On Tue, Sep 09, 2025 at 10:49:53AM +0200, Maciej Wieczor-Retman wrote: > >Specifically, look at arch/x86/kernel/traps.h:decode_bug(), UBSan uses > >UD1 /0, I would suggest KASAN to use UD1 /1. > > Okay, that sounds great, I'll change it in this patchset and write the LLVM > patch later. Thanks! Also note how UBSAN encodes an immediate in the UD1 instruction. You can use that same to pass through your meta-data thing. MOD=1 gives you a single byte immediate, and MOD=2 gives you 4 bytes, eg: 0f b9 49 xx -- ud1 xx(%rcx), %rcx When poking at LLVM, try and convince the thing to not emit that 'operand address size prefix' byte like UBSAN does, that's just a waste of bytes.
