modpost: add a helper to get data pointed by a symbol

When CONFIG_MODULE_REL_CRCS is enabled, the value of __crc_* is not
an absolute value, but the address to the CRC data embedded in the
.rodata section.

Getting the data pointed by the symbol value is somewhat complex.
Split it out into a new helper, sym_get_data().

I will reuse it to refactor namespace_from_kstrtabns() in the next
commit.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

scripts/mod/modpost.c

@@ -308,6 +308,18 @@ static const char *sec_name(struct elf_info *elf, int secindex)
 	return sech_name(elf, &elf->sechdrs[secindex]);
 }
 
+static void *sym_get_data(const struct elf_info *info, const Elf_Sym *sym)
+{
+	Elf_Shdr *sechdr = &info->sechdrs[sym->st_shndx];
+	unsigned long offset;
+
+	offset = sym->st_value;
+	if (info->hdr->e_type != ET_REL)
+		offset -= sechdr->sh_addr;
+
+	return (void *)info->hdr + sechdr->sh_offset + offset;
+}
+
 #define strstarts(str, prefix) (strncmp(str, prefix, strlen(prefix)) == 0)
 
 static enum export export_from_secname(struct elf_info *elf, unsigned int sec)
@@ -697,10 +709,7 @@ static void handle_modversions(struct module *mod, struct elf_info *info,
 			unsigned int *crcp;
 
 			/* symbol points to the CRC in the ELF object */
-			crcp = (void *)info->hdr + sym->st_value +
-			       info->sechdrs[sym->st_shndx].sh_offset -
-			       (info->hdr->e_type != ET_REL ?
-				info->sechdrs[sym->st_shndx].sh_addr : 0);
+			crcp = sym_get_data(info, sym);
 			crc = TO_NATIVE(*crcp);
 		}
 		sym_update_crc(symname + strlen("__crc_"), mod, crc,