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

Peter Jakubek via llvm-dev llvm-dev at lists.llvm.org
Wed Apr 5 11:40:22 PDT 2017

I recommend the other incarnation of the call to divby0 at line 256 is also
modified to use bl instead of b for the same reason.

Or just remove one of the two to avoid confusion in the future?



Am 05.04.2017 um 19:14 schrieb Zhao, Weiming:
> 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
>>> 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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