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

To: gcc@gcc.gnu.org, linux-mips@linux-mips.org
Subject: [RFC] MIPS division by zero and libgcj...
From: David Daney <ddaney@avtrex.com>
Date: Thu, 10 Jun 2004 12:12:27 -0700
Cc: java@gcc.gnu.org
Original-recipient: rfc822;linux-mips@linux-mips.org
Sender: linux-mips-bounce@linux-mips.org
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.4.1) Gecko/20031030
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.

Gcj when configured for this platform uses the -f-use-divide-subroutine option, causing it to never generate inline division instructions (nor the accompanying break 7), but instead call a runtime function that properly handles throwing ArithmeticException.

Q1: Is this behavior (use of break 7 and SIGTRAP) part of some ABI specification? I'll admit a bit of ignorance in this area.

Q2: Does anyone see any reason that libgcj should not be configured to handle the SIGTRAP and throw the ArithmeticException from the signal handler (similar to what is done on i386).

Q3: Will using SIGTRAP in this manner make debugging programs that divide things by zero very difficult to debug under gdb?

Q4: I appears that on the i386, a divide overflow causes SIGFPE. Why doesn't the mips-linux kernel sent SIGFPE on "break 7"

Q5: prims.cc in libgcj implies that we should be handling SIGFPE to do all this. If I make these changes, won't it be a little confusing that all references to SIGFPE are really SIGTRAP?


David Daney








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