The following commit has been merged into the objtool/core branch of tip:
Commit-ID: ab3257042c26d0cd44793c741e2f89bf38b21fe8
Gitweb: https://git.kernel.org/tip/ab3257042c26d0cd44793c741e2f89bf38b21fe8
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Thu, 06 May 2021 21:34:05 +02:00
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Wed, 12 May 2021 14:54:56 +02:00
jump_label, x86: Allow short NOPs
Now that objtool is able to rewrite jump_label instructions, have the
compiler emit a JMP, such that it can decide on the optimal encoding,
and set jump_entry::key bit1 to indicate that objtool should rewrite
the instruction to a matching NOP.
For x86_64-allyesconfig this gives:
jl\ NOP JMP
short: 22997 124
long: 30874 90
IOW, we save (22997+124) * 3 bytes of kernel text in hotpaths.
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20210506194158.216763632@xxxxxxxxxxxxx
---
arch/x86/include/asm/jump_label.h | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)
diff --git a/arch/x86/include/asm/jump_label.h b/arch/x86/include/asm/jump_label.h
index ef819e3..0449b12 100644
--- a/arch/x86/include/asm/jump_label.h
+++ b/arch/x86/include/asm/jump_label.h
@@ -20,6 +20,22 @@
_ASM_PTR "%c0 + %c1 - .\n\t" \
".popsection \n\t"
+#ifdef CONFIG_STACK_VALIDATION
+
+static __always_inline bool arch_static_branch(struct static_key *key, bool branch)
+{
+ asm_volatile_goto("1:"
+ "jmp %l[l_yes] # objtool NOPs this \n\t"
+ JUMP_TABLE_ENTRY
+ : : "i" (key), "i" (2 | branch) : : l_yes);
+
+ return false;
+l_yes:
+ return true;
+}
+
+#else
+
static __always_inline bool arch_static_branch(struct static_key * const key, const bool branch)
{
asm_volatile_goto("1:"
@@ -32,6 +48,8 @@ l_yes:
return true;
}
+#endif /* STACK_VALIDATION */
+
static __always_inline bool arch_static_branch_jump(struct static_key * const key, const bool branch)
{
asm_volatile_goto("1:"
|