modpost: work around unaligned data access error

With the latest binutils, modpost fails with a bus error on some
architectures such as ARM and sparc64.

Since binutils commit 1f1b5e506bf0 ("bfd/ELF: restrict file alignment
for object files"), the byte offset to each section (sh_offset) in
relocatable ELF is no longer guaranteed to be aligned.

modpost parses MODULE_DEVICE_TABLE() data structures, which are usually
located in the .rodata section. If it is not properly aligned, unaligned
access errors may occur.

To address the issue, this commit imports the get_unaligned() helper
from include/linux/unaligned.h.

The get_unaligned_native() helper caters to the endianness in addition
to handling the unaligned access.

I slightly refactored do_pcmcia_entry() and do_input() to avoid writing
back to an unaligned address. (We would need the put_unaligned() helper
to do that.)

The addend_*_rel() functions need similar adjustments because the .text
sections are not aligned either.

It seems that the .symtab, .rel.* and .rela.* sections are still aligned.
Keep normal pointer access for these sections to avoid unnecessary
performance costs.

Reported-by: Paulo Pisati <paolo.pisati@canonical.com>
Reported-by: Matthias Klose <doko@debian.org>
Closes: https://sourceware.org/bugzilla/show_bug.cgi?id=32435
Reported-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Closes: https://sourceware.org/bugzilla/show_bug.cgi?id=32493
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>

1 files changed, 14 insertions, 0 deletions

diff --git a/scripts/mod/modpost.h b/scripts/mod/modpost.h
index 8b72c227ebf4..ffd0a52a606e 100644
--- a/scripts/mod/modpost.h
+++ b/scripts/mod/modpost.h
@@ -65,6 +65,20 @@
 #define TO_NATIVE(x)	\
 	(target_is_big_endian == host_is_big_endian ? x : bswap(x))
 
+#define __get_unaligned_t(type, ptr) ({					\
+	const struct { type x; } __attribute__((__packed__)) *__pptr =	\
+						(typeof(__pptr))(ptr);	\
+	__pptr->x;							\
+})
+
+#define get_unaligned(ptr)	__get_unaligned_t(typeof(*(ptr)), (ptr))
+
+#define get_unaligned_native(ptr) \
+({ \
+	typeof(*(ptr)) _val = get_unaligned(ptr); \
+	TO_NATIVE(_val); \
+})
+
 #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]))
 
 #define strstarts(str, prefix) (strncmp(str, prefix, strlen(prefix)) == 0)