modpost: Add flag -E for making section mismatches fatal

The section mismatch warning can be easy to miss during the kernel build
process. Allow it to be marked as fatal to be easily caught and prevent
bugs from slipping in.

Setting CONFIG_SECTION_MISMATCH_WARN_ONLY=y causes these warnings to be
non-fatal, since there are a number of section mismatches when using
allmodconfig on some architectures, and we do not want to break these
builds by default.
Signed-off-by: Nicolas Boichat <drinkcat@chromium.org>
Change-Id: Ic346706e3297c9f0d790e3552aa94e5cff9897a6
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

lib/Kconfig.debug

@@ -311,6 +311,15 @@ config DEBUG_SECTION_MISMATCH
 	  - Enable verbose reporting from modpost in order to help resolve
 	    the section mismatches that are reported.
 
+config SECTION_MISMATCH_WARN_ONLY
+	bool "Make section mismatch errors non-fatal"
+	default y
+	help
+	  If you say N here, the build process will fail if there are any
+	  section mismatch, instead of just throwing warnings.
+
+	  If unsure, say Y.
+
 #
 # Select this config option from the architecture Kconfig, if it
 # is preferred to always offer frame pointers as a config

scripts/Makefile.modpost

@@ -77,6 +77,7 @@ modpost = scripts/mod/modpost                    \
  $(if $(KBUILD_EXTRA_SYMBOLS), $(patsubst %, -e %,$(KBUILD_EXTRA_SYMBOLS))) \
  $(if $(KBUILD_EXTMOD),-o $(modulesymfile))      \
  $(if $(CONFIG_DEBUG_SECTION_MISMATCH),,-S)      \
+ $(if $(CONFIG_SECTION_MISMATCH_WARN_ONLY),,-E)  \
  $(if $(KBUILD_EXTMOD)$(KBUILD_MODPOST_WARN),-w)
 
 MODPOST_OPT=$(subst -i,-n,$(filter -i,$(MAKEFLAGS)))

scripts/mod/modpost.c

@@ -38,6 +38,7 @@ static int warn_unresolved = 0;
 /* How a symbol is exported */
 static int sec_mismatch_count = 0;
 static int sec_mismatch_verbose = 1;
+static int sec_mismatch_fatal = 0;
 /* ignore missing files */
 static int ignore_missing_files;
 
@@ -2385,7 +2386,7 @@ int main(int argc, char **argv)
 	struct ext_sym_list *extsym_iter;
 	struct ext_sym_list *extsym_start = NULL;
 
-	while ((opt = getopt(argc, argv, "i:I:e:mnsST:o:awM:K:")) != -1) {
+	while ((opt = getopt(argc, argv, "i:I:e:mnsST:o:awM:K:E")) != -1) {
 		switch (opt) {
 		case 'i':
 			kernel_read = optarg;
@@ -2426,6 +2427,9 @@ int main(int argc, char **argv)
 		case 'w':
 			warn_unresolved = 1;
 			break;
+		case 'E':
+			sec_mismatch_fatal = 1;
+			break;
 		default:
 			exit(1);
 		}
@@ -2475,14 +2479,20 @@ int main(int argc, char **argv)
 		sprintf(fname, "%s.mod.c", mod->name);
 		write_if_changed(&buf, fname);
 	}
-
 	if (dump_write)
 		write_dump(dump_write);
-	if (sec_mismatch_count && !sec_mismatch_verbose)
-		warn("modpost: Found %d section mismatch(es).\n"
-		     "To see full details build your kernel with:\n"
-		     "'make CONFIG_DEBUG_SECTION_MISMATCH=y'\n",
-		     sec_mismatch_count);
+	if (sec_mismatch_count) {
+		if (!sec_mismatch_verbose) {
+			warn("modpost: Found %d section mismatch(es).\n"
+			     "To see full details build your kernel with:\n"
+			     "'make CONFIG_DEBUG_SECTION_MISMATCH=y'\n",
+			     sec_mismatch_count);
+		}
+		if (sec_mismatch_fatal) {
+			fatal("modpost: Section mismatches detected.\n"
+			      "Set CONFIG_SECTION_MISMATCH_WARN_ONLY=y to allow them.\n");
+		}
+	}
 
 	return err;
 }