From: ard.biesheuvel@linaro.org (Ard Biesheuvel)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH v3 6/9] x86/kernel: jump_table: use relative references
Date: Tue, 18 Sep 2018 23:51:41 -0700 [thread overview]
Message-ID: <20180919065144.25010-7-ard.biesheuvel@linaro.org> (raw)
In-Reply-To: <20180919065144.25010-1-ard.biesheuvel@linaro.org>
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>
---
arch/x86/Kconfig | 1 +
arch/x86/include/asm/jump_label.h | 24 +++++++-------------
tools/objtool/special.c | 4 ++--
3 files changed, 11 insertions(+), 18 deletions(-)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 1a0be022f91d..603f374f871d 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -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
diff --git a/arch/x86/include/asm/jump_label.h b/arch/x86/include/asm/jump_label.h
index 8c0de4282659..21efc9d07ed9 100644
--- a/arch/x86/include/asm/jump_label.h
+++ b/arch/x86/include/asm/jump_label.h
@@ -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 @@ static __always_inline bool arch_static_branch_jump(struct static_key *key, bool
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
diff --git a/tools/objtool/special.c b/tools/objtool/special.c
index 84f001d52322..50af4e1274b3 100644
--- a/tools/objtool/special.c
+++ b/tools/objtool/special.c
@@ -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
--
2.17.1
next prev parent reply other threads:[~2018-09-19 6:51 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-19 6:51 [PATCH v3 0/9] add support for relative references in jump tables Ard Biesheuvel
2018-09-19 6:51 ` [PATCH v3 1/9] kernel/jump_label: abstract jump_entry member accessors Ard Biesheuvel
2018-09-19 6:51 ` [PATCH v3 2/9] kernel/jump_label: implement generic support for relative references Ard Biesheuvel
2018-09-19 6:51 ` [PATCH v3 3/9] arm64/kernel: jump_label: switch to " Ard Biesheuvel
2018-09-19 6:51 ` [PATCH v3 4/9] x86: add support for 64-bit place relative relocations Ard Biesheuvel
2018-09-19 6:51 ` [PATCH v3 5/9] x86: jump_label: switch to jump_entry accessors Ard Biesheuvel
2018-09-19 6:51 ` Ard Biesheuvel [this message]
2018-09-19 6:51 ` [PATCH v3 7/9] jump_label: annotate entries that operate on __init code earlier Ard Biesheuvel
2018-09-19 6:51 ` [PATCH v3 8/9] jump_table: move entries into ro_after_init region Ard Biesheuvel
2018-09-30 15:42 ` Guenter Roeck
2018-09-19 6:51 ` [PATCH v3 9/9] s390/jump_label: switch to relative references Ard Biesheuvel
2018-09-19 13:08 ` [PATCH v3 0/9] add support for relative references in jump tables Peter Zijlstra
2018-09-27 15:22 ` Ard Biesheuvel
2018-09-27 15:46 ` Kees Cook
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