On Mon, Aug 24, 2020 at 07:54:07PM +0800, Guohua Zhong wrote: > >> Yet, I have noticed that there is no checking of 'base' in these functions. > >> But I am not sure how to check is better.As we know that the result is > >> undefined when divisor is zero. It maybe good to print error and dump stack. > >> Let the process to know that the divisor is zero by sending SIGFPE. > > > That is now what the PowerPC integer divide insns do: they just leave > > the result undefined (and they can set the overflow flag then, but no > > one uses that). > > OK ,So just keep the patch as below. If this patch looks good for you, please > help to review. I will send the new patch later. > > Thanks for your reply. > > diff --git a/arch/powerpc/boot/div64.S b/arch/powerpc/boot/div64.S > index 4354928ed62e..1d3561cf16fa 100644 > --- a/arch/powerpc/boot/div64.S > +++ b/arch/powerpc/boot/div64.S > @@ -13,8 +13,10 @@ > > .globl __div64_32 > .globl __div64_32 > __div64_32: > + cmplwi r4,0 # check if divisor r4 is zero > lwz r5,0(r3) # get the dividend into r5/r6 > lwz r6,4(r3) > + beq 5f # jump to label 5 if r4(divisor) is zero Just "beqlr". This instruction scheduling hurts all CPUs that aren't 8xx, fwiw (but likely only in the case where r4 *is* zero, so who cares :-) ) So... What is the *goal* of this patch? It looks like the routine would not get into a loop if r4 is 0, just return the wrong result? But, it *always* will, there *is* no right result? No caller should call it with zero as divisor ever, so in that sense, checking for it in the division routine is just pure wasted work. Segher
