In generic version in lib/math/div64.c, there is no checking of 'base' either. Do we really want to add this check in the powerpc version only ?
The only user of __div64_32() is do_div() in include/asm-generic/div64.h. Wouldn't it be better to do the check there ?
Christophe
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.
diff --git a/include/asm-generic/div64.h b/include/asm-generic/div64.h index a3b98c86f077..161c656ee3ee 100644 --- a/include/asm-generic/div64.h +++ b/include/asm-generic/div64.h @@ -43,6 +43,11 @@ # define do_div(n,base) ({ \ uint32_t __base = (base); \ uint32_t __rem; \
- if (unlikely(base == 0)) { \
pr_err("do_div base=%d\n",base); \dump_stack(); \force_sig(SIGFPE); \- }
I suspect this will generate a strong reaction. SIGFPE is for user space instruction attempting a division by zero. A division by zero in the kernel is a kernel bug, period, and you don't want to kill a user process for this reason.
If it happens in an interrupt, the context of the kernel may not even be related to the current process.
Many other architectures (x86 for example) already trigger an exception on a division by zero but the handler will find that the exception happened in kernel context and generate an Oops, not raise a signal in a (possibly innocent) userland process.
OK. So just don't touch do_div functions in include/asm-generic/div64.h But for powerpc it can not trigger an exception when divisor is 0 in __div64_32.
So the patch as below is still useful for powerpc. 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 cmplw r5,r4 li r7,0 li r8,0 @@ -52,7 +54,7 @@ __div64_32: 4: stw r7,0(r3) # return the quotient in *r3 stw r8,4(r3) mr r3,r6 # return the remainder in r3 - blr +5: blr # return if divisor r4 is zero
/* * Extended precision shifts. diff --git a/arch/powerpc/lib/div64.S b/arch/powerpc/lib/div64.S index 3d5426e7dcc4..570774d9782d 100644 --- a/arch/powerpc/lib/div64.S +++ b/arch/powerpc/lib/div64.S @@ -13,8 +13,10 @@ #include <asm/processor.h>
_GLOBAL(__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 cmplw r5,r4 li r7,0 li r8,0 @@ -52,4 +54,4 @@ _GLOBAL(__div64_32) 4: stw r7,0(r3) # return the quotient in *r3 stw r8,4(r3) mr r3,r6 # return the remainder in r3 - blr +5: blr # return if divisor r4 is zero
Guohua