Link modules to DYN type
- Reply: Hans Petter Selasky : "Re: Link modules to DYN type"
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Date: Wed, 26 Apr 2023 10:36:20 UTC
Hi, I'm recently working on https://reviews.freebsd.org/D39638 (sysctl(9): Enable vnet sysctl variables be loader tunable), the changes to `sys/kern/link_elf_obj.c` are runtime tested, but not those to `sys/kern/link_elf.c` . After some hacking I realized that `link_elf.c` is for EXEC (Executable file) or DYN (Shared object file), and `link_elf_obj.c` is for REL (Relocatable file). ``` /* link_elf.c */ static int link_elf_load_file(linker_class_t cls, const char* filename, linker_file_t* result) { ... if (hdr->e_type != ET_EXEC && hdr->e_type != ET_DYN) { error = ENOSYS; goto out; } ... } /* link_elf_obj.c */ static int link_elf_load_file(linker_class_t cls, const char *filename, linker_file_t *result) { ... if (hdr->e_type != ET_REL) { error = ENOSYS; goto out; } ... } ``` Run the following snip: ``` # find /boot/kernel -type f -name "*.ko" -exec readelf -h {} \; | grep Type ``` shows that all the kernel modules' types are `REL (Relocatable file)`. I guess if some module such as if_bridge is linked to DYN type, then I can do runtime for the changes to `sys/kern/link_elf.c`. I'm not familiar with elf and linkers, is that ( compile module and link it to DYN type ) possible ? Best regards, Zhenlei