From: Ard Biesheuvel <ardb@kernel.org>
Date: Tue, 25 Jan 2022 10:20:49 +0000 (+0100)
Subject: ARM: ftrace: enable HAVE_FUNCTION_GRAPH_FP_TEST
X-Git-Tag: howlett/maple/20220722_2~952^2~7^2~6
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=953f534a7ed6b725d4f101d2949393acc9262880;p=users%2Fjedix%2Flinux-maple.git

ARM: ftrace: enable HAVE_FUNCTION_GRAPH_FP_TEST

Fix the frame pointer handling in the function graph tracer entry and
exit code so we can enable HAVE_FUNCTION_GRAPH_FP_TEST. Instead of using
FP directly (which will have different values between the entry and exit
pieces of the function graph tracer), use the value of SP at entry and
exit, as we can derive the former value from the frame pointer.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---

diff --git a/arch/arm/include/asm/ftrace.h b/arch/arm/include/asm/ftrace.h
index a4dbac07e4ef0..b4f5fab6b04e4 100644
--- a/arch/arm/include/asm/ftrace.h
+++ b/arch/arm/include/asm/ftrace.h
@@ -2,6 +2,8 @@
 #ifndef _ASM_ARM_FTRACE
 #define _ASM_ARM_FTRACE
 
+#define HAVE_FUNCTION_GRAPH_FP_TEST
+
 #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
 #define ARCH_SUPPORTS_FTRACE_OPS 1
 #endif
diff --git a/arch/arm/kernel/entry-ftrace.S b/arch/arm/kernel/entry-ftrace.S
index 99720064a4c57..bbfa0954c385e 100644
--- a/arch/arm/kernel/entry-ftrace.S
+++ b/arch/arm/kernel/entry-ftrace.S
@@ -247,7 +247,7 @@ ENDPROC(ftrace_graph_regs_caller)
 	.globl return_to_handler
 return_to_handler:
 	stmdb	sp!, {r0-r3}
-	mov	r0, fp			@ frame pointer
+	add	r0, sp, #16		@ sp at exit of instrumented routine
 	bl	ftrace_return_to_handler
 	mov	lr, r0			@ r0 has real ret addr
 	ldmia	sp!, {r0-r3}
diff --git a/arch/arm/kernel/ftrace.c b/arch/arm/kernel/ftrace.c
index 74d3913f5590d..ea2396900c7dc 100644
--- a/arch/arm/kernel/ftrace.c
+++ b/arch/arm/kernel/ftrace.c
@@ -233,6 +233,11 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
 	if (unlikely(atomic_read(&current->tracing_graph_pause)))
 		return;
 
+	if (IS_ENABLED(CONFIG_UNWINDER_FRAME_POINTER)) {
+		/* FP points one word below parent's top of stack */
+		frame_pointer += 4;
+	}
+
 	old = *parent;
 	*parent = return_hooker;