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authorArnd Bergmann <arnd@arndb.de>2021-05-08 00:07:52 +0200
committerArnd Bergmann <arnd@arndb.de>2021-05-10 17:50:47 +0200
commit778aaefb8e864fc61f850539ea479554dd4caea1 (patch)
tree3f017f34981cb9ae52bf8f29cd6ebd04fd8878da /include/asm-generic/unaligned.h
parent0652035a57945e14e611dafae2ec5b46a05bc1d1 (diff)
downloadlinux-778aaefb8e864fc61f850539ea479554dd4caea1.tar.gz
asm-generic: unaligned always use struct helpers
As found by Vineet Gupta and Linus Torvalds, gcc has somewhat unexpected behavior when faced with overlapping unaligned pointers. The kernel's unaligned/access-ok.h header technically invokes undefined behavior that happens to usually work on the architectures using it, but if the compiler optimizes code based on the assumption that undefined behavior doesn't happen, it can create output that actually causes data corruption. A related problem was previously found on 32-bit ARMv7, where most instructions can be used on unaligned data, but 64-bit ldrd/strd causes an exception. The workaround was to always use the unaligned/le_struct.h helper instead of unaligned/access-ok.h, in commit 1cce91dfc8f7 ("ARM: 8715/1: add a private asm/unaligned.h"). The same solution should work on all other architectures as well, so remove the access-ok.h variant and use the other one unconditionally on all architectures, picking either the big-endian or little-endian version. With this, the arm specific header can be removed as well, and the only file including linux/unaligned/access_ok.h gets moved to including the normal file. Fortunately, this made almost no difference to the object code produced by gcc-11. On x86, s390, powerpc, and arc, the resulting binary appears to be identical to the previous version, while on arm64 and m68k there are minimal differences that looks like an optimization pass went into a different direction, usually using fewer stack spills on the new version. Signed-off-by: Arnd Bergmann <arnd@arndb.de> Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100363
Diffstat (limited to 'include/asm-generic/unaligned.h')
-rw-r--r--include/asm-generic/unaligned.h13
1 files changed, 2 insertions, 11 deletions
diff --git a/include/asm-generic/unaligned.h b/include/asm-generic/unaligned.h
index d79df721ae60..36bf03aaa674 100644
--- a/include/asm-generic/unaligned.h
+++ b/include/asm-generic/unaligned.h
@@ -8,22 +8,13 @@
*/
#include <asm/byteorder.h>
-/* Set by the arch if it can handle unaligned accesses in hardware. */
-#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
-# include <linux/unaligned/access_ok.h>
-#endif
-
#if defined(__LITTLE_ENDIAN)
-# ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
-# include <linux/unaligned/le_struct.h>
-# endif
+# include <linux/unaligned/le_struct.h>
# include <linux/unaligned/generic.h>
# define get_unaligned __get_unaligned_le
# define put_unaligned __put_unaligned_le
#elif defined(__BIG_ENDIAN)
-# ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
-# include <linux/unaligned/be_struct.h>
-# endif
+# include <linux/unaligned/be_struct.h>
# include <linux/unaligned/generic.h>
# define get_unaligned __get_unaligned_be
# define put_unaligned __put_unaligned_be