SIGBUS si_code 12

[Konstantin Belousov]

On Fri, May 22, 2020 at 05:32:37PM +0200, Paul Floyd wrote:
> A bit more on this.
> 
> The code in question is in trap.c:
> 
> 			if (signo == SIGSEGV) {
> 				ucode = SEGV_MAPERR;
> 			} else if (prot_fault_translation == 0) {
> 				/*
> 				 * Autodetect.  This check also covers
> 				 * the images without the ABI-tag ELF
> 				 * note.
> 				 */
> 				if (SV_CURPROC_ABI() == SV_ABI_FREEBSD &&
> 				    p->p_osrel >= P_OSREL_SIGSEGV) {
> 					signo = SIGSEGV;
> 					ucode = SEGV_ACCERR;
> 				} else {
> 					signo = SIGBUS;
> 					ucode = T_PAGEFLT;
> 				}
> 			} else if (prot_fault_translation == 1) {
> 				/*
> 				 * Always compat mode.
> 				 */
> 				signo = SIGBUS;
> 				ucode = T_PAGEFLT;
> 			} else {
> 				/*
> 				 * Always SIGSEGV mode.
> 				 */
> 				signo = SIGSEGV;
> 				ucode = SEGV_ACCERR;
> 			}
> 
> 
> I have machte.prot_fault_translation set to 0 (the default I believe) so this enters the first ‘else if’ branch.
> 
> The value of p_osrel looks like it comes from retold.c. I see two mechanisms - passed via auxv AT_OSRELDATE (with a backup of using a sysctl) and reading the NT_FREEBSD_ABI_TAG note - I’m not sure which is used in this case.
I do not know what retold.c is.

> 
> The auxv value seems to be sent and I can’t see why either should be failing.

auxv has nothing to do with p_osrel as seen by kernel.  In-kernel
ELF image activator parses notes and reads osrel if available.