- 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.
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