1 This is a loose collection of notes for people hacking on simulators.
2 If this document gets big enough it can be prettied up then.
6 - The "common" directory
7 - Common Makefile Support
9 - Generating "configure" files
10 - C Language Assumptions
11 - "dump" commands under gdb
13 The "common" directory
14 ======================
16 The common directory contains:
18 - common documentation files (e.g. run.1, and maybe in time .texi files)
19 - common source files (e.g. run.c)
20 - common Makefile fragment and configury (e.g. Make-common.in, aclocal.m4).
22 In addition "common" contains portions of the system call support
23 (e.g. callback.c, nltvals.def).
25 Even though no files are built in this directory, it is still configured
26 so support for regenerating nltvals.def is present.
28 Common Makefile Support
29 =======================
31 A common configuration framework is available for simulators that want
32 to use it. The common framework exists to remove a lot of duplication
33 in configure.ac and Makefile.in, and it also provides a foundation for
34 enhancing the simulators uniformly (e.g. the more they share in common
35 the easier a feature added to one is added to all).
37 The configure.ac of a simulator using the common framework should look like:
40 dnl Process this file with autoconf to produce a configure script.
42 AC_CONFIG_MACRO_DIRS([../common ../.. ../../config])
44 ... target specific additions ...
51 - creates the symbolic links defined in sim_link_{files,links}
53 - creates the Makefile
55 The Makefile.in of a simulator using the common framework should look like:
58 # Makefile for blah ...
61 ## COMMON_PRE_CONFIG_FRAG
63 # These variables are given default values in COMMON_PRE_CONFIG_FRAG.
64 # We override the ones we need to here.
65 # Not all of these need to be mentioned, only the necessary ones.
66 # In fact it is better to *not* mention ones if the value is the default.
68 # List of object files, less common parts.
70 # List of extra dependencies.
71 # Generally this consists of simulator specific files included by sim-main.h.
73 # List of flags to always pass to $(CC).
75 # List of extra libraries to link with.
77 # Dependency of `install' to install any extra files.
79 # Dependency of `clean' to clean any extra files.
82 ## COMMON_POST_CONFIG_FRAG
84 # Rules need to build $(SIM_OBJS), plus whatever else the target wants.
86 ... target specific rules ...
89 COMMON_{PRE,POST}_CONFIG_FRAG are markers for SIM_AC_OUTPUT to tell it
90 where to insert the two pieces of common/Make-common.in.
91 The resulting Makefile is created by doing autoconf substitions on
92 both the target's Makefile.in and Make-common.in, and inserting
93 the two pieces of Make-common.in into the target's Makefile.in at
94 COMMON_{PRE,POST}_CONFIG_FRAG.
96 Note that SIM_EXTRA_{INSTALL,CLEAN} could be removed and "::" targets
97 could be used instead. However, it's not clear yet whether "::" targets
103 Many files generate program symbols at compile time.
104 Such symbols can't be found with grep nor do they normally appear in
105 the TAGS file. To get around this, source files can add the comment
107 /* TAGS: foo1 foo2 */
109 where foo1, foo2 are program symbols. Symbols found in such comments
110 are greppable and appear in the TAGS file.
112 Generating "configure" files
113 ============================
115 For targets using the common framework, "configure" can be generated
116 by running `autoconf'.
118 To regenerate the configure files for all targets using the common framework:
121 $ make -f Makefile.in SHELL=/bin/sh autoconf-common
123 To add a change-log entry to the ChangeLog file for each updated
124 directory (WARNING - check the modified new-ChangeLog files before
127 $ make -f Makefile.in SHELL=/bin/sh autoconf-changelog
128 $ more */new-ChangeLog
129 $ make -f Makefile.in SHELL=/bin/sh autoconf-install
131 In a similar vein, both the configure and config.in files can be
132 updated using the sequence:
135 $ make -f Makefile.in SHELL=/bin/sh autoheader-common
136 $ make -f Makefile.in SHELL=/bin/sh autoheader-changelog
137 $ more */new-ChangeLog
138 $ make -f Makefile.in SHELL=/bin/sh autoheader-install
140 To add the entries to an alternative ChangeLog file, use:
142 $ make ChangeLog=MyChangeLog ....
145 C Language Assumptions
146 ======================
148 An ISO C11 compiler is required, as is an ISO C standard library.
150 "dump" commands under gdb
151 =========================
153 gdbinit.in contains the following
156 set sim_debug_dump ()
159 Simulators that define the sim_debug_dump function can then have their
160 internal state pretty printed from gdb.
162 FIXME: This can obviously be made more elaborate. As needed it will be.
164 Rebuilding nltvals.def
165 ======================
167 Checkout a copy of the SIM and LIBGLOSS modules (Unless you've already
172 $ cvs checkout sim-no-testsuite libgloss-no-testsuite newlib-no-testsuite
174 Configure things for an arbitrary simulator target (d10v is used here for
177 $ mkdir /tmp/$$/build
179 $ /tmp/$$/devo/configure --target=d10v-elf
181 In the sim/ directory rebuild the headers:
186 If the target uses the common syscall table (libgloss/syscall.h), then you're
187 all set! If the target has a custom syscall table, you need to declare it:
189 devo/sim/common/gennltvals.py
191 Add your new processor target (you'll need to grub
192 around to find where your syscall.h lives).
194 devo/sim/<processor>/Makefile.in
198 ``NL_TARGET = -DNL_TARGET_d10v''
200 just before the line COMMON_POST_CONFIG_FRAG.
202 devo/sim/<processor>/*.[ch]
204 Include targ-vals.h instead of syscall.h.
209 For ports based on CGEN, tracing instrumentation should largely be for free,
210 so we will cover the basic non-CGEN setup here. The assumption is that your
211 target is using the common autoconf macros and so the build system already
212 includes the sim-trace configure flag.
214 The full tracing API is covered in sim-trace.h, so this section is an overview.
216 Before calling any trace function, you should make a call to the trace_prefix()
217 function. This is usually done in the main sim_engine_run() loop before
218 simulating the next instruction. You should make this call before every
219 simulated insn. You can probably copy & paste this:
220 if (TRACE_ANY_P (cpu))
221 trace_prefix (sd, cpu, NULL_CIA, oldpc, TRACE_LINENUM_P (cpu), NULL, 0, "");
223 You will then need to instrument your simulator code with calls to the
224 trace_generic() function with the appropriate trace index. Typically, this
225 will take a form similar to the above snippet. So to trace instructions, you
226 would use something like:
227 if (TRACE_INSN_P (cpu))
228 trace_generic (sd, cpu, TRACE_INSN_IDX, "NOP;");
230 The exact output format is up to you. See the trace index enum in sim-trace.h
231 to see the different tracing info available.
233 To utilize the tracing features at runtime, simply use the --trace-xxx flags.
234 run --trace-insn ./some-program
239 Similar to the tracing section, this is merely an overview for non-CGEN based
240 ports. The full API may be found in sim-profile.h. Its API is also similar
243 Note that unlike the tracing command line options, in addition to the profile
244 flags, you have to use the --verbose option to view the summary report after
245 execution. Tracing output is displayed on the fly, but the profile output is
248 To profile core accesses (such as data reads/writes and insn fetches), add
249 calls to PROFILE_COUNT_CORE() to your read/write functions. So in your data
250 fetch function, you'd use something like:
251 PROFILE_COUNT_CORE (cpu, target_addr, size_in_bytes, map_read);
252 Then in your data write function:
253 PROFILE_COUNT_CORE (cpu, target_addr, size_in_bytes, map_write);
254 And in your insn fetcher:
255 PROFILE_COUNT_CORE (cpu, target_addr, size_in_bytes, map_exec);
257 To use the PC profiling code, you simply have to tell the system where to find
258 your simulator's PC. So in your model initialization function:
259 CPU_PC_FETCH (cpu) = function_that_fetches_the_pc;
261 To profile branches, in every location where a branch insn is executed, call
262 one of the related helpers:
263 PROFILE_BRANCH_TAKEN (cpu);
264 PROFILE_BRANCH_UNTAKEN (cpu);
265 If you have stall information, you can utilize the other helpers too.
267 Environment Simulation
268 ======================
270 The simplest simulator doesn't include environment support -- it merely
271 simulates the Instruction Set Architecture (ISA). Once you're ready to move
272 on to the next level, it's time to start handling the --env option. It's
273 enabled by default for all ports already.
275 This will support for the user, virtual, and operating environments. See the
276 sim-config.h header for a more detailed description of them. The former are
277 pretty straight forward as things like exceptions (making system calls) are
278 handled in the simulator. Which is to say, an exception does not trigger an
279 exception handler in the simulator target -- that is what the operating env
280 is about. See the following userspace section for more information.
282 Userspace System Calls
283 ======================
285 By default, the libgloss userspace is simulated. That means the system call
286 numbers and calling convention matches that of libgloss. Simulating other
287 userspaces (such as Linux) is pretty straightforward, but let's first focus
288 on the basics. The basic API is covered in include/sim/callback.h.
290 When an instruction is simulated that invokes the system call method (such as
291 forcing a hardware trap or exception), your simulator code should set up the
292 CB_SYSCALL data structure before calling the common cb_syscall() function.
295 syscall_read_mem (host_callback *cb, struct cb_syscall *sc,
296 unsigned long taddr, char *buf, int bytes)
298 SIM_DESC sd = (SIM_DESC) sc->p1;
299 SIM_CPU *cpu = (SIM_CPU *) sc->p2;
300 return sim_core_read_buffer (sd, cpu, read_map, buf, taddr, bytes);
303 syscall_write_mem (host_callback *cb, struct cb_syscall *sc,
304 unsigned long taddr, const char *buf, int bytes)
306 SIM_DESC sd = (SIM_DESC) sc->p1;
307 SIM_CPU *cpu = (SIM_CPU *) sc->p2;
308 return sim_core_write_buffer (sd, cpu, write_map, buf, taddr, bytes);
310 void target_sim_syscall (SIM_CPU *cpu)
312 SIM_DESC sd = CPU_STATE (cpu);
313 host_callback *cb = STATE_CALLBACK (sd);
316 CB_SYSCALL_INIT (&sc);
318 sc.func = <fetch system call number>;
319 sc.arg1 = <fetch first system call argument>;
320 sc.arg2 = <fetch second system call argument>;
321 sc.arg3 = <fetch third system call argument>;
322 sc.arg4 = <fetch fourth system call argument>;
325 sc.read_mem = syscall_read_mem;
326 sc.write_mem = syscall_write_mem;
328 cb_syscall (cb, &sc);
330 <store system call result from sc.result>;
331 <store system call error from sc.errcode>;
333 Some targets store the result and error code in different places, while others
334 only store the error code when the result is an error.
336 Keep in mind that the CB_SYS_xxx defines are normalized values with no real
337 meaning with respect to the target. They provide a unique map on the host so
338 that it can parse things sanely. For libgloss, the common/nltvals.def file
339 creates the target's system call numbers to the CB_SYS_xxx values.
341 To simulate other userspace targets, you really only need to update the maps
342 pointers that are part of the callback interface. So create CB_TARGET_DEFS_MAP
343 arrays for each set (system calls, errnos, open bits, etc...) and in a place
344 you find useful, do something like:
347 static CB_TARGET_DEFS_MAP cb_linux_syscall_map[] = {
348 # define TARGET_LINUX_SYS_open 5
349 { CB_SYS_open, TARGET_LINUX_SYS_open },
354 host_callback *cb = STATE_CALLBACK (sd);
355 cb->syscall_map = cb_linux_syscall_map;
356 cb->errno_map = cb_linux_errno_map;
357 cb->open_map = cb_linux_open_map;
358 cb->signal_map = cb_linux_signal_map;
359 cb->stat_map = cb_linux_stat_map;
362 Each of these cb_linux_*_map's are manually declared by the arch target.
364 The target_sim_syscall() example above will then work unchanged (ignoring the
365 system call convention) because all of the callback functions go through these
371 Events are scheduled and executed on behalf of either a cpu or hardware devices.
372 The API is pretty much the same and can be found in common/sim-events.h and
375 For simulator targets, you really just have to worry about the schedule and
376 deschedule functions.
381 The device tree model is based on the OpenBoot specification. Since this is
382 largely inherited from the psim code, consult the existing psim documentation
383 for some in-depth details.
384 http://sourceware.org/psim/manual/
389 The simplest simulator doesn't include hardware device support. Once you're
390 ready to move on to the next level, declare in your Makefile.in:
391 SIM_EXTRA_HW_DEVICES = devone devtwo devthree
393 The basic hardware API is documented in common/hw-device.h.
395 Each device has to have a matching file name with a "dv-" prefix. So there has
396 to be a dv-devone.c, dv-devtwo.c, and dv-devthree.c files. Further, each file
397 has to have a matching hw_descriptor structure. So the dv-devone.c file has to
399 const struct hw_descriptor dv_devone_descriptor[] = {
400 {"devone", devone_finish,},
404 The "devone" string as well as the "devone_finish" function are not hard
405 requirements, just common conventions. The structure name is a hard
408 The devone_finish() callback function is used to instantiate this device by
409 parsing the corresponding properties in the device tree.
411 Hardware devices typically attach address ranges to themselves. Then when
412 accesses to those addresses are made, the hardware will have its callback
413 invoked. The exact callback could be a normal I/O read/write access, as
414 well as a DMA access. This makes it easy to simulate memory mapped registers.
416 Keep in mind that like a proper device driver, it may be instantiated many
417 times over. So any device state it needs to be maintained should be allocated
418 during the finish callback and attached to the hardware device via set_hw_data.
419 Any hardware functions can access this private data via the hw_data function.
421 Ports (Interrupts / IRQs)
422 =========================
424 First, a note on terminology. A "port" is an aspect of a hardware device that
425 accepts or generates interrupts. So devices with input ports may be the target
426 of an interrupt (accept it), and/or they have output ports so that they may be
427 the source of an interrupt (generate it).
429 Each port has a symbolic name and a unique number. These are used to identify
430 the port in different contexts. The output port name has no hard relationship
431 to the input port name (same for the unique number). The callback that accepts
432 the interrupt uses the name/id of its input port, while the generator function
433 uses the name/id of its output port.
435 The device tree is used to connect the output port of a device to the input
436 port of another device. There are no limits on the number of inputs connected
437 to an output, or outputs to an input, or the devices attached to the ports.
438 In other words, the input port and output port could be the same device.
441 - each hardware device declares an array of ports (hw_port_descriptor).
442 any mix of input and output ports is allowed.
443 - when setting up the device, attach the array (set_hw_ports).
444 - if the device accepts interrupts, it will have to attach a port callback
445 function (set_hw_port_event)
446 - connect ports with the device tree
447 - handle incoming interrupts with the callback
448 - generate outgoing interrupts with hw_port_event