Commit b34006c4 authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Thomas Gleixner
Browse files

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: default avatarArd Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarPeter 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
parent 9fc0f798

arch/x86/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -119,6 +119,7 @@ config X86 
	select HAVE_ARCH_AUDITSYSCALL

	select HAVE_ARCH_HUGE_VMAP		if X86_64 || X86_PAE

	select HAVE_ARCH_JUMP_LABEL

	select HAVE_ARCH_JUMP_LABEL_RELATIVE

	select HAVE_ARCH_KASAN			if X86_64

	select HAVE_ARCH_KGDB

	select HAVE_ARCH_MMAP_RND_BITS		if MMU

arch/x86/include/asm/jump_label.h

+8 −16
Original line number Diff line number Diff line
@@ -37,7 +37,8 @@ static __always_inline bool arch_static_branch(struct static_key *key, bool bran 
		".byte " __stringify(STATIC_KEY_INIT_NOP) "\n\t"

		".pushsection __jump_table,  \"aw\" \n\t"

		_ASM_ALIGN "\n\t"

		_ASM_PTR "1b, %l[l_yes], %c0 + %c1 \n\t"

		".long 1b - ., %l[l_yes] - . \n\t"

		_ASM_PTR "%c0 + %c1 - .\n\t"

		".popsection \n\t"

		: :  "i" (key), "i" (branch) : : l_yes);
@@ -53,7 +54,8 @@ static __always_inline bool arch_static_branch_jump(struct static_key *key, bool 
		"2:\n\t"

		".pushsection __jump_table,  \"aw\" \n\t"

		_ASM_ALIGN "\n\t"

		_ASM_PTR "1b, %l[l_yes], %c0 + %c1 \n\t"

		".long 1b - ., %l[l_yes] - . \n\t"

		_ASM_PTR "%c0 + %c1 - .\n\t"

		".popsection \n\t"

		: :  "i" (key), "i" (branch) : : l_yes);
@@ -62,18 +64,6 @@ l_yes: 
	return true;

}



#ifdef CONFIG_X86_64

typedef u64 jump_label_t;

#else

typedef u32 jump_label_t;

#endif



struct jump_entry {

	jump_label_t code;

	jump_label_t target;

	jump_label_t key;

};



#else	/* __ASSEMBLY__ */



.macro STATIC_JUMP_IF_TRUE target, key, def
@@ -88,7 +78,8 @@ struct jump_entry { 
	.endif

	.pushsection __jump_table, "aw"

	_ASM_ALIGN

	_ASM_PTR	.Lstatic_jump_\@, \target, \key

	.long		.Lstatic_jump_\@ - ., \target - .

	_ASM_PTR	\key - .

	.popsection

.endm
@@ -104,7 +95,8 @@ struct jump_entry { 
	.endif

	.pushsection __jump_table, "aw"

	_ASM_ALIGN

	_ASM_PTR	.Lstatic_jump_\@, \target, \key + 1

	.long		.Lstatic_jump_\@ - ., \target - .

	_ASM_PTR	\key + 1 - .

	.popsection

.endm

tools/objtool/special.c

+2 −2
Original line number Diff line number Diff line
@@ -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

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