Message-ID:	<01BE1264.A6BD3580@PLUM.engr.rendition.com>
From:	Jay Tseng <jay DOT tseng AT rendition DOT com>
To:	"Eli Zaretskii (E-mail)" <eliz AT is DOT elta DOT co DOT il>
Cc:	"Djgpp AT Delorie. Com (E-mail)" <djgpp AT delorie DOT com>,
	"'jay DOT tseng AT rendition DOT com'" <jay DOT tseng AT rendition DOT com>
Subject:	Inline Assembly to access control registers C0 and C3
Date:	Tue, 17 Nov 1998 19:58:30 -0800
MIME-Version:	1.0
Reply-To:	djgpp AT delorie DOT com

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Hi Eli,


Help needed.

I wrote C code with inline assembly. It accesses control registers CR0 =
and CR3. The code is as shown after this message. The problem is that it =
runs under WINDOWS DOS environment but fails when runs under pure DOS =
environment  with error message "Exiting due to signal SIGSEGV, General =
Protection Fault at eip=3D........".   I use djgcc version 2.1 and =
compiled the code with  " gcc -fomit-frame-pointer -m386 -Wall ".  =
Inside the code, I intentionally created v_test0 and v_test3 =
corresponding to v_getCR0 and v_getCR3 respectively with minor changes. =
In  DOS environment,  v_test0 and v_test3 went through but failed when =
v_getCR0 is encountered. Any idea? By the way the processor is a  =
Pentium-s 166.

Thanks,

Jay
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
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=3D=3D=3D=3D=3D
#include <stdio.h>

unsigned long result=3D0;


void=20
v_test0()
{

	__asm__ __volatile__
	(
	 "movl $0x11111111, %eax\n"
	 "movl %eax, _result\n"
	);
	return;
}
void=20
v_getCR0()
{

	__asm__ __volatile__
	(
	 "movl %cr0, %eax\n"
	 "movl %eax, _result\n"
	);
	return;
}

void
v_test3()
{

	asm volatile
	(
	 "movl $0x22222222, %0\n"
	 : "=3Db" (result)
	 :=20
	 : "%ebx" , "memory"
	);
	return;
}
void
v_getCR3()
{

	asm volatile
	(
	 "movl %%cr3, %0\n"
	 : "=3Db" (result)
	 :=20
	 : "%ebx" , "memory"
	);
	return;
}

#define disable() __asm__ __volatile__ ("cli");



void main()
{
  =20
	disable();
	v_test0();
	printf("result=3D0x%x\n", result);
	v_test3();
	printf("result=3D0x%x\n", result);
	v_getCR0();
	printf("result=3Dcr0=3D0x%x\n", result);
	v_getCR3();
	printf("result=3Dcr3=3D0x%x\n", result);

	return;
}

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=20

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