x86/jump_table: Use relative references

Similar to the arm64 case, 64-bit x86 can benefit from using relative
references rather than absolute ones when emitting struct jump_entry
instances. Not only does this reduce the memory footprint of the entries
themselves by 33%, it also removes the need for carrying relocation
metadata on relocatable builds (i.e., for KASLR) which saves a fair
chunk of .init space as well (although the savings are not as dramatic
as on arm64)

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-s390@vger.kernel.org
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Jessica Yu <jeyu@kernel.org>
Link: https://lkml.kernel.org/r/20180919065144.25010-7-ard.biesheuvel@linaro.org

This commit is contained in:

Ard Biesheuvel

2018-09-18 23:51:41 -07:00

committed by

Thomas Gleixner

parent 9fc0f798ab

commit b34006c425

3 changed files with 11 additions and 18 deletions

									
										tools/objtool/special.c
									
		+2
		-2
	
												View File
												
				@@ -30,9 +30,9 @@

				#define EX_ORIG_OFFSET		0

				#define EX_NEW_OFFSET		4

				#define JUMP_ENTRY_SIZE		24

				#define JUMP_ENTRY_SIZE		16

				#define JUMP_ORIG_OFFSET	0

				#define JUMP_NEW_OFFSET		8

				#define JUMP_NEW_OFFSET		4

				#define ALT_ENTRY_SIZE		13

				#define ALT_ORIG_OFFSET		0