readme
1 The perl scripts in this directory are my 'hack' to generate
2 multiple different assembler formats via the one origional script.
3
4 The way to use this library is to start with adding the path to this directory
5 and then include it.
6
7 push(@INC,"perlasm","../../perlasm");
8 require "x86asm.pl";
9
10 The first thing we do is setup the file and type of assembler
11
12 &asm_init($ARGV[0]);
13
14 The first argument is the 'type'. Currently
15 'cpp', 'sol', 'a.out', 'elf' or 'win32'.
16 Argument 2 is the file name.
17
18 The reciprocal function is
19 &asm_finish() which should be called at the end.
20
21 There are 2 main 'packages'. x86ms.pl, which is the Microsoft assembler,
22 and x86unix.pl which is the unix (gas) version.
23
24 Functions of interest are:
25 &external_label("des_SPtrans"); declare and external variable
26 &LB(reg); Low byte for a register
27 &HB(reg); High byte for a register
28 &BP(off,base,index,scale) Byte pointer addressing
29 &DWP(off,base,index,scale) Word pointer addressing
30 &stack_push(num) Basically a 'sub esp, num*4' with extra
31 &stack_pop(num) inverse of stack_push
32 &function_begin(name,extra) Start a function with pushing of
33 edi, esi, ebx and ebp. extra is extra win32
34 external info that may be required.
35 &function_begin_B(name,extra) Same as normal function_begin but no pushing.
36 &function_end(name) Call at end of function.
37 &function_end_A(name) Standard pop and ret, for use inside functions
38 &function_end_B(name) Call at end but with poping or 'ret'.
39 &swtmp(num) Address on stack temp word.
40 &wparam(num) Parameter number num, that was push
41 in C convention. This all works over pushes
42 and pops.
43 &comment("hello there") Put in a comment.
44 &label("loop") Refer to a label, normally a jmp target.
45 &set_label("loop") Set a label at this point.
46 &data_word(word) Put in a word of data.
47
48 So how does this all hold together? Given
49
50 int calc(int len, int *data)
51 {
52 int i,j=0;
53
54 for (i=0; i<len; i++)
55 {
56 j+=other(data[i]);
57 }
58 }
59
60 So a very simple version of this function could be coded as
61
62 push(@INC,"perlasm","../../perlasm");
63 require "x86asm.pl";
64
65 &asm_init($ARGV[0]);
66
67 &external_label("other");
68
69 $tmp1= "eax";
70 $j= "edi";
71 $data= "esi";
72 $i= "ebp";
73
74 &comment("a simple function");
75 &function_begin("calc");
76 &mov( $data, &wparam(1)); # data
77 &xor( $j, $j);
78 &xor( $i, $i);
79
80 &set_label("loop");
81 &cmp( $i, &wparam(0));
82 &jge( &label("end"));
83
84 &mov( $tmp1, &DWP(0,$data,$i,4));
85 &push( $tmp1);
86 &call( "other");
87 &add( $j, "eax");
88 &pop( $tmp1);
89 &inc( $i);
90 &jmp( &label("loop"));
91
92 &set_label("end");
93 &mov( "eax", $j);
94
95 &function_end("calc");
96
97 &asm_finish();
98
99 The above example is very very unoptimised but gives an idea of how
100 things work.
101