From: "Andrew Crabtree" Newsgroups: comp.os.msdos.djgpp Subject: Re: Inline ASM: movsx? Date: Wed, 27 May 1998 13:59:37 -0700 Organization: Hewlett-Packard, Roseville Lines: 111 Message-ID: <6khure$orl$1@rosenews.rose.hp.com> References: NNTP-Posting-Host: ros51675cra.rose.hp.com To: djgpp AT delorie DOT com DJ-Gateway: from newsgroup comp.os.msdos.djgpp Precedence: bulk Krian U wrote in message ... >>Instructions like movsx and movcx give an "unrecognized 386 instruction" Perhaps you forgot the size suffix? Or perhaps you are trying to program with intel style assembly, instead of at&t? Check the FAQ for pointers to assembly stuff. > I can't seem to find much info on GCC inline asm in the FAQ >or around the web. Are you sure you looked? Relevant info cpoied from the FAQ and pasted at the bottom of message. >but I was wondering if >there is a way to access local variables in inline asm, without having to pass >them in as arguments, or fiddling around with the bp. You could have shadow global variables and assign them to globals, but its easiest to just pass then in and reference with gcc inline asm style. Andy 17.1 GCC/Gas won't accept valid assembly code ... ================================================= **Q*: I have some code written in assembly which compiles under `MASM' and `TASM', but GCC gives me a long list of error messages.* *A* : The GNU Assembler (`as.exe'), or `Gas' called by GCC accepts "AT&T" syntax, which is different from "Intel" syntax. Notable differences between the two syntaxes are: * AT&T immediate operands are preceded by `$'; Intel immediate operands are undelimited (Intel `push 4' is AT&T `pushl $4'). * AT&T register operands are preceded by `%'; Intel register operands are undelimited. AT&T absolute (as opposed to PC-relative) `jump'/`call' operands are prefixed by `*'; they are undelimited in Intel syntax. * AT&T and Intel syntax use the opposite order for source and destination operands. Intel `add eax, 4' is `addl $4, %eax' in AT&T syntax. The `source, dest' convention is maintained for compatibility with previous Unix assemblers, so that GCC won't care about the assembler with which it is configured, as some of GCC installations (on systems other than MS-DOS) don't use GNU Binutils. * In AT&T syntax, the size of memory operands is determined from the last character of the opcode name. Opcode suffixes of `b', `w', and `l' specify byte (8-bit), word (16-bit), and long (32-bit) memory references. Intel syntax accomplishes this by prefixing memory operands (*not* the opcodes themselves) with ``byte ptr'', ``word ptr'', and ``dword ptr'.' Thus, Intel `mov al, byte ptr FOO' is `movb FOO, %al' in AT&T syntax. * Immediate form long jumps and calls are `lcall/ljmp $SECTION, $OFFSET' in AT&T syntax; the Intel syntax is `call/jmp far SECTION:OFFSET.' Also, the far return instruction is `lret $STACK-ADJUST' in AT&T syntax; Intel syntax is `ret far STACK-ADJUST.' * The AT&T assembler does not provide support for multiple-section (aka multi-segment) programs. Unix style systems expect all programs to be single-section. * An Intel syntax indirect memory reference of the form SECTION:[BASE + INDEX*SCALE + DISP] is translated into the AT&T syntax SECTION:DISP(BASE, INDEX, SCALE) Examples: *Intel:* [ebp - 4] *AT&T:* -4(%ebp) *Intel:* [foo + eax*4] *AT&T:* foo(,%eax,4) *Intel:* [foo] *AT&T:* foo(,1) *Intel:* gs:foo *AT&T:* %gs:foo For a complete description of the differences, get and unzip the files named `as.iN' (where `N' is a digit) from the bnu27b.zip, e.g. ftp://ftp.simtel.net/pub/simtelnet/gnu/djgpp/v2gnu/bnu27b.zip archive, then see See i386-dependent features in "GNU assembler documentation", or point your Web browser to http://www.delorie.com/gnu/docs/gas/as_190.html#SEC192. If you don't read this FAQ with an Info browser, type at the DOS prompt: info as machine i386 You will see a menu of `Gas' features specific to x86 architecture. A guide is available which was written by Brennan Mr. Wacko Underwood ; it describes how to use inline assembly programming with DJGPP and includes a tutorial on the AT&T assembly syntax. Check out the DJGPP inline assembly tutorial, at this URL: http://www.rt66.com/~brennan/djgpp/djgpp_asm.html Many people who used Intel syntax and then converted to the AT&T style say that they like the AT&T variant more. However, if you prefer to stick with the Intel syntax, download and install NASM, e.g. ftp://ftp.simtel.net/pub/simtelnet/msdos/asmutl/nasm091.zip, which is a free portable assembler. It is compatible with DJGPP and accepts a syntax which is almost 100% compatible with the Intel style.