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c8317ea346
Allow compilation warnings (the downsides are that it generates LOTS of warnings...) svn path=/branches/ntvdm/; revision=59247
238 lines
9.4 KiB
Plaintext
238 lines
9.4 KiB
Plaintext
Frequently Asked Questions v0.00.0033
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Q. When will Softx86 become a full-fledged PC emulator?
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A. It won't. It will however become a full-fledged Intel 80x86 CPU
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clone that you can tie into your PC emulation software.
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Q. Where are the sample DOS binaries used to test the emulator?
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A. Prebuilt binaries are now distributed separately from the
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source tarball. The source code is still provided, so you
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can assemble them yourself if you have NASM (Netwide Assembler)
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installed on your system.
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Q. How do I use softx86dbg?
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A. Bring up the command prompt (Windows or Linux), change to the
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root directory of the source tree and type "bin/softx86dbg"
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followed by a path to a DOS .COM executable.
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For example, to run samples/test11.com in the emulator, type:
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bin/softx86dbg samples/test11.com
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Linux users may benefit from running the statically linked
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version (especially if they cannot "su root" and "make install")
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because a previous version of the library installed in
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/usr/local/lib might be incompatible with the latest version
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of softx86dbg. You can run the statically linked version by
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typing:
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bin/softx86dbg-static samples/test11.com
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softx86dbg will let you know if it couldn't load the file.
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Q. Softx86dbg is running and it found the COM file I want
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to run. Now what?
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Softx86dbg more or less follows the DOS DEBUG.COM style
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interface. For each step, the values of the registers
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are shown. Commands are parsed one line at a time and
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each command is entered as one or more letters. The
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commands are:
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r [REGISTER] Change a register value
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r Show the register contents
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t Single-step (execute one instruction)
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q Quit
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d [[seg:]offset] Dump memory at given address. If no
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address is given, ds:0x0000 is assumed.
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If no segment value is given, the offset
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is assumed to be within the current
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data (DS) segment.
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u [[seg:]offset] Unassemble (disassemble) instructions
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at given address. If no address is given,
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disassembly starts at the current location
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of the instruction pointer (CS:IP). If
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no segment value is given, the offset is
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assumed to be within the current code
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(CS) segment.
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? print help.
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Softx86dbg also recognizes commands that the original DOS DEBUG.COM
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never had:
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t [x] Single-step <x> times. In other words,
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execute <x> instructions then return.
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UPDATE: It turns out DEBUG.COM for Windows
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XP has this feature after all
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!reset Resets the virtual CPU.
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!ramdump Dumps the virtual RAM to a file named
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1MB_MEM.BIN
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Q. What kind of environment does Softx86dbg emulate?
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A. Softx86dbg emulates a very simple DOS-style environment. An INT 21h
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interface is provided for the program to terminate by, and A simple
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PSP structure is built for the program. Softx86dbg also demonstrates
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the I/O port callback functions by emulating hypothetical hardware
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that takes input and performs a simple calculation with it.
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When the program terminates through INT 21h, softx86dbg prints a
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notice on the screen indicating that the program terminated.
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Q. How do I talk to the hypothetical hardware?
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A. Currently (as of v0.00.0020) there are two I/O ports that the
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hardware exists on.
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Port 0x1234 is a simple register. Every time it is read, the value
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is incremented by 0x22 or 0x2222 (depending on how much is read)
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and then returned to the CPU. When written, the value is copied
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verbatim to the register.
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Port 0x9A is a byte-sized register. When written, the value is
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incremented by 1 and then stored in the register. Then read,
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the value of the register is returned as-is.
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Since this can change in the future (not to mention conflicts with
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actual PC hardware) do not rely on these I/O ports being emulated.
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They are used only by samples/test04.com to test the I/O port
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emulation of Softx86.
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Q. I wrote a program that uses Softx86. How do I make it execute
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instructions? Is there a call that starts a background thread?
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A. Softx86 does not execute or decompile anything by itself. It expects
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your program to execute instructions one at a time using
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softx86_step().
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Q. What is this "context structure" that every API function requires?
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A. The context structure represents one CPU and it's current state.
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All registers, modes, caches, and such are stored in that state.
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The design favors this over the use of static variables so that
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one copy of libsoftx86 can potentially emulate several CPUs at
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once.
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To "create" a CPU, allocate memory in your program for one
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context structure and call softx86_init().
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/* example of C code creating and initializing softx86 context structure */
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softx86_ctx* cpu;
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cpu = (softx86_ctx*)malloc(sizeof(softx86_ctx));
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memset(cpu,0,sizeof(softx86_ctx)); /* recommended, not strictly necessary */
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softx86_init(cpu);
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/* example of C++ code creating and initializing softx86 context structure */
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softx86_ctx* cpu;
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cpu = new softx86_ctx;
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memset(cpu,0,sizeof(softx86_ctx)); /* recommended, not strictly necessary */
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softx86_init(cpu);
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/* example of C++ code pushing softx86 to the extreme by creating 32 separate CPUs */
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softx86_ctx* cpu;
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int x;
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cpu = new softx86_ctx[32];
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memset(cpu,0,sizeof(softx86_ctx)*32); /* recommended, not strictly necessary */
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for (x=0;x < 32;x++) /* 32 brains are better than one! */
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softx86_init(&cpu[x]);
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The Softx86 API functions require this context structure so
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that they know what CPU to perform the operation on and so that
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they have access to the CPU state. To execute an instruction
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on cpu0 and decompile something on cpu1, for example, you would
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write:
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char cpu1_output[256];
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softx86_step(&cpu0);
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softx86_decompile(&cpu1,cpu1_output);
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To delete a CPU and free the resources associated with it
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(including caches stored in the context structure), pass
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the context structure one last time to soft86_free().
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Once it has been freed by softx86_free() you may free
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the memory used by the context structure itself (or
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do whatever you want to it).
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/* example of C code freeing a CPU */
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softx86_free(cpu);
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free(cpu);
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cpu=NULL;
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/* example of C++ code freeing a CPU */
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softx86_free(cpu);
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delete cpu;
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cpu=NULL;
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/* example of hot-shot C++ code (above) freeing all 32 CPUs he created */
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int x;
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for (x=0;x < 32;x++)
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softx86_free(&cpu[x]);
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delete cpu;
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cpu=NULL;
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/* example of C code creating, freeing a CPU, then dancing on it's grave */
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char *ptr;
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softx86_ctx* cpu;
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ptr = malloc(sizeof(softx86_ctx));
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cpu = (softx86_ctx*)ptr;
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softx86_init(cpu); /* create CPU */
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softx86_step(cpu); /* execute something */
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softx86_free(cpu); /* you've served your purpose now get outta here! */
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strcpy(ptr, /* alright yeah! Now I can safely use the same area of memory */
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"Blah Blah Yadda Yadda"); /* to store funny weird ASCIIZ strings! Whoo! */
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free(ptr); /* but I have better things to do... */
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Q. I get strange errors from make or Bash even though the scripts and Makefiles
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look perfectly fine.
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A. The install.sh script may have gotten munged with DOS-style CR LF line breaks.
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This seems to happen when I pack the source code into a .tar.gz tarball then
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copy the tarball to my Windows machine and unpack it using WinZIP or 7-Zip.
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It doesn't immediately seem broken because Notepad and Wordpad show it perfectly,
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but when the extracted files are tar and gzip'd and moved back to the Linux box
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to be tested, the problems show up almost immediately. Bash expects to see
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only LF line breaks, which is why it panics the way it does. GNU Make as far
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as I know is generally tolerant of DOS CR/LF sequences so perhaps the
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Makefile is corrupt in some way.
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A quick fix can be done by changing to the directory containing Makefile and
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install.sh and typing:
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dos2unix install.sh; dos2unix Makefile
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Bash shouldn't have any more problems.
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NOTE: I've also found that WinZIP can't extract tar files properly if they
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contain symlinks. 7-Zip does just fine.
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Q. There are all these makefiles to make a static library and a DLL. There are
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also two makefiles to produce the same program: Softx86dbg. What's the point?
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why are you doing this?
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A. Producing Softx86 as a static library AND a DLL allows software developers to
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incorporate it into their programs in whatever flavor they like. Some people
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especially those producting standalone programs, like statically linked
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versions so that they don't have to deal with messy DLL dependencies or carry
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extra luggage around with the main executable. Other developers, especially
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those working on large projects, like modular designs so that DLLs and
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resources can be loaded and unloaded dynamically (imagine a large project
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that uses Softx86 as one of many emulation engines to simulate everything
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ranging from a PC to a Z-80 to a Super-NES, for example). For these large
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projects, Softx86 in DLL form is the best choice.
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