kbuild: soften modpost checks when doing cross builds

The module alias support in the kernel have a consistency
check where it is checked that the size of a structure
in the kernel and on the build host are the same.
For cross builds this check does not make sense so detect
when we do cross builds and silently skip the check in these
situations.
This fixes a build bug for a wireless driver when cross building
for arm.

Acked-by: Michael Buesch <mb@bu3sch.de>
Tested-by: Gordon Farquharson <gordonfarquharson@gmail.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: stable@kernel.org

5 files changed, 15 insertions, 3 deletions

diff --git a/Makefile b/Makefile
index 7a4d34b91e0..1c4c8f87f6c 100644
--- a/Makefile
+++ b/Makefile
@@ -189,7 +189,7 @@ SUBARCH := $(shell uname -m | sed -e s/i.86/i386/ -e s/sun4u/sparc64/ \
 # Alternatively CROSS_COMPILE can be set in the environment.
 # Default value for CROSS_COMPILE is not to prefix executables
 # Note: Some architectures assign CROSS_COMPILE in their arch/*/Makefile
-
+export KBUILD_BUILDHOST := $(SUBARCH)
 ARCH		?= $(SUBARCH)
 CROSS_COMPILE	?=
 
diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
index cfc004e0441..2d20640854b 100644
--- a/scripts/Makefile.modpost
+++ b/scripts/Makefile.modpost
@@ -58,6 +58,9 @@ modules   := $(patsubst %.o,%.ko, $(wildcard $(__modules:.ko=.o)))
 # Stop after building .o files if NOFINAL is set. Makes compile tests quicker
 _modpost: $(if $(KBUILD_MODPOST_NOFINAL), $(modules:.ko:.o),$(modules))
 
+ifneq ($(KBUILD_BUILDHOST),$(ARCH))
+        cross_build := 1
+endif
 
 # Step 2), invoke modpost
 #  Includes step 3,4
@@ -70,7 +73,8 @@ modpost = scripts/mod/modpost                    \
  $(if $(CONFIG_DEBUG_SECTION_MISMATCH),,-S)      \
  $(if $(CONFIG_MARKERS),-K $(kernelmarkersfile)) \
  $(if $(CONFIG_MARKERS),-M $(markersfile))	 \
- $(if $(KBUILD_EXTMOD)$(KBUILD_MODPOST_WARN),-w)
+ $(if $(KBUILD_EXTMOD)$(KBUILD_MODPOST_WARN),-w) \
+ $(if $(cross_build),-c)
 
 quiet_cmd_modpost = MODPOST $(words $(filter-out vmlinux FORCE, $^)) modules
       cmd_modpost = $(modpost) -s
diff --git a/scripts/mod/file2alias.c b/scripts/mod/file2alias.c
index 9ddf944cce2..348d8687b7c 100644
--- a/scripts/mod/file2alias.c
+++ b/scripts/mod/file2alias.c
@@ -51,11 +51,13 @@ do {                                                            \
                 sprintf(str + strlen(str), "*");                \
 } while(0)
 
+unsigned int cross_build = 0;
 /**
  * Check that sizeof(device_id type) are consistent with size of section
  * in .o file. If in-consistent then userspace and kernel does not agree
  * on actual size which is a bug.
  * Also verify that the final entry in the table is all zeros.
+ * Ignore both checks if build host differ from target host and size differs.
  **/
 static void device_id_check(const char *modname, const char *device_id,
 			    unsigned long size, unsigned long id_size,
@@ -64,6 +66,8 @@ static void device_id_check(const char *modname, const char *device_id,
 	int i;
 
 	if (size % id_size || size < id_size) {
+		if (cross_build != 0)
+			return;
 		fatal("%s: sizeof(struct %s_device_id)=%lu is not a modulo "
 		      "of the size of section __mod_%s_device_table=%lu.\n"
 		      "Fix definition of struct %s_device_id "
diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 695b5d657cf..110cf243fa4 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -2026,7 +2026,7 @@ int main(int argc, char **argv)
 	int opt;
 	int err;
 
-	while ((opt = getopt(argc, argv, "i:I:msSo:awM:K:")) != -1) {
+	while ((opt = getopt(argc, argv, "i:I:cmsSo:awM:K:")) != -1) {
 		switch (opt) {
 		case 'i':
 			kernel_read = optarg;
@@ -2035,6 +2035,9 @@ int main(int argc, char **argv)
 			module_read = optarg;
 			external_module = 1;
 			break;
+		case 'c':
+			cross_build = 1;
+			break;
 		case 'm':
 			modversions = 1;
 			break;
diff --git a/scripts/mod/modpost.h b/scripts/mod/modpost.h
index 565c5872407..09f58e33d22 100644
--- a/scripts/mod/modpost.h
+++ b/scripts/mod/modpost.h
@@ -135,6 +135,7 @@ struct elf_info {
 };
 
 /* file2alias.c */
+extern unsigned int cross_build;
 void handle_moddevtable(struct module *mod, struct elf_info *info,
 			Elf_Sym *sym, const char *symname);
 void add_moddevtable(struct buffer *buf, struct module *mod);