needs some fixes (maybe aligned bytecode 123 would also improve speed for hosts which support byte alignment). 124 125* A better disassembler for the pseudo code would be nice (a very primitive 126 disassembler is included in tcg-target.c.inc). 127 128* It might be useful to have a runtime option which selects the native TCG 129 or TCI, so QEMU would have to include two TCGs. Today, selecting TCI 130 is a configure option, so you need two compilations of QEMU. 131