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

To: linux-mips@linux-mips.org, binutils@sources.redhat.com
Subject: Re: [Patch] / 0 should send SIGFPE not SIGTRAP...
From: David Daney <ddaney@avtrex.com>
Date: Fri, 11 Jun 2004 11:20:32 -0700
In-reply-to: <40C9F5FE.8030607@avtrex.com>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <40C9F5A4.2050606@avtrex.com> <40C9F5FE.8030607@avtrex.com>
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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



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