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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 | |
75 | @item Using mmap() system calls to simulate the 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 | ||
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113 | @item Full system emulation only works if no data are mapped above the virtual address |
114 | 0xc0000000 (yet). | |
115 | ||
116 | @item Some priviledged instructions or behaviors are missing. Only the ones | |
117 | needed for proper Linux kernel operation are emulated. | |
118 | ||
119 | @item No memory separation between the kernel and the user processes is done. | |
120 | It will be implemented very soon. | |
121 | ||
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122 | @end itemize |
123 | ||
322d0c66 FB |
124 | @section ARM emulation |
125 | ||
126 | @itemize | |
127 | ||
128 | @item ARM emulation can currently launch small programs while using the | |
129 | generic dynamic code generation architecture of QEMU. | |
130 | ||
131 | @item No FPU support (yet). | |
132 | ||
133 | @item No automatic regression testing (yet). | |
134 | ||
135 | @end itemize | |
136 | ||
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137 | @section SPARC emulation |
138 | ||
139 | The SPARC emulation is currently in development. | |
140 | ||
d5a0b50c | 141 | @chapter QEMU User space emulator invocation |
386405f7 | 142 | |
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143 | @section Quick Start |
144 | ||
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145 | If you need to compile QEMU, please read the @file{README} which gives |
146 | the related information. | |
147 | ||
386405f7 | 148 | In order to launch a Linux process, QEMU needs the process executable |
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149 | itself and all the target (x86) dynamic libraries used by it. |
150 | ||
151 | @itemize | |
386405f7 | 152 | |
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153 | @item On x86, you can just try to launch any process by using the native |
154 | libraries: | |
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155 | |
156 | @example | |
0806e3f6 | 157 | qemu-i386 -L / /bin/ls |
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158 | @end example |
159 | ||
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160 | @code{-L /} tells that the x86 dynamic linker must be searched with a |
161 | @file{/} prefix. | |
386405f7 | 162 | |
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163 | @item Since QEMU is also a linux process, you can launch qemu with qemu: |
164 | ||
165 | @example | |
0806e3f6 | 166 | qemu-i386 -L / qemu-i386 -L / /bin/ls |
1eb87257 | 167 | @end example |
386405f7 | 168 | |
d691f669 | 169 | @item On non x86 CPUs, you need first to download at least an x86 glibc |
1eb87257 | 170 | (@file{qemu-XXX-i386-glibc21.tar.gz} on the QEMU web page). Ensure that |
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171 | @code{LD_LIBRARY_PATH} is not set: |
172 | ||
173 | @example | |
174 | unset LD_LIBRARY_PATH | |
175 | @end example | |
176 | ||
177 | Then you can launch the precompiled @file{ls} x86 executable: | |
178 | ||
d691f669 | 179 | @example |
0806e3f6 | 180 | qemu-i386 /usr/local/qemu-i386/bin/ls-i386 |
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181 | @end example |
182 | You can look at @file{/usr/local/qemu-i386/bin/qemu-conf.sh} so that | |
183 | QEMU is automatically launched by the Linux kernel when you try to | |
184 | launch x86 executables. It requires the @code{binfmt_misc} module in the | |
185 | Linux kernel. | |
186 | ||
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187 | @item The x86 version of QEMU is also included. You can try weird things such as: |
188 | @example | |
0806e3f6 | 189 | qemu-i386 /usr/local/qemu-i386/bin/qemu-i386 /usr/local/qemu-i386/bin/ls-i386 |
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190 | @end example |
191 | ||
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192 | @end itemize |
193 | ||
df0f11a0 | 194 | @section Wine launch |
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195 | |
196 | @itemize | |
197 | ||
198 | @item Ensure that you have a working QEMU with the x86 glibc | |
199 | distribution (see previous section). In order to verify it, you must be | |
200 | able to do: | |
201 | ||
202 | @example | |
0806e3f6 | 203 | qemu-i386 /usr/local/qemu-i386/bin/ls-i386 |
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204 | @end example |
205 | ||
fd429f2f | 206 | @item Download the binary x86 Wine install |
1eb87257 | 207 | (@file{qemu-XXX-i386-wine.tar.gz} on the QEMU web page). |
168485b7 | 208 | |
fd429f2f | 209 | @item Configure Wine on your account. Look at the provided script |
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210 | @file{/usr/local/qemu-i386/bin/wine-conf.sh}. Your previous |
211 | @code{$@{HOME@}/.wine} directory is saved to @code{$@{HOME@}/.wine.org}. | |
212 | ||
213 | @item Then you can try the example @file{putty.exe}: | |
214 | ||
215 | @example | |
0806e3f6 | 216 | qemu-i386 /usr/local/qemu-i386/wine/bin/wine /usr/local/qemu-i386/wine/c/Program\ Files/putty.exe |
386405f7 | 217 | @end example |
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218 | |
219 | @end itemize | |
220 | ||
221 | @section Command line options | |
222 | ||
223 | @example | |
0806e3f6 | 224 | usage: qemu-i386 [-h] [-d] [-L path] [-s size] program [arguments...] |
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225 | @end example |
226 | ||
df0f11a0 | 227 | @table @option |
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228 | @item -h |
229 | Print the help | |
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230 | @item -L path |
231 | Set the x86 elf interpreter prefix (default=/usr/local/qemu-i386) | |
232 | @item -s size | |
233 | Set the x86 stack size in bytes (default=524288) | |
234 | @end table | |
386405f7 | 235 | |
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236 | Debug options: |
237 | ||
238 | @table @option | |
239 | @item -d | |
240 | Activate log (logfile=/tmp/qemu.log) | |
241 | @item -p pagesize | |
242 | Act as if the host page size was 'pagesize' bytes | |
243 | @end table | |
244 | ||
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245 | @chapter QEMU System emulator invocation |
246 | ||
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247 | @section Introduction |
248 | ||
249 | @c man begin DESCRIPTION | |
250 | ||
251 | The QEMU System emulator simulates a complete PC. It can either boot | |
252 | directly a Linux kernel (without any BIOS or boot loader) or boot like a | |
253 | real PC with the included BIOS. | |
254 | ||
255 | In order to meet specific user needs, two versions of QEMU are | |
256 | available: | |
257 | ||
258 | @enumerate | |
259 | ||
260 | @item | |
261 | @code{qemu} uses the host Memory Management Unit (MMU) to simulate | |
262 | the x86 MMU. It is @emph{fast} but has limitations because the whole 4 GB | |
263 | address space cannot be used and some memory mapped peripherials | |
264 | cannot be emulated accurately yet. Therefore, a specific Linux kernel | |
265 | must be used (@xref{linux_compile}). | |
266 | ||
267 | @item | |
268 | @code{qemu-softmmu} uses a software MMU. It is about @emph{two times | |
269 | slower} but gives a more accurate emulation. (XXX: Linux cannot be ran | |
270 | unpatched yet). | |
271 | ||
272 | @end enumerate | |
273 | ||
274 | QEMU emulates the following PC peripherials: | |
275 | ||
276 | @itemize @minus | |
277 | @item | |
278 | VGA (hardware level, including all non standard modes) | |
279 | @item | |
280 | PS/2 mouse and keyboard | |
281 | @item | |
282 | IDE disk interface (port=0x1f0, irq=14) | |
283 | @item | |
284 | NE2000 network adapter (port=0x300, irq=9) | |
285 | @item | |
286 | Serial port (port=0x3f8, irq=4) | |
287 | @item | |
288 | PIC (interrupt controler) | |
289 | @item | |
290 | PIT (timers) | |
291 | @item | |
292 | CMOS memory | |
293 | @end itemize | |
294 | ||
295 | @c man end | |
296 | ||
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297 | @section Quick Start |
298 | ||
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299 | Download the linux image (@file{linux.img}) and type: |
300 | ||
301 | @example | |
302 | qemu-softmmu linux.img | |
303 | @end example | |
304 | ||
305 | Linux should boot and give you a prompt. | |
306 | ||
307 | @section Direct Linux Boot and Network emulation | |
308 | ||
309 | This section explains how to launch a Linux kernel inside QEMU without | |
310 | having to make a full bootable image. It is very useful for fast Linux | |
311 | kernel testing. The QEMU network configuration is also explained. | |
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312 | |
313 | @enumerate | |
314 | @item | |
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315 | Download the archive @file{linux-test-xxx.tar.gz} containing a Linux |
316 | kernel and a disk image. | |
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317 | |
318 | @item Optional: If you want network support (for example to launch X11 examples), you | |
0806e3f6 | 319 | must copy the script @file{qemu-ifup} in @file{/etc} and configure |
1eb20527 | 320 | properly @code{sudo} so that the command @code{ifconfig} contained in |
0806e3f6 | 321 | @file{qemu-ifup} can be executed as root. You must verify that your host |
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322 | kernel supports the TUN/TAP network interfaces: the device |
323 | @file{/dev/net/tun} must be present. | |
324 | ||
325 | When network is enabled, there is a virtual network connection between | |
326 | the host kernel and the emulated kernel. The emulated kernel is seen | |
327 | from the host kernel at IP address 172.20.0.2 and the host kernel is | |
328 | seen from the emulated kernel at IP address 172.20.0.1. | |
329 | ||
0806e3f6 | 330 | @item Launch @code{qemu.sh}. You should have the following output: |
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331 | |
332 | @example | |
0806e3f6 | 333 | > ./qemu.sh |
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334 | connected to host network interface: tun0 |
335 | Uncompressing Linux... Ok, booting the kernel. | |
4690764b | 336 | 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 | 337 | BIOS-provided physical RAM map: |
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338 | BIOS-e801: 0000000000000000 - 000000000009f000 (usable) |
339 | BIOS-e801: 0000000000100000 - 0000000002000000 (usable) | |
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340 | 32MB LOWMEM available. |
341 | On node 0 totalpages: 8192 | |
342 | zone(0): 4096 pages. | |
343 | zone(1): 4096 pages. | |
344 | zone(2): 0 pages. | |
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345 | Kernel command line: root=/dev/hda ide1=noprobe ide2=noprobe ide3=noprobe ide4=noprobe ide5=noprobe |
346 | ide_setup: ide1=noprobe | |
347 | ide_setup: ide2=noprobe | |
348 | ide_setup: ide3=noprobe | |
349 | ide_setup: ide4=noprobe | |
350 | ide_setup: ide5=noprobe | |
1eb20527 | 351 | Initializing CPU#0 |
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352 | Detected 501.285 MHz processor. |
353 | Calibrating delay loop... 989.59 BogoMIPS | |
354 | Memory: 29268k/32768k available (907k kernel code, 3112k reserved, 212k data, 52k init, 0k highmem) | |
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355 | Dentry cache hash table entries: 4096 (order: 3, 32768 bytes) |
356 | Inode cache hash table entries: 2048 (order: 2, 16384 bytes) | |
357 | Mount-cache hash table entries: 512 (order: 0, 4096 bytes) | |
358 | Buffer-cache hash table entries: 1024 (order: 0, 4096 bytes) | |
359 | Page-cache hash table entries: 8192 (order: 3, 32768 bytes) | |
360 | CPU: Intel Pentium Pro stepping 03 | |
361 | Checking 'hlt' instruction... OK. | |
362 | POSIX conformance testing by UNIFIX | |
363 | Linux NET4.0 for Linux 2.4 | |
364 | Based upon Swansea University Computer Society NET3.039 | |
365 | Initializing RT netlink socket | |
366 | apm: BIOS not found. | |
367 | Starting kswapd | |
4690764b | 368 | Journalled Block Device driver loaded |
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369 | pty: 256 Unix98 ptys configured |
370 | Serial driver version 5.05c (2001-07-08) with no serial options enabled | |
371 | ttyS00 at 0x03f8 (irq = 4) is a 16450 | |
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372 | Uniform Multi-Platform E-IDE driver Revision: 6.31 |
373 | ide: Assuming 50MHz system bus speed for PIO modes; override with idebus=xx | |
374 | hda: QEMU HARDDISK, ATA DISK drive | |
375 | ide0 at 0x1f0-0x1f7,0x3f6 on irq 14 | |
376 | hda: 12288 sectors (6 MB) w/256KiB Cache, CHS=12/16/63 | |
377 | Partition check: | |
378 | hda: unknown partition table | |
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379 | ne.c:v1.10 9/23/94 Donald Becker (becker@scyld.com) |
380 | Last modified Nov 1, 2000 by Paul Gortmaker | |
381 | NE*000 ethercard probe at 0x300: 52 54 00 12 34 56 | |
382 | eth0: NE2000 found at 0x300, using IRQ 9. | |
4690764b | 383 | RAMDISK driver initialized: 16 RAM disks of 4096K size 1024 blocksize |
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384 | NET4: Linux TCP/IP 1.0 for NET4.0 |
385 | IP Protocols: ICMP, UDP, TCP, IGMP | |
386 | IP: routing cache hash table of 512 buckets, 4Kbytes | |
4690764b | 387 | TCP: Hash tables configured (established 2048 bind 4096) |
1eb20527 | 388 | NET4: Unix domain sockets 1.0/SMP for Linux NET4.0. |
4690764b | 389 | EXT2-fs warning: mounting unchecked fs, running e2fsck is recommended |
1eb20527 | 390 | VFS: Mounted root (ext2 filesystem). |
4690764b | 391 | Freeing unused kernel memory: 52k freed |
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392 | sh: can't access tty; job control turned off |
393 | # | |
394 | @end example | |
395 | ||
396 | @item | |
397 | Then you can play with the kernel inside the virtual serial console. You | |
398 | can launch @code{ls} for example. Type @key{Ctrl-a h} to have an help | |
399 | about the keys you can type inside the virtual serial console. In | |
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400 | particular, use @key{Ctrl-a x} to exit QEMU and use @key{Ctrl-a b} as |
401 | the Magic SysRq key. | |
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402 | |
403 | @item | |
404 | If the network is enabled, launch the script @file{/etc/linuxrc} in the | |
405 | emulator (don't forget the leading dot): | |
406 | @example | |
407 | . /etc/linuxrc | |
408 | @end example | |
409 | ||
410 | Then enable X11 connections on your PC from the emulated Linux: | |
411 | @example | |
412 | xhost +172.20.0.2 | |
413 | @end example | |
414 | ||
415 | You can now launch @file{xterm} or @file{xlogo} and verify that you have | |
416 | a real Virtual Linux system ! | |
417 | ||
418 | @end enumerate | |
419 | ||
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420 | NOTES: |
421 | @enumerate | |
422 | @item | |
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423 | A 2.5.74 kernel is also included in the archive. Just |
424 | replace the bzImage in qemu.sh to try it. | |
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425 | |
426 | @item | |
0806e3f6 | 427 | vl creates a temporary file in @var{$QEMU_TMPDIR} (@file{/tmp} is the |
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428 | default) containing all the simulated PC memory. If possible, try to use |
429 | a temporary directory using the tmpfs filesystem to avoid too many | |
430 | unnecessary disk accesses. | |
431 | ||
432 | @item | |
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433 | In order to exit cleanly for vl, you can do a @emph{shutdown} inside |
434 | vl. vl will automatically exit when the Linux shutdown is done. | |
435 | ||
436 | @item | |
437 | You can boot slightly faster by disabling the probe of non present IDE | |
438 | interfaces. To do so, add the following options on the kernel command | |
439 | line: | |
440 | @example | |
441 | ide1=noprobe ide2=noprobe ide3=noprobe ide4=noprobe ide5=noprobe | |
442 | @end example | |
443 | ||
444 | @item | |
445 | The example disk image is a modified version of the one made by Kevin | |
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446 | Lawton for the plex86 Project (@url{www.plex86.org}). |
447 | ||
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448 | @end enumerate |
449 | ||
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450 | @section Invocation |
451 | ||
452 | @example | |
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453 | @c man begin SYNOPSIS |
454 | usage: qemu [options] [disk_image] | |
455 | @c man end | |
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456 | @end example |
457 | ||
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458 | @c man begin OPTIONS |
459 | @var{disk_image} is a raw hard image image for IDE hard disk 0. | |
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460 | |
461 | General options: | |
462 | @table @option | |
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463 | @item -hda file |
464 | @item -hdb file | |
0806e3f6 | 465 | Use @var{file} as hard disk 0 or 1 image (@xref{disk_images}). |
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466 | |
467 | @item -snapshot | |
468 | ||
469 | Write to temporary files instead of disk image files. In this case, | |
470 | the raw disk image you use is not written back. You can however force | |
471 | the write back by pressing @key{C-a s} (@xref{disk_images}). | |
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472 | |
473 | @item -m megs | |
474 | Set virtual RAM size to @var{megs} megabytes. | |
475 | ||
476 | @item -n script | |
477 | Set network init script [default=/etc/vl-ifup]. This script is | |
478 | launched to configure the host network interface (usually tun0) | |
479 | corresponding to the virtual NE2000 card. | |
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480 | |
481 | @item -initrd file | |
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482 | Use @var{file} as initial ram disk. |
483 | ||
484 | @item -tun-fd fd | |
485 | Assumes @var{fd} talks to tap/tun and use it. Read | |
486 | @url{http://bellard.org/qemu/tetrinet.html} to have an example of its | |
487 | use. | |
488 | ||
489 | @item -nographic | |
490 | ||
491 | Normally, QEMU uses SDL to display the VGA output. With this option, | |
492 | you can totally disable graphical output so that QEMU is a simple | |
493 | command line application. The emulated serial port is redirected on | |
494 | the console. Therefore, you can still use QEMU to debug a Linux kernel | |
495 | with a serial console. | |
496 | ||
497 | @end table | |
498 | ||
499 | Linux boot specific (does not require a full PC boot with a BIOS): | |
500 | @table @option | |
501 | ||
502 | @item -kernel bzImage | |
503 | Use @var{bzImage} as kernel image. | |
504 | ||
505 | @item -append cmdline | |
506 | Use @var{cmdline} as kernel command line | |
507 | ||
508 | @item -initrd file | |
509 | Use @var{file} as initial ram disk. | |
510 | ||
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511 | @end table |
512 | ||
513 | Debug options: | |
514 | @table @option | |
515 | @item -s | |
0806e3f6 | 516 | Wait gdb connection to port 1234 (@xref{gdb_usage}). |
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517 | @item -p port |
518 | Change gdb connection port. | |
519 | @item -d | |
520 | Output log in /tmp/vl.log | |
521 | @end table | |
522 | ||
523 | During emulation, use @key{C-a h} to get terminal commands: | |
524 | ||
525 | @table @key | |
526 | @item C-a h | |
527 | Print this help | |
528 | @item C-a x | |
529 | Exit emulatior | |
1f47a922 FB |
530 | @item C-a s |
531 | Save disk data back to file (if -snapshot) | |
532 | @item C-a b | |
ec410fc9 | 533 | Send break (magic sysrq) |
1f47a922 | 534 | @item C-a C-a |
ec410fc9 FB |
535 | Send C-a |
536 | @end table | |
0806e3f6 FB |
537 | @c man end |
538 | ||
539 | @ignore | |
540 | ||
541 | @setfilename qemu | |
542 | @settitle QEMU System Emulator | |
543 | ||
544 | @c man begin SEEALSO | |
545 | The HTML documentation of QEMU for more precise information and Linux | |
546 | user mode emulator invocation. | |
547 | @c man end | |
548 | ||
549 | @c man begin AUTHOR | |
550 | Fabrice Bellard | |
551 | @c man end | |
552 | ||
553 | @end ignore | |
ec410fc9 | 554 | |
0806e3f6 | 555 | @end ignore |
1f47a922 FB |
556 | @node disk_images |
557 | @section Disk Images | |
558 | ||
559 | @subsection Raw disk images | |
560 | ||
561 | The disk images can simply be raw images of the hard disk. You can | |
562 | create them with the command: | |
563 | @example | |
564 | dd if=/dev/zero of=myimage bs=1024 count=mysize | |
565 | @end example | |
566 | where @var{myimage} is the image filename and @var{mysize} is its size | |
567 | in kilobytes. | |
568 | ||
569 | @subsection Snapshot mode | |
570 | ||
571 | If you use the option @option{-snapshot}, all disk images are | |
572 | considered as read only. When sectors in written, they are written in | |
573 | a temporary file created in @file{/tmp}. You can however force the | |
574 | write back to the raw disk images by pressing @key{C-a s}. | |
575 | ||
576 | NOTE: The snapshot mode only works with raw disk images. | |
577 | ||
578 | @subsection Copy On Write disk images | |
579 | ||
580 | QEMU also supports user mode Linux | |
581 | (@url{http://user-mode-linux.sourceforge.net/}) Copy On Write (COW) | |
582 | disk images. The COW disk images are much smaller than normal images | |
583 | as they store only modified sectors. They also permit the use of the | |
584 | same disk image template for many users. | |
585 | ||
586 | To create a COW disk images, use the command: | |
587 | ||
588 | @example | |
0806e3f6 | 589 | qemu-mkcow -f myrawimage.bin mycowimage.cow |
1f47a922 FB |
590 | @end example |
591 | ||
592 | @file{myrawimage.bin} is a raw image you want to use as original disk | |
593 | image. It will never be written to. | |
594 | ||
595 | @file{mycowimage.cow} is the COW disk image which is created by | |
0806e3f6 | 596 | @code{qemu-mkcow}. You can use it directly with the @option{-hdx} |
1f47a922 FB |
597 | options. You must not modify the original raw disk image if you use |
598 | COW images, as COW images only store the modified sectors from the raw | |
599 | disk image. QEMU stores the original raw disk image name and its | |
600 | modified time in the COW disk image so that chances of mistakes are | |
601 | reduced. | |
602 | ||
9d0fe224 FB |
603 | If the raw disk image is not read-only, by pressing @key{C-a s} you |
604 | can flush the COW disk image back into the raw disk image, as in | |
605 | snapshot mode. | |
1f47a922 FB |
606 | |
607 | COW disk images can also be created without a corresponding raw disk | |
608 | image. It is useful to have a big initial virtual disk image without | |
609 | using much disk space. Use: | |
610 | ||
611 | @example | |
0806e3f6 | 612 | qemu-mkcow mycowimage.cow 1024 |
1f47a922 FB |
613 | @end example |
614 | ||
615 | to create a 1 gigabyte empty COW disk image. | |
616 | ||
617 | NOTES: | |
618 | @enumerate | |
619 | @item | |
620 | COW disk images must be created on file systems supporting | |
621 | @emph{holes} such as ext2 or ext3. | |
622 | @item | |
623 | Since holes are used, the displayed size of the COW disk image is not | |
624 | the real one. To know it, use the @code{ls -ls} command. | |
625 | @end enumerate | |
626 | ||
0806e3f6 | 627 | @node linux_compile |
4690764b FB |
628 | @section Linux Kernel Compilation |
629 | ||
630 | You should be able to use any kernel with QEMU provided you make the | |
631 | following changes (only 2.4.x and 2.5.x were tested): | |
1eb20527 | 632 | |
4690764b FB |
633 | @enumerate |
634 | @item | |
635 | The kernel must be mapped at 0x90000000 (the default is | |
636 | 0xc0000000). You must modify only two lines in the kernel source: | |
1eb20527 | 637 | |
4690764b | 638 | In @file{include/asm/page.h}, replace |
1eb20527 FB |
639 | @example |
640 | #define __PAGE_OFFSET (0xc0000000) | |
641 | @end example | |
642 | by | |
643 | @example | |
644 | #define __PAGE_OFFSET (0x90000000) | |
645 | @end example | |
646 | ||
4690764b | 647 | And in @file{arch/i386/vmlinux.lds}, replace |
1eb20527 FB |
648 | @example |
649 | . = 0xc0000000 + 0x100000; | |
650 | @end example | |
651 | by | |
652 | @example | |
653 | . = 0x90000000 + 0x100000; | |
654 | @end example | |
655 | ||
4690764b FB |
656 | @item |
657 | If you want to enable SMP (Symmetric Multi-Processing) support, you | |
658 | must make the following change in @file{include/asm/fixmap.h}. Replace | |
1eb20527 | 659 | @example |
4690764b | 660 | #define FIXADDR_TOP (0xffffX000UL) |
1eb20527 | 661 | @end example |
4690764b FB |
662 | by |
663 | @example | |
664 | #define FIXADDR_TOP (0xa7ffX000UL) | |
665 | @end example | |
666 | (X is 'e' or 'f' depending on the kernel version). Although you can | |
667 | use an SMP kernel with QEMU, it only supports one CPU. | |
1eb20527 | 668 | |
4690764b | 669 | @item |
d5a0b50c FB |
670 | If you are not using a 2.5 kernel as host kernel but if you use a target |
671 | 2.5 kernel, you must also ensure that the 'HZ' define is set to 100 | |
672 | (1000 is the default) as QEMU cannot currently emulate timers at | |
673 | frequencies greater than 100 Hz on host Linux systems < 2.5. In | |
4690764b | 674 | @file{include/asm/param.h}, replace: |
d5a0b50c FB |
675 | |
676 | @example | |
677 | # define HZ 1000 /* Internal kernel timer frequency */ | |
678 | @end example | |
679 | by | |
680 | @example | |
681 | # define HZ 100 /* Internal kernel timer frequency */ | |
682 | @end example | |
683 | ||
4690764b FB |
684 | @end enumerate |
685 | ||
686 | The file config-2.x.x gives the configuration of the example kernels. | |
687 | ||
688 | Just type | |
689 | @example | |
690 | make bzImage | |
691 | @end example | |
692 | ||
693 | As you would do to make a real kernel. Then you can use with QEMU | |
694 | exactly the same kernel as you would boot on your PC (in | |
695 | @file{arch/i386/boot/bzImage}). | |
da415d54 | 696 | |
0806e3f6 | 697 | @node gdb_usage |
da415d54 FB |
698 | @section GDB usage |
699 | ||
700 | QEMU has a primitive support to work with gdb, so that you can do | |
0806e3f6 | 701 | 'Ctrl-C' while the virtual machine is running and inspect its state. |
da415d54 FB |
702 | |
703 | In order to use gdb, launch vl with the '-s' option. It will wait for a | |
704 | gdb connection: | |
705 | @example | |
d6b49367 | 706 | > vl -s arch/i386/boot/bzImage -hda root-2.4.20.img root=/dev/hda |
da415d54 FB |
707 | Connected to host network interface: tun0 |
708 | Waiting gdb connection on port 1234 | |
709 | @end example | |
710 | ||
711 | Then launch gdb on the 'vmlinux' executable: | |
712 | @example | |
713 | > gdb vmlinux | |
714 | @end example | |
715 | ||
716 | In gdb, connect to QEMU: | |
717 | @example | |
718 | (gdb) target remote locahost:1234 | |
719 | @end example | |
720 | ||
721 | Then you can use gdb normally. For example, type 'c' to launch the kernel: | |
722 | @example | |
723 | (gdb) c | |
724 | @end example | |
725 | ||
726 | WARNING: breakpoints and single stepping are not yet supported. | |
727 | ||
0806e3f6 FB |
728 | Here are some useful tips in order to use gdb on system code: |
729 | ||
730 | @enumerate | |
731 | @item | |
732 | Use @code{info reg} to display all the CPU registers. | |
733 | @item | |
734 | Use @code{x/10i $eip} to display the code at the PC position. | |
735 | @item | |
736 | Use @code{set architecture i8086} to dump 16 bit code. Then use | |
737 | @code{x/10i $cs*16+*eip} to dump the code at the PC position. | |
738 | @end enumerate | |
739 | ||
386405f7 FB |
740 | @chapter QEMU Internals |
741 | ||
742 | @section QEMU compared to other emulators | |
743 | ||
1eb20527 FB |
744 | Like bochs [3], QEMU emulates an x86 CPU. But QEMU is much faster than |
745 | bochs as it uses dynamic compilation and because it uses the host MMU to | |
746 | simulate the x86 MMU. The downside is that currently the emulation is | |
747 | not as accurate as bochs (for example, you cannot currently run Windows | |
748 | inside QEMU). | |
386405f7 FB |
749 | |
750 | Like Valgrind [2], QEMU does user space emulation and dynamic | |
751 | translation. Valgrind is mainly a memory debugger while QEMU has no | |
1eb20527 FB |
752 | support for it (QEMU could be used to detect out of bound memory |
753 | accesses as Valgrind, but it has no support to track uninitialised data | |
d5a0b50c | 754 | as Valgrind does). The Valgrind dynamic translator generates better code |
1eb20527 | 755 | than QEMU (in particular it does register allocation) but it is closely |
d5a0b50c | 756 | tied to an x86 host and target and has no support for precise exceptions |
1eb20527 FB |
757 | and system emulation. |
758 | ||
759 | EM86 [4] is the closest project to user space QEMU (and QEMU still uses | |
760 | some of its code, in particular the ELF file loader). EM86 was limited | |
761 | to an alpha host and used a proprietary and slow interpreter (the | |
762 | interpreter part of the FX!32 Digital Win32 code translator [5]). | |
386405f7 | 763 | |
fd429f2f FB |
764 | TWIN [6] is a Windows API emulator like Wine. It is less accurate than |
765 | Wine but includes a protected mode x86 interpreter to launch x86 Windows | |
766 | executables. Such an approach as greater potential because most of the | |
767 | Windows API is executed natively but it is far more difficult to develop | |
768 | because all the data structures and function parameters exchanged | |
769 | between the API and the x86 code must be converted. | |
770 | ||
1eb20527 FB |
771 | User mode Linux [7] was the only solution before QEMU to launch a Linux |
772 | kernel as a process while not needing any host kernel patches. However, | |
773 | user mode Linux requires heavy kernel patches while QEMU accepts | |
774 | unpatched Linux kernels. It would be interesting to compare the | |
775 | performance of the two approaches. | |
776 | ||
777 | The new Plex86 [8] PC virtualizer is done in the same spirit as the QEMU | |
778 | system emulator. It requires a patched Linux kernel to work (you cannot | |
779 | launch the same kernel on your PC), but the patches are really small. As | |
780 | it is a PC virtualizer (no emulation is done except for some priveledged | |
781 | instructions), it has the potential of being faster than QEMU. The | |
d5a0b50c FB |
782 | downside is that a complicated (and potentially unsafe) host kernel |
783 | patch is needed. | |
1eb20527 | 784 | |
386405f7 FB |
785 | @section Portable dynamic translation |
786 | ||
787 | QEMU is a dynamic translator. When it first encounters a piece of code, | |
788 | it converts it to the host instruction set. Usually dynamic translators | |
322d0c66 | 789 | are very complicated and highly CPU dependent. QEMU uses some tricks |
386405f7 FB |
790 | which make it relatively easily portable and simple while achieving good |
791 | performances. | |
792 | ||
793 | The basic idea is to split every x86 instruction into fewer simpler | |
794 | instructions. Each simple instruction is implemented by a piece of C | |
795 | code (see @file{op-i386.c}). Then a compile time tool (@file{dyngen}) | |
796 | takes the corresponding object file (@file{op-i386.o}) to generate a | |
797 | dynamic code generator which concatenates the simple instructions to | |
798 | build a function (see @file{op-i386.h:dyngen_code()}). | |
799 | ||
800 | In essence, the process is similar to [1], but more work is done at | |
801 | compile time. | |
802 | ||
803 | A key idea to get optimal performances is that constant parameters can | |
804 | be passed to the simple operations. For that purpose, dummy ELF | |
805 | relocations are generated with gcc for each constant parameter. Then, | |
806 | the tool (@file{dyngen}) can locate the relocations and generate the | |
807 | appriopriate C code to resolve them when building the dynamic code. | |
808 | ||
809 | That way, QEMU is no more difficult to port than a dynamic linker. | |
810 | ||
811 | To go even faster, GCC static register variables are used to keep the | |
812 | state of the virtual CPU. | |
813 | ||
814 | @section Register allocation | |
815 | ||
816 | Since QEMU uses fixed simple instructions, no efficient register | |
817 | allocation can be done. However, because RISC CPUs have a lot of | |
818 | register, most of the virtual CPU state can be put in registers without | |
819 | doing complicated register allocation. | |
820 | ||
821 | @section Condition code optimisations | |
822 | ||
823 | Good CPU condition codes emulation (@code{EFLAGS} register on x86) is a | |
824 | critical point to get good performances. QEMU uses lazy condition code | |
825 | evaluation: instead of computing the condition codes after each x86 | |
fd429f2f | 826 | instruction, it just stores one operand (called @code{CC_SRC}), the |
386405f7 FB |
827 | result (called @code{CC_DST}) and the type of operation (called |
828 | @code{CC_OP}). | |
829 | ||
830 | @code{CC_OP} is almost never explicitely set in the generated code | |
831 | because it is known at translation time. | |
832 | ||
833 | In order to increase performances, a backward pass is performed on the | |
834 | generated simple instructions (see | |
835 | @code{translate-i386.c:optimize_flags()}). When it can be proved that | |
836 | the condition codes are not needed by the next instructions, no | |
837 | condition codes are computed at all. | |
838 | ||
fd429f2f | 839 | @section CPU state optimisations |
386405f7 FB |
840 | |
841 | The x86 CPU has many internal states which change the way it evaluates | |
842 | instructions. In order to achieve a good speed, the translation phase | |
843 | considers that some state information of the virtual x86 CPU cannot | |
844 | change in it. For example, if the SS, DS and ES segments have a zero | |
845 | base, then the translator does not even generate an addition for the | |
846 | segment base. | |
847 | ||
848 | [The FPU stack pointer register is not handled that way yet]. | |
849 | ||
850 | @section Translation cache | |
851 | ||
852 | A 2MByte cache holds the most recently used translations. For | |
853 | simplicity, it is completely flushed when it is full. A translation unit | |
854 | contains just a single basic block (a block of x86 instructions | |
855 | terminated by a jump or by a virtual CPU state change which the | |
856 | translator cannot deduce statically). | |
857 | ||
df0f11a0 FB |
858 | @section Direct block chaining |
859 | ||
860 | After each translated basic block is executed, QEMU uses the simulated | |
861 | Program Counter (PC) and other cpu state informations (such as the CS | |
862 | segment base value) to find the next basic block. | |
863 | ||
864 | In order to accelerate the most common cases where the new simulated PC | |
865 | is known, QEMU can patch a basic block so that it jumps directly to the | |
866 | next one. | |
867 | ||
868 | The most portable code uses an indirect jump. An indirect jump makes it | |
869 | easier to make the jump target modification atomic. On some | |
870 | architectures (such as PowerPC), the @code{JUMP} opcode is directly | |
871 | patched so that the block chaining has no overhead. | |
872 | ||
873 | @section Self-modifying code and translated code invalidation | |
874 | ||
875 | Self-modifying code is a special challenge in x86 emulation because no | |
876 | instruction cache invalidation is signaled by the application when code | |
877 | is modified. | |
878 | ||
879 | When translated code is generated for a basic block, the corresponding | |
880 | host page is write protected if it is not already read-only (with the | |
881 | system call @code{mprotect()}). Then, if a write access is done to the | |
882 | page, Linux raises a SEGV signal. QEMU then invalidates all the | |
883 | translated code in the page and enables write accesses to the page. | |
884 | ||
885 | Correct translated code invalidation is done efficiently by maintaining | |
886 | a linked list of every translated block contained in a given page. Other | |
887 | linked lists are also maintained to undo direct block chaining. | |
888 | ||
4690764b | 889 | Although the overhead of doing @code{mprotect()} calls is important, |
df0f11a0 FB |
890 | most MSDOS programs can be emulated at reasonnable speed with QEMU and |
891 | DOSEMU. | |
892 | ||
893 | Note that QEMU also invalidates pages of translated code when it detects | |
894 | that memory mappings are modified with @code{mmap()} or @code{munmap()}. | |
386405f7 FB |
895 | |
896 | @section Exception support | |
897 | ||
898 | longjmp() is used when an exception such as division by zero is | |
df0f11a0 | 899 | encountered. |
386405f7 | 900 | |
df0f11a0 FB |
901 | The host SIGSEGV and SIGBUS signal handlers are used to get invalid |
902 | memory accesses. The exact CPU state can be retrieved because all the | |
903 | x86 registers are stored in fixed host registers. The simulated program | |
904 | counter is found by retranslating the corresponding basic block and by | |
905 | looking where the host program counter was at the exception point. | |
906 | ||
907 | The virtual CPU cannot retrieve the exact @code{EFLAGS} register because | |
908 | in some cases it is not computed because of condition code | |
909 | optimisations. It is not a big concern because the emulated code can | |
910 | still be restarted in any cases. | |
386405f7 FB |
911 | |
912 | @section Linux system call translation | |
913 | ||
914 | QEMU includes a generic system call translator for Linux. It means that | |
915 | the parameters of the system calls can be converted to fix the | |
916 | endianness and 32/64 bit issues. The IOCTLs are converted with a generic | |
917 | type description system (see @file{ioctls.h} and @file{thunk.c}). | |
918 | ||
df0f11a0 FB |
919 | QEMU supports host CPUs which have pages bigger than 4KB. It records all |
920 | the mappings the process does and try to emulated the @code{mmap()} | |
921 | system calls in cases where the host @code{mmap()} call would fail | |
922 | because of bad page alignment. | |
923 | ||
386405f7 FB |
924 | @section Linux signals |
925 | ||
926 | Normal and real-time signals are queued along with their information | |
927 | (@code{siginfo_t}) as it is done in the Linux kernel. Then an interrupt | |
928 | request is done to the virtual CPU. When it is interrupted, one queued | |
929 | signal is handled by generating a stack frame in the virtual CPU as the | |
930 | Linux kernel does. The @code{sigreturn()} system call is emulated to return | |
931 | from the virtual signal handler. | |
932 | ||
933 | Some signals (such as SIGALRM) directly come from the host. Other | |
934 | signals are synthetized from the virtual CPU exceptions such as SIGFPE | |
935 | when a division by zero is done (see @code{main.c:cpu_loop()}). | |
936 | ||
937 | The blocked signal mask is still handled by the host Linux kernel so | |
938 | that most signal system calls can be redirected directly to the host | |
939 | Linux kernel. Only the @code{sigaction()} and @code{sigreturn()} system | |
940 | calls need to be fully emulated (see @file{signal.c}). | |
941 | ||
942 | @section clone() system call and threads | |
943 | ||
944 | The Linux clone() system call is usually used to create a thread. QEMU | |
945 | uses the host clone() system call so that real host threads are created | |
946 | for each emulated thread. One virtual CPU instance is created for each | |
947 | thread. | |
948 | ||
949 | The virtual x86 CPU atomic operations are emulated with a global lock so | |
950 | that their semantic is preserved. | |
951 | ||
df0f11a0 FB |
952 | Note that currently there are still some locking issues in QEMU. In |
953 | particular, the translated cache flush is not protected yet against | |
954 | reentrancy. | |
955 | ||
1eb87257 FB |
956 | @section Self-virtualization |
957 | ||
4690764b | 958 | QEMU was conceived so that ultimately it can emulate itself. Although |
1eb87257 FB |
959 | it is not very useful, it is an important test to show the power of the |
960 | emulator. | |
961 | ||
962 | Achieving self-virtualization is not easy because there may be address | |
6cd9f35b FB |
963 | space conflicts. QEMU solves this problem by being an executable ELF |
964 | shared object as the ld-linux.so ELF interpreter. That way, it can be | |
965 | relocated at load time. | |
1eb87257 | 966 | |
1eb20527 FB |
967 | @section MMU emulation |
968 | ||
969 | For system emulation, QEMU uses the mmap() system call to emulate the | |
970 | target CPU MMU. It works as long the emulated OS does not use an area | |
971 | reserved by the host OS (such as the area above 0xc0000000 on x86 | |
972 | Linux). | |
973 | ||
974 | It is planned to add a slower but more precise MMU emulation | |
975 | with a software MMU. | |
976 | ||
386405f7 FB |
977 | @section Bibliography |
978 | ||
979 | @table @asis | |
980 | ||
981 | @item [1] | |
982 | @url{http://citeseer.nj.nec.com/piumarta98optimizing.html}, Optimizing | |
983 | direct threaded code by selective inlining (1998) by Ian Piumarta, Fabio | |
984 | Riccardi. | |
985 | ||
986 | @item [2] | |
987 | @url{http://developer.kde.org/~sewardj/}, Valgrind, an open-source | |
988 | memory debugger for x86-GNU/Linux, by Julian Seward. | |
989 | ||
990 | @item [3] | |
991 | @url{http://bochs.sourceforge.net/}, the Bochs IA-32 Emulator Project, | |
992 | by Kevin Lawton et al. | |
993 | ||
994 | @item [4] | |
995 | @url{http://www.cs.rose-hulman.edu/~donaldlf/em86/index.html}, the EM86 | |
996 | x86 emulator on Alpha-Linux. | |
997 | ||
998 | @item [5] | |
999 | @url{http://www.usenix.org/publications/library/proceedings/usenix-nt97/full_papers/chernoff/chernoff.pdf}, | |
1000 | DIGITAL FX!32: Running 32-Bit x86 Applications on Alpha NT, by Anton | |
1001 | Chernoff and Ray Hookway. | |
1002 | ||
fd429f2f FB |
1003 | @item [6] |
1004 | @url{http://www.willows.com/}, Windows API library emulation from | |
1005 | Willows Software. | |
1006 | ||
1eb20527 FB |
1007 | @item [7] |
1008 | @url{http://user-mode-linux.sourceforge.net/}, | |
1009 | The User-mode Linux Kernel. | |
1010 | ||
1011 | @item [8] | |
1012 | @url{http://www.plex86.org/}, | |
1013 | The new Plex86 project. | |
1014 | ||
386405f7 FB |
1015 | @end table |
1016 | ||
1017 | @chapter Regression Tests | |
1018 | ||
322d0c66 | 1019 | In the directory @file{tests/}, various interesting testing programs |
386405f7 FB |
1020 | are available. There are used for regression testing. |
1021 | ||
322d0c66 | 1022 | @section @file{hello-i386} |
386405f7 FB |
1023 | |
1024 | Very simple statically linked x86 program, just to test QEMU during a | |
1025 | port to a new host CPU. | |
1026 | ||
322d0c66 FB |
1027 | @section @file{hello-arm} |
1028 | ||
1029 | Very simple statically linked ARM program, just to test QEMU during a | |
1030 | port to a new host CPU. | |
1031 | ||
386405f7 FB |
1032 | @section @file{test-i386} |
1033 | ||
1034 | This program executes most of the 16 bit and 32 bit x86 instructions and | |
1035 | generates a text output. It can be compared with the output obtained with | |
1036 | a real CPU or another emulator. The target @code{make test} runs this | |
1037 | program and a @code{diff} on the generated output. | |
1038 | ||
1039 | The Linux system call @code{modify_ldt()} is used to create x86 selectors | |
1040 | to test some 16 bit addressing and 32 bit with segmentation cases. | |
1041 | ||
df0f11a0 | 1042 | The Linux system call @code{vm86()} is used to test vm86 emulation. |
386405f7 | 1043 | |
df0f11a0 FB |
1044 | Various exceptions are raised to test most of the x86 user space |
1045 | exception reporting. | |
386405f7 FB |
1046 | |
1047 | @section @file{sha1} | |
1048 | ||
1049 | It is a simple benchmark. Care must be taken to interpret the results | |
1050 | because it mostly tests the ability of the virtual CPU to optimize the | |
1051 | @code{rol} x86 instruction and the condition code computations. | |
1052 |