| Message ID | 20180627160604.8154-6-ard.biesheuvel@linaro.org |
|---|---|
| State | New |
| Headers | show |
| Series | add support for relative references in jump tables | expand |
On Wed, Jun 27, 2018 at 06:06:04PM +0200, Ard Biesheuvel wrote: > Similar to the arm64 case, 64-bit x86 can benefit from using 32-bit > relative references rather than 64-bit absolute ones when emitting > struct jump_entry instances. Not only does this reduce the memory > footprint of the entries themselves by 50%, 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) This will conflict with: https://lkml.kernel.org/r/20180622172212.199633-10-namit@vmware.com
On 28 June 2018 at 10:31, Peter Zijlstra <peterz@infradead.org> wrote: > On Wed, Jun 27, 2018 at 06:06:04PM +0200, Ard Biesheuvel wrote: >> Similar to the arm64 case, 64-bit x86 can benefit from using 32-bit >> relative references rather than 64-bit absolute ones when emitting >> struct jump_entry instances. Not only does this reduce the memory >> footprint of the entries themselves by 50%, 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) > > This will conflict with: > > https://lkml.kernel.org/r/20180622172212.199633-10-namit@vmware.com Thanks for the head's up. Fortunately, it does not conflict fundamentally, so it should be a straight-forward rebase after that code is merged. Do you think this is likely to get merged for v4.19?
On Thu, Jun 28, 2018 at 10:34:54AM +0200, Ard Biesheuvel wrote: > On 28 June 2018 at 10:31, Peter Zijlstra <peterz@infradead.org> wrote: > > On Wed, Jun 27, 2018 at 06:06:04PM +0200, Ard Biesheuvel wrote: > >> Similar to the arm64 case, 64-bit x86 can benefit from using 32-bit > >> relative references rather than 64-bit absolute ones when emitting > >> struct jump_entry instances. Not only does this reduce the memory > >> footprint of the entries themselves by 50%, 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) > > > > This will conflict with: > > > > https://lkml.kernel.org/r/20180622172212.199633-10-namit@vmware.com > > Thanks for the head's up. Fortunately, it does not conflict > fundamentally, so it should be a straight-forward rebase after that > code is merged. Yeah, shouldn't be hard to cure. There's another patch set that might have a little conflict, but that's not near ready I think, so that'll have to just cope with things shifting underneath (and there too, the fixup shouldn't be hard). > Do you think this is likely to get merged for v4.19? I'm thinking it is near ready so it might, but I'm not in charge of those bits :-)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index e10a3542db7e..dd71258ec1cc 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -118,6 +118,7 @@ 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..d0f1f25b41d5 100644 --- a/arch/x86/include/asm/jump_label.h +++ b/arch/x86/include/asm/jump_label.h @@ -36,8 +36,8 @@ static __always_inline bool arch_static_branch(struct static_key *key, bool bran asm_volatile_goto("1:" ".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" + ".balign 4\n\t" + ".long 1b - ., %l[l_yes] - ., %c0 + %c1 - .\n\t" ".popsection \n\t" : : "i" (key), "i" (branch) : : l_yes); @@ -52,8 +52,8 @@ static __always_inline bool arch_static_branch_jump(struct static_key *key, bool ".byte 0xe9\n\t .long %l[l_yes] - 2f\n\t" "2:\n\t" ".pushsection __jump_table, \"aw\" \n\t" - _ASM_ALIGN "\n\t" - _ASM_PTR "1b, %l[l_yes], %c0 + %c1 \n\t" + ".balign 4\n\t" + ".long 1b - ., %l[l_yes] - ., %c0 + %c1 - .\n\t" ".popsection \n\t" : : "i" (key), "i" (branch) : : l_yes); @@ -62,18 +62,6 @@ 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 @@ -87,8 +75,8 @@ struct jump_entry { .byte STATIC_KEY_INIT_NOP .endif .pushsection __jump_table, "aw" - _ASM_ALIGN - _ASM_PTR .Lstatic_jump_\@, \target, \key + .balign 4 + .long .Lstatic_jump_\@ - ., \target - ., \key - . .popsection .endm @@ -103,8 +91,8 @@ struct jump_entry { .Lstatic_jump_after_\@: .endif .pushsection __jump_table, "aw" - _ASM_ALIGN - _ASM_PTR .Lstatic_jump_\@, \target, \key + 1 + .balign 4 + .long .Lstatic_jump_\@ - ., \target - ., \key + 1 - . .popsection .endm diff --git a/tools/objtool/special.c b/tools/objtool/special.c index 84f001d52322..98ae55b39037 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 12 #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
Similar to the arm64 case, 64-bit x86 can benefit from using 32-bit relative references rather than 64-bit absolute ones when emitting struct jump_entry instances. Not only does this reduce the memory footprint of the entries themselves by 50%, 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 | 28 ++++++-------------- tools/objtool/special.c | 4 +-- 3 files changed, 11 insertions(+), 22 deletions(-) -- 2.11.0