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      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 assember
     11 
     12 &asm_init($ARGV[0],$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 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 
     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],"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 
     99 The above example is very very unoptimised but gives an idea of how
    100 things work.
    101 
    102 There 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 
    114 So for example, given
    115 void BF_encrypt(BF_LONG *data,BF_KEY *key);
    116 void BF_decrypt(BF_LONG *data,BF_KEY *key);
    117 void 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