Implement the static (branch) assertion. It simply emits the address
of the next instruction into a special section which objtool will read
and validate against either __jump_table or .altinstructions.
Use like:
if (static_branch_likely(_key)) {
arch_static_assert();
/* do stuff */
}
Or
if (static_cpu_has(_feat)) {
arch_static_assert();
/* do stuff */
}
Cc: Borislav Petkov <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Josh Poimboeuf <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
---
arch/x86/include/asm/jump_label.h | 23 +++++++++++++++++++++++
1 file changed, 23 insertions(+)
--- a/arch/x86/include/asm/jump_label.h
+++ b/arch/x86/include/asm/jump_label.h
@@ -62,6 +62,29 @@ static __always_inline bool arch_static_
return true;
}
+/*
+ * Annotation for objtool; asserts that the previous instruction is the
+ * jump_label patch site. Or rather, that the next instruction is a static
+ * branch target.
+ *
+ * Use like:
+ *
+ * if (static_branch_likely(key)) {
+ * arch_static_assert();
+ * do_code();
+ * }
+ *
+ * Also works with static_cpu_has().
+ */
+static __always_inline void arch_static_assert(void)
+{
+ asm volatile ("1:\n\t"
+ ".pushsection .discard.jump_assert \n\t"
+ _ASM_ALIGN "\n\t"
+ _ASM_PTR "1b \n\t"
+ ".popsection \n\t");
+}
+
#ifdef CONFIG_X86_64
typedef u64 jump_label_t;
#else
