[PATCH RFC 21/43] x86/ftrace: Adapt assembly for PIE support

[Hou Wenlong]

Change the assembly code to use only relative references of symbols for
the kernel to be PIE compatible.

Signed-off-by: Hou Wenlong <houwenlong.hwl@xxxxxxxxxxxx>
Cc: Thomas Garnier <thgarnie@xxxxxxxxxxxx>
Cc: Lai Jiangshan <jiangshan.ljs@xxxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
---
 arch/x86/kernel/ftrace_64.S | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S
index eddb4fabc16f..411fa4148e18 100644
--- a/arch/x86/kernel/ftrace_64.S
+++ b/arch/x86/kernel/ftrace_64.S
@@ -315,7 +315,14 @@ STACK_FRAME_NON_STANDARD_FP(ftrace_regs_caller)
 SYM_FUNC_START(__fentry__)
 	CALL_DEPTH_ACCOUNT
 
+#ifdef CONFIG_X86_PIE
+	pushq %r8
+	leaq ftrace_stub(%rip), %r8
+	cmpq %r8, ftrace_trace_function(%rip)
+	popq %r8
+#else
 	cmpq $ftrace_stub, ftrace_trace_function
+#endif
 	jnz trace
 	RET
 
@@ -329,7 +336,7 @@ trace:
 	 * ip and parent ip are used and the list function is called when
 	 * function tracing is enabled.
 	 */
-	movq ftrace_trace_function, %r8
+	movq ftrace_trace_function(%rip), %r8
 	CALL_NOSPEC r8
 	restore_mcount_regs
 
-- 
2.31.1