Division by zero [LWN.net]

Division by zero

Posted Jan 4, 2025 18:10 UTC (Sat) by dskoll (subscriber, #1630)
In reply to: Division by zero by khim
Parent article: Preventing data races with Pony

Huh, you are right! Even though my Pi 4 is running an aarch64 kernel, userspace is 32-bit armhf and the test program raised SIGFPE. I tried the test program on a fully 64-bit Pi 4 with 64-bit userspace and it ran without complaint, assigning 0 to z.

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Division by zero

Posted Jan 4, 2025 20:34 UTC (Sat) by pm215 (subscriber, #98099) [Link]

My guess is that your compiler is generating code that assumes the CPU doesn't implement the division instructions (because armhf includes v7-without-VE CPUs in its remit) and instead calls into the gcc runtime, and the runtime function is then manually raising a SIGFPE. (Possibly also the compiler figures out that it is a div by zero and generates a call to the div-by-zero runtime function.)

You can probably pass the compiler some kind of -march or -mcpu options to tell it to generate code assuming the v8 CPU you have, and then it ought to emit the udiv or sdiv inline, if you want to look at the behaviour in that situation.