kbuild: ignore powerpc specific symbols in modpost

Kumar Gala <galak@kernel.crashing.org> wrote:
We have a case in powerpc in which we want to link some library
routines with all module objects.  The routines are intended for
handling out-of-line function call register save/restore so having
them as EXPORT_SYMBOL() is counter productive (we do also need to
link the same "library" code into the kernel).

Without this patch a powerpc build would error out and fail
to build modules with the added register save/restore module.

There were two obvious solutions:
1) To link the .o file before the modpost stage
2) To ignore the symbols in modpost

Option 1) was ruled out because we do not have any separate
linking stage for single file modules.

This patch implements option 2 - and do so only for powerpc.

The symbols we ignore are all undefined symbols named:
_restgpr_*, _savegpr_*, _rest32gpr_*, _save32gpr_*
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Kumar Gala <galak@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>

scripts/mod/modpost.c

@@ -467,6 +467,25 @@ static void parse_elf_finish(struct elf_info *info)
 	release_file(info->hdr, info->size);
 }
 
+static int ignore_undef_symbol(struct elf_info *info, const char *symname)
+{
+	/* ignore __this_module, it will be resolved shortly */
+	if (strcmp(symname, MODULE_SYMBOL_PREFIX "__this_module") == 0)
+		return 1;
+	/* ignore global offset table */
+	if (strcmp(symname, "_GLOBAL_OFFSET_TABLE_") == 0)
+		return 1;
+	if (info->hdr->e_machine == EM_PPC)
+		/* Special register function linked on all modules during final link of .ko */
+		if (strncmp(symname, "_restgpr_", sizeof("_restgpr_") - 1) == 0 ||
+		    strncmp(symname, "_savegpr_", sizeof("_savegpr_") - 1) == 0 ||
+		    strncmp(symname, "_rest32gpr_", sizeof("_rest32gpr_") - 1) == 0 ||
+		    strncmp(symname, "_save32gpr_", sizeof("_save32gpr_") - 1) == 0)
+			return 1;
+	/* Do not ignore this symbol */
+	return 0;
+}
+
 #define CRC_PFX     MODULE_SYMBOL_PREFIX "__crc_"
 #define KSYMTAB_PFX MODULE_SYMBOL_PREFIX "__ksymtab_"
 
@@ -493,11 +512,7 @@ static void handle_modversions(struct module *mod, struct elf_info *info,
 		if (ELF_ST_BIND(sym->st_info) != STB_GLOBAL &&
 		    ELF_ST_BIND(sym->st_info) != STB_WEAK)
 			break;
-		/* ignore global offset table */
-		if (strcmp(symname, "_GLOBAL_OFFSET_TABLE_") == 0)
-			break;
-		/* ignore __this_module, it will be resolved shortly */
-		if (strcmp(symname, MODULE_SYMBOL_PREFIX "__this_module") == 0)
+		if (ignore_undef_symbol(info, symname))
 			break;
 /* cope with newer glibc (2.3.4 or higher) STT_ definition in elf.h */
 #if defined(STT_REGISTER) || defined(STT_SPARC_REGISTER)