module: simplify load_module.

Linus' recent catch of stack overflow in load_module lead me to look
at the code.  A couple of helpers to get a section address and get
objects from a section can help clean things up a little.

(And in case you're wondering, the stack size also dropped from 328 to
284 bytes).

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

2 files changed, 100 insertions, 137 deletions

diff --git a/include/linux/module.h b/include/linux/module.h
index 5d2970cdce9..eddf27db442 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -277,7 +277,7 @@ struct module
 
         /* Exception table */
         unsigned int num_exentries;
-        const struct exception_table_entry *extable;
+        struct exception_table_entry *extable;
 
         /* Startup function. */
         int (*init)(void);
diff --git a/kernel/module.c b/kernel/module.c
index 0d8d21ee792..3d256681ab6 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -132,6 +132,29 @@ static unsigned int find_sec(Elf_Ehdr *hdr,
         return 0;
 }
 
+/* Find a module section, or NULL. */
+static void *section_addr(Elf_Ehdr *hdr, Elf_Shdr *shdrs,
+                          const char *secstrings, const char *name)
+{
+        /* Section 0 has sh_addr 0. */
+        return (void *)shdrs[find_sec(hdr, shdrs, secstrings, name)].sh_addr;
+}
+
+/* Find a module section, or NULL.  Fill in number of "objects" in section. */
+static void *section_objs(Elf_Ehdr *hdr,
+                          Elf_Shdr *sechdrs,
+                          const char *secstrings,
+                          const char *name,
+                          size_t object_size,
+                          unsigned int *num)
+{
+        unsigned int sec = find_sec(hdr, sechdrs, secstrings, name);
+
+        /* Section 0 has sh_addr 0 and sh_size 0. */
+        *num = sechdrs[sec].sh_size / object_size;
+        return (void *)sechdrs[sec].sh_addr;
+}
+
 /* Provided by the linker */
 extern const struct kernel_symbol __start___ksymtab[];
 extern const struct kernel_symbol __stop___ksymtab[];
@@ -1789,32 +1812,20 @@ static inline void add_kallsyms(struct module *mod,
 }
 #endif /* CONFIG_KALLSYMS */
 
-#ifdef CONFIG_DYNAMIC_PRINTK_DEBUG
-static void dynamic_printk_setup(Elf_Shdr *sechdrs, unsigned int verboseindex)
+static void dynamic_printk_setup(struct mod_debug *debug, unsigned int num)
 {
-        struct mod_debug *debug_info;
-        unsigned long pos, end;
-        unsigned int num_verbose;
-
-        pos = sechdrs[verboseindex].sh_addr;
-        num_verbose = sechdrs[verboseindex].sh_size /
-                                sizeof(struct mod_debug);
-        end = pos + (num_verbose * sizeof(struct mod_debug));
+#ifdef CONFIG_DYNAMIC_PRINTK_DEBUG
+        unsigned int i;
 
-        for (; pos < end; pos += sizeof(struct mod_debug)) {
-                debug_info = (struct mod_debug *)pos;
-                register_dynamic_debug_module(debug_info->modname,
-                        debug_info->type, debug_info->logical_modname,
-                        debug_info->flag_names, debug_info->hash,
-                        debug_info->hash2);
+        for (i = 0; i < num; i++) {
+                register_dynamic_debug_module(debug[i].modname,
+                                              debug[i].type,
+                                              debug[i].logical_modname,
+                                              debug[i].flag_names,
+                                              debug[i].hash, debug[i].hash2);
         }
-}
-#else
-static inline void dynamic_printk_setup(Elf_Shdr *sechdrs,
-                                        unsigned int verboseindex)
-{
-}
 #endif /* CONFIG_DYNAMIC_PRINTK_DEBUG */
+}
 
 static void *module_alloc_update_bounds(unsigned long size)
 {
@@ -1843,37 +1854,14 @@ static noinline struct module *load_module(void __user *umod,
         unsigned int i;
         unsigned int symindex = 0;
         unsigned int strindex = 0;
-        unsigned int setupindex;
-        unsigned int exindex;
-        unsigned int exportindex;
-        unsigned int modindex;
-        unsigned int obsparmindex;
-        unsigned int infoindex;
-        unsigned int gplindex;
-        unsigned int crcindex;
-        unsigned int gplcrcindex;
-        unsigned int versindex;
-        unsigned int pcpuindex;
-        unsigned int gplfutureindex;
-        unsigned int gplfuturecrcindex;
+        unsigned int modindex, versindex, infoindex, pcpuindex;
         unsigned int unwindex = 0;
-#ifdef CONFIG_UNUSED_SYMBOLS
-        unsigned int unusedindex;
-        unsigned int unusedcrcindex;
-        unsigned int unusedgplindex;
-        unsigned int unusedgplcrcindex;
-#endif
-        unsigned int markersindex;
-        unsigned int markersstringsindex;
-        unsigned int verboseindex;
-        unsigned int tracepointsindex;
-        unsigned int tracepointsstringsindex;
-        unsigned int mcountindex;
+        unsigned int num_kp, num_mcount;
+        struct kernel_param *kp;
         struct module *mod;
         long err = 0;
         void *percpu = NULL, *ptr = NULL; /* Stops spurious gcc warning */
-        void *mseg;
-        struct exception_table_entry *extable;
+        unsigned long *mseg;
         mm_segment_t old_fs;
 
         DEBUGP("load_module: umod=%p, len=%lu, uargs=%p\n",
@@ -1937,6 +1925,7 @@ static noinline struct module *load_module(void __user *umod,
                 err = -ENOEXEC;
                 goto free_hdr;
         }
+        /* This is temporary: point mod into copy of data. */
         mod = (void *)sechdrs[modindex].sh_addr;
 
         if (symindex == 0) {
@@ -1946,22 +1935,6 @@ static noinline struct module *load_module(void __user *umod,
                 goto free_hdr;
         }
 
-        /* Optional sections */
-        exportindex = find_sec(hdr, sechdrs, secstrings, "__ksymtab");
-        gplindex = find_sec(hdr, sechdrs, secstrings, "__ksymtab_gpl");
-        gplfutureindex = find_sec(hdr, sechdrs, secstrings, "__ksymtab_gpl_future");
-        crcindex = find_sec(hdr, sechdrs, secstrings, "__kcrctab");
-        gplcrcindex = find_sec(hdr, sechdrs, secstrings, "__kcrctab_gpl");
-        gplfuturecrcindex = find_sec(hdr, sechdrs, secstrings, "__kcrctab_gpl_future");
-#ifdef CONFIG_UNUSED_SYMBOLS
-        unusedindex = find_sec(hdr, sechdrs, secstrings, "__ksymtab_unused");
-        unusedgplindex = find_sec(hdr, sechdrs, secstrings, "__ksymtab_unused_gpl");
-        unusedcrcindex = find_sec(hdr, sechdrs, secstrings, "__kcrctab_unused");
-        unusedgplcrcindex = find_sec(hdr, sechdrs, secstrings, "__kcrctab_unused_gpl");
-#endif
-        setupindex = find_sec(hdr, sechdrs, secstrings, "__param");
-        exindex = find_sec(hdr, sechdrs, secstrings, "__ex_table");
-        obsparmindex = find_sec(hdr, sechdrs, secstrings, "__obsparm");
         versindex = find_sec(hdr, sechdrs, secstrings, "__versions");
         infoindex = find_sec(hdr, sechdrs, secstrings, ".modinfo");
         pcpuindex = find_pcpusec(hdr, sechdrs, secstrings);
@@ -2117,42 +2090,57 @@ static noinline struct module *load_module(void __user *umod,
         if (err < 0)
                 goto cleanup;
 
-        /* Set up EXPORTed & EXPORT_GPLed symbols (section 0 is 0 length) */
-        mod->num_syms = sechdrs[exportindex].sh_size / sizeof(*mod->syms);
-        mod->syms = (void *)sechdrs[exportindex].sh_addr;
-        if (crcindex)
-                mod->crcs = (void *)sechdrs[crcindex].sh_addr;
-        mod->num_gpl_syms = sechdrs[gplindex].sh_size / sizeof(*mod->gpl_syms);
-        mod->gpl_syms = (void *)sechdrs[gplindex].sh_addr;
-        if (gplcrcindex)
-                mod->gpl_crcs = (void *)sechdrs[gplcrcindex].sh_addr;
-        mod->num_gpl_future_syms = sechdrs[gplfutureindex].sh_size /
-                                        sizeof(*mod->gpl_future_syms);
-        mod->gpl_future_syms = (void *)sechdrs[gplfutureindex].sh_addr;
-        if (gplfuturecrcindex)
-                mod->gpl_future_crcs = (void *)sechdrs[gplfuturecrcindex].sh_addr;
+        /* Now we've got everything in the final locations, we can
+         * find optional sections. */
+        kp = section_objs(hdr, sechdrs, secstrings, "__param", sizeof(*kp),
+                          &num_kp);
+        mod->syms = section_objs(hdr, sechdrs, secstrings, "__ksymtab",
+                                 sizeof(*mod->syms), &mod->num_syms);
+        mod->crcs = section_addr(hdr, sechdrs, secstrings, "__kcrctab");
+        mod->gpl_syms = section_objs(hdr, sechdrs, secstrings, "__ksymtab_gpl",
+                                     sizeof(*mod->gpl_syms),
+                                     &mod->num_gpl_syms);
+        mod->gpl_crcs = section_addr(hdr, sechdrs, secstrings, "__kcrctab_gpl");
+        mod->gpl_future_syms = section_objs(hdr, sechdrs, secstrings,
+                                            "__ksymtab_gpl_future",
+                                            sizeof(*mod->gpl_future_syms),
+                                            &mod->num_gpl_future_syms);
+        mod->gpl_future_crcs = section_addr(hdr, sechdrs, secstrings,
+                                            "__kcrctab_gpl_future");
 
 #ifdef CONFIG_UNUSED_SYMBOLS
-        mod->num_unused_syms = sechdrs[unusedindex].sh_size /
-                                        sizeof(*mod->unused_syms);
-        mod->num_unused_gpl_syms = sechdrs[unusedgplindex].sh_size /
-                                        sizeof(*mod->unused_gpl_syms);
-        mod->unused_syms = (void *)sechdrs[unusedindex].sh_addr;
-        if (unusedcrcindex)
-                mod->unused_crcs = (void *)sechdrs[unusedcrcindex].sh_addr;
-        mod->unused_gpl_syms = (void *)sechdrs[unusedgplindex].sh_addr;
-        if (unusedgplcrcindex)
-                mod->unused_gpl_crcs
-                        = (void *)sechdrs[unusedgplcrcindex].sh_addr;
+        mod->unused_syms = section_objs(hdr, sechdrs, secstrings,
+                                        "__ksymtab_unused",
+                                        sizeof(*mod->unused_syms),
+                                        &mod->num_unused_syms);
+        mod->unused_crcs = section_addr(hdr, sechdrs, secstrings,
+                                        "__kcrctab_unused");
+        mod->unused_gpl_syms = section_objs(hdr, sechdrs, secstrings,
+                                            "__ksymtab_unused_gpl",
+                                            sizeof(*mod->unused_gpl_syms),
+                                            &mod->num_unused_gpl_syms);
+        mod->unused_gpl_crcs = section_addr(hdr, sechdrs, secstrings,
+                                            "__kcrctab_unused_gpl");
+#endif
+
+#ifdef CONFIG_MARKERS
+        mod->markers = section_objs(hdr, sechdrs, secstrings, "__markers",
+                                    sizeof(*mod->markers), &mod->num_markers);
+#endif
+#ifdef CONFIG_TRACEPOINTS
+        mod->tracepoints = section_objs(hdr, sechdrs, secstrings,
+                                        "__tracepoints",
+                                        sizeof(*mod->tracepoints),
+                                        &mod->num_tracepoints);
 #endif
 
 #ifdef CONFIG_MODVERSIONS
-        if ((mod->num_syms && !crcindex)
-            || (mod->num_gpl_syms && !gplcrcindex)
-            || (mod->num_gpl_future_syms && !gplfuturecrcindex)
+        if ((mod->num_syms && !mod->crcs)
+            || (mod->num_gpl_syms && !mod->gpl_crcs)
+            || (mod->num_gpl_future_syms && !mod->gpl_future_crcs)
 #ifdef CONFIG_UNUSED_SYMBOLS
-            || (mod->num_unused_syms && !unusedcrcindex)
-            || (mod->num_unused_gpl_syms && !unusedgplcrcindex)
+            || (mod->num_unused_syms && !mod->unused_crcs)
+            || (mod->num_unused_gpl_syms && !mod->unused_gpl_crcs)
 #endif
                 ) {
                 printk(KERN_WARNING "%s: No versions for exported symbols.\n", mod->name);
@@ -2161,16 +2149,6 @@ static noinline struct module *load_module(void __user *umod,
                         goto cleanup;
         }
 #endif
-        markersindex = find_sec(hdr, sechdrs, secstrings, "__markers");
-        markersstringsindex = find_sec(hdr, sechdrs, secstrings,
-                                        "__markers_strings");
-        verboseindex = find_sec(hdr, sechdrs, secstrings, "__verbose");
-        tracepointsindex = find_sec(hdr, sechdrs, secstrings, "__tracepoints");
-        tracepointsstringsindex = find_sec(hdr, sechdrs, secstrings,
-                                        "__tracepoints_strings");
-
-        mcountindex = find_sec(hdr, sechdrs, secstrings,
-                               "__mcount_loc");
 
         /* Now do relocations. */
         for (i = 1; i < hdr->e_shnum; i++) {
@@ -2193,28 +2171,16 @@ static noinline struct module *load_module(void __user *umod,
                 if (err < 0)
                         goto cleanup;
         }
-#ifdef CONFIG_MARKERS
-        mod->markers = (void *)sechdrs[markersindex].sh_addr;
-        mod->num_markers =
-                sechdrs[markersindex].sh_size / sizeof(*mod->markers);
-#endif
-#ifdef CONFIG_TRACEPOINTS
-        mod->tracepoints = (void *)sechdrs[tracepointsindex].sh_addr;
-        mod->num_tracepoints =
-                sechdrs[tracepointsindex].sh_size / sizeof(*mod->tracepoints);
-#endif
-
 
         /* Find duplicate symbols */
         err = verify_export_symbols(mod);
-
         if (err < 0)
                 goto cleanup;
 
         /* Set up and sort exception table */
-        mod->num_exentries = sechdrs[exindex].sh_size / sizeof(*mod->extable);
-        mod->extable = extable = (void *)sechdrs[exindex].sh_addr;
-        sort_extable(extable, extable + mod->num_exentries);
+        mod->extable = section_objs(hdr, sechdrs, secstrings, "__ex_table",
+                                    sizeof(*mod->extable), &mod->num_exentries);
+        sort_extable(mod->extable, mod->extable + mod->num_exentries);
 
         /* Finally, copy percpu area over. */
         percpu_modcopy(mod->percpu, (void *)sechdrs[pcpuindex].sh_addr,
@@ -2223,11 +2189,17 @@ static noinline struct module *load_module(void __user *umod,
         add_kallsyms(mod, sechdrs, symindex, strindex, secstrings);
 
         if (!mod->taints) {
+                struct mod_debug *debug;
+                unsigned int num_debug;
+
 #ifdef CONFIG_MARKERS
                 marker_update_probe_range(mod->markers,
                         mod->markers + mod->num_markers);
 #endif
-        dynamic_printk_setup(sechdrs, verboseindex);
+                debug = section_objs(hdr, sechdrs, secstrings, "__verbose",
+                                     sizeof(*debug), &num_debug);
+                dynamic_printk_setup(debug, num_debug);
+
 #ifdef CONFIG_TRACEPOINTS
                 tracepoint_update_probe_range(mod->tracepoints,
                         mod->tracepoints + mod->num_tracepoints);
@@ -2235,8 +2207,9 @@ static noinline struct module *load_module(void __user *umod,
         }
 
         /* sechdrs[0].sh_size is always zero */
-        mseg = (void *)sechdrs[mcountindex].sh_addr;
-        ftrace_init_module(mseg, mseg + sechdrs[mcountindex].sh_size);
+        mseg = section_objs(hdr, sechdrs, secstrings, "__mcount_loc",
+                            sizeof(*mseg), &num_mcount);
+        ftrace_init_module(mseg, mseg + num_mcount);
 
         err = module_finalize(hdr, sechdrs, mod);
         if (err < 0)
@@ -2261,7 +2234,7 @@ static noinline struct module *load_module(void __user *umod,
         set_fs(old_fs);
 
         mod->args = args;
-        if (obsparmindex)
+        if (section_addr(hdr, sechdrs, secstrings, "__obsparm"))
                 printk(KERN_WARNING "%s: Ignoring obsolete parameters\n",
                        mod->name);
 
@@ -2270,21 +2243,11 @@ static noinline struct module *load_module(void __user *umod,
          * strong_try_module_get() will fail. */
         stop_machine(__link_module, mod, NULL);
 
-        /* Size of section 0 is 0, so this works well if no params */
-        err = parse_args(mod->name, mod->args,
-                         (struct kernel_param *)
-                         sechdrs[setupindex].sh_addr,
-                         sechdrs[setupindex].sh_size
-                         / sizeof(struct kernel_param),
-                         NULL);
+        err = parse_args(mod->name, mod->args, kp, num_kp, NULL);
         if (err < 0)
                 goto unlink;
 
-        err = mod_sysfs_setup(mod,
-                              (struct kernel_param *)
-                              sechdrs[setupindex].sh_addr,
-                              sechdrs[setupindex].sh_size
-                              / sizeof(struct kernel_param));
+        err = mod_sysfs_setup(mod, kp, num_kp);
         if (err < 0)
                 goto unlink;
         add_sect_attrs(mod, hdr->e_shnum, secstrings, sechdrs);