Date: Mon, 18 Mar 2013 10:21:50 -0700 From: Godfrey van der Linden <gvdl@mac.com> To: freebsd-hackers@freebsd.org Subject: kmod linking is very strange Message-ID: <8B0E0420-3E21-4230-97BC-1689225E1B5A@mac.com> References: <A649469B-7760-42FA-9859-316FA04AFE4E@juniper.net>
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I posted this to current, but was steered to hackers. Begin forwarded message: > From: Godfrey Van der Linden <gvdl@juniper.net> > Subject: kmod linking is very strange > Date: 15March, 2013 16:46:13 PDT > To: freebsd-current@freebsd.org > > G'day, All. > > First post so please be gentle ;-). Are the barracudas here? > > Summary: > > Module link-elf will link against static symbols and will fail if the kernel is not compiled with DDB or the required MODULE_DEPEND has been stripped of local symbols, see nm -g miibus.ko. I propose that we add a sysctl & associated boot arg that only allows kmod loading against externally visible symbols. Then in 11 we can enable this flag by default. > > In Detail: > > Due to another bug in sys/conf/kmod.mk, (http://www.freebsd.org/cgi/query-pr.cgi?pr=177008, contains a patch) the miibus.ko exports no symbols. I.e. symbols are 'static'. > > sys/kern/link-elf.c:link_elf_lookup_symbol() is the culprit. After determining that an external symbol can't be found, it does the following. > > /* If we have not found it, look at the full table (if loaded) */ > if (ef->symtab == ef->ddbsymtab) > return (ENOENT); > > /* Exhaustive search */ > for (i = 0, symp = ef->ddbsymtab; i < ef->ddbsymcnt; i++, symp++) { > strp = ef->ddbstrtab + symp->st_name; > if (strcmp(name, strp) == 0) { > if (symp->st_shndx != SHN_UNDEF || > (symp->st_value != 0 && > ELF_ST_TYPE(symp->st_info) == STT_FUNC)) { > *sym = (c_linker_sym_t) symp; > return (0); > } > return (ENOENT); > } > } > > This code walks the ddbsymtab looking for any symbol, including locals. > > Any kernel that is not built with DDB or any MODULE_DEPEND dependency .ko that is stripped will break module loading. > > > Godfrey van der Linden > _______________________________________________ > freebsd-current@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-current > To unsubscribe, send any mail to "freebsd-current-unsubscribe@freebsd.org"
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