Messages in this thread | | | Subject | Re: [PATCH] kallsyms: store type information in its own array | From | Eugene Loh <> | Date | Thu, 7 Mar 2019 15:37:20 -0800 |
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It's been 1.5 weeks. Could I get some feedback on this patch? Thanks.
On 02/25/2019 11:59 AM, eugene.loh@oracle.com wrote: > From: Eugene Loh <eugene.loh@oracle.com> > > When a module is loaded, its symbols' Elf_Sym information is stored > in a symtab. Further, type information is also captured. Since > Elf_Sym has no type field, historically the st_info field has been > hijacked for storing type: st_info was overwritten. > > commit 5439c985c5a83a8419f762115afdf560ab72a452 ("module: Overwrite > st_size instead of st_info") changes that practice, as its one-liner > indicates. Unfortunately, this change overwrites symbol size, > information that a tool like DTrace expects to find. > > Allocate a typetab array to store type information so that no Elf_Sym > field needs to be overwritten. > > Fixes: 5439c985c5a8 ("module: Overwrite st_size instead of st_info") > Signed-off-by: Eugene Loh <eugene.loh@oracle.com> > Reviewed-by: Nick Alcock <nick.alcock@oracle.com> > --- > include/linux/module.h | 1 + > kernel/module-internal.h | 2 +- > kernel/module.c | 21 ++++++++++++++------- > 3 files changed, 16 insertions(+), 8 deletions(-) > > diff --git a/include/linux/module.h b/include/linux/module.h > index f5bc4c0..9c1bc21 100644 > --- a/include/linux/module.h > +++ b/include/linux/module.h > @@ -315,6 +315,7 @@ struct mod_kallsyms { > Elf_Sym *symtab; > unsigned int num_symtab; > char *strtab; > + char *typetab; > }; > > #ifdef CONFIG_LIVEPATCH > diff --git a/kernel/module-internal.h b/kernel/module-internal.h > index 79c9be2..67828af 100644 > --- a/kernel/module-internal.h > +++ b/kernel/module-internal.h > @@ -20,7 +20,7 @@ struct load_info { > unsigned long len; > Elf_Shdr *sechdrs; > char *secstrings, *strtab; > - unsigned long symoffs, stroffs; > + unsigned long symoffs, stroffs, init_typeoff, core_typeoff; > struct _ddebug *debug; > unsigned int num_debug; > bool sig_ok; > diff --git a/kernel/module.c b/kernel/module.c > index 2ad1b52..c7c1bcd 100644 > --- a/kernel/module.c > +++ b/kernel/module.c > @@ -2647,6 +2647,8 @@ static void layout_symtab(struct module *mod, struct load_info *info) > info->symoffs = ALIGN(mod->core_layout.size, symsect->sh_addralign ?: 1); > info->stroffs = mod->core_layout.size = info->symoffs + ndst * sizeof(Elf_Sym); > mod->core_layout.size += strtab_size; > + info->core_typeoff = mod->core_layout.size; > + mod->core_layout.size += ndst * sizeof(char); > mod->core_layout.size = debug_align(mod->core_layout.size); > > /* Put string table section at end of init part of module. */ > @@ -2660,6 +2662,8 @@ static void layout_symtab(struct module *mod, struct load_info *info) > __alignof__(struct mod_kallsyms)); > info->mod_kallsyms_init_off = mod->init_layout.size; > mod->init_layout.size += sizeof(struct mod_kallsyms); > + info->init_typeoff = mod->init_layout.size; > + mod->init_layout.size += nsrc * sizeof(char); > mod->init_layout.size = debug_align(mod->init_layout.size); > } > > @@ -2683,20 +2687,23 @@ static void add_kallsyms(struct module *mod, const struct load_info *info) > mod->kallsyms->num_symtab = symsec->sh_size / sizeof(Elf_Sym); > /* Make sure we get permanent strtab: don't use info->strtab. */ > mod->kallsyms->strtab = (void *)info->sechdrs[info->index.str].sh_addr; > + mod->kallsyms->typetab = mod->init_layout.base + info->init_typeoff; > > - /* Set types up while we still have access to sections. */ > - for (i = 0; i < mod->kallsyms->num_symtab; i++) > - mod->kallsyms->symtab[i].st_size > - = elf_type(&mod->kallsyms->symtab[i], info); > - > - /* Now populate the cut down core kallsyms for after init. */ > + /* > + * Now populate the cut down core kallsyms for after init > + * and set types up while we still have access to sections. > + */ > mod->core_kallsyms.symtab = dst = mod->core_layout.base + info->symoffs; > mod->core_kallsyms.strtab = s = mod->core_layout.base + info->stroffs; > + mod->core_kallsyms.typetab = mod->core_layout.base + info->core_typeoff; > src = mod->kallsyms->symtab; > for (ndst = i = 0; i < mod->kallsyms->num_symtab; i++) { > + mod->kallsyms->typetab[i] = elf_type(src + i, info); > if (i == 0 || is_livepatch_module(mod) || > is_core_symbol(src+i, info->sechdrs, info->hdr->e_shnum, > info->index.pcpu)) { > + mod->core_kallsyms.typetab[ndst] = > + mod->kallsyms->typetab[i]; > dst[ndst] = src[i]; > dst[ndst++].st_name = s - mod->core_kallsyms.strtab; > s += strlcpy(s, &mod->kallsyms->strtab[src[i].st_name], > @@ -4084,7 +4091,7 @@ int module_get_kallsym(unsigned int symnum, unsigned long *value, char *type, > const Elf_Sym *sym = &kallsyms->symtab[symnum]; > > *value = kallsyms_symbol_value(sym); > - *type = sym->st_size; > + *type = kallsyms->typetab[symnum]; > strlcpy(name, kallsyms_symbol_name(kallsyms, symnum), KSYM_NAME_LEN); > strlcpy(module_name, mod->name, MODULE_NAME_LEN); > *exported = is_exported(name, *value, mod);
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