| The perl scripts in this directory are my 'hack' to generate |
| multiple different assembler formats via the one origional script. |
| |
| The way to use this library is to start with adding the path to this directory |
| and then include it. |
| |
| push(@INC,"perlasm","../../perlasm"); |
| require "x86asm.pl"; |
| |
| The first thing we do is setup the file and type of assembler |
| |
| &asm_init($ARGV[0],$0); |
| |
| The first argument is the 'type'. Currently |
| 'cpp', 'sol', 'a.out', 'elf' or 'win32'. |
| Argument 2 is the file name. |
| |
| The reciprocal function is |
| &asm_finish() which should be called at the end. |
| |
| There are 2 main 'packages'. x86ms.pl, which is the Microsoft assembler, |
| and x86unix.pl which is the unix (gas) version. |
| |
| Functions of interest are: |
| &external_label("des_SPtrans"); declare and external variable |
| &LB(reg); Low byte for a register |
| &HB(reg); High byte for a register |
| &BP(off,base,index,scale) Byte pointer addressing |
| &DWP(off,base,index,scale) Word pointer addressing |
| &stack_push(num) Basically a 'sub esp, num*4' with extra |
| &stack_pop(num) inverse of stack_push |
| &function_begin(name,extra) Start a function with pushing of |
| edi, esi, ebx and ebp. extra is extra win32 |
| external info that may be required. |
| &function_begin_B(name,extra) Same as normal function_begin but no pushing. |
| &function_end(name) Call at end of function. |
| &function_end_A(name) Standard pop and ret, for use inside functions |
| &function_end_B(name) Call at end but with poping or 'ret'. |
| &swtmp(num) Address on stack temp word. |
| &wparam(num) Parameter number num, that was push |
| in C convention. This all works over pushes |
| and pops. |
| &comment("hello there") Put in a comment. |
| &label("loop") Refer to a label, normally a jmp target. |
| &set_label("loop") Set a label at this point. |
| &data_word(word) Put in a word of data. |
| |
| So how does this all hold together? Given |
| |
| int calc(int len, int *data) |
| { |
| int i,j=0; |
| |
| for (i=0; i<len; i++) |
| { |
| j+=other(data[i]); |
| } |
| } |
| |
| So a very simple version of this function could be coded as |
| |
| push(@INC,"perlasm","../../perlasm"); |
| require "x86asm.pl"; |
| |
| &asm_init($ARGV[0],"cacl.pl"); |
| |
| &external_label("other"); |
| |
| $tmp1= "eax"; |
| $j= "edi"; |
| $data= "esi"; |
| $i= "ebp"; |
| |
| &comment("a simple function"); |
| &function_begin("calc"); |
| &mov( $data, &wparam(1)); # data |
| &xor( $j, $j); |
| &xor( $i, $i); |
| |
| &set_label("loop"); |
| &cmp( $i, &wparam(0)); |
| &jge( &label("end")); |
| |
| &mov( $tmp1, &DWP(0,$data,$i,4)); |
| &push( $tmp1); |
| &call( "other"); |
| &add( $j, "eax"); |
| &pop( $tmp1); |
| &inc( $i); |
| &jmp( &label("loop")); |
| |
| &set_label("end"); |
| &mov( "eax", $j); |
| |
| &function_end("calc"); |
| |
| &asm_finish(); |
| |
| The above example is very very unoptimised but gives an idea of how |
| things work. |