[Patch] / 0 should send SIGFPE not SIGTRAP...

[David Daney]

I guess I didn't fully read the comment above this section of code.

    /*
     * There is the ancient bug in the MIPS assemblers that the break
     * code starts left to bit 16 instead to bit 6 in the opcode.
     * Gas is bug-compatible ...
     */

I am using gcc-3.3.1/binutils-2.15.  With this toolchain, I get break 
instructions that comply with the MIPS documentation for break instructions:


00000000 <do_div>:
   0:   3c1c0000        lui     gp,0x0
   4:   279c0000        addiu   gp,gp,0
   8:   0399e021        addu    gp,gp,t9
   c:   0085001a        div     zero,a0,a1
  10:   14a00002        bnez    a1,1c <do_div+0x1c>
  14:   00000000        nop
  18:   000001cd        break   0x7
  1c:   00001012        mflo    v0
  20:   03e00008        jr      ra
  24:   00000000        nop
 

What to do?

David Daney

David Daney wrote:

> It might help if I attached the patch.  Here it is...
>
> David Daney wrote:
>
>> I am getting a SIGTRAP whenever an integer divide by 0 happens.  It 
>> should be sending SIGFPE.
>>
>> It looks like kernel/traps.c is a little messed up.
>>
>> The attached patch fixes it for me.
>>
>> The decoding of the break instruction was selecting the wrong bits.  
>> It looks like the trap instruction decoding was messed up also.  The 
>> patch fixes trap also, but I could not figure out how to get gcc to 
>> generate the trap form of division, so that part is untested.
>>
>> David Daney.
>>
>
>------------------------------------------------------------------------
>
>--- ../linux-avtrex/linux/arch/mips/kernel/traps.c	2004-02-26 11:14:09.000000000 -0800
>+++ arch/mips/kernel/traps.c	2004-06-11 10:13:59.000000000 -0700
>@@ -598,7 +598,7 @@
> 	 * code starts left to bit 16 instead to bit 6 in the opcode.
> 	 * Gas is bug-compatible ...
> 	 */
>-	bcode = ((opcode >> 16) & ((1 << 20) - 1));
>+	bcode = ((opcode >> 6) & ((1 << 20) - 1));
> 
> 	/*
> 	 * (A short test says that IRIX 5.3 sends SIGTRAP for all break
>@@ -633,7 +633,7 @@
> 
> 	/* Immediate versions don't provide a code.  */
> 	if (!(opcode & OPCODE))
>-		tcode = ((opcode >> 6) & ((1 << 20) - 1));
>+		tcode = ((opcode >> 6) & ((1 << 10) - 1));
> 
> 	/*
> 	 * (A short test says that IRIX 5.3 sends SIGTRAP for all trap
>  
>