module: fix out-by-one error in kallsyms

commit 59ef28b1 upstream.

Masaki found and patched a kallsyms issue: the last symbol in a
module's symtab wasn't transferred.  This is because we manually copy
the zero'th entry (which is always empty) then copy the rest in a loop
starting at 1, though from src[0].  His fix was minimal, I prefer to
rewrite the loops in more standard form.

There are two loops: one to get the size, and one to copy.  Make these
identical: always count entry 0 and any defined symbol in an allocated
non-init section.

This bug exists since the following commit was introduced.
   module: reduce symbol table for loaded modules (v2)
   commit: 4a496226

LKML: http://lkml.org/lkml/2012/10/24/27Reported-by: Masaki Kimura <masaki.kimura.kz@hitachi.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
[bwh: Backported to 3.2: we're still using a bitmap to compress the string
 table]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

kernel/module.c

@@ -2193,15 +2193,17 @@ static void layout_symtab(struct module *mod, struct load_info *info)
 
 	src = (void *)info->hdr + symsect->sh_offset;
 	nsrc = symsect->sh_size / sizeof(*src);
-	for (ndst = i = 1; i < nsrc; ++i, ++src)
-		if (is_core_symbol(src, info->sechdrs, info->hdr->e_shnum)) {
-			unsigned int j = src->st_name;
+	for (ndst = i = 0; i < nsrc; i++) {
+		if (i == 0 ||
+		    is_core_symbol(src+i, info->sechdrs, info->hdr->e_shnum)) {
+			unsigned int j = src[i].st_name;
 
 			while (!__test_and_set_bit(j, info->strmap)
 			       && info->strtab[j])
 				++j;
 			++ndst;
 		}
+	}
 
 	/* Append room for core symbols at end of core part. */
 	info->symoffs = ALIGN(mod->core_size, symsect->sh_addralign ?: 1);
@@ -2238,15 +2240,15 @@ static void add_kallsyms(struct module *mod, const struct load_info *info)
 
 	mod->core_symtab = dst = mod->module_core + info->symoffs;
 	src = mod->symtab;
-	*dst = *src;
-	for (ndst = i = 1; i < mod->num_symtab; ++i, ++src) {
-		if (!is_core_symbol(src, info->sechdrs, info->hdr->e_shnum))
-			continue;
-		dst[ndst] = *src;
+	for (ndst = i = 0; i < mod->num_symtab; i++) {
+		if (i == 0 ||
+		    is_core_symbol(src+i, info->sechdrs, info->hdr->e_shnum)) {
+			dst[ndst] = src[i];
 			dst[ndst].st_name = bitmap_weight(info->strmap,
 							  dst[ndst].st_name);
 			++ndst;
 		}
+	}
 	mod->core_num_syms = ndst;
 
 	mod->core_strtab = s = mod->module_core + info->stroffs;