1The perl scripts in this directory are my 'hack' to generate
2multiple different assembler formats via the one origional script.
3
4The way to use this library is to start with adding the path to this directory
5and then include it.
6
7push(@INC,"perlasm","../../perlasm");
8require "x86asm.pl";
9
10The first thing we do is setup the file and type of assember
11
12&asm_init($ARGV[0],$0);
13
14The first argument is the 'type'. Currently
15'cpp', 'sol', 'a.out', 'elf' or 'win32'.
16Argument 2 is the file name.
17
18The reciprocal function is
19&asm_finish() which should be called at the end.
20
21There are 2 main 'packages'. x86ms.pl, which is the microsoft assembler,
22and x86unix.pl which is the unix (gas) version.
23
24Functions of interest are:
25&external_label("des_SPtrans"); declare and external variable
26&LB(reg); Low byte for a register
27&HB(reg); High byte for a register
28&BP(off,base,index,scale) Byte pointer addressing
29&DWP(off,base,index,scale) Word pointer addressing
30&stack_push(num) Basically a 'sub esp, num*4' with extra
31&stack_pop(num) inverse of stack_push
32&function_begin(name,extra) Start a function with pushing of
33 edi, esi, ebx and ebp. extra is extra win32
34 external info that may be required.
35&function_begin_B(name,extra) Same as norma function_begin but no pushing.
36&function_end(name) Call at end of function.
37&function_end_A(name) Standard pop and ret, for use inside functions
38&function_end_B(name) Call at end but with poping or 'ret'.
39&swtmp(num) Address on stack temp word.
40&wparam(num) Parameter number num, that was push
41 in C convention. This all works over pushes
42 and pops.
43&comment("hello there") Put in a comment.
44&label("loop") Refer to a label, normally a jmp target.
45&set_label("loop") Set a label at this point.
46&data_word(word) Put in a word of data.
47
48So how does this all hold together? Given
49
50int calc(int len, int *data)
51 {
52 int i,j=0;
53
54 for (i=0; i<len; i++)
55 {
56 j+=other(data[i]);
57 }
58 }
59
60So a very simple version of this function could be coded as
61
62 push(@INC,"perlasm","../../perlasm");
63 require "x86asm.pl";
64
65 &asm_init($ARGV[0],"cacl.pl");
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
99The above example is very very unoptimised but gives an idea of how
100things work.
101
102There is also a cbc mode function generator in cbc.pl
103
104&cbc( $name,
105 $encrypt_function_name,
106 $decrypt_function_name,
107 $true_if_byte_swap_needed,
108 $parameter_number_for_iv,
109 $parameter_number_for_encrypt_flag,
110 $first_parameter_to_pass,
111 $second_parameter_to_pass,
112 $third_parameter_to_pass);
113
114So for example, given
115void BF_encrypt(BF_LONG *data,BF_KEY *key);
116void BF_decrypt(BF_LONG *data,BF_KEY *key);
117void BF_cbc_encrypt(unsigned char *in, unsigned char *out, long length,
118 BF_KEY *ks, unsigned char *iv, int enc);
119
120&cbc("BF_cbc_encrypt","BF_encrypt","BF_encrypt",1,4,5,3,-1,-1);
121
122&cbc("des_ncbc_encrypt","des_encrypt","des_encrypt",0,4,5,3,5,-1);
123&cbc("des_ede3_cbc_encrypt","des_encrypt3","des_decrypt3",0,6,7,3,4,5);
124
125