module: reduce string table for loaded modules (v2)

Also remove all parts of the string table (referenced by the symbol
table) that are not needed for kallsyms use (i.e. which were only
referenced by symbols discarded by the previous patch, or not
referenced at all for whatever reason).
Signed-off-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

include/linux/module.h

@@ -315,7 +315,7 @@ struct module
 	 */
 	Elf_Sym *symtab, *core_symtab;
 	unsigned int num_symtab, core_num_syms;
-	char *strtab;
+	char *strtab, *core_strtab;
 
 	/* Section attributes */
 	struct module_sect_attrs *sect_attrs;

kernel/module.c

@@ -1886,12 +1886,17 @@ static bool is_core_symbol(const Elf_Sym *src, const Elf_Shdr *sechdrs,
 static unsigned long layout_symtab(struct module *mod,
 				   Elf_Shdr *sechdrs,
 				   unsigned int symindex,
+				   unsigned int strindex,
 				   const Elf_Ehdr *hdr,
-				   const char *secstrings)
+				   const char *secstrings,
+				   unsigned long *pstroffs,
+				   unsigned long *strmap)
 {
 	unsigned long symoffs;
 	Elf_Shdr *symsect = sechdrs + symindex;
+	Elf_Shdr *strsect = sechdrs + strindex;
 	const Elf_Sym *src;
+	const char *strtab;
 	unsigned int i, nsrc, ndst;
 
 	/* Put symbol section at end of init part of module. */
@@ -1902,14 +1907,31 @@ static unsigned long layout_symtab(struct module *mod,
 
 	src = (void *)hdr + symsect->sh_offset;
 	nsrc = symsect->sh_size / sizeof(*src);
+	strtab = (void *)hdr + strsect->sh_offset;
 	for (ndst = i = 1; i < nsrc; ++i, ++src)
-		if (is_core_symbol(src, sechdrs, hdr->e_shnum))
+		if (is_core_symbol(src, sechdrs, hdr->e_shnum)) {
+			unsigned int j = src->st_name;
+
+			while(!__test_and_set_bit(j, strmap) && strtab[j])
+				++j;
 			++ndst;
+		}
 
 	/* Append room for core symbols at end of core part. */
 	symoffs = ALIGN(mod->core_size, symsect->sh_addralign ?: 1);
 	mod->core_size = symoffs + ndst * sizeof(Elf_Sym);
 
+	/* Put string table section at end of init part of module. */
+	strsect->sh_flags |= SHF_ALLOC;
+	strsect->sh_entsize = get_offset(mod, &mod->init_size, strsect,
+					 strindex) | INIT_OFFSET_MASK;
+	DEBUGP("\t%s\n", secstrings + strsect->sh_name);
+
+	/* Append room for core symbols' strings at end of core part. */
+	*pstroffs = mod->core_size;
+	__set_bit(0, strmap);
+	mod->core_size += bitmap_weight(strmap, strsect->sh_size);
+
 	return symoffs;
 }
 
@@ -1919,11 +1941,14 @@ static void add_kallsyms(struct module *mod,
 			 unsigned int symindex,
 			 unsigned int strindex,
 			 unsigned long symoffs,
-			 const char *secstrings)
+			 unsigned long stroffs,
+			 const char *secstrings,
+			 unsigned long *strmap)
 {
 	unsigned int i, ndst;
 	const Elf_Sym *src;
 	Elf_Sym *dst;
+	char *s;
 
 	mod->symtab = (void *)sechdrs[symindex].sh_addr;
 	mod->num_symtab = sechdrs[symindex].sh_size / sizeof(Elf_Sym);
@@ -1941,16 +1966,25 @@ static void add_kallsyms(struct module *mod,
 		if (!is_core_symbol(src, sechdrs, shnum))
 			continue;
 		dst[ndst] = *src;
+		dst[ndst].st_name = bitmap_weight(strmap, dst[ndst].st_name);
 		++ndst;
 	}
 	mod->core_num_syms = ndst;
+
+	mod->core_strtab = s = mod->module_core + stroffs;
+	for (*s = 0, i = 1; i < sechdrs[strindex].sh_size; ++i)
+		if (test_bit(i, strmap))
+			*++s = mod->strtab[i];
 }
 #else
 static inline unsigned long layout_symtab(struct module *mod,
 					  Elf_Shdr *sechdrs,
 					  unsigned int symindex,
+					  unsigned int strindex,
 					  const Elf_Hdr *hdr,
-					  const char *secstrings)
+					  const char *secstrings,
+					  unsigned long *pstroffs,
+					  unsigned long *strmap)
 {
 }
 static inline void add_kallsyms(struct module *mod,
@@ -1959,7 +1993,9 @@ static inline void add_kallsyms(struct module *mod,
 				unsigned int symindex,
 				unsigned int strindex,
 				unsigned long symoffs,
-				const char *secstrings)
+				unsigned long stroffs,
+				const char *secstrings,
+				const unsigned long *strmap)
 {
 }
 #endif /* CONFIG_KALLSYMS */
@@ -2035,7 +2071,7 @@ static noinline struct module *load_module(void __user *umod,
 	long err = 0;
 	void *percpu = NULL, *ptr = NULL; /* Stops spurious gcc warning */
 #ifdef CONFIG_KALLSYMS
-	unsigned long symoffs;
+	unsigned long symoffs, stroffs, *strmap;
 #endif
 	mm_segment_t old_fs;
 
@@ -2118,10 +2154,6 @@ static noinline struct module *load_module(void __user *umod,
 	/* Don't keep modinfo and version sections. */
 	sechdrs[infoindex].sh_flags &= ~(unsigned long)SHF_ALLOC;
 	sechdrs[versindex].sh_flags &= ~(unsigned long)SHF_ALLOC;
-#ifdef CONFIG_KALLSYMS
-	/* Keep string table for decoding later. */
-	sechdrs[strindex].sh_flags |= SHF_ALLOC;
-#endif
 
 	/* Check module struct version now, before we try to use module. */
 	if (!check_modstruct_version(sechdrs, versindex, mod)) {
@@ -2157,6 +2189,13 @@ static noinline struct module *load_module(void __user *umod,
 		goto free_hdr;
 	}
 
+	strmap = kzalloc(BITS_TO_LONGS(sechdrs[strindex].sh_size)
+			 * sizeof(long), GFP_KERNEL);
+	if (!strmap) {
+		err = -ENOMEM;
+		goto free_mod;
+	}
+
 	if (find_module(mod->name)) {
 		err = -EEXIST;
 		goto free_mod;
@@ -2186,7 +2225,8 @@ static noinline struct module *load_module(void __user *umod,
 	   this is done generically; there doesn't appear to be any
 	   special cases for the architectures. */
 	layout_sections(mod, hdr, sechdrs, secstrings);
-	symoffs = layout_symtab(mod, sechdrs, symindex, hdr, secstrings);
+	symoffs = layout_symtab(mod, sechdrs, symindex, strindex, hdr,
+				secstrings, &stroffs, strmap);
 
 	/* Do the allocs. */
 	ptr = module_alloc_update_bounds(mod->core_size);
@@ -2392,7 +2432,9 @@ static noinline struct module *load_module(void __user *umod,
 		       sechdrs[pcpuindex].sh_size);
 
 	add_kallsyms(mod, sechdrs, hdr->e_shnum, symindex, strindex,
-		     symoffs, secstrings);
+		     symoffs, stroffs, secstrings, strmap);
+	kfree(strmap);
+	strmap = NULL;
 
 	if (!mod->taints) {
 		struct _ddebug *debug;
@@ -2481,6 +2523,7 @@ static noinline struct module *load_module(void __user *umod,
 		percpu_modfree(percpu);
  free_mod:
 	kfree(args);
+	kfree(strmap);
  free_hdr:
 	vfree(hdr);
 	return ERR_PTR(err);
@@ -2573,6 +2616,7 @@ SYSCALL_DEFINE3(init_module, void __user *, umod,
 #ifdef CONFIG_KALLSYMS
 	mod->num_symtab = mod->core_num_syms;
 	mod->symtab = mod->core_symtab;
+	mod->strtab = mod->core_strtab;
 #endif
 	module_free(mod, mod->module_init);
 	mod->module_init = NULL;