Messages in this thread | | | Date | Mon, 21 Mar 2016 14:07:43 -0400 | From | Jessica Yu <> | Subject | Re: livepatch: reuse module loader code to write relocations |
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+++ Josh Poimboeuf [21/03/16 12:36 -0500]: >On Mon, Mar 21, 2016 at 11:46:51AM -0500, Josh Poimboeuf wrote: >> On Mon, Mar 21, 2016 at 05:31:57PM +0100, Petr Mladek wrote: >> > > diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c >> > > index 780f00c..2aa20fa 100644 >> > > --- a/kernel/livepatch/core.c >> > > +++ b/kernel/livepatch/core.c >> > > +static int klp_resolve_symbols(Elf_Shdr *relasec, struct module *pmod) >> > > +{ >> > > + int i, cnt, vmlinux, ret; >> > > + struct klp_buf bufs = {0}; >> > > + Elf_Rela *relas; >> > > + Elf_Sym *sym; >> > > + char *symname; >> > > + unsigned long sympos; >> > > + >> > > + relas = (Elf_Rela *) relasec->sh_addr; >> > > + /* For each rela in this klp relocation section */ >> > > + for (i = 0; i < relasec->sh_size / sizeof(Elf_Rela); i++) { >> > > + sym = pmod->core_kallsyms.symtab + ELF_R_SYM(relas[i].r_info); >> > > + if (sym->st_shndx != SHN_LIVEPATCH) >> > > + return -EINVAL; >> > > + >> > > + klp_clear_buf(&bufs); >> > > + >> > > + /* Format: .klp.sym.objname.symbol_name,sympos */ >> > > + symname = pmod->core_kallsyms.strtab + sym->st_name; >> > > + cnt = sscanf(symname, ".klp.sym.%64[^.].%128[^,],%lu", >> > > + bufs.objname, bufs.symname, &sympos); >> > >> > Note that MODULE_NAME_LEN even is not 64. It is defined by: >> > >> > #define MAX_PARAM_PREFIX_LEN (64 - sizeof(unsigned long)) >> > >> > I strongly suggest to use the proposal from Josh. >> >> Hm, looks like my suggestion to use __stringify(MODULE_NAME_LEN) doesn't >> work. It results in the string "MODULE_NAME_LEN". Which surprises me: >> isn't is supposed to resolve the macro before applying the '#' operation >> to it? > >Turns out I hadn't included module.h. When I do so, >__stringify(MODULE_NAME_LEN) becomes "(64 - sizeof(unsigned long))". >Which is still not going to work :-/ >
Hm, we probably won't be able to make use of preprocessor tricks here, since I don't think the preprocessor can even evaluate that expression (esp. with that sizeof there). This might mean building the format string at runtime, which may be more trouble than it's worth...
>> I was going to suggest another idea: hard-code it at 63 and then do >> something like >> >> BUILD_BUG_ON(MODULE_NAME_LEN != 64) >> >> But you're right... it's not even 64! >> >> Need to think on this some more... > >-- >Josh
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