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

Thu Jun 10 19:59:00 GMT 2004

David Daney writes:
 > Andrew Haley wrote:
 > 
 > MIPS div instructions never trap. However I think that GCC always emits 
 > things like this when it cannot determine that the divisor is non zero:
 > 
 > div 0,ドル17,ドル16ドル
 > bne 16,ドル0,1ドルf
 > nop
 > break 7
 > 1:
 > 
 > 
 > >No, there's no reason not to do it. You'll have to write some hairy
 > >code to satisfy all the rules, though.
 > >
 > What are the rules? Are they more complicated then throw an 
 > ArithmeticException when the divisor is zero?
Yes. You also have to do
 if (dividend == (jint) 0x80000000L && divisor == -1)
 return dividend;
 
and not throw an exception.
 > > > Q3: Will using SIGTRAP in this manner make debugging programs that 
 > > > divide things by zero very difficult to debug under gdb?
 > >
 > >No.
 > > 
 > >
 > I have not tried it. But I think gdb uses "break" and SIGTRAP for 
 > breakpoints. Is it possible to get gdb to pass the signal to the 
 > debugee, so that it could be handled by the runtime support?
Well, gcj will generate either break or trap instructions. You can
tell gdb to ignore either.
Andrew.