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Re: [RFC] MIPS division by zero and libgcj...

To: "Maciej W. Rozycki" <macro@ds2.pg.gda.pl>
Subject: Re: [RFC] MIPS division by zero and libgcj...
From: David Daney <ddaney@avtrex.com>
Date: Fri, 11 Jun 2004 08:34:25 -0700
Cc: gcc@gcc.gnu.org, linux-mips@linux-mips.org, java@gcc.gnu.org
In-reply-to: <Pine.LNX.4.55.0406111554420.13062@jurand.ds.pg.gda.pl>
Original-recipient: rfc822;linux-mips@linux-mips.org
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Maciej W. Rozycki wrote:

On Thu, 10 Jun 2004, David Daney wrote:

It appears that gcc configured for mipsel-linux will execute a "break 7" instruction on integer division by zero.

This causes the kernel (I am using 2.4.25) to send SIGTRAP.

It looks like you have a problem in your configuration. A "break 7" (or "teq <divisor>,$zero,7" -- but that's currently implemented in gas
only) is indeed emitted and exectuted in the case of division by zero, but
Linux has the ability to recognize this special break code and sends
SIGFPE instead.  There are actually two special codes defined, the other
being "6" for an overflow.  Both are handled by Linux, with si_code in
struct siginfo being set to FPE_INTDIV or FPE_INTOVF, respectively.  You
can handle this appropriately in a signal handler.

My kernel sources are from linux-mips.org, it is little-endian running on:

# cat /proc/cpuinfo
system type             : ATI-Xilleon
processor               : 0
cpu model               : MIPS 4Kc V0.7
BogoMIPS                : 299.00
wait instruction        : yes
microsecond timers      : yes
tlb_entries             : 16
extra interrupt vector  : yes
hardware watchpoint     : yes
VCED exceptions         : not available
VCEI exceptions         : not available

Could you point me to where in the kernel source this is handled? I will try to see what when wrong.

David Daney.


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