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20060626	Continuing on SPARC emulation (beginning on the 'save'
		instruction, register windows, etc).
20060629	Planning statistics gathering (new -s command line option),
		and renaming speed_tricks to allow_instruction_combinations.
20060630	Some minor manual page updates.
		Various cleanups.
		Implementing the -s command line option.
20060701	FINALLY found the bug which prevented Linux and Ultrix from
		running without the ugly hack in the R2000/R3000 cache isol
		code; it was the phystranslation hint array which was buggy.
		Removing the phystranslation hint code completely, for now.
20060702	Minor dyntrans cleanups; invalidation of physpages now only
		invalidate those parts of a page that have actually been
		translated. (32 parts per page.)
		Some MIPS non-R3000 speed fixes.
		Experimenting with MIPS instruction combination for some
		addiu+bne+sw loops, and sw+sw+sw.
		Adding support (again) for larger-than-4KB pages in MIPS tlbw*.
		Continuing on SPARC emulation: adding load/store instructions.
20060704	Fixing a virtual vs physical page shift bug in the new tlbw*
		implementation. Problem noticed by Jakub Jermar. (Many thanks.)
		Moving rfe and eret to cpu_mips_instr.c, since that is the
		only place that uses them nowadays.
20060705	Removing the BSD license from the "testmachine" include files,
		placing them in the public domain instead; this enables the
		testmachine stuff to be used from projects which are
		incompatible with the BSD license for some reason.
20060707	Adding instruction combinations for the R2000/R3000 L1
		I-cache invalidation code used by NetBSD/pmax 3.0, lui+addiu,
		various branches followed by addiu or nop, and jr ra followed
		by addiu. The time it takes to perform a full NetBSD/pmax R3000
		install on the laptop has dropped from 573 seconds to 539. :-)
20060708	Adding a framebuffer controller device (dev_fbctrl), which so
		far can be used to change the fb resolution during runtime, but
		in the future will also be useful for accelerated block fill/
		copy, and possibly also simplified character output.
		Adding an instruction combination for NetBSD/pmax' strlen.
20060709	Minor fixes: reading raw files in src/file.c wasn't memblock
		aligned, removing buggy multi_sw MIPS instruction combination,
		etc.
20060711	Adding a machine_qemu.c, which contains a "qemu_mips" machine.
		(It mimics QEMU's MIPS machine mode, so that a test kernel
		made for QEMU_MIPS also can run in GXemul... at least to some
		extent.)  Adding a short section about how to run this mode to
		doc/guestoses.html.
20060714	Misc. minor code cleanups.
20060715	Applying a patch which adds getchar() to promemul/yamon.c
		(from Oleksandr Tymoshenko).
		Adding yamon.h from NetBSD, and rewriting yamon.c to use it
		(instead of ugly hardcoded numbers) + some cleanup.
20060716	Found and fixed the bug which broke single-stepping of 64-bit
		programs between 0.4.0 and 0.4.0.1 (caused by too quick
		refactoring and no testing). Hopefully this fix will not
		break too many other things.
20060718	Continuing on the 8253 PIT; it now works with Linux/QEMU_MIPS.
		Re-adding the sw+sw+sw instr comb (the problem was that I had
		ignored endian issues); however, it doesn't seem to give any
		big performance gain.
20060720	Adding a dummy Transputer mode (T414, T800 etc) skeleton (only
		the 'j' and 'ldc' instructions are implemented so far). :-}
20060721	Adding gtreg.h from NetBSD, updating dev_gt.c to use it, plus
		misc. other updates to get Linux 2.6 for evbmips/malta working
		(thanks to Alec Voropay for the details).
		FINALLY found and fixed the bug which made tlbw* for non-R3000
		buggy; it was a reference count problem in the dyntrans core.
20060722	Testing stuff; things seem stable enough for a new release.

==============  RELEASE 0.4.1  ==============


1 <html><head><title>Gavare's eXperimental Emulator:&nbsp;&nbsp;&nbsp;Introduction</title>
2 <meta name="robots" content="noarchive,nofollow,noindex"></head>
3 <body bgcolor="#f8f8f8" text="#000000" link="#4040f0" vlink="#404040" alink="#ff0000">
4 <table border=0 width=100% bgcolor="#d0d0d0"><tr>
5 <td width=100% align=center valign=center><table border=0 width=100%><tr>
6 <td align="left" valign=center bgcolor="#d0efff"><font color="#6060e0" size="6">
7 <b>Gavare's eXperimental Emulator:</b></font><br>
8 <font color="#000000" size="6"><b>Introduction</b>
9 </font></td></tr></table></td></tr></table><p>
10
11 <!--
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15 Copyright (C) 2003-2006 Anders Gavare. All rights reserved.
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18 modification, are permitted provided that the following conditions are met:
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41
42 <a href="./">Back to the index</a>
43
44 <p><br>
45 <h2>Introduction</h2>
46
47 <p>
48 <table border="0" width="99%"><tr><td valign="top" align="left">
49 <ul>
50 <li><a href="#overview">Overview</a>
51 <li><a href="#free">Is GXemul Free software?</a>
52 <li><a href="#build">How to compile/build the emulator</a>
53 <li><a href="#run">How to run the emulator</a>
54 <li><a href="#cpus">Which processor architectures does GXemul emulate?</a>
55 <li><a href="#hosts">Which host architectures are supported?</a>
56 <li><a href="#translation">What kind of translation does GXemul use?</a>
57 <li><a href="#accuracy">Emulation accuracy</a>
58 <li><a href="#emulmodes">Which machines does GXemul emulate?</a>
59 </ul>
60 </td><td valign="center" align="center">
61 <a href="20050317-example.png"><img src="20050317-example_small.png"></a>
62 <p>NetBSD/pmax 1.6.2 with X11<br>running in GXemul</td></tr></table>
63
64
65
66
67 <p><br>
68 <a name="overview"></a>
69 <h3>Overview:</h3>
70
71 GXemul is an experimental instruction-level machine emulator. Several
72 emulation modes are available. In some modes, processors and surrounding
73 hardware components are emulated well enough to let unmodified operating
74 systems (e.g. NetBSD) run as if they were running on a real machine.
75
76 <p>Devices and processors (ARM, MIPS, PowerPC) are not simulated with 100%
77 accuracy. They are only ``faked'' well enough to allow guest operating
78 systems run without complaining too much. Still, the emulator could be of
79 interest for academic research and experiments, such as when learning how
80 to write operating system code.
81
82 <p>The emulator is written in C, does not depend on third-party libraries,
83 and should compile and run on most 64-bit and 32-bit Unix-like systems.
84
85 <p>The emulator contains code which tries to emulate the workings of CPUs
86 and surrounding hardware found in real machines, but it does not contain
87 any ROM code. You will need some form of program (in binary form) to run
88 in the emulator. For many emulation modes, PROM calls are handled by the
89 emulator itself, so you do not need to use any ROM image at all.
90
91 <p>You can use pre-compiled kernels (for example NetBSD kernels, or
92 Linux), or other programs that are in binary format, and in some cases
93 even actual ROM images. A couple of different file formats are supported
94 (ELF, a.out, ECOFF, SREC, and raw binaries).
95
96 <p>If you do not have a kernel as a separate file, but you have a bootable
97 disk image, then it is sometimes possible to boot directly from that
98 image. (This works for example with DECstation emulation, or when booting
99 from ISO9660 CDROM images.)
100
101
102
103
104
105
106
107
108 <p><br>
109 <a name="free"></a>
110 <h3>Is GXemul Free software?</h3>
111
112 Yes. I have released GXemul under a Free license. The code in GXemul is
113 Copyrighted software, it is <i>not</i> public domain. (If this is
114 confusing to you, you might want to read up on the definitions of the
115 four freedoms associated with Free software, <a
116 href="http://www.gnu.org/philosophy/free-sw.html">http://www.gnu.org/philosophy/free-sw.html</a>.)
117
118 <p>The code I have written is released under a 3-clause BSD-style license
119 (or "revised BSD-style" if one wants to use <a
120 href="http://www.gnu.org/philosophy/bsd.html">GNU jargon</a>). Apart from
121 the code I have written, some files are copied from other sources such as
122 NetBSD, for example header files containing symbolic names of bitfields in
123 device registers. They are also covered by similar licenses, but with some
124 additional clauses. The main point, however, is that the licenses require
125 that the original Copyright and license terms are included when you make a
126 copy or modification.
127
128 <p>If you plan to redistribute GXemul <i>without</i> supplying the source
129 code, then you need to comply with each individual source file some other
130 way, for example by writing additional documentation containing copyright
131 notes. I have not done this, since I do not plan on making distributions
132 without source code. You need to check all individual files for details.
133 The "easiest way out" if you plan to redistribute code from GXemul is, of
134 course, to let it remain open source and simply supply the source code.
135
136 <p>In case you want to reuse parts of GXemul, but you need to do that
137 under a different license (e.g. the GPL), then contact me and I might
138 re-license/dual-license files on a case-by-case basis.
139
140
141
142
143
144 <p><br>
145 <a name="build"></a>
146 <h3>How to compile/build the emulator:</h3>
147
148 Uncompress the .tar.gz distribution file, and run
149 <pre>
150 $ <b>./configure</b>
151 $ <b>make</b>
152 </pre>
153
154 <p>This should work on most Unix-like systems. GXemul does not require any
155 specific libraries to build, however, if you build on a system which does
156 not have X11 libraries installed, some functionality will be lost.
157
158 <p>The emulator's performance is highly dependent on both runtime settings
159 and on compiler settings, so you might want to experiment with different
160 CC and CFLAGS environment variable values. For example, on an AMD Athlon
161 host, you might want to try setting <tt>CFLAGS</tt> to <tt>-march=athlon</tt>
162 before running <tt>configure</tt>.
163
164
165
166
167
168
169
170 <p><br>
171 <a name="run"></a>
172 <h3>How to run the emulator:</h3>
173
174 Once you have built GXemul, running it should be rather straight-forward.
175 Running <tt><b>gxemul</b></tt> without arguments (or with the
176 <b><tt>-h</tt></b> or <b><tt>-H</tt></b> command line options) will
177 display a help message.
178
179 <p>
180 To get some ideas about what is possible to run in the emulator, please
181 read the section about <a href="guestoses.html">installing "guest"
182 operating systems</a>. If you are interested in using the emulator to
183 develop code on your own, then you should also read the section about
184 <a href="experiments.html#hello">Hello World</a>.
185
186 <p>
187 To exit the emulator, type CTRL-C to enter the
188 single-step debugger, and then type <tt><b>quit</b></tt>.
189
190 <p>
191 If you are starting an emulation by entering settings directly on the
192 command line, and you are not using the <tt><b>-x</b></tt> option, then all
193 terminal input and output will go to the main controlling terminal.
194 CTRL-C is used to break into the debugger, so in order to send CTRL-C to
195 the running (emulated) program, you may use CTRL-B.
196 (This should be a reasonable compromise to allow the emulator to be usable
197 even on systems without X Windows.)
198
199 <p>
200 There is no way to send an actual CTRL-B to the emulated program, when
201 typing in the main controlling terminal window. The solution is to either
202 use <a href="configfiles.html">configuration files</a>, or use
203 <tt><b>-x</b></tt>. Both these solutions cause new xterms to be opened for
204 each emulated serial port that is written to. CTRL-B and CTRL-C both have
205 their original meaning in those xterm windows.
206
207
208
209
210
211 <p><br>
212 <a name="cpus"></a>
213 <h3>Which processor architectures does GXemul emulate?</h3>
214
215 The architectures that are emulated well enough to let at least one
216 guest operating system run (per architecture) are ARM, MIPS, and
217 PowerPC.
218
219
220
221
222
223 <p><br>
224 <a name="hosts"></a>
225 <h3>Which host architectures are supported?</h3>
226
227 As of release 0.4.0 of GXemul, the old binary translation subsystem, which
228 was used for emulation of MIPS processors on Alpha and i386 hosts, has
229 been removed. The current dynamic translation subsystem should work on any
230 host.
231
232
233
234
235
236 <p><br>
237 <a name="translation"></a>
238 <h3>What kind of translation does GXemul use?</h3>
239
240 <b>Static vs. dynamic:</b>
241
242 <p>In order to support guest operating systems, which can overwrite old
243 code pages in memory with new code, it is necessary to translate code
244 dynamically. It is not possible to do a "one-pass" (static) translation.
245 Self-modifying code and Just-in-Time compilers running inside
246 the emulator are other things that would not work with a static
247 translator. GXemul is a dynamic translator. However, it does not
248 necessarily translate into native code, like many other emulators.
249
250 <p><b>"Runnable" Intermediate Representation:</b>
251
252 <p>Dynamic translators usually translate from the emulated architecture
253 (e.g. MIPS) into a kind of <i>intermediate representation</i> (IR), and then
254 to native code (e.g. AMD64 or x86 code). Since one of my main goals for
255 GXemul is to keep everything as portable as possible, I have tried to make
256 sure that the IR is something which can be executed regardless of whether
257 the final step (translation from IR to native code) has been implemented
258 or not.
259
260 <p>The IR in GXemul consists of arrays of pointers to functions, and a few
261 arguments which are passed along to those functions. The functions are
262 implemented in either manually hand-coded C, or automatically generated C.
263 In any case, this is all statically linked into the GXemul binary at link
264 time.
265
266 <p>Here is a simplified diagram of how these arrays work.
267
268 <p><center><img src="simplified_dyntrans.png"></center>
269
270 <p>There is one instruction call slot for every possible program counter
271 location. In the MIPS case, instruction words are 32 bits in length,
272 and pages are (usually) 4 KB large, resulting in 1024 instruction call
273 slots. After the last of these instruction calls, there is an additional
274 call to a special "end of page" function (which doesn't count as an executed
275 instruction). This function switches to the first instruction
276 on the next virtual page (which might cause exceptions, etc).
277
278 <p>The complexity of individual instructions vary. A simple example of
279 what an instruction can look like is the MIPS <tt>addiu</tt> instruction:
280 <pre>
281 X(addiu)
282 {
283 reg(ic->arg[1]) = (int32_t)
284 ((int32_t)reg(ic->arg[0]) + (int32_t)ic->arg[2]);
285 }
286 </pre>
287
288 <p>It stores the result of a 32-bit addition of the register at arg[0]
289 with the immediate value arg[2] (treating both as signed 32-bit
290 integers) into register arg[1]. If the emulated CPU is a 64-bit CPU,
291 then this will store a correctly sign-extended value into arg[1].
292 If it is a 32-bit CPU, then only the lowest 32 bits will be stored,
293 and the high part ignored. <tt>X(addiu)</tt> is expanded to
294 <tt>mips_instr_addiu</tt> in the 64-bit case, and <tt>mips32_instr_addiu</tt>
295 in the 32-bit case. Both are compiled into the GXemul executable; no code
296 is created during run-time.
297
298 <p>Here are examples of what the <tt>addiu</tt> instruction actually
299 looks like when it is compiled, on various host architectures:
300
301 <p><center><table border="0">
302 <tr><td><b>GCC 4.0.1 on Alpha:</b></td>
303 <td width="35"></td><td></td>
304 <tr>
305 <td valign="top">
306 <pre>mips_instr_addiu:
307 ldq t1,8(a1)
308 ldq t2,24(a1)
309 ldq t3,16(a1)
310 ldq t0,0(t1)
311 addl t0,t2,t0
312 stq t0,0(t3)
313 ret</pre>
314 </td>
315 <td></td>
316 <td valign="top">
317 <pre>mips32_instr_addiu:
318 ldq t2,8(a1)
319 ldq t0,24(a1)
320 ldq t3,16(a1)
321 ldl t1,0(t2)
322 addq t0,t1,t0
323 stl t0,0(t3)
324 ret</pre>
325 </td>
326 </tr>
327
328 <tr><td><b><br>GCC 3.4.4 on AMD64:</b></td>
329 <tr>
330 <td valign="top">
331 <pre>mips_instr_addiu:
332 mov 0x8(%rsi),%rdx
333 mov 0x18(%rsi),%rax
334 mov 0x10(%rsi),%rcx
335 add (%rdx),%eax
336 cltq
337 mov %rax,(%rcx)
338 retq</pre>
339 </td>
340 <td></td>
341 <td valign="top">
342 <pre>mips32_instr_addiu:
343 mov 0x8(%rsi),%rcx
344 mov 0x10(%rsi),%rdx
345 mov (%rcx),%eax
346 add 0x18(%rsi),%eax
347 mov %eax,(%rdx)
348 retq</pre>
349 </td>
350 </tr>
351
352 <tr><td><b><br>GCC 4.0.1 on i386:</b></td>
353 <tr>
354 <td valign="top">
355 <pre>mips_instr_addiu:
356 mov 0x8(%esp),%eax
357 mov 0x8(%eax),%ecx
358 mov 0x4(%eax),%edx
359 mov 0xc(%eax),%eax
360 add (%edx),%eax
361 mov %eax,(%ecx)
362 cltd
363 mov %edx,0x4(%ecx)
364 ret</pre>
365 </td>
366 <td></td>
367 <td valign="top">
368 <pre>mips32_instr_addiu:
369 mov 0x8(%esp),%eax
370 mov 0x8(%eax),%ecx
371 mov 0x4(%eax),%edx
372 mov 0xc(%eax),%eax
373 add (%edx),%eax
374 mov %eax,(%ecx)
375 ret</pre>
376 </td>
377 </tr>
378 </table></center>
379
380 <p>On 64-bit hosts, there is not much difference, but on 32-bit hosts (and
381 to some extent on AMD64), the difference is enough to make it worthwhile.
382
383
384 <p><b>Performance:</b>
385
386 <p>The performance of using this kind of runnable IR is obviously lower
387 than what can be achieved by emulators using native code generation, but
388 can be significantly higher than using a naive fetch-decode-execute
389 interpretation loop. In my opinion, using a runnable IR is an interesting
390 compromise.
391
392 <p>The overhead per emulated instruction is usually around or below
393 approximately 10 host instructions. This is very much dependent on your
394 host architecture and what compiler and compiler switches you are using.
395 Added to this instruction count is (of course) also the C code used to
396 implement each specific instruction.
397
398 <p><b>Instruction Combinations:</b>
399
400 <p>Short, common instruction sequences can sometimes be replaced by a
401 "compound" instruction. An example could be a compare instruction followed
402 by a conditional branch instruction. The advantages of instruction
403 combinations are that
404 <ul>
405 <li>the amortized overhead per instruction is slightly reduced, and
406 <p>
407 <li>the host's compiler can make a good job at optimizing the common
408 instruction sequence.
409 </ul>
410
411 <p>The special cases where instruction combinations give the most gain
412 are in the cores of string/memory manipulation functions such as
413 <tt>memset()</tt> or <tt>strlen()</tt>. The core loop can then (at least
414 to some extent) be replaced by a native call to the equivalent function.
415
416 <p>The implementations of compound instructions still keep track of the
417 number of executed instructions, etc. When single-stepping, these
418 translations are invalidated, and replaced by normal instruction calls
419 (one per emulated instruction).
420
421 <p><b>Native Code Back-ends: (not in this release)</b>
422
423 <p>In theory, it will be possible to implement native code generation
424 (similar to what is used in high-performance emulators such as QEMU),
425 as long as that generated code abides to the C ABI on the host, but
426 for now I wanted to make sure that GXemul works without such native
427 code back-ends. For this reason, as of release 0.4.0, GXemul is
428 completely free of native code back-ends.
429
430
431
432
433
434
435 <p><br>
436 <a name="accuracy"></a>
437 <h3>Emulation accuracy:</h3>
438
439 GXemul is an instruction-level emulator; things that would happen in
440 several steps within a real CPU are not taken into account (e.g. pipe-line
441 stalls or out-of-order execution). Still, instruction-level accuracy seems
442 to be enough to be able to run complete guest operating systems inside the
443 emulator.
444
445 <p>The existance of instruction and data caches is "faked" to let
446 operating systems think that they are there, but for all practical
447 purposes, these caches are non-working.
448
449 <p>The emulator is <i>not</i> timing-accurate. It can be run in a
450 "deterministic" mode, <tt><b>-D</b></tt>. The meaning of deterministic is
451 simply that running two emulations with the same settings will result in
452 identical runs. Obviously, this requires that no user interaction is
453 taking place, and that clock speeds are fixed with the <tt><b>-I</b></tt>
454 option. (Deterministic in this case does <i>not</i> mean that the
455 emulation will be identical to some actual real-world machine.)
456
457 <p>(Note that user interaction means <i>both</i> input to the emulated
458 program/OS, and interaction with the emulator's debugger. Breaking into the
459 debugger and then continuing execution may affect when/how interrupts
460 occur.)
461
462
463
464
465
466
467 <p><br>
468 <a name="emulmodes"></a>
469 <h3>Which machines does GXemul emulate?</h3>
470
471 A few different machine types are emulated. The following machine types
472 are emulated well enough to run at least one "guest OS":
473
474 <p>
475 <ul>
476 <li><b><u>ARM</u></b>
477 <ul>
478 <li><b>CATS</b> (<a href="guestoses.html#netbsdcatsinstall">NetBSD/cats</a>,
479 <a href="guestoses.html#openbsdcatsinstall">OpenBSD/cats</a>)
480 <li><b>IQ80321</b> (<a href="guestoses.html#netbsdevbarminstall">NetBSD/evbarm</a>)
481 </ul>
482 <p>
483 <li><b><u>MIPS</u></b>
484 <ul>
485 <li><b>DECstation 5000/200</b> (<a href="guestoses.html#netbsdpmaxinstall">NetBSD/pmax</a>,
486 <a href="guestoses.html#openbsdpmaxinstall">OpenBSD/pmax</a>,
487 <a href="guestoses.html#ultrixinstall">Ultrix</a>,
488 <a href="guestoses.html#declinux">Linux/DECstation</a>,
489 <a href="guestoses.html#sprite">Sprite</a>)
490 <li><b>Acer Pica-61</b> (<a href="guestoses.html#netbsdarcinstall">NetBSD/arc</a>)
491 <li><b>NEC MobilePro 770, 780, 800, and 880</b> (<a href="guestoses.html#netbsdhpcmipsinstall">NetBSD/hpcmips</a>)
492 <li><b>Cobalt</b> (<a href="guestoses.html#netbsdcobaltinstall">NetBSD/cobalt</a>)
493 <li><b>Malta</b> (<a href="guestoses.html#netbsdevbmipsinstall">NetBSD/evbmips</a>)
494 <li><b>SGI O2 (aka IP32)</b> <font color="#0000e0">(<super>*</super>)</font>
495 (<a href="guestoses.html#netbsdsgimips">NetBSD/sgi</a>)
496 </ul>
497 <p>
498 <li><b><u>PowerPC</u></b>
499 <ul>
500 <li><b>IBM 6050/6070 (PReP, PowerPC Reference Platform)</b> (<a href="guestoses.html#netbsdprepinstall">NetBSD/prep</a>)
501 </ul>
502 </ul>
503
504 <p><small><font color="#0000e0">(<super>*</super>)</font> =
505 Enough for root-on-nfs, but not for disk boot.)</small>
506
507 <p>There is code in GXemul for emulation of many other machine types; the
508 degree to which these work range from almost being able to run a complete
509 OS, to almost completely unsupported (perhaps just enough support to
510 output a few boot messages via serial console).
511
512 <p>In addition to emulating real machines, there is also a "test-machine".
513 A test-machine consists of one or more CPUs and a few experimental devices
514 such as:
515
516 <p>
517 <ul>
518 <li>a console I/O device (putchar() and getchar()...)
519 <li>an inter-processor communication device, for SMP experiments
520 <li>a very simple linear framebuffer device (for graphics output)
521 <li>a simple SCSI disk controller
522 <li>a simple ethernet controller
523 </ul>
524
525 <p>This mode is useful if you wish to run experimental code, but do not
526 wish to target any specific real-world machine type, for example for
527 educational purposes.
528
529 <p>You can read more about these experimental devices <a
530 href="experiments.html#expdevices">here</a>.
531
532
533
534
535
536
537 </body>
538 </html>

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