modpost: detect endianness on run-time

Endianness is currently detected on compile-time, but we can defer this
until run-time. This change avoids re-executing scripts/mod/mk_elfconfig
even if modpost in the linux-headers package needs to be rebuilt for a
foreign architecture.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>

1 files changed, 36 insertions, 0 deletions

diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index d16d0ace2775..bfd758ad9e4f 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -50,6 +50,9 @@ static bool error_occurred;
 
 static bool extra_warn;
 
+bool target_is_big_endian;
+bool host_is_big_endian;
+
 /*
  * Cut off the warnings when there are too many. This typically occurs when
  * vmlinux is missing. ('make modules' without building vmlinux.)
@@ -438,6 +441,18 @@ static int parse_elf(struct elf_info *info, const char *filename)
 		/* Not an ELF file - silently ignore it */
 		return 0;
 	}
+
+	switch (hdr->e_ident[EI_DATA]) {
+	case ELFDATA2LSB:
+		target_is_big_endian = false;
+		break;
+	case ELFDATA2MSB:
+		target_is_big_endian = true;
+		break;
+	default:
+		fatal("target endian is unknown\n");
+	}
+
 	/* Fix endianness in ELF header */
 	hdr->e_type      = TO_NATIVE(hdr->e_type);
 	hdr->e_machine   = TO_NATIVE(hdr->e_machine);
@@ -2117,6 +2132,25 @@ struct dump_list {
 	const char *file;
 };
 
+static void check_host_endian(void)
+{
+	static const union {
+		short s;
+		char c[2];
+	} endian_test = { .c = {0x01, 0x02} };
+
+	switch (endian_test.s) {
+	case 0x0102:
+		host_is_big_endian = true;
+		break;
+	case 0x0201:
+		host_is_big_endian = false;
+		break;
+	default:
+		fatal("Unknown host endian\n");
+	}
+}
+
 int main(int argc, char **argv)
 {
 	struct module *mod;
@@ -2181,6 +2215,8 @@ int main(int argc, char **argv)
 		}
 	}
 
+	check_host_endian();
+
 	list_for_each_entry_safe(dl, dl2, &dump_lists, list) {
 		read_dump(dl->file);
 		list_del(&dl->list);