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Date: Thu, 10 Jun 2004 12:12:27 -0700
From: David Daney <ddaney@avtrex.com>
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Subject: [RFC] MIPS division by zero and libgcj...
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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