From: tuukka DOT kalliokoski AT nokia DOT com (Tuukka Kalliokoski)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Problems with LWP 2.0 / djgpp 2.03
Organization: Nokia PMR
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Date: Mon, 18 Dec 2000 09:27:37 GMT
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To: djgpp AT delorie DOT com
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On Mon, 18 Dec 2000 09:47:52 +0200 (IST), Eli Zaretskii
<eliz AT is DOT elta DOT co DOT il> wrote:

>If you can post the relevant fragments from LWP here, perhaps we could
>give you some directions for untangling this riddle.


That would be great. Here is the timer interrupt routine, that raises
the SIGILL scheduling signal:

__lwpPmIrq8TimerHook: 
  pushl %eax
  pushl %ds
	
  .byte 0x2E   /* CS: */
  movw ___djgpp_ds_alias, %ds 

  cmp $0, lwpInterruptPending
  jne L2

  movl $1, lwpInterruptPending

  cmp $1, __lwpEnable
  jne  L1
  movb $0x99,%al 
  call ___djgpp_hw_exception
  jmp L2

L1:  movl $0, lwpInterruptPending 
L2:   popl %ds
  popl %eax
  ljmp %cs:__lwpOldIrq8Handler


And here is main part of the SIGILL handler:

.align 4
__lwpScheduler:

  movl $1, lwpInterruptPending

  movl  ___djgpp_exception_state_ptr, %edi
  cmpl $0, %edi    /* SIGILL was raise()'d, not by interrupt */
  je raised               
  cmpl $0x99, 56(%edi)    /* our exception or real exception? */
  jne raised

  movl 0(%edi), %eax
  pushl %eax
  movl 4(%edi), %ebx
  movl 8(%edi), %ecx
  movl 12(%edi), %edx
  movl 16(%edi), %esi
  movl 24(%edi), %ebp
  
  movl 28(%edi), %eax
  movl %eax, tmp1    /* esp */
  movl 32(%edi), %eax
  movl %eax, tmp2    /* eip */
  movl 36(%edi), %eax
  movl %eax, tmp3    /* eflags */
  movl 20(%edi), %eax  /* edi */

  movw 44(%edi), %es
  movw 46(%edi), %fs
  movw 48(%edi), %gs
  movw 42(%edi), %ds

  movl %eax, %edi
  popl %eax
  .byte 0x2e
  movl tmp1, %esp       /* stack switched to exception state stack */
  .byte 0x2e
  pushl tmp2            /* push exeception state ret address */
  .byte 0x2e
  pushl tmp3   /* eflags */
  popfl

  /* now it's setup to look just like a yield happened in the code  */
  /* This little bit is what does the priorities */
  pushl %eax
  pushl %esi
  pushl %ds
  pushfl
  .byte 0x2e
  movw ___djgpp_ds_alias, %ds
  movl __lwpCur, %esi
  decl 20(%esi)      /* pcount */
  jnz noYld      /* pcount == 0 ? */
  movl 16(%esi), %eax    /* yes, pcount = priority */
  movl %eax, 20(%esi)    
  popfl
  popl %ds
  popl %esi
  popl %eax
  jmpl _lwpYield
noYld:  popfl
  popl %ds
  popl %esi
  popl %eax
raised:  pushl %ds
  .byte 0x2e
  movw ___djgpp_ds_alias, %ds  
  movl $0, lwpInterruptPending 
  popl %ds
  ret


Here is the C fragment that vectors the IRQ and signal handlers:

 /* SIGILL is raised when an unhandled exception is raised */
 _lwpOldHandler = signal(SIGILL,_lwpScheduler); 
 _lwpOldFpuHandler = signal(SIGFPE, _lwpFpuHandler);
 irq8.offset32 = (int)_lwpPmIrq8TimerHook;
 irq8.selector = _my_cs();
 __dpmi_get_protected_mode_interrupt_vector(IRQ8,&_lwpOldIrq8Handler);
__dpmi_set_protected_mode_interrupt_vector(IRQ8, &irq8);


I suspect that the registers are pushed to stack on incorrect order,
or something is missing from SIGILL handler. I am quite sure that
this code has worked with older gcc version.


Tuukka