I'm getting a core dump on 'config -x /boot/kernel/kernel' on 9.1-RELEASE i386. Assertion failed: (r != '\0' && ("Char present in the configuration " "string mustn't be equal to 0")), function kernconfdump, file /usr/src/usr.sbin/config/main.c, line 710. I have double checked that my config file is sane and does not have any funny characters anywhere. The system is i386 9.1-RELEASE r249856. The world and kernel are built with clang and I'm suspecting that the use of clang has something to do with this segfault. Looking at the kernel files I can see one very obvious difference. This is the 'elfdump -c kernel | grep -A 8 kern_conf' output (what config -x seems to use for finding out the config file from the kernel image) for the GENERIC kernel from the stock installation: sh_name: kern_conf sh_type: SHT_PROGBITS sh_flags: SHF_ALLOC sh_addr: 0xc1039f80 sh_offset: 12820352 sh_size: 3771 sh_link: 0 sh_info: 0 sh_addralign: 32 And this is from the kernel I have built myself using clang and a custom config file: sh_name: kern_conf sh_type: SHT_PROGBITS sh_flags: SHF_ALLOC sh_addr: 0xc09aee9c sh_offset: 5959324 sh_size: 1994 sh_link: 0 sh_info: 0 sh_addralign: 1 The align field looks suspicious, config -x seems to use it to check for padding but to me it looks like the logic may not work if the alignment is 1. This the relevant bit from main.c of config(8) if (r == '\0' && (size - i) < align) break; assert(r != '\0' && ("Char present in the configuration " "string mustn't be equal to 0")); fputc(r, stdout); -Kimmo