From: "Theo de Raadt" <deraadt@openbsd.org>
Subject: Re: www/hugo exits with illegal instruction
To: Rafael Sadowski <rafael@sizeofvoid.org>
Cc: Isaac Meerleo <spritskillshot@gmail.com>, ports@openbsd.org
Date: Wed, 21 Feb 2024 08:58:24 -0700

Rafael Sadowski <rafael@sizeofvoid.org> wrote:

> I see the same illegal instruction with the latest packages and latest
> base:
> 
> fuckup$ hugo
> Illegal instruction (core dumped)
> 
> fuckup$ dmesg | head -1
> OpenBSD 7.5-beta (GENERIC.MP) #7: Tue Feb 20 11:09:18 MST 2024
> 
> ktrace:
> 
>  92986 hugo     CALL  mmap(0,0x40000,0x3<PROT_READ|PROT_WRITE>,0x1002<MAP_PRIVATE|MAP_ANON>,-1,0)
>  92986 hugo     RET   mmap 11072319488/0x293f63000
>  92986 hugo     CALL  mmap(0,0x40000,0x3<PROT_READ|PROT_WRITE>,0x1002<MAP_PRIVATE|MAP_ANON>,-1,0)
>  92986 hugo     RET   mmap 10030714880/0x255e09000
>  92986 hugo     CALL  mmap(0,0x3000,0x3<PROT_READ|PROT_WRITE>,0x1002<MAP_PRIVATE|MAP_ANON>,-1,0)
>  92986 hugo     RET   mmap 11094835200/0x2954dc000
>  92986 hugo     CALL  kbind(0x7e5873ba8528,24,0x47f5f02b048179b4)
>  92986 hugo     RET   kbind 0
>  92986 hugo     CALL  kbind(0x7e5873ba8528,24,0x47f5f02b048179b4)
>  92986 hugo     RET   kbind 0
>  92986 hugo     CALL  kbind(0x7e5873ba8508,24,0x47f5f02b048179b4)
>  92986 hugo     RET   kbind 0
>  92986 hugo     PSIG  SIGILL SIG_DFL code=ILL_ILLOPC addr=0x2ff6d00 trapno=21
>  92986 hugo     NAMI  "hugo.core"

ktrace helped you find it is a SIGILL, with code=ILL_ILLOPC.  I can already
see trapno=21, and assuming this is amd64, that is

#define T_CP            21      /* control protection exception */

That ILL_ILLOPC will change to ILL_BTCFI in the near future.

OK, so this is a missing IBT instruction.  ktrace helped you find that out
quickly.

Now you go into gdb, re-create the condition live, and find out what function
it is related to.