[llvm-dev] compiler-rt, v4.0: arm\udivsi3.S broken for division by zero

Zhao, Weiming via llvm-dev llvm-dev at lists.llvm.org
Wed Apr 5 10:14:14 PDT 2017

Yes, it's a bug.

Please review https://reviews.llvm.org/D31716

On 4/5/2017 3:50 AM, Renato Golin wrote:
> On 21 March 2017 at 18:32, Peter Jakubek via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
>> I think the current implementation for the call "bl __aeabi_idiv0" in
>> builtins\arm\udivsi3.S is broken.
>> At least for the case that __aeabi_idiv0 returns. (the provided
>> implementation does)
>> Since LR is not preserved, the following JMP(lr) results in an endless loop.
>> Or is this an intentional change of the behavior?
> Hi Peter,
> That is most certainly a bug. Weiming's patch was supposed to only
> introduce Thumb1 code, not transform div0 into a busy loop. :)
>> The file contains another implementation enabled by __ARM_ARCH_EXT_IDIV__.
>> This uses "b" instead of "bl".
>> (This works as in previous versions)
> The comment on the patch makes that clear:
> bl  __aeabi_idiv0 // due to relocation limit, can't use b.
> I'm not sure why the bottom one is fine and the top one isn't, wrt.
> range, but we may have to add a trampoline here.
> Weiming, Saleem, comments?
> cheers,
> --renato

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