Adam Langley 0dd93002dd Revert section changes for ASM.
This change reverts the following commits:
  72d9cba7cb78ddc9c8ec3f27a9367c407f7d0915
  5b61b9ebc5ad0e25475f2aa633d3a6592dd65ba1
  3f85e04f40c12282021241b393d94901e5c1027b
  2ab24a2d40fd193a25d7c94072596a1180cbb460

Change-Id: I669b83f2269cf96aa71a649a346147b9407a811e
Reviewed-on: https://boringssl-review.googlesource.com/6056
Reviewed-by: David Benjamin <davidben@chromium.org>
Reviewed-by: Adam Langley <agl@google.com>
2015-09-30 22:09:52 +00:00
..
2015-09-30 22:09:52 +00:00
2014-06-20 13:17:32 -07:00
2014-06-20 13:17:32 -07:00
2014-10-29 23:13:20 +00:00
2014-07-31 22:03:11 +00:00
2015-02-23 19:45:30 +00:00

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 assember

&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 norma 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.

There is also a cbc mode function generator in cbc.pl

&cbc(	$name,
	$encrypt_function_name,
	$decrypt_function_name,
	$true_if_byte_swap_needed,
	$parameter_number_for_iv,
	$parameter_number_for_encrypt_flag,
	$first_parameter_to_pass,
	$second_parameter_to_pass,
	$third_parameter_to_pass);

So for example, given
void BF_encrypt(BF_LONG *data,BF_KEY *key);
void BF_decrypt(BF_LONG *data,BF_KEY *key);
void BF_cbc_encrypt(unsigned char *in, unsigned char *out, long length,
        BF_KEY *ks, unsigned char *iv, int enc);

&cbc("BF_cbc_encrypt","BF_encrypt","BF_encrypt",1,4,5,3,-1,-1);

&cbc("des_ncbc_encrypt","des_encrypt","des_encrypt",0,4,5,3,5,-1);
&cbc("des_ede3_cbc_encrypt","des_encrypt3","des_decrypt3",0,6,7,3,4,5);