boringssl/crypto/perlasm
David Benjamin 4281bcd5d2 Revert assembly changes in "Hide CPU capability symbols in C."
This partially reverts commit 38636aba74.
Some build on Android seems to break now. I'm not really sure what the
situation is, but if the weird common symbols are still there (can we
remove them?), they probably ought to have the right flags.

Change-Id: Ief589d763d16b995ac6be536505acf7596a87b30
Reviewed-on: https://boringssl-review.googlesource.com/22404
Commit-Queue: David Benjamin <davidben@google.com>
Commit-Queue: Steven Valdez <svaldez@google.com>
Reviewed-by: Steven Valdez <svaldez@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
2017-10-30 20:39:57 +00:00
..
arm-xlate.pl Sync ARM assembly up to 609b0852e4d50251857dbbac3141ba042e35a9ae. 2017-06-13 17:47:20 +00:00
ppc-xlate.pl
readme Remove filename argument to x86 asm_init. 2017-05-12 14:58:27 +00:00
x86_64-xlate.pl Revert assembly changes in "Hide CPU capability symbols in C." 2017-10-30 20:39:57 +00:00
x86asm.pl Remove filename argument to x86 asm_init. 2017-05-12 14:58:27 +00:00
x86gas.pl Fixing assembly coverage reporting. 2017-05-11 16:55:29 +00:00
x86masm.pl Remove filename argument to x86 asm_init. 2017-05-12 14:58:27 +00:00
x86nasm.pl

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]);

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]);

	&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.