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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 | |
284 | IDE disk interface (port=0x1f0, irq=14) | |
285 | @item | |
286 | NE2000 network adapter (port=0x300, irq=9) | |
287 | @item | |
288 | Serial port (port=0x3f8, irq=4) | |
289 | @item | |
290 | PIC (interrupt controler) | |
291 | @item | |
292 | PIT (timers) | |
293 | @item | |
294 | CMOS memory | |
295 | @end itemize | |
296 | ||
297 | @c man end | |
298 | ||
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299 | @section Quick Start |
300 | ||
285dc330 | 301 | Download and uncompress the linux image (@file{linux.img}) and type: |
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302 | |
303 | @example | |
285dc330 | 304 | qemu linux.img |
0806e3f6 FB |
305 | @end example |
306 | ||
307 | Linux should boot and give you a prompt. | |
308 | ||
309 | @section Direct Linux Boot and Network emulation | |
310 | ||
311 | This section explains how to launch a Linux kernel inside QEMU without | |
312 | having to make a full bootable image. It is very useful for fast Linux | |
313 | kernel testing. The QEMU network configuration is also explained. | |
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314 | |
315 | @enumerate | |
316 | @item | |
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317 | Download the archive @file{linux-test-xxx.tar.gz} containing a Linux |
318 | kernel and a disk image. | |
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319 | |
320 | @item Optional: If you want network support (for example to launch X11 examples), you | |
0806e3f6 | 321 | must copy the script @file{qemu-ifup} in @file{/etc} and configure |
1eb20527 | 322 | properly @code{sudo} so that the command @code{ifconfig} contained in |
0806e3f6 | 323 | @file{qemu-ifup} can be executed as root. You must verify that your host |
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324 | kernel supports the TUN/TAP network interfaces: the device |
325 | @file{/dev/net/tun} must be present. | |
326 | ||
327 | When network is enabled, there is a virtual network connection between | |
328 | the host kernel and the emulated kernel. The emulated kernel is seen | |
329 | from the host kernel at IP address 172.20.0.2 and the host kernel is | |
330 | seen from the emulated kernel at IP address 172.20.0.1. | |
331 | ||
0806e3f6 | 332 | @item Launch @code{qemu.sh}. You should have the following output: |
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333 | |
334 | @example | |
0806e3f6 | 335 | > ./qemu.sh |
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336 | connected to host network interface: tun0 |
337 | Uncompressing Linux... Ok, booting the kernel. | |
4690764b | 338 | Linux version 2.4.20 (fabrice@localhost.localdomain) (gcc version 2.96 20000731 (Red Hat Linux 7.3 2.96-110)) #22 lun jui 7 13:37:41 CEST 2003 |
1eb20527 | 339 | BIOS-provided physical RAM map: |
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340 | BIOS-e801: 0000000000000000 - 000000000009f000 (usable) |
341 | BIOS-e801: 0000000000100000 - 0000000002000000 (usable) | |
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342 | 32MB LOWMEM available. |
343 | On node 0 totalpages: 8192 | |
344 | zone(0): 4096 pages. | |
345 | zone(1): 4096 pages. | |
346 | zone(2): 0 pages. | |
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347 | Kernel command line: root=/dev/hda ide1=noprobe ide2=noprobe ide3=noprobe ide4=noprobe ide5=noprobe |
348 | ide_setup: ide1=noprobe | |
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 501.285 MHz processor. |
355 | Calibrating delay loop... 989.59 BogoMIPS | |
356 | Memory: 29268k/32768k available (907k kernel code, 3112k reserved, 212k data, 52k init, 0k highmem) | |
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357 | Dentry cache hash table entries: 4096 (order: 3, 32768 bytes) |
358 | Inode cache hash table entries: 2048 (order: 2, 16384 bytes) | |
359 | Mount-cache hash table entries: 512 (order: 0, 4096 bytes) | |
360 | Buffer-cache hash table entries: 1024 (order: 0, 4096 bytes) | |
361 | Page-cache hash table entries: 8192 (order: 3, 32768 bytes) | |
362 | CPU: Intel Pentium Pro stepping 03 | |
363 | Checking 'hlt' instruction... OK. | |
364 | POSIX conformance testing by UNIFIX | |
365 | Linux NET4.0 for Linux 2.4 | |
366 | Based upon Swansea University Computer Society NET3.039 | |
367 | Initializing RT netlink socket | |
368 | apm: BIOS not found. | |
369 | Starting kswapd | |
4690764b | 370 | Journalled Block Device driver loaded |
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371 | pty: 256 Unix98 ptys configured |
372 | Serial driver version 5.05c (2001-07-08) with no serial options enabled | |
373 | ttyS00 at 0x03f8 (irq = 4) is a 16450 | |
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374 | Uniform Multi-Platform E-IDE driver Revision: 6.31 |
375 | ide: Assuming 50MHz system bus speed for PIO modes; override with idebus=xx | |
376 | hda: QEMU HARDDISK, ATA DISK drive | |
377 | ide0 at 0x1f0-0x1f7,0x3f6 on irq 14 | |
378 | hda: 12288 sectors (6 MB) w/256KiB Cache, CHS=12/16/63 | |
379 | Partition check: | |
380 | hda: unknown partition table | |
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381 | ne.c:v1.10 9/23/94 Donald Becker (becker@scyld.com) |
382 | Last modified Nov 1, 2000 by Paul Gortmaker | |
383 | NE*000 ethercard probe at 0x300: 52 54 00 12 34 56 | |
384 | eth0: NE2000 found at 0x300, using IRQ 9. | |
4690764b | 385 | RAMDISK driver initialized: 16 RAM disks of 4096K size 1024 blocksize |
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386 | NET4: Linux TCP/IP 1.0 for NET4.0 |
387 | IP Protocols: ICMP, UDP, TCP, IGMP | |
388 | IP: routing cache hash table of 512 buckets, 4Kbytes | |
4690764b | 389 | TCP: Hash tables configured (established 2048 bind 4096) |
1eb20527 | 390 | NET4: Unix domain sockets 1.0/SMP for Linux NET4.0. |
4690764b | 391 | EXT2-fs warning: mounting unchecked fs, running e2fsck is recommended |
1eb20527 | 392 | VFS: Mounted root (ext2 filesystem). |
4690764b | 393 | Freeing unused kernel memory: 52k freed |
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394 | sh: can't access tty; job control turned off |
395 | # | |
396 | @end example | |
397 | ||
398 | @item | |
399 | Then you can play with the kernel inside the virtual serial console. You | |
400 | can launch @code{ls} for example. Type @key{Ctrl-a h} to have an help | |
401 | about the keys you can type inside the virtual serial console. In | |
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402 | particular, use @key{Ctrl-a x} to exit QEMU and use @key{Ctrl-a b} as |
403 | the Magic SysRq key. | |
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404 | |
405 | @item | |
406 | If the network is enabled, launch the script @file{/etc/linuxrc} in the | |
407 | emulator (don't forget the leading dot): | |
408 | @example | |
409 | . /etc/linuxrc | |
410 | @end example | |
411 | ||
412 | Then enable X11 connections on your PC from the emulated Linux: | |
413 | @example | |
414 | xhost +172.20.0.2 | |
415 | @end example | |
416 | ||
417 | You can now launch @file{xterm} or @file{xlogo} and verify that you have | |
418 | a real Virtual Linux system ! | |
419 | ||
420 | @end enumerate | |
421 | ||
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422 | NOTES: |
423 | @enumerate | |
424 | @item | |
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425 | A 2.5.74 kernel is also included in the archive. Just |
426 | replace the bzImage in qemu.sh to try it. | |
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427 | |
428 | @item | |
9d4520d0 | 429 | qemu creates a temporary file in @var{$QEMU_TMPDIR} (@file{/tmp} is the |
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430 | default) containing all the simulated PC memory. If possible, try to use |
431 | a temporary directory using the tmpfs filesystem to avoid too many | |
432 | unnecessary disk accesses. | |
433 | ||
434 | @item | |
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435 | In order to exit cleanly from qemu, you can do a @emph{shutdown} inside |
436 | qemu. qemu will automatically exit when the Linux shutdown is done. | |
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437 | |
438 | @item | |
439 | You can boot slightly faster by disabling the probe of non present IDE | |
440 | interfaces. To do so, add the following options on the kernel command | |
441 | line: | |
442 | @example | |
443 | ide1=noprobe ide2=noprobe ide3=noprobe ide4=noprobe ide5=noprobe | |
444 | @end example | |
445 | ||
446 | @item | |
447 | The example disk image is a modified version of the one made by Kevin | |
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448 | Lawton for the plex86 Project (@url{www.plex86.org}). |
449 | ||
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450 | @end enumerate |
451 | ||
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452 | @section Invocation |
453 | ||
454 | @example | |
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455 | @c man begin SYNOPSIS |
456 | usage: qemu [options] [disk_image] | |
457 | @c man end | |
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458 | @end example |
459 | ||
0806e3f6 | 460 | @c man begin OPTIONS |
9d4520d0 | 461 | @var{disk_image} is a raw hard disk image for IDE hard disk 0. |
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462 | |
463 | General options: | |
464 | @table @option | |
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465 | @item -hda file |
466 | @item -hdb file | |
0806e3f6 | 467 | Use @var{file} as hard disk 0 or 1 image (@xref{disk_images}). |
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468 | |
469 | @item -snapshot | |
470 | ||
471 | Write to temporary files instead of disk image files. In this case, | |
472 | the raw disk image you use is not written back. You can however force | |
473 | the write back by pressing @key{C-a s} (@xref{disk_images}). | |
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474 | |
475 | @item -m megs | |
476 | Set virtual RAM size to @var{megs} megabytes. | |
477 | ||
478 | @item -n script | |
9d4520d0 | 479 | Set network init script [default=/etc/qemu-ifup]. This script is |
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480 | launched to configure the host network interface (usually tun0) |
481 | corresponding to the virtual NE2000 card. | |
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482 | |
483 | @item -initrd file | |
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484 | Use @var{file} as initial ram disk. |
485 | ||
486 | @item -tun-fd fd | |
487 | Assumes @var{fd} talks to tap/tun and use it. Read | |
488 | @url{http://bellard.org/qemu/tetrinet.html} to have an example of its | |
489 | use. | |
490 | ||
491 | @item -nographic | |
492 | ||
493 | Normally, QEMU uses SDL to display the VGA output. With this option, | |
494 | you can totally disable graphical output so that QEMU is a simple | |
495 | command line application. The emulated serial port is redirected on | |
496 | the console. Therefore, you can still use QEMU to debug a Linux kernel | |
497 | with a serial console. | |
498 | ||
499 | @end table | |
500 | ||
501 | Linux boot specific (does not require a full PC boot with a BIOS): | |
502 | @table @option | |
503 | ||
504 | @item -kernel bzImage | |
505 | Use @var{bzImage} as kernel image. | |
506 | ||
507 | @item -append cmdline | |
508 | Use @var{cmdline} as kernel command line | |
509 | ||
510 | @item -initrd file | |
511 | Use @var{file} as initial ram disk. | |
512 | ||
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513 | @end table |
514 | ||
515 | Debug options: | |
516 | @table @option | |
517 | @item -s | |
0806e3f6 | 518 | Wait gdb connection to port 1234 (@xref{gdb_usage}). |
ec410fc9 FB |
519 | @item -p port |
520 | Change gdb connection port. | |
521 | @item -d | |
9d4520d0 | 522 | Output log in /tmp/qemu.log |
ec410fc9 FB |
523 | @end table |
524 | ||
525 | During emulation, use @key{C-a h} to get terminal commands: | |
526 | ||
527 | @table @key | |
528 | @item C-a h | |
529 | Print this help | |
530 | @item C-a x | |
531 | Exit emulatior | |
1f47a922 FB |
532 | @item C-a s |
533 | Save disk data back to file (if -snapshot) | |
534 | @item C-a b | |
ec410fc9 | 535 | Send break (magic sysrq) |
1f47a922 | 536 | @item C-a C-a |
ec410fc9 FB |
537 | Send C-a |
538 | @end table | |
0806e3f6 FB |
539 | @c man end |
540 | ||
541 | @ignore | |
542 | ||
543 | @setfilename qemu | |
544 | @settitle QEMU System Emulator | |
545 | ||
546 | @c man begin SEEALSO | |
547 | The HTML documentation of QEMU for more precise information and Linux | |
548 | user mode emulator invocation. | |
549 | @c man end | |
550 | ||
551 | @c man begin AUTHOR | |
552 | Fabrice Bellard | |
553 | @c man end | |
554 | ||
555 | @end ignore | |
ec410fc9 | 556 | |
0806e3f6 | 557 | @end ignore |
1f47a922 FB |
558 | @node disk_images |
559 | @section Disk Images | |
560 | ||
561 | @subsection Raw disk images | |
562 | ||
563 | The disk images can simply be raw images of the hard disk. You can | |
564 | create them with the command: | |
565 | @example | |
566 | dd if=/dev/zero of=myimage bs=1024 count=mysize | |
567 | @end example | |
568 | where @var{myimage} is the image filename and @var{mysize} is its size | |
569 | in kilobytes. | |
570 | ||
571 | @subsection Snapshot mode | |
572 | ||
573 | If you use the option @option{-snapshot}, all disk images are | |
574 | considered as read only. When sectors in written, they are written in | |
575 | a temporary file created in @file{/tmp}. You can however force the | |
576 | write back to the raw disk images by pressing @key{C-a s}. | |
577 | ||
578 | NOTE: The snapshot mode only works with raw disk images. | |
579 | ||
580 | @subsection Copy On Write disk images | |
581 | ||
582 | QEMU also supports user mode Linux | |
583 | (@url{http://user-mode-linux.sourceforge.net/}) Copy On Write (COW) | |
584 | disk images. The COW disk images are much smaller than normal images | |
585 | as they store only modified sectors. They also permit the use of the | |
586 | same disk image template for many users. | |
587 | ||
588 | To create a COW disk images, use the command: | |
589 | ||
590 | @example | |
0806e3f6 | 591 | qemu-mkcow -f myrawimage.bin mycowimage.cow |
1f47a922 FB |
592 | @end example |
593 | ||
594 | @file{myrawimage.bin} is a raw image you want to use as original disk | |
595 | image. It will never be written to. | |
596 | ||
597 | @file{mycowimage.cow} is the COW disk image which is created by | |
0806e3f6 | 598 | @code{qemu-mkcow}. You can use it directly with the @option{-hdx} |
1f47a922 FB |
599 | options. You must not modify the original raw disk image if you use |
600 | COW images, as COW images only store the modified sectors from the raw | |
601 | disk image. QEMU stores the original raw disk image name and its | |
602 | modified time in the COW disk image so that chances of mistakes are | |
603 | reduced. | |
604 | ||
9d0fe224 FB |
605 | If the raw disk image is not read-only, by pressing @key{C-a s} you |
606 | can flush the COW disk image back into the raw disk image, as in | |
607 | snapshot mode. | |
1f47a922 FB |
608 | |
609 | COW disk images can also be created without a corresponding raw disk | |
610 | image. It is useful to have a big initial virtual disk image without | |
611 | using much disk space. Use: | |
612 | ||
613 | @example | |
0806e3f6 | 614 | qemu-mkcow mycowimage.cow 1024 |
1f47a922 FB |
615 | @end example |
616 | ||
617 | to create a 1 gigabyte empty COW disk image. | |
618 | ||
619 | NOTES: | |
620 | @enumerate | |
621 | @item | |
622 | COW disk images must be created on file systems supporting | |
623 | @emph{holes} such as ext2 or ext3. | |
624 | @item | |
625 | Since holes are used, the displayed size of the COW disk image is not | |
626 | the real one. To know it, use the @code{ls -ls} command. | |
627 | @end enumerate | |
628 | ||
0806e3f6 | 629 | @node linux_compile |
4690764b FB |
630 | @section Linux Kernel Compilation |
631 | ||
285dc330 FB |
632 | You can use any linux kernel with QEMU. However, if you want to use |
633 | @code{qemu-fast} to get maximum performances, you should make the | |
634 | following changes to the Linux kernel (only 2.4.x and 2.5.x were | |
635 | tested): | |
1eb20527 | 636 | |
4690764b FB |
637 | @enumerate |
638 | @item | |
639 | The kernel must be mapped at 0x90000000 (the default is | |
640 | 0xc0000000). You must modify only two lines in the kernel source: | |
1eb20527 | 641 | |
4690764b | 642 | In @file{include/asm/page.h}, replace |
1eb20527 FB |
643 | @example |
644 | #define __PAGE_OFFSET (0xc0000000) | |
645 | @end example | |
646 | by | |
647 | @example | |
648 | #define __PAGE_OFFSET (0x90000000) | |
649 | @end example | |
650 | ||
4690764b | 651 | And in @file{arch/i386/vmlinux.lds}, replace |
1eb20527 FB |
652 | @example |
653 | . = 0xc0000000 + 0x100000; | |
654 | @end example | |
655 | by | |
656 | @example | |
657 | . = 0x90000000 + 0x100000; | |
658 | @end example | |
659 | ||
4690764b FB |
660 | @item |
661 | If you want to enable SMP (Symmetric Multi-Processing) support, you | |
662 | must make the following change in @file{include/asm/fixmap.h}. Replace | |
1eb20527 | 663 | @example |
4690764b | 664 | #define FIXADDR_TOP (0xffffX000UL) |
1eb20527 | 665 | @end example |
4690764b FB |
666 | by |
667 | @example | |
668 | #define FIXADDR_TOP (0xa7ffX000UL) | |
669 | @end example | |
670 | (X is 'e' or 'f' depending on the kernel version). Although you can | |
671 | use an SMP kernel with QEMU, it only supports one CPU. | |
1eb20527 | 672 | |
4690764b | 673 | @item |
d5a0b50c FB |
674 | If you are not using a 2.5 kernel as host kernel but if you use a target |
675 | 2.5 kernel, you must also ensure that the 'HZ' define is set to 100 | |
676 | (1000 is the default) as QEMU cannot currently emulate timers at | |
677 | frequencies greater than 100 Hz on host Linux systems < 2.5. In | |
4690764b | 678 | @file{include/asm/param.h}, replace: |
d5a0b50c FB |
679 | |
680 | @example | |
681 | # define HZ 1000 /* Internal kernel timer frequency */ | |
682 | @end example | |
683 | by | |
684 | @example | |
685 | # define HZ 100 /* Internal kernel timer frequency */ | |
686 | @end example | |
687 | ||
4690764b FB |
688 | @end enumerate |
689 | ||
690 | The file config-2.x.x gives the configuration of the example kernels. | |
691 | ||
692 | Just type | |
693 | @example | |
694 | make bzImage | |
695 | @end example | |
696 | ||
697 | As you would do to make a real kernel. Then you can use with QEMU | |
698 | exactly the same kernel as you would boot on your PC (in | |
699 | @file{arch/i386/boot/bzImage}). | |
da415d54 | 700 | |
0806e3f6 | 701 | @node gdb_usage |
da415d54 FB |
702 | @section GDB usage |
703 | ||
704 | QEMU has a primitive support to work with gdb, so that you can do | |
0806e3f6 | 705 | 'Ctrl-C' while the virtual machine is running and inspect its state. |
da415d54 | 706 | |
9d4520d0 | 707 | In order to use gdb, launch qemu with the '-s' option. It will wait for a |
da415d54 FB |
708 | gdb connection: |
709 | @example | |
9d4520d0 | 710 | > qemu -s arch/i386/boot/bzImage -hda root-2.4.20.img root=/dev/hda |
da415d54 FB |
711 | Connected to host network interface: tun0 |
712 | Waiting gdb connection on port 1234 | |
713 | @end example | |
714 | ||
715 | Then launch gdb on the 'vmlinux' executable: | |
716 | @example | |
717 | > gdb vmlinux | |
718 | @end example | |
719 | ||
720 | In gdb, connect to QEMU: | |
721 | @example | |
722 | (gdb) target remote locahost:1234 | |
723 | @end example | |
724 | ||
725 | Then you can use gdb normally. For example, type 'c' to launch the kernel: | |
726 | @example | |
727 | (gdb) c | |
728 | @end example | |
729 | ||
0806e3f6 FB |
730 | Here are some useful tips in order to use gdb on system code: |
731 | ||
732 | @enumerate | |
733 | @item | |
734 | Use @code{info reg} to display all the CPU registers. | |
735 | @item | |
736 | Use @code{x/10i $eip} to display the code at the PC position. | |
737 | @item | |
738 | Use @code{set architecture i8086} to dump 16 bit code. Then use | |
739 | @code{x/10i $cs*16+*eip} to dump the code at the PC position. | |
740 | @end enumerate | |
741 | ||
386405f7 FB |
742 | @chapter QEMU Internals |
743 | ||
744 | @section QEMU compared to other emulators | |
745 | ||
1eb20527 FB |
746 | Like bochs [3], QEMU emulates an x86 CPU. But QEMU is much faster than |
747 | bochs as it uses dynamic compilation and because it uses the host MMU to | |
748 | simulate the x86 MMU. The downside is that currently the emulation is | |
749 | not as accurate as bochs (for example, you cannot currently run Windows | |
750 | inside QEMU). | |
386405f7 FB |
751 | |
752 | Like Valgrind [2], QEMU does user space emulation and dynamic | |
753 | translation. Valgrind is mainly a memory debugger while QEMU has no | |
1eb20527 FB |
754 | support for it (QEMU could be used to detect out of bound memory |
755 | accesses as Valgrind, but it has no support to track uninitialised data | |
d5a0b50c | 756 | as Valgrind does). The Valgrind dynamic translator generates better code |
1eb20527 | 757 | than QEMU (in particular it does register allocation) but it is closely |
d5a0b50c | 758 | tied to an x86 host and target and has no support for precise exceptions |
1eb20527 FB |
759 | and system emulation. |
760 | ||
761 | EM86 [4] is the closest project to user space QEMU (and QEMU still uses | |
762 | some of its code, in particular the ELF file loader). EM86 was limited | |
763 | to an alpha host and used a proprietary and slow interpreter (the | |
764 | interpreter part of the FX!32 Digital Win32 code translator [5]). | |
386405f7 | 765 | |
fd429f2f FB |
766 | TWIN [6] is a Windows API emulator like Wine. It is less accurate than |
767 | Wine but includes a protected mode x86 interpreter to launch x86 Windows | |
768 | executables. Such an approach as greater potential because most of the | |
769 | Windows API is executed natively but it is far more difficult to develop | |
770 | because all the data structures and function parameters exchanged | |
771 | between the API and the x86 code must be converted. | |
772 | ||
1eb20527 FB |
773 | User mode Linux [7] was the only solution before QEMU to launch a Linux |
774 | kernel as a process while not needing any host kernel patches. However, | |
775 | user mode Linux requires heavy kernel patches while QEMU accepts | |
776 | unpatched Linux kernels. It would be interesting to compare the | |
777 | performance of the two approaches. | |
778 | ||
779 | The new Plex86 [8] PC virtualizer is done in the same spirit as the QEMU | |
780 | system emulator. It requires a patched Linux kernel to work (you cannot | |
781 | launch the same kernel on your PC), but the patches are really small. As | |
782 | it is a PC virtualizer (no emulation is done except for some priveledged | |
783 | instructions), it has the potential of being faster than QEMU. The | |
d5a0b50c FB |
784 | downside is that a complicated (and potentially unsafe) host kernel |
785 | patch is needed. | |
1eb20527 | 786 | |
386405f7 FB |
787 | @section Portable dynamic translation |
788 | ||
789 | QEMU is a dynamic translator. When it first encounters a piece of code, | |
790 | it converts it to the host instruction set. Usually dynamic translators | |
322d0c66 | 791 | are very complicated and highly CPU dependent. QEMU uses some tricks |
386405f7 FB |
792 | which make it relatively easily portable and simple while achieving good |
793 | performances. | |
794 | ||
795 | The basic idea is to split every x86 instruction into fewer simpler | |
796 | instructions. Each simple instruction is implemented by a piece of C | |
797 | code (see @file{op-i386.c}). Then a compile time tool (@file{dyngen}) | |
798 | takes the corresponding object file (@file{op-i386.o}) to generate a | |
799 | dynamic code generator which concatenates the simple instructions to | |
800 | build a function (see @file{op-i386.h:dyngen_code()}). | |
801 | ||
802 | In essence, the process is similar to [1], but more work is done at | |
803 | compile time. | |
804 | ||
805 | A key idea to get optimal performances is that constant parameters can | |
806 | be passed to the simple operations. For that purpose, dummy ELF | |
807 | relocations are generated with gcc for each constant parameter. Then, | |
808 | the tool (@file{dyngen}) can locate the relocations and generate the | |
809 | appriopriate C code to resolve them when building the dynamic code. | |
810 | ||
811 | That way, QEMU is no more difficult to port than a dynamic linker. | |
812 | ||
813 | To go even faster, GCC static register variables are used to keep the | |
814 | state of the virtual CPU. | |
815 | ||
816 | @section Register allocation | |
817 | ||
818 | Since QEMU uses fixed simple instructions, no efficient register | |
819 | allocation can be done. However, because RISC CPUs have a lot of | |
820 | register, most of the virtual CPU state can be put in registers without | |
821 | doing complicated register allocation. | |
822 | ||
823 | @section Condition code optimisations | |
824 | ||
825 | Good CPU condition codes emulation (@code{EFLAGS} register on x86) is a | |
826 | critical point to get good performances. QEMU uses lazy condition code | |
827 | evaluation: instead of computing the condition codes after each x86 | |
fd429f2f | 828 | instruction, it just stores one operand (called @code{CC_SRC}), the |
386405f7 FB |
829 | result (called @code{CC_DST}) and the type of operation (called |
830 | @code{CC_OP}). | |
831 | ||
832 | @code{CC_OP} is almost never explicitely set in the generated code | |
833 | because it is known at translation time. | |
834 | ||
835 | In order to increase performances, a backward pass is performed on the | |
836 | generated simple instructions (see | |
837 | @code{translate-i386.c:optimize_flags()}). When it can be proved that | |
838 | the condition codes are not needed by the next instructions, no | |
839 | condition codes are computed at all. | |
840 | ||
fd429f2f | 841 | @section CPU state optimisations |
386405f7 FB |
842 | |
843 | The x86 CPU has many internal states which change the way it evaluates | |
844 | instructions. In order to achieve a good speed, the translation phase | |
845 | considers that some state information of the virtual x86 CPU cannot | |
846 | change in it. For example, if the SS, DS and ES segments have a zero | |
847 | base, then the translator does not even generate an addition for the | |
848 | segment base. | |
849 | ||
850 | [The FPU stack pointer register is not handled that way yet]. | |
851 | ||
852 | @section Translation cache | |
853 | ||
854 | A 2MByte cache holds the most recently used translations. For | |
855 | simplicity, it is completely flushed when it is full. A translation unit | |
856 | contains just a single basic block (a block of x86 instructions | |
857 | terminated by a jump or by a virtual CPU state change which the | |
858 | translator cannot deduce statically). | |
859 | ||
df0f11a0 FB |
860 | @section Direct block chaining |
861 | ||
862 | After each translated basic block is executed, QEMU uses the simulated | |
863 | Program Counter (PC) and other cpu state informations (such as the CS | |
864 | segment base value) to find the next basic block. | |
865 | ||
866 | In order to accelerate the most common cases where the new simulated PC | |
867 | is known, QEMU can patch a basic block so that it jumps directly to the | |
868 | next one. | |
869 | ||
870 | The most portable code uses an indirect jump. An indirect jump makes it | |
871 | easier to make the jump target modification atomic. On some | |
872 | architectures (such as PowerPC), the @code{JUMP} opcode is directly | |
873 | patched so that the block chaining has no overhead. | |
874 | ||
875 | @section Self-modifying code and translated code invalidation | |
876 | ||
877 | Self-modifying code is a special challenge in x86 emulation because no | |
878 | instruction cache invalidation is signaled by the application when code | |
879 | is modified. | |
880 | ||
881 | When translated code is generated for a basic block, the corresponding | |
882 | host page is write protected if it is not already read-only (with the | |
883 | system call @code{mprotect()}). Then, if a write access is done to the | |
884 | page, Linux raises a SEGV signal. QEMU then invalidates all the | |
885 | translated code in the page and enables write accesses to the page. | |
886 | ||
887 | Correct translated code invalidation is done efficiently by maintaining | |
888 | a linked list of every translated block contained in a given page. Other | |
889 | linked lists are also maintained to undo direct block chaining. | |
890 | ||
4690764b | 891 | Although the overhead of doing @code{mprotect()} calls is important, |
df0f11a0 FB |
892 | most MSDOS programs can be emulated at reasonnable speed with QEMU and |
893 | DOSEMU. | |
894 | ||
895 | Note that QEMU also invalidates pages of translated code when it detects | |
896 | that memory mappings are modified with @code{mmap()} or @code{munmap()}. | |
386405f7 FB |
897 | |
898 | @section Exception support | |
899 | ||
900 | longjmp() is used when an exception such as division by zero is | |
df0f11a0 | 901 | encountered. |
386405f7 | 902 | |
df0f11a0 FB |
903 | The host SIGSEGV and SIGBUS signal handlers are used to get invalid |
904 | memory accesses. The exact CPU state can be retrieved because all the | |
905 | x86 registers are stored in fixed host registers. The simulated program | |
906 | counter is found by retranslating the corresponding basic block and by | |
907 | looking where the host program counter was at the exception point. | |
908 | ||
909 | The virtual CPU cannot retrieve the exact @code{EFLAGS} register because | |
910 | in some cases it is not computed because of condition code | |
911 | optimisations. It is not a big concern because the emulated code can | |
912 | still be restarted in any cases. | |
386405f7 FB |
913 | |
914 | @section Linux system call translation | |
915 | ||
916 | QEMU includes a generic system call translator for Linux. It means that | |
917 | the parameters of the system calls can be converted to fix the | |
918 | endianness and 32/64 bit issues. The IOCTLs are converted with a generic | |
919 | type description system (see @file{ioctls.h} and @file{thunk.c}). | |
920 | ||
df0f11a0 FB |
921 | QEMU supports host CPUs which have pages bigger than 4KB. It records all |
922 | the mappings the process does and try to emulated the @code{mmap()} | |
923 | system calls in cases where the host @code{mmap()} call would fail | |
924 | because of bad page alignment. | |
925 | ||
386405f7 FB |
926 | @section Linux signals |
927 | ||
928 | Normal and real-time signals are queued along with their information | |
929 | (@code{siginfo_t}) as it is done in the Linux kernel. Then an interrupt | |
930 | request is done to the virtual CPU. When it is interrupted, one queued | |
931 | signal is handled by generating a stack frame in the virtual CPU as the | |
932 | Linux kernel does. The @code{sigreturn()} system call is emulated to return | |
933 | from the virtual signal handler. | |
934 | ||
935 | Some signals (such as SIGALRM) directly come from the host. Other | |
936 | signals are synthetized from the virtual CPU exceptions such as SIGFPE | |
937 | when a division by zero is done (see @code{main.c:cpu_loop()}). | |
938 | ||
939 | The blocked signal mask is still handled by the host Linux kernel so | |
940 | that most signal system calls can be redirected directly to the host | |
941 | Linux kernel. Only the @code{sigaction()} and @code{sigreturn()} system | |
942 | calls need to be fully emulated (see @file{signal.c}). | |
943 | ||
944 | @section clone() system call and threads | |
945 | ||
946 | The Linux clone() system call is usually used to create a thread. QEMU | |
947 | uses the host clone() system call so that real host threads are created | |
948 | for each emulated thread. One virtual CPU instance is created for each | |
949 | thread. | |
950 | ||
951 | The virtual x86 CPU atomic operations are emulated with a global lock so | |
952 | that their semantic is preserved. | |
953 | ||
df0f11a0 FB |
954 | Note that currently there are still some locking issues in QEMU. In |
955 | particular, the translated cache flush is not protected yet against | |
956 | reentrancy. | |
957 | ||
1eb87257 FB |
958 | @section Self-virtualization |
959 | ||
4690764b | 960 | QEMU was conceived so that ultimately it can emulate itself. Although |
1eb87257 FB |
961 | it is not very useful, it is an important test to show the power of the |
962 | emulator. | |
963 | ||
964 | Achieving self-virtualization is not easy because there may be address | |
6cd9f35b FB |
965 | space conflicts. QEMU solves this problem by being an executable ELF |
966 | shared object as the ld-linux.so ELF interpreter. That way, it can be | |
967 | relocated at load time. | |
1eb87257 | 968 | |
1eb20527 FB |
969 | @section MMU emulation |
970 | ||
971 | For system emulation, QEMU uses the mmap() system call to emulate the | |
972 | target CPU MMU. It works as long the emulated OS does not use an area | |
973 | reserved by the host OS (such as the area above 0xc0000000 on x86 | |
974 | Linux). | |
975 | ||
976 | It is planned to add a slower but more precise MMU emulation | |
977 | with a software MMU. | |
978 | ||
386405f7 FB |
979 | @section Bibliography |
980 | ||
981 | @table @asis | |
982 | ||
983 | @item [1] | |
984 | @url{http://citeseer.nj.nec.com/piumarta98optimizing.html}, Optimizing | |
985 | direct threaded code by selective inlining (1998) by Ian Piumarta, Fabio | |
986 | Riccardi. | |
987 | ||
988 | @item [2] | |
989 | @url{http://developer.kde.org/~sewardj/}, Valgrind, an open-source | |
990 | memory debugger for x86-GNU/Linux, by Julian Seward. | |
991 | ||
992 | @item [3] | |
993 | @url{http://bochs.sourceforge.net/}, the Bochs IA-32 Emulator Project, | |
994 | by Kevin Lawton et al. | |
995 | ||
996 | @item [4] | |
997 | @url{http://www.cs.rose-hulman.edu/~donaldlf/em86/index.html}, the EM86 | |
998 | x86 emulator on Alpha-Linux. | |
999 | ||
1000 | @item [5] | |
1001 | @url{http://www.usenix.org/publications/library/proceedings/usenix-nt97/full_papers/chernoff/chernoff.pdf}, | |
1002 | DIGITAL FX!32: Running 32-Bit x86 Applications on Alpha NT, by Anton | |
1003 | Chernoff and Ray Hookway. | |
1004 | ||
fd429f2f FB |
1005 | @item [6] |
1006 | @url{http://www.willows.com/}, Windows API library emulation from | |
1007 | Willows Software. | |
1008 | ||
1eb20527 FB |
1009 | @item [7] |
1010 | @url{http://user-mode-linux.sourceforge.net/}, | |
1011 | The User-mode Linux Kernel. | |
1012 | ||
1013 | @item [8] | |
1014 | @url{http://www.plex86.org/}, | |
1015 | The new Plex86 project. | |
1016 | ||
386405f7 FB |
1017 | @end table |
1018 | ||
1019 | @chapter Regression Tests | |
1020 | ||
322d0c66 | 1021 | In the directory @file{tests/}, various interesting testing programs |
386405f7 FB |
1022 | are available. There are used for regression testing. |
1023 | ||
386405f7 FB |
1024 | @section @file{test-i386} |
1025 | ||
1026 | This program executes most of the 16 bit and 32 bit x86 instructions and | |
1027 | generates a text output. It can be compared with the output obtained with | |
1028 | a real CPU or another emulator. The target @code{make test} runs this | |
1029 | program and a @code{diff} on the generated output. | |
1030 | ||
1031 | The Linux system call @code{modify_ldt()} is used to create x86 selectors | |
1032 | to test some 16 bit addressing and 32 bit with segmentation cases. | |
1033 | ||
df0f11a0 | 1034 | The Linux system call @code{vm86()} is used to test vm86 emulation. |
386405f7 | 1035 | |
df0f11a0 FB |
1036 | Various exceptions are raised to test most of the x86 user space |
1037 | exception reporting. | |
386405f7 | 1038 | |
285dc330 FB |
1039 | @section @file{linux-test} |
1040 | ||
1041 | This program tests various Linux system calls. It is used to verify | |
1042 | that the system call parameters are correctly converted between target | |
1043 | and host CPUs. | |
1044 | ||
1045 | @section @file{hello-i386} | |
1046 | ||
1047 | Very simple statically linked x86 program, just to test QEMU during a | |
1048 | port to a new host CPU. | |
1049 | ||
1050 | @section @file{hello-arm} | |
1051 | ||
1052 | Very simple statically linked ARM program, just to test QEMU during a | |
1053 | port to a new host CPU. | |
1054 | ||
386405f7 FB |
1055 | @section @file{sha1} |
1056 | ||
1057 | It is a simple benchmark. Care must be taken to interpret the results | |
1058 | because it mostly tests the ability of the virtual CPU to optimize the | |
1059 | @code{rol} x86 instruction and the condition code computations. | |
1060 |