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1 | \input texinfo @c -*- texinfo -*- |
2 | ||
0806e3f6 | 3 | @iftex |
322d0c66 | 4 | @settitle QEMU CPU Emulator Reference Documentation |
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5 | @titlepage |
6 | @sp 7 | |
322d0c66 | 7 | @center @titlefont{QEMU CPU Emulator Reference Documentation} |
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8 | @sp 3 |
9 | @end titlepage | |
0806e3f6 | 10 | @end iftex |
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11 | |
12 | @chapter Introduction | |
13 | ||
322d0c66 | 14 | @section Features |
386405f7 | 15 | |
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16 | QEMU is a FAST! processor emulator. By using dynamic translation it |
17 | achieves a reasonnable speed while being easy to port on new host | |
18 | CPUs. | |
19 | ||
20 | QEMU has two operating modes: | |
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21 | |
22 | @itemize @minus | |
23 | ||
24 | @item | |
25 | User mode emulation. In this mode, QEMU can launch Linux processes | |
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26 | compiled for one CPU on another CPU. Linux system calls are converted |
27 | because of endianness and 32/64 bit mismatches. The Wine Windows API | |
28 | emulator (@url{http://www.winehq.org}) and the DOSEMU DOS emulator | |
29 | (@url{www.dosemu.org}) are the main targets for QEMU. | |
30 | ||
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31 | @item |
32 | Full system emulation. In this mode, QEMU emulates a full | |
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33 | system, including a processor and various peripherials. Currently, it |
34 | is only used to launch an x86 Linux kernel on an x86 Linux system. It | |
35 | enables easier testing and debugging of system code. It can also be | |
36 | used to provide virtual hosting of several virtual PCs on a single | |
37 | server. | |
38 | ||
39 | @end itemize | |
40 | ||
41 | As QEMU requires no host kernel patches to run, it is very safe and | |
42 | easy to use. | |
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43 | |
44 | QEMU generic features: | |
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45 | |
46 | @itemize | |
47 | ||
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48 | @item User space only or full system emulation. |
49 | ||
50 | @item Using dynamic translation to native code for reasonnable speed. | |
386405f7 | 51 | |
322d0c66 | 52 | @item Working on x86 and PowerPC hosts. Being tested on ARM, Sparc32, Alpha and S390. |
386405f7 | 53 | |
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54 | @item Self-modifying code support. |
55 | ||
d5a0b50c | 56 | @item Precise exceptions support. |
386405f7 | 57 | |
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58 | @item The virtual CPU is a library (@code{libqemu}) which can be used |
59 | in other projects. | |
60 | ||
61 | @end itemize | |
62 | ||
63 | QEMU user mode emulation features: | |
64 | @itemize | |
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65 | @item Generic Linux system call converter, including most ioctls. |
66 | ||
67 | @item clone() emulation using native CPU clone() to use Linux scheduler for threads. | |
68 | ||
322d0c66 | 69 | @item Accurate signal handling by remapping host signals to target signals. |
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70 | @end itemize |
71 | @end itemize | |
df0f11a0 | 72 | |
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73 | QEMU full system emulation features: |
74 | @itemize | |
285dc330 | 75 | @item QEMU can either use a full software MMU for maximum portability or use the host system call mmap() to simulate the target MMU. |
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76 | @end itemize |
77 | ||
78 | @section x86 emulation | |
79 | ||
80 | QEMU x86 target features: | |
81 | ||
82 | @itemize | |
83 | ||
84 | @item The virtual x86 CPU supports 16 bit and 32 bit addressing with segmentation. | |
1eb20527 | 85 | LDT/GDT and IDT are emulated. VM86 mode is also supported to run DOSEMU. |
322d0c66 | 86 | |
1eb20527 | 87 | @item Support of host page sizes bigger than 4KB in user mode emulation. |
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88 | |
89 | @item QEMU can emulate itself on x86. | |
1eb87257 | 90 | |
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91 | @item An extensive Linux x86 CPU test program is included @file{tests/test-i386}. |
92 | It can be used to test other x86 virtual CPUs. | |
93 | ||
94 | @end itemize | |
95 | ||
df0f11a0 | 96 | Current QEMU limitations: |
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97 | |
98 | @itemize | |
99 | ||
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100 | @item No SSE/MMX support (yet). |
101 | ||
102 | @item No x86-64 support. | |
103 | ||
df0f11a0 | 104 | @item IPC syscalls are missing. |
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105 | |
106 | @item The x86 segment limits and access rights are not tested at every | |
1eb20527 | 107 | memory access. |
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108 | |
109 | @item On non x86 host CPUs, @code{double}s are used instead of the non standard | |
110 | 10 byte @code{long double}s of x86 for floating point emulation to get | |
111 | maximum performances. | |
112 | ||
285dc330 | 113 | @item Some priviledged instructions or behaviors are missing, especially for segment protection testing (yet). |
1eb20527 | 114 | |
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115 | @end itemize |
116 | ||
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117 | @section ARM emulation |
118 | ||
119 | @itemize | |
120 | ||
121 | @item ARM emulation can currently launch small programs while using the | |
122 | generic dynamic code generation architecture of QEMU. | |
123 | ||
124 | @item No FPU support (yet). | |
125 | ||
126 | @item No automatic regression testing (yet). | |
127 | ||
128 | @end itemize | |
129 | ||
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130 | @section SPARC emulation |
131 | ||
132 | The SPARC emulation is currently in development. | |
133 | ||
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134 | @chapter Installation |
135 | ||
136 | If you want to compile QEMU, please read the @file{README} which gives | |
137 | the related information. Otherwise just download the binary | |
138 | distribution (@file{qemu-XXX-i386.tar.gz}) and untar it as root in | |
139 | @file{/}: | |
140 | ||
141 | @example | |
142 | su | |
143 | cd / | |
144 | tar zxvf /tmp/qemu-XXX-i386.tar.gz | |
145 | @end example | |
146 | ||
d5a0b50c | 147 | @chapter QEMU User space emulator invocation |
386405f7 | 148 | |
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149 | @section Quick Start |
150 | ||
386405f7 | 151 | In order to launch a Linux process, QEMU needs the process executable |
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152 | itself and all the target (x86) dynamic libraries used by it. |
153 | ||
154 | @itemize | |
386405f7 | 155 | |
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156 | @item On x86, you can just try to launch any process by using the native |
157 | libraries: | |
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158 | |
159 | @example | |
0806e3f6 | 160 | qemu-i386 -L / /bin/ls |
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161 | @end example |
162 | ||
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163 | @code{-L /} tells that the x86 dynamic linker must be searched with a |
164 | @file{/} prefix. | |
386405f7 | 165 | |
5b9f457a | 166 | @item Since QEMU is also a linux process, you can launch qemu with qemu (NOTE: you can only do that if you compiled QEMU from the sources): |
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167 | |
168 | @example | |
0806e3f6 | 169 | qemu-i386 -L / qemu-i386 -L / /bin/ls |
1eb87257 | 170 | @end example |
386405f7 | 171 | |
d691f669 | 172 | @item On non x86 CPUs, you need first to download at least an x86 glibc |
5b9f457a | 173 | (@file{qemu-runtime-i386-XXX-.tar.gz} on the QEMU web page). Ensure that |
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174 | @code{LD_LIBRARY_PATH} is not set: |
175 | ||
176 | @example | |
177 | unset LD_LIBRARY_PATH | |
178 | @end example | |
179 | ||
180 | Then you can launch the precompiled @file{ls} x86 executable: | |
181 | ||
d691f669 | 182 | @example |
285dc330 | 183 | qemu-i386 tests/i386/ls |
168485b7 | 184 | @end example |
285dc330 | 185 | You can look at @file{qemu-binfmt-conf.sh} so that |
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186 | QEMU is automatically launched by the Linux kernel when you try to |
187 | launch x86 executables. It requires the @code{binfmt_misc} module in the | |
188 | Linux kernel. | |
189 | ||
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190 | @item The x86 version of QEMU is also included. You can try weird things such as: |
191 | @example | |
0806e3f6 | 192 | qemu-i386 /usr/local/qemu-i386/bin/qemu-i386 /usr/local/qemu-i386/bin/ls-i386 |
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193 | @end example |
194 | ||
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195 | @end itemize |
196 | ||
df0f11a0 | 197 | @section Wine launch |
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198 | |
199 | @itemize | |
200 | ||
201 | @item Ensure that you have a working QEMU with the x86 glibc | |
202 | distribution (see previous section). In order to verify it, you must be | |
203 | able to do: | |
204 | ||
205 | @example | |
0806e3f6 | 206 | qemu-i386 /usr/local/qemu-i386/bin/ls-i386 |
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207 | @end example |
208 | ||
fd429f2f | 209 | @item Download the binary x86 Wine install |
1eb87257 | 210 | (@file{qemu-XXX-i386-wine.tar.gz} on the QEMU web page). |
168485b7 | 211 | |
fd429f2f | 212 | @item Configure Wine on your account. Look at the provided script |
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213 | @file{/usr/local/qemu-i386/bin/wine-conf.sh}. Your previous |
214 | @code{$@{HOME@}/.wine} directory is saved to @code{$@{HOME@}/.wine.org}. | |
215 | ||
216 | @item Then you can try the example @file{putty.exe}: | |
217 | ||
218 | @example | |
0806e3f6 | 219 | qemu-i386 /usr/local/qemu-i386/wine/bin/wine /usr/local/qemu-i386/wine/c/Program\ Files/putty.exe |
386405f7 | 220 | @end example |
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221 | |
222 | @end itemize | |
223 | ||
224 | @section Command line options | |
225 | ||
226 | @example | |
0806e3f6 | 227 | usage: qemu-i386 [-h] [-d] [-L path] [-s size] program [arguments...] |
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228 | @end example |
229 | ||
df0f11a0 | 230 | @table @option |
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231 | @item -h |
232 | Print the help | |
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233 | @item -L path |
234 | Set the x86 elf interpreter prefix (default=/usr/local/qemu-i386) | |
235 | @item -s size | |
236 | Set the x86 stack size in bytes (default=524288) | |
237 | @end table | |
386405f7 | 238 | |
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239 | Debug options: |
240 | ||
241 | @table @option | |
242 | @item -d | |
243 | Activate log (logfile=/tmp/qemu.log) | |
244 | @item -p pagesize | |
245 | Act as if the host page size was 'pagesize' bytes | |
246 | @end table | |
247 | ||
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248 | @chapter QEMU System emulator invocation |
249 | ||
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250 | @section Introduction |
251 | ||
252 | @c man begin DESCRIPTION | |
253 | ||
254 | The QEMU System emulator simulates a complete PC. It can either boot | |
255 | directly a Linux kernel (without any BIOS or boot loader) or boot like a | |
256 | real PC with the included BIOS. | |
257 | ||
258 | In order to meet specific user needs, two versions of QEMU are | |
259 | available: | |
260 | ||
261 | @enumerate | |
262 | ||
263 | @item | |
285dc330 | 264 | @code{qemu-fast} uses the host Memory Management Unit (MMU) to simulate |
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265 | the x86 MMU. It is @emph{fast} but has limitations because the whole 4 GB |
266 | address space cannot be used and some memory mapped peripherials | |
267 | cannot be emulated accurately yet. Therefore, a specific Linux kernel | |
268 | must be used (@xref{linux_compile}). | |
269 | ||
270 | @item | |
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271 | @code{qemu} uses a software MMU. It is about @emph{two times |
272 | slower} but gives a more accurate emulation. | |
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273 | |
274 | @end enumerate | |
275 | ||
276 | QEMU emulates the following PC peripherials: | |
277 | ||
278 | @itemize @minus | |
279 | @item | |
280 | VGA (hardware level, including all non standard modes) | |
281 | @item | |
282 | PS/2 mouse and keyboard | |
283 | @item | |
181f1558 | 284 | 2 IDE interfaces with hard disk and CD-ROM support |
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285 | @item |
286 | NE2000 network adapter (port=0x300, irq=9) | |
287 | @item | |
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288 | Serial port |
289 | @item | |
290 | Soundblaster 16 card | |
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291 | @item |
292 | PIC (interrupt controler) | |
293 | @item | |
294 | PIT (timers) | |
295 | @item | |
296 | CMOS memory | |
297 | @end itemize | |
298 | ||
299 | @c man end | |
300 | ||
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301 | @section Quick Start |
302 | ||
285dc330 | 303 | Download and uncompress the linux image (@file{linux.img}) and type: |
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304 | |
305 | @example | |
285dc330 | 306 | qemu linux.img |
0806e3f6 FB |
307 | @end example |
308 | ||
309 | Linux should boot and give you a prompt. | |
310 | ||
311 | @section Direct Linux Boot and Network emulation | |
312 | ||
313 | This section explains how to launch a Linux kernel inside QEMU without | |
314 | having to make a full bootable image. It is very useful for fast Linux | |
315 | kernel testing. The QEMU network configuration is also explained. | |
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316 | |
317 | @enumerate | |
318 | @item | |
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319 | Download the archive @file{linux-test-xxx.tar.gz} containing a Linux |
320 | kernel and a disk image. | |
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321 | |
322 | @item Optional: If you want network support (for example to launch X11 examples), you | |
0806e3f6 | 323 | must copy the script @file{qemu-ifup} in @file{/etc} and configure |
1eb20527 | 324 | properly @code{sudo} so that the command @code{ifconfig} contained in |
0806e3f6 | 325 | @file{qemu-ifup} can be executed as root. You must verify that your host |
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326 | kernel supports the TUN/TAP network interfaces: the device |
327 | @file{/dev/net/tun} must be present. | |
328 | ||
329 | When network is enabled, there is a virtual network connection between | |
330 | the host kernel and the emulated kernel. The emulated kernel is seen | |
331 | from the host kernel at IP address 172.20.0.2 and the host kernel is | |
332 | seen from the emulated kernel at IP address 172.20.0.1. | |
333 | ||
0806e3f6 | 334 | @item Launch @code{qemu.sh}. You should have the following output: |
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335 | |
336 | @example | |
0806e3f6 | 337 | > ./qemu.sh |
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338 | Connected to host network interface: tun0 |
339 | Linux version 2.4.21 (bellard@voyager.localdomain) (gcc version 3.2.2 20030222 (Red Hat Linux 3.2.2-5)) #5 Tue Nov 11 18:18:53 CET 2003 | |
1eb20527 | 340 | BIOS-provided physical RAM map: |
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341 | BIOS-e801: 0000000000000000 - 000000000009f000 (usable) |
342 | BIOS-e801: 0000000000100000 - 0000000002000000 (usable) | |
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343 | 32MB LOWMEM available. |
344 | On node 0 totalpages: 8192 | |
345 | zone(0): 4096 pages. | |
346 | zone(1): 4096 pages. | |
347 | zone(2): 0 pages. | |
181f1558 | 348 | Kernel command line: root=/dev/hda sb=0x220,5,1,5 ide2=noprobe ide3=noprobe ide4=noprobe ide5=noprobe console=ttyS0 |
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349 | ide_setup: ide2=noprobe |
350 | ide_setup: ide3=noprobe | |
351 | ide_setup: ide4=noprobe | |
352 | ide_setup: ide5=noprobe | |
1eb20527 | 353 | Initializing CPU#0 |
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354 | Detected 2399.621 MHz processor. |
355 | Console: colour EGA 80x25 | |
356 | Calibrating delay loop... 4744.80 BogoMIPS | |
357 | Memory: 28872k/32768k available (1210k kernel code, 3508k reserved, 266k data, 64k init, 0k highmem) | |
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358 | Dentry cache hash table entries: 4096 (order: 3, 32768 bytes) |
359 | Inode cache hash table entries: 2048 (order: 2, 16384 bytes) | |
181f1558 | 360 | Mount cache hash table entries: 512 (order: 0, 4096 bytes) |
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361 | Buffer-cache hash table entries: 1024 (order: 0, 4096 bytes) |
362 | Page-cache hash table entries: 8192 (order: 3, 32768 bytes) | |
363 | CPU: Intel Pentium Pro stepping 03 | |
364 | Checking 'hlt' instruction... OK. | |
365 | POSIX conformance testing by UNIFIX | |
366 | Linux NET4.0 for Linux 2.4 | |
367 | Based upon Swansea University Computer Society NET3.039 | |
368 | Initializing RT netlink socket | |
369 | apm: BIOS not found. | |
370 | Starting kswapd | |
4690764b | 371 | Journalled Block Device driver loaded |
181f1558 | 372 | Detected PS/2 Mouse Port. |
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373 | pty: 256 Unix98 ptys configured |
374 | Serial driver version 5.05c (2001-07-08) with no serial options enabled | |
375 | ttyS00 at 0x03f8 (irq = 4) is a 16450 | |
376 | ne.c:v1.10 9/23/94 Donald Becker (becker@scyld.com) | |
377 | Last modified Nov 1, 2000 by Paul Gortmaker | |
378 | NE*000 ethercard probe at 0x300: 52 54 00 12 34 56 | |
379 | eth0: NE2000 found at 0x300, using IRQ 9. | |
4690764b | 380 | RAMDISK driver initialized: 16 RAM disks of 4096K size 1024 blocksize |
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381 | Uniform Multi-Platform E-IDE driver Revision: 7.00beta4-2.4 |
382 | ide: Assuming 50MHz system bus speed for PIO modes; override with idebus=xx | |
383 | hda: QEMU HARDDISK, ATA DISK drive | |
384 | ide0 at 0x1f0-0x1f7,0x3f6 on irq 14 | |
385 | hda: attached ide-disk driver. | |
386 | hda: 20480 sectors (10 MB) w/256KiB Cache, CHS=20/16/63 | |
387 | Partition check: | |
388 | hda: | |
389 | Soundblaster audio driver Copyright (C) by Hannu Savolainen 1993-1996 | |
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390 | NET4: Linux TCP/IP 1.0 for NET4.0 |
391 | IP Protocols: ICMP, UDP, TCP, IGMP | |
392 | IP: routing cache hash table of 512 buckets, 4Kbytes | |
4690764b | 393 | TCP: Hash tables configured (established 2048 bind 4096) |
1eb20527 | 394 | NET4: Unix domain sockets 1.0/SMP for Linux NET4.0. |
4690764b | 395 | EXT2-fs warning: mounting unchecked fs, running e2fsck is recommended |
1eb20527 | 396 | VFS: Mounted root (ext2 filesystem). |
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397 | Freeing unused kernel memory: 64k freed |
398 | ||
399 | Linux version 2.4.21 (bellard@voyager.localdomain) (gcc version 3.2.2 20030222 (Red Hat Linux 3.2.2-5)) #5 Tue Nov 11 18:18:53 CET 2003 | |
400 | ||
401 | QEMU Linux test distribution (based on Redhat 9) | |
402 | ||
403 | Type 'exit' to halt the system | |
404 | ||
405 | sh-2.05b# | |
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406 | @end example |
407 | ||
408 | @item | |
409 | Then you can play with the kernel inside the virtual serial console. You | |
410 | can launch @code{ls} for example. Type @key{Ctrl-a h} to have an help | |
411 | about the keys you can type inside the virtual serial console. In | |
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412 | particular, use @key{Ctrl-a x} to exit QEMU and use @key{Ctrl-a b} as |
413 | the Magic SysRq key. | |
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414 | |
415 | @item | |
416 | If the network is enabled, launch the script @file{/etc/linuxrc} in the | |
417 | emulator (don't forget the leading dot): | |
418 | @example | |
419 | . /etc/linuxrc | |
420 | @end example | |
421 | ||
422 | Then enable X11 connections on your PC from the emulated Linux: | |
423 | @example | |
424 | xhost +172.20.0.2 | |
425 | @end example | |
426 | ||
427 | You can now launch @file{xterm} or @file{xlogo} and verify that you have | |
428 | a real Virtual Linux system ! | |
429 | ||
430 | @end enumerate | |
431 | ||
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432 | NOTES: |
433 | @enumerate | |
434 | @item | |
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435 | A 2.5.74 kernel is also included in the archive. Just |
436 | replace the bzImage in qemu.sh to try it. | |
d5a0b50c FB |
437 | |
438 | @item | |
9d4520d0 | 439 | qemu creates a temporary file in @var{$QEMU_TMPDIR} (@file{/tmp} is the |
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440 | default) containing all the simulated PC memory. If possible, try to use |
441 | a temporary directory using the tmpfs filesystem to avoid too many | |
442 | unnecessary disk accesses. | |
443 | ||
444 | @item | |
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445 | In order to exit cleanly from qemu, you can do a @emph{shutdown} inside |
446 | qemu. qemu will automatically exit when the Linux shutdown is done. | |
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447 | |
448 | @item | |
449 | You can boot slightly faster by disabling the probe of non present IDE | |
450 | interfaces. To do so, add the following options on the kernel command | |
451 | line: | |
452 | @example | |
453 | ide1=noprobe ide2=noprobe ide3=noprobe ide4=noprobe ide5=noprobe | |
454 | @end example | |
455 | ||
456 | @item | |
457 | The example disk image is a modified version of the one made by Kevin | |
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458 | Lawton for the plex86 Project (@url{www.plex86.org}). |
459 | ||
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460 | @end enumerate |
461 | ||
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462 | @section Invocation |
463 | ||
464 | @example | |
0806e3f6 FB |
465 | @c man begin SYNOPSIS |
466 | usage: qemu [options] [disk_image] | |
467 | @c man end | |
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468 | @end example |
469 | ||
0806e3f6 | 470 | @c man begin OPTIONS |
9d4520d0 | 471 | @var{disk_image} is a raw hard disk image for IDE hard disk 0. |
ec410fc9 FB |
472 | |
473 | General options: | |
474 | @table @option | |
ec410fc9 FB |
475 | @item -hda file |
476 | @item -hdb file | |
181f1558 FB |
477 | @item -hdc file |
478 | @item -hdd file | |
479 | Use @var{file} as hard disk 0, 1, 2 or 3 image (@xref{disk_images}). | |
1f47a922 | 480 | |
181f1558 FB |
481 | @item -cdrom file |
482 | Use @var{file} as CD-ROM image (you cannot use @option{-hdc} and and | |
483 | @option{-cdrom} at the same time). | |
484 | ||
485 | @item -boot [c|d] | |
486 | Boot on hard disk (c) or CD-ROM (d). Hard disk boot is the default. | |
1f47a922 | 487 | |
181f1558 | 488 | @item -snapshot |
1f47a922 FB |
489 | Write to temporary files instead of disk image files. In this case, |
490 | the raw disk image you use is not written back. You can however force | |
491 | the write back by pressing @key{C-a s} (@xref{disk_images}). | |
ec410fc9 FB |
492 | |
493 | @item -m megs | |
494 | Set virtual RAM size to @var{megs} megabytes. | |
495 | ||
496 | @item -n script | |
9d4520d0 | 497 | Set network init script [default=/etc/qemu-ifup]. This script is |
ec410fc9 FB |
498 | launched to configure the host network interface (usually tun0) |
499 | corresponding to the virtual NE2000 card. | |
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500 | |
501 | @item -initrd file | |
0806e3f6 FB |
502 | Use @var{file} as initial ram disk. |
503 | ||
504 | @item -tun-fd fd | |
505 | Assumes @var{fd} talks to tap/tun and use it. Read | |
506 | @url{http://bellard.org/qemu/tetrinet.html} to have an example of its | |
507 | use. | |
508 | ||
509 | @item -nographic | |
510 | ||
511 | Normally, QEMU uses SDL to display the VGA output. With this option, | |
512 | you can totally disable graphical output so that QEMU is a simple | |
513 | command line application. The emulated serial port is redirected on | |
514 | the console. Therefore, you can still use QEMU to debug a Linux kernel | |
515 | with a serial console. | |
516 | ||
517 | @end table | |
518 | ||
519 | Linux boot specific (does not require a full PC boot with a BIOS): | |
520 | @table @option | |
521 | ||
522 | @item -kernel bzImage | |
523 | Use @var{bzImage} as kernel image. | |
524 | ||
525 | @item -append cmdline | |
526 | Use @var{cmdline} as kernel command line | |
527 | ||
528 | @item -initrd file | |
529 | Use @var{file} as initial ram disk. | |
530 | ||
ec410fc9 FB |
531 | @end table |
532 | ||
533 | Debug options: | |
534 | @table @option | |
535 | @item -s | |
0806e3f6 | 536 | Wait gdb connection to port 1234 (@xref{gdb_usage}). |
ec410fc9 FB |
537 | @item -p port |
538 | Change gdb connection port. | |
539 | @item -d | |
9d4520d0 | 540 | Output log in /tmp/qemu.log |
ec410fc9 FB |
541 | @end table |
542 | ||
543 | During emulation, use @key{C-a h} to get terminal commands: | |
544 | ||
545 | @table @key | |
546 | @item C-a h | |
547 | Print this help | |
548 | @item C-a x | |
549 | Exit emulatior | |
1f47a922 FB |
550 | @item C-a s |
551 | Save disk data back to file (if -snapshot) | |
552 | @item C-a b | |
ec410fc9 | 553 | Send break (magic sysrq) |
1f47a922 | 554 | @item C-a C-a |
ec410fc9 FB |
555 | Send C-a |
556 | @end table | |
0806e3f6 FB |
557 | @c man end |
558 | ||
559 | @ignore | |
560 | ||
561 | @setfilename qemu | |
562 | @settitle QEMU System Emulator | |
563 | ||
564 | @c man begin SEEALSO | |
565 | The HTML documentation of QEMU for more precise information and Linux | |
566 | user mode emulator invocation. | |
567 | @c man end | |
568 | ||
569 | @c man begin AUTHOR | |
570 | Fabrice Bellard | |
571 | @c man end | |
572 | ||
573 | @end ignore | |
ec410fc9 | 574 | |
0806e3f6 | 575 | @end ignore |
1f47a922 FB |
576 | @node disk_images |
577 | @section Disk Images | |
578 | ||
579 | @subsection Raw disk images | |
580 | ||
581 | The disk images can simply be raw images of the hard disk. You can | |
582 | create them with the command: | |
583 | @example | |
584 | dd if=/dev/zero of=myimage bs=1024 count=mysize | |
585 | @end example | |
586 | where @var{myimage} is the image filename and @var{mysize} is its size | |
587 | in kilobytes. | |
588 | ||
589 | @subsection Snapshot mode | |
590 | ||
591 | If you use the option @option{-snapshot}, all disk images are | |
592 | considered as read only. When sectors in written, they are written in | |
593 | a temporary file created in @file{/tmp}. You can however force the | |
594 | write back to the raw disk images by pressing @key{C-a s}. | |
595 | ||
596 | NOTE: The snapshot mode only works with raw disk images. | |
597 | ||
598 | @subsection Copy On Write disk images | |
599 | ||
600 | QEMU also supports user mode Linux | |
601 | (@url{http://user-mode-linux.sourceforge.net/}) Copy On Write (COW) | |
602 | disk images. The COW disk images are much smaller than normal images | |
603 | as they store only modified sectors. They also permit the use of the | |
604 | same disk image template for many users. | |
605 | ||
606 | To create a COW disk images, use the command: | |
607 | ||
608 | @example | |
0806e3f6 | 609 | qemu-mkcow -f myrawimage.bin mycowimage.cow |
1f47a922 FB |
610 | @end example |
611 | ||
612 | @file{myrawimage.bin} is a raw image you want to use as original disk | |
613 | image. It will never be written to. | |
614 | ||
615 | @file{mycowimage.cow} is the COW disk image which is created by | |
0806e3f6 | 616 | @code{qemu-mkcow}. You can use it directly with the @option{-hdx} |
1f47a922 FB |
617 | options. You must not modify the original raw disk image if you use |
618 | COW images, as COW images only store the modified sectors from the raw | |
619 | disk image. QEMU stores the original raw disk image name and its | |
620 | modified time in the COW disk image so that chances of mistakes are | |
621 | reduced. | |
622 | ||
9d0fe224 FB |
623 | If the raw disk image is not read-only, by pressing @key{C-a s} you |
624 | can flush the COW disk image back into the raw disk image, as in | |
625 | snapshot mode. | |
1f47a922 FB |
626 | |
627 | COW disk images can also be created without a corresponding raw disk | |
628 | image. It is useful to have a big initial virtual disk image without | |
629 | using much disk space. Use: | |
630 | ||
631 | @example | |
0806e3f6 | 632 | qemu-mkcow mycowimage.cow 1024 |
1f47a922 FB |
633 | @end example |
634 | ||
635 | to create a 1 gigabyte empty COW disk image. | |
636 | ||
637 | NOTES: | |
638 | @enumerate | |
639 | @item | |
640 | COW disk images must be created on file systems supporting | |
641 | @emph{holes} such as ext2 or ext3. | |
642 | @item | |
643 | Since holes are used, the displayed size of the COW disk image is not | |
644 | the real one. To know it, use the @code{ls -ls} command. | |
645 | @end enumerate | |
646 | ||
0806e3f6 | 647 | @node linux_compile |
4690764b FB |
648 | @section Linux Kernel Compilation |
649 | ||
285dc330 FB |
650 | You can use any linux kernel with QEMU. However, if you want to use |
651 | @code{qemu-fast} to get maximum performances, you should make the | |
652 | following changes to the Linux kernel (only 2.4.x and 2.5.x were | |
653 | tested): | |
1eb20527 | 654 | |
4690764b FB |
655 | @enumerate |
656 | @item | |
657 | The kernel must be mapped at 0x90000000 (the default is | |
658 | 0xc0000000). You must modify only two lines in the kernel source: | |
1eb20527 | 659 | |
4690764b | 660 | In @file{include/asm/page.h}, replace |
1eb20527 FB |
661 | @example |
662 | #define __PAGE_OFFSET (0xc0000000) | |
663 | @end example | |
664 | by | |
665 | @example | |
666 | #define __PAGE_OFFSET (0x90000000) | |
667 | @end example | |
668 | ||
4690764b | 669 | And in @file{arch/i386/vmlinux.lds}, replace |
1eb20527 FB |
670 | @example |
671 | . = 0xc0000000 + 0x100000; | |
672 | @end example | |
673 | by | |
674 | @example | |
675 | . = 0x90000000 + 0x100000; | |
676 | @end example | |
677 | ||
4690764b FB |
678 | @item |
679 | If you want to enable SMP (Symmetric Multi-Processing) support, you | |
680 | must make the following change in @file{include/asm/fixmap.h}. Replace | |
1eb20527 | 681 | @example |
4690764b | 682 | #define FIXADDR_TOP (0xffffX000UL) |
1eb20527 | 683 | @end example |
4690764b FB |
684 | by |
685 | @example | |
686 | #define FIXADDR_TOP (0xa7ffX000UL) | |
687 | @end example | |
688 | (X is 'e' or 'f' depending on the kernel version). Although you can | |
689 | use an SMP kernel with QEMU, it only supports one CPU. | |
1eb20527 | 690 | |
4690764b | 691 | @item |
d5a0b50c FB |
692 | If you are not using a 2.5 kernel as host kernel but if you use a target |
693 | 2.5 kernel, you must also ensure that the 'HZ' define is set to 100 | |
694 | (1000 is the default) as QEMU cannot currently emulate timers at | |
695 | frequencies greater than 100 Hz on host Linux systems < 2.5. In | |
4690764b | 696 | @file{include/asm/param.h}, replace: |
d5a0b50c FB |
697 | |
698 | @example | |
699 | # define HZ 1000 /* Internal kernel timer frequency */ | |
700 | @end example | |
701 | by | |
702 | @example | |
703 | # define HZ 100 /* Internal kernel timer frequency */ | |
704 | @end example | |
705 | ||
4690764b FB |
706 | @end enumerate |
707 | ||
708 | The file config-2.x.x gives the configuration of the example kernels. | |
709 | ||
710 | Just type | |
711 | @example | |
712 | make bzImage | |
713 | @end example | |
714 | ||
715 | As you would do to make a real kernel. Then you can use with QEMU | |
716 | exactly the same kernel as you would boot on your PC (in | |
717 | @file{arch/i386/boot/bzImage}). | |
da415d54 | 718 | |
0806e3f6 | 719 | @node gdb_usage |
da415d54 FB |
720 | @section GDB usage |
721 | ||
722 | QEMU has a primitive support to work with gdb, so that you can do | |
0806e3f6 | 723 | 'Ctrl-C' while the virtual machine is running and inspect its state. |
da415d54 | 724 | |
9d4520d0 | 725 | In order to use gdb, launch qemu with the '-s' option. It will wait for a |
da415d54 FB |
726 | gdb connection: |
727 | @example | |
9d4520d0 | 728 | > qemu -s arch/i386/boot/bzImage -hda root-2.4.20.img root=/dev/hda |
da415d54 FB |
729 | Connected to host network interface: tun0 |
730 | Waiting gdb connection on port 1234 | |
731 | @end example | |
732 | ||
733 | Then launch gdb on the 'vmlinux' executable: | |
734 | @example | |
735 | > gdb vmlinux | |
736 | @end example | |
737 | ||
738 | In gdb, connect to QEMU: | |
739 | @example | |
740 | (gdb) target remote locahost:1234 | |
741 | @end example | |
742 | ||
743 | Then you can use gdb normally. For example, type 'c' to launch the kernel: | |
744 | @example | |
745 | (gdb) c | |
746 | @end example | |
747 | ||
0806e3f6 FB |
748 | Here are some useful tips in order to use gdb on system code: |
749 | ||
750 | @enumerate | |
751 | @item | |
752 | Use @code{info reg} to display all the CPU registers. | |
753 | @item | |
754 | Use @code{x/10i $eip} to display the code at the PC position. | |
755 | @item | |
756 | Use @code{set architecture i8086} to dump 16 bit code. Then use | |
757 | @code{x/10i $cs*16+*eip} to dump the code at the PC position. | |
758 | @end enumerate | |
759 | ||
386405f7 FB |
760 | @chapter QEMU Internals |
761 | ||
762 | @section QEMU compared to other emulators | |
763 | ||
1eb20527 FB |
764 | Like bochs [3], QEMU emulates an x86 CPU. But QEMU is much faster than |
765 | bochs as it uses dynamic compilation and because it uses the host MMU to | |
766 | simulate the x86 MMU. The downside is that currently the emulation is | |
767 | not as accurate as bochs (for example, you cannot currently run Windows | |
768 | inside QEMU). | |
386405f7 FB |
769 | |
770 | Like Valgrind [2], QEMU does user space emulation and dynamic | |
771 | translation. Valgrind is mainly a memory debugger while QEMU has no | |
1eb20527 FB |
772 | support for it (QEMU could be used to detect out of bound memory |
773 | accesses as Valgrind, but it has no support to track uninitialised data | |
d5a0b50c | 774 | as Valgrind does). The Valgrind dynamic translator generates better code |
1eb20527 | 775 | than QEMU (in particular it does register allocation) but it is closely |
d5a0b50c | 776 | tied to an x86 host and target and has no support for precise exceptions |
1eb20527 FB |
777 | and system emulation. |
778 | ||
779 | EM86 [4] is the closest project to user space QEMU (and QEMU still uses | |
780 | some of its code, in particular the ELF file loader). EM86 was limited | |
781 | to an alpha host and used a proprietary and slow interpreter (the | |
782 | interpreter part of the FX!32 Digital Win32 code translator [5]). | |
386405f7 | 783 | |
fd429f2f FB |
784 | TWIN [6] is a Windows API emulator like Wine. It is less accurate than |
785 | Wine but includes a protected mode x86 interpreter to launch x86 Windows | |
786 | executables. Such an approach as greater potential because most of the | |
787 | Windows API is executed natively but it is far more difficult to develop | |
788 | because all the data structures and function parameters exchanged | |
789 | between the API and the x86 code must be converted. | |
790 | ||
1eb20527 FB |
791 | User mode Linux [7] was the only solution before QEMU to launch a Linux |
792 | kernel as a process while not needing any host kernel patches. However, | |
793 | user mode Linux requires heavy kernel patches while QEMU accepts | |
794 | unpatched Linux kernels. It would be interesting to compare the | |
795 | performance of the two approaches. | |
796 | ||
797 | The new Plex86 [8] PC virtualizer is done in the same spirit as the QEMU | |
798 | system emulator. It requires a patched Linux kernel to work (you cannot | |
799 | launch the same kernel on your PC), but the patches are really small. As | |
800 | it is a PC virtualizer (no emulation is done except for some priveledged | |
801 | instructions), it has the potential of being faster than QEMU. The | |
d5a0b50c FB |
802 | downside is that a complicated (and potentially unsafe) host kernel |
803 | patch is needed. | |
1eb20527 | 804 | |
386405f7 FB |
805 | @section Portable dynamic translation |
806 | ||
807 | QEMU is a dynamic translator. When it first encounters a piece of code, | |
808 | it converts it to the host instruction set. Usually dynamic translators | |
322d0c66 | 809 | are very complicated and highly CPU dependent. QEMU uses some tricks |
386405f7 FB |
810 | which make it relatively easily portable and simple while achieving good |
811 | performances. | |
812 | ||
813 | The basic idea is to split every x86 instruction into fewer simpler | |
814 | instructions. Each simple instruction is implemented by a piece of C | |
815 | code (see @file{op-i386.c}). Then a compile time tool (@file{dyngen}) | |
816 | takes the corresponding object file (@file{op-i386.o}) to generate a | |
817 | dynamic code generator which concatenates the simple instructions to | |
818 | build a function (see @file{op-i386.h:dyngen_code()}). | |
819 | ||
820 | In essence, the process is similar to [1], but more work is done at | |
821 | compile time. | |
822 | ||
823 | A key idea to get optimal performances is that constant parameters can | |
824 | be passed to the simple operations. For that purpose, dummy ELF | |
825 | relocations are generated with gcc for each constant parameter. Then, | |
826 | the tool (@file{dyngen}) can locate the relocations and generate the | |
827 | appriopriate C code to resolve them when building the dynamic code. | |
828 | ||
829 | That way, QEMU is no more difficult to port than a dynamic linker. | |
830 | ||
831 | To go even faster, GCC static register variables are used to keep the | |
832 | state of the virtual CPU. | |
833 | ||
834 | @section Register allocation | |
835 | ||
836 | Since QEMU uses fixed simple instructions, no efficient register | |
837 | allocation can be done. However, because RISC CPUs have a lot of | |
838 | register, most of the virtual CPU state can be put in registers without | |
839 | doing complicated register allocation. | |
840 | ||
841 | @section Condition code optimisations | |
842 | ||
843 | Good CPU condition codes emulation (@code{EFLAGS} register on x86) is a | |
844 | critical point to get good performances. QEMU uses lazy condition code | |
845 | evaluation: instead of computing the condition codes after each x86 | |
fd429f2f | 846 | instruction, it just stores one operand (called @code{CC_SRC}), the |
386405f7 FB |
847 | result (called @code{CC_DST}) and the type of operation (called |
848 | @code{CC_OP}). | |
849 | ||
850 | @code{CC_OP} is almost never explicitely set in the generated code | |
851 | because it is known at translation time. | |
852 | ||
853 | In order to increase performances, a backward pass is performed on the | |
854 | generated simple instructions (see | |
855 | @code{translate-i386.c:optimize_flags()}). When it can be proved that | |
856 | the condition codes are not needed by the next instructions, no | |
857 | condition codes are computed at all. | |
858 | ||
fd429f2f | 859 | @section CPU state optimisations |
386405f7 FB |
860 | |
861 | The x86 CPU has many internal states which change the way it evaluates | |
862 | instructions. In order to achieve a good speed, the translation phase | |
863 | considers that some state information of the virtual x86 CPU cannot | |
864 | change in it. For example, if the SS, DS and ES segments have a zero | |
865 | base, then the translator does not even generate an addition for the | |
866 | segment base. | |
867 | ||
868 | [The FPU stack pointer register is not handled that way yet]. | |
869 | ||
870 | @section Translation cache | |
871 | ||
872 | A 2MByte cache holds the most recently used translations. For | |
873 | simplicity, it is completely flushed when it is full. A translation unit | |
874 | contains just a single basic block (a block of x86 instructions | |
875 | terminated by a jump or by a virtual CPU state change which the | |
876 | translator cannot deduce statically). | |
877 | ||
df0f11a0 FB |
878 | @section Direct block chaining |
879 | ||
880 | After each translated basic block is executed, QEMU uses the simulated | |
881 | Program Counter (PC) and other cpu state informations (such as the CS | |
882 | segment base value) to find the next basic block. | |
883 | ||
884 | In order to accelerate the most common cases where the new simulated PC | |
885 | is known, QEMU can patch a basic block so that it jumps directly to the | |
886 | next one. | |
887 | ||
888 | The most portable code uses an indirect jump. An indirect jump makes it | |
889 | easier to make the jump target modification atomic. On some | |
890 | architectures (such as PowerPC), the @code{JUMP} opcode is directly | |
891 | patched so that the block chaining has no overhead. | |
892 | ||
893 | @section Self-modifying code and translated code invalidation | |
894 | ||
895 | Self-modifying code is a special challenge in x86 emulation because no | |
896 | instruction cache invalidation is signaled by the application when code | |
897 | is modified. | |
898 | ||
899 | When translated code is generated for a basic block, the corresponding | |
900 | host page is write protected if it is not already read-only (with the | |
901 | system call @code{mprotect()}). Then, if a write access is done to the | |
902 | page, Linux raises a SEGV signal. QEMU then invalidates all the | |
903 | translated code in the page and enables write accesses to the page. | |
904 | ||
905 | Correct translated code invalidation is done efficiently by maintaining | |
906 | a linked list of every translated block contained in a given page. Other | |
907 | linked lists are also maintained to undo direct block chaining. | |
908 | ||
4690764b | 909 | Although the overhead of doing @code{mprotect()} calls is important, |
df0f11a0 FB |
910 | most MSDOS programs can be emulated at reasonnable speed with QEMU and |
911 | DOSEMU. | |
912 | ||
913 | Note that QEMU also invalidates pages of translated code when it detects | |
914 | that memory mappings are modified with @code{mmap()} or @code{munmap()}. | |
386405f7 FB |
915 | |
916 | @section Exception support | |
917 | ||
918 | longjmp() is used when an exception such as division by zero is | |
df0f11a0 | 919 | encountered. |
386405f7 | 920 | |
df0f11a0 FB |
921 | The host SIGSEGV and SIGBUS signal handlers are used to get invalid |
922 | memory accesses. The exact CPU state can be retrieved because all the | |
923 | x86 registers are stored in fixed host registers. The simulated program | |
924 | counter is found by retranslating the corresponding basic block and by | |
925 | looking where the host program counter was at the exception point. | |
926 | ||
927 | The virtual CPU cannot retrieve the exact @code{EFLAGS} register because | |
928 | in some cases it is not computed because of condition code | |
929 | optimisations. It is not a big concern because the emulated code can | |
930 | still be restarted in any cases. | |
386405f7 FB |
931 | |
932 | @section Linux system call translation | |
933 | ||
934 | QEMU includes a generic system call translator for Linux. It means that | |
935 | the parameters of the system calls can be converted to fix the | |
936 | endianness and 32/64 bit issues. The IOCTLs are converted with a generic | |
937 | type description system (see @file{ioctls.h} and @file{thunk.c}). | |
938 | ||
df0f11a0 FB |
939 | QEMU supports host CPUs which have pages bigger than 4KB. It records all |
940 | the mappings the process does and try to emulated the @code{mmap()} | |
941 | system calls in cases where the host @code{mmap()} call would fail | |
942 | because of bad page alignment. | |
943 | ||
386405f7 FB |
944 | @section Linux signals |
945 | ||
946 | Normal and real-time signals are queued along with their information | |
947 | (@code{siginfo_t}) as it is done in the Linux kernel. Then an interrupt | |
948 | request is done to the virtual CPU. When it is interrupted, one queued | |
949 | signal is handled by generating a stack frame in the virtual CPU as the | |
950 | Linux kernel does. The @code{sigreturn()} system call is emulated to return | |
951 | from the virtual signal handler. | |
952 | ||
953 | Some signals (such as SIGALRM) directly come from the host. Other | |
954 | signals are synthetized from the virtual CPU exceptions such as SIGFPE | |
955 | when a division by zero is done (see @code{main.c:cpu_loop()}). | |
956 | ||
957 | The blocked signal mask is still handled by the host Linux kernel so | |
958 | that most signal system calls can be redirected directly to the host | |
959 | Linux kernel. Only the @code{sigaction()} and @code{sigreturn()} system | |
960 | calls need to be fully emulated (see @file{signal.c}). | |
961 | ||
962 | @section clone() system call and threads | |
963 | ||
964 | The Linux clone() system call is usually used to create a thread. QEMU | |
965 | uses the host clone() system call so that real host threads are created | |
966 | for each emulated thread. One virtual CPU instance is created for each | |
967 | thread. | |
968 | ||
969 | The virtual x86 CPU atomic operations are emulated with a global lock so | |
970 | that their semantic is preserved. | |
971 | ||
df0f11a0 FB |
972 | Note that currently there are still some locking issues in QEMU. In |
973 | particular, the translated cache flush is not protected yet against | |
974 | reentrancy. | |
975 | ||
1eb87257 FB |
976 | @section Self-virtualization |
977 | ||
4690764b | 978 | QEMU was conceived so that ultimately it can emulate itself. Although |
1eb87257 FB |
979 | it is not very useful, it is an important test to show the power of the |
980 | emulator. | |
981 | ||
982 | Achieving self-virtualization is not easy because there may be address | |
6cd9f35b FB |
983 | space conflicts. QEMU solves this problem by being an executable ELF |
984 | shared object as the ld-linux.so ELF interpreter. That way, it can be | |
985 | relocated at load time. | |
1eb87257 | 986 | |
1eb20527 FB |
987 | @section MMU emulation |
988 | ||
989 | For system emulation, QEMU uses the mmap() system call to emulate the | |
990 | target CPU MMU. It works as long the emulated OS does not use an area | |
991 | reserved by the host OS (such as the area above 0xc0000000 on x86 | |
992 | Linux). | |
993 | ||
994 | It is planned to add a slower but more precise MMU emulation | |
995 | with a software MMU. | |
996 | ||
386405f7 FB |
997 | @section Bibliography |
998 | ||
999 | @table @asis | |
1000 | ||
1001 | @item [1] | |
1002 | @url{http://citeseer.nj.nec.com/piumarta98optimizing.html}, Optimizing | |
1003 | direct threaded code by selective inlining (1998) by Ian Piumarta, Fabio | |
1004 | Riccardi. | |
1005 | ||
1006 | @item [2] | |
1007 | @url{http://developer.kde.org/~sewardj/}, Valgrind, an open-source | |
1008 | memory debugger for x86-GNU/Linux, by Julian Seward. | |
1009 | ||
1010 | @item [3] | |
1011 | @url{http://bochs.sourceforge.net/}, the Bochs IA-32 Emulator Project, | |
1012 | by Kevin Lawton et al. | |
1013 | ||
1014 | @item [4] | |
1015 | @url{http://www.cs.rose-hulman.edu/~donaldlf/em86/index.html}, the EM86 | |
1016 | x86 emulator on Alpha-Linux. | |
1017 | ||
1018 | @item [5] | |
1019 | @url{http://www.usenix.org/publications/library/proceedings/usenix-nt97/full_papers/chernoff/chernoff.pdf}, | |
1020 | DIGITAL FX!32: Running 32-Bit x86 Applications on Alpha NT, by Anton | |
1021 | Chernoff and Ray Hookway. | |
1022 | ||
fd429f2f FB |
1023 | @item [6] |
1024 | @url{http://www.willows.com/}, Windows API library emulation from | |
1025 | Willows Software. | |
1026 | ||
1eb20527 FB |
1027 | @item [7] |
1028 | @url{http://user-mode-linux.sourceforge.net/}, | |
1029 | The User-mode Linux Kernel. | |
1030 | ||
1031 | @item [8] | |
1032 | @url{http://www.plex86.org/}, | |
1033 | The new Plex86 project. | |
1034 | ||
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1035 | @end table |
1036 | ||
1037 | @chapter Regression Tests | |
1038 | ||
322d0c66 | 1039 | In the directory @file{tests/}, various interesting testing programs |
386405f7 FB |
1040 | are available. There are used for regression testing. |
1041 | ||
386405f7 FB |
1042 | @section @file{test-i386} |
1043 | ||
1044 | This program executes most of the 16 bit and 32 bit x86 instructions and | |
1045 | generates a text output. It can be compared with the output obtained with | |
1046 | a real CPU or another emulator. The target @code{make test} runs this | |
1047 | program and a @code{diff} on the generated output. | |
1048 | ||
1049 | The Linux system call @code{modify_ldt()} is used to create x86 selectors | |
1050 | to test some 16 bit addressing and 32 bit with segmentation cases. | |
1051 | ||
df0f11a0 | 1052 | The Linux system call @code{vm86()} is used to test vm86 emulation. |
386405f7 | 1053 | |
df0f11a0 FB |
1054 | Various exceptions are raised to test most of the x86 user space |
1055 | exception reporting. | |
386405f7 | 1056 | |
285dc330 FB |
1057 | @section @file{linux-test} |
1058 | ||
1059 | This program tests various Linux system calls. It is used to verify | |
1060 | that the system call parameters are correctly converted between target | |
1061 | and host CPUs. | |
1062 | ||
1063 | @section @file{hello-i386} | |
1064 | ||
1065 | Very simple statically linked x86 program, just to test QEMU during a | |
1066 | port to a new host CPU. | |
1067 | ||
1068 | @section @file{hello-arm} | |
1069 | ||
1070 | Very simple statically linked ARM program, just to test QEMU during a | |
1071 | port to a new host CPU. | |
1072 | ||
386405f7 FB |
1073 | @section @file{sha1} |
1074 | ||
1075 | It is a simple benchmark. Care must be taken to interpret the results | |
1076 | because it mostly tests the ability of the virtual CPU to optimize the | |
1077 | @code{rol} x86 instruction and the condition code computations. | |
1078 |