Debian Lenny

Kobaz · #1 11-06-2008, 04:25 PM

I'm no expert on asm coding by any means, but in crc32.cpp, why does the code go:

Code:

__asm __volatile (
             "xorl   %%ebx, %%ebx\n"
              "movl   %1, %%esi\n"   

(cut many lines)

              "xorl   (%%edi,%%ebx,4), %%eax\n"
      "2:\n"
              :
              : "a" (val), "g" (buf), "g" (bufsize)
              : "bx", "cx", "dx", "si", "di"
      );
        
      return val;

instead of:

Code:

__asm __volatile (

             "push  %%ebx"

             "xorl   %%ebx, %%ebx\n"
              "movl   %1, %%esi\n"   

(cut many lines)

              "xorl   (%%edi,%%ebx,4), %%eax\n"

              "pop  %%ebx"

      "2:\n"
              :
              : "a" (val), "g" (buf), "g" (bufsize)
              : "cx", "dx", "si", "di"
      );
        
      return val;

This bug has nothing to do with the Perl version btw.

Kobaz · #2 11-06-2008, 04:46 PM

Fixed code seems to be:

Code:

__asm __volatile (

             "push  %%ebx\n"

             "xorl   %%ebx, %%ebx\n"
              "movl   %1, %%esi\n"   

(cut many lines)

              "xorl   (%%edi,%%ebx,4), %%eax\n"

      "2:\n"
               "pop  %%ebx\n"

              :
              : "a" (val), "g" (buf), "g" (bufsize)
              : "cx", "dx", "si", "di"
      );
        
      return val;

**Derision** · #3 11-06-2008, 04:53 PM

I'll test those changes out and incorporate them. I'll probably also get around to downloading the latest GCC and updating the source at some point so it compiles under it, as these issues come up on a fairly regular basis. Thanks.

Angelox · #4 11-06-2008, 06:25 PM

Am I doing this right;

Code:

__asm __volatile (
		"push  %%ebx"  //Kobaz
		"xorl	%%ebx, %%ebx\n"
		"movl	%1, %%esi\n" 
		"movl	%2, %%ecx\n" 
		"movl	$CRC32Table, %%edi\n"
		"shrl	$2, %%ecx\n"
		"jz	1f\n"

		".align 4\n"
		"0:\n"
		"movb	%%al, %%bl\n"
		"movl	(%%esi), %%edx\n"
		"shrl	$8, %%eax\n"
		"xorb	%%dl, %%bl\n"
		"shrl	$8, %%edx\n"
		"xorl	(%%edi,%%ebx,4), %%eax\n"

		"movb	%%al, %%bl\n"
		"shrl	$8, %%eax\n"
		"xorb	%%dl, %%bl\n"
		"shrl	$8, %%edx\n"
		"xorl	(%%edi,%%ebx,4), %%eax\n"

		"movb	%%al, %%bl\n"
		"shrl	$8, %%eax\n"
		"xorb	%%dl, %%bl\n"
		"movb	%%dh, %%dl\n" 
		"xorl	(%%edi,%%ebx,4), %%eax\n"

		"movb	%%al, %%bl\n"
		"shrl	$8, %%eax\n"
		"xorb	%%dl, %%bl\n"
		"addl	$4, %%esi\n"
		"xorl	(%%edi,%%ebx,4), %%eax\n"

		"decl	%%ecx\n"
		"jnz	0b\n"

		"1:\n"
		"movl	%2, %%ecx\n"
		"andl	$3, %%ecx\n"
		"jz	2f\n"

		"movb	%%al, %%bl\n"
		"shrl	$8, %%eax\n"
		"xorb	(%%esi), %%bl\n"
		"xorl	(%%edi,%%ebx,4), %%eax\n"

		"decl	%%ecx\n"
		"jz	2f\n"

		"movb	%%al, %%bl\n"
		"shrl	$8, %%eax\n"
		"xorb	1(%%esi), %%bl\n"
		"xorl	(%%edi,%%ebx,4), %%eax\n"

		"decl	%%ecx\n"
		"jz	2f\n"

		"movb	%%al, %%bl\n"
		"shrl	$8, %%eax\n"
		"xorb	2(%%esi), %%bl\n"
		"xorl	(%%edi,%%ebx,4), %%eax\n"
	"2:\n"
		"pop  %%ebx" //Kobaz
		:
		: "a" (val), "g" (buf), "g" (bufsize)
		: "bx", "cx", "dx", "si", "di"
	);
	
	return val;
}

It still 'clobbers' on the clobber machine, and on the server where the code works I get 'Bad register name' error

Kobaz · #5 11-06-2008, 07:25 PM

You have to change

Code:

: "bx", "cx", "dx", "si", "di"

to

Code:

: "cx", "dx", "si", "di"

as well as save and restore ebx

Angelox · #6 11-06-2008, 07:42 PM

Ok, but now I get this;

Quote:

../common/crc32.cpp:240: Error: bad register name `%ebxxorl %ebx'
../common/crc32.cpp:291: Error: bad register name `%ebx2:'

If you need a SSH to my machine so you can make tests, send me a PM

Kobaz · #7 11-06-2008, 07:51 PM

I really need new glasses....

You are missing the \n at the end of the push and pop lines. Look at the last post I made that starts "Fixed code seems to be:".

It's things like that that remind me how much I hated assembler back in the day when I had to do it. And that was on 8 and 16 bit processors.