Message-Id:	<9712090224.AA26406@gcef.gc.maricopa.edu>
Date:	Mon, 8 Dec 1997 19:24:25 -0700 (MST)
From:	"Joshua James Turpen" <44699 AT ef DOT gc DOT maricopa DOT edu>
To:	djgpp AT delorie DOT com
Subject:	Re: Win95 DPMI and ___djgpp_hw_exception

Ok, after being pointed out that my code doesn't lock the touched code and
variables, here is a completely bulletproof program (as far as I can
tell) that crashes under Win95 DPMI.  It may take a while, but it does
crash.  I've had it crash anywhere from 1 minute to 15 minutes after
starting it.  

I would post a symified traceback, except it doesn't get there.  Windows
intercepts the crash with the "This program has violated...." message and
gives a pointer to 0028:c0002840, which is inside the VMM function
Build_Int_Stack_Frame.


This is a very scary bug.  If it does turn out to be a bug in Win95 DPMI,
it's really going to hurt DJGPP, since the ___djgpp_hw_exception trick is
the basis of signals under DJGPP.


Josh Turpen 
44699 AT ef DOT gc DOT maricopa DOT edu

compiled with: gcc -o test1.exe test1.c test1asm.S
------------------Begin Test1.c-----------------------
#include <stdio.h>
#include <dpmi.h>
#include <signal.h>
#include <sys/segments.h>
extern void int_handler(void);
extern void end_int_handler(void);
void sig_handler(int signum);
static void bottom_of_functions(void);
static int _lwp_lock_data( void *lockaddr, unsigned long locksize );
static int _lwp_lock_code( void *lockaddr, unsigned long locksize );

static void top_of_vars() {};
int tick;
int old_sel, old_off;
static void bottom_of_vars() {};

static void top_of_functions() {};
void main()
{
	__dpmi_paddr old, new;
	void (*old_handler)(int);

	if(_lwp_lock_code(top_of_functions, (long) bottom_of_functions -
(long) top_of_functions) == -1)
		{
		printf("Unable to lock code\n");
		exit(-1);
		}
	if(_lwp_lock_code(int_handler, (long) end_int_handler - (long)
int_handler) == -1)
		{
		printf("Unable to lock int_handler\n");
		exit(-1);
		}
	if(_lwp_lock_data(top_of_vars, (long) bottom_of_vars - (long)
top_of_vars) == -1)
		{
		printf("Unable to lock variables\n");
		exit(-1);
		}

	old_handler = signal(SIGILL, sig_handler);
	
	__dpmi_get_protected_mode_interrupt_vector(0x8, &old);
	old_sel = old.selector;
	old_off = old.offset32;
	new.offset32 = (long) int_handler;
	new.selector = _my_cs();
	__dpmi_set_protected_mode_interrupt_vector(0x8, &new);
	
	while(!kbhit())
		{
		printf("Tick %d\n", tick);
		}
	__dpmi_set_protected_mode_interrupt_vector(0x8, &old);
	signal(SIGILL, old_handler);

}

void sig_handler(signum)
{
	tick++;
}
static void bottom_of_functions() {};

static int _lwp_lock_data( void *lockaddr, unsigned long locksize )
{
	unsigned long baseaddr;
	__dpmi_meminfo memregion;


	if( __dpmi_get_segment_base_address( _my_ds(), &baseaddr) == -1 ) 
		{
		return( -1 );
		}

	memset( &memregion, 0, sizeof(memregion) );
	memregion.address = baseaddr + (unsigned long) lockaddr;
	memregion.size = locksize;

	if( __dpmi_lock_linear_region( &memregion ) == -1 ) 
		{
		return( -1 );
		}
	return( 0 );
}


static int _lwp_lock_code( void *lockaddr, unsigned long locksize )
{
	unsigned long baseaddr;
	__dpmi_meminfo memregion;
	if( __dpmi_get_segment_base_address( _my_cs(), &baseaddr) == -1 ) 
		{
		return( -1 );
		}
	memset( &memregion, 0, sizeof(memregion) );
	memregion.address = baseaddr + (unsigned long) lockaddr;
	memregion.size = locksize;

	if( __dpmi_lock_linear_region( &memregion ) == -1 ) 
		{
		return( -1 );
		}
	return( 0 );
}
--------------------------end Test1.c---------------------------


-------------------------Begin Test1asm.S----------------------
.globl _int_handler
.globl _end_int_handler
.align 4
_int_handler:
	pushl $0
	pushl $0
	pushl %eax
	pushl %ds
	.byte 0x2e
	movw ___djgpp_ds_alias, %ds
	movl $0x99, %eax
	call ___djgpp_hw_exception
	movl _old_sel, %eax
	movl %eax, 12(%esp)
	movl _old_off, %eax
	movl %eax, 8(%esp)
	popl %ds
	popl %eax
	lret
_end_int_handler:

------------------------end test1asm.S-----------------------

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