linux-kernel - [RFC PATCH v2 15/20] arm64: Add unwind hints to specific points in code

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Date:   Mon, 23 May 2022 19:16:32 -0500
From:   madvenka@...ux.microsoft.com
To:     jpoimboe@...hat.com, peterz@...radead.org, chenzhongjin@...wei.com,
        mark.rutland@....com, broonie@...nel.org, nobuta.keiya@...itsu.com,
        sjitindarsingh@...il.com, catalin.marinas@....com, will@...nel.org,
        jamorris@...ux.microsoft.com, linux-arm-kernel@...ts.infradead.org,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
        madvenka@...ux.microsoft.com
Subject: [RFC PATCH v2 15/20] arm64: Add unwind hints to specific points in code

From: "Madhavan T. Venkataraman" <madvenka@...ux.microsoft.com>

Add unwind hints to the following:

	- Ftrace entry code

	- Interrupt and Exception handlers

	- Kretprobe trampoline

Signed-off-by: Madhavan T. Venkataraman <madvenka@...ux.microsoft.com>
---
 arch/arm64/kernel/entry-ftrace.S              | 23 +++++++++++++++++++
 arch/arm64/kernel/entry.S                     |  3 +++
 arch/arm64/kernel/probes/kprobes_trampoline.S |  3 +++
 3 files changed, 29 insertions(+)

diff --git a/arch/arm64/kernel/entry-ftrace.S b/arch/arm64/kernel/entry-ftrace.S
index e535480a4069..6d68833e8cec 100644
--- a/arch/arm64/kernel/entry-ftrace.S
+++ b/arch/arm64/kernel/entry-ftrace.S
@@ -11,6 +11,7 @@
 #include <asm/assembler.h>
 #include <asm/ftrace.h>
 #include <asm/insn.h>
+#include <asm/unwind_hints.h>
 
 #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
 /*
@@ -95,7 +96,14 @@ SYM_CODE_START(ftrace_common)
 	mov	x3, sp				// regs
 
 SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL)
+	/*
+	 * Tracer functions are patched at ftrace_stub. Stack traces
+	 * taken from tracer functions will end up here. Place an
+	 * unwind hint based on the stackframe setup in ftrace_regs_entry.
+	 */
 	bl	ftrace_stub
+SYM_INNER_LABEL(ftrace_call_entry, SYM_L_GLOBAL)
+	UNWIND_HINT_REGS PT_REGS_SIZE
 
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 SYM_INNER_LABEL(ftrace_graph_call, SYM_L_GLOBAL) // ftrace_graph_caller();
@@ -134,10 +142,25 @@ SYM_CODE_START(ftrace_graph_caller)
 	add	x1, sp, #S_LR			// parent_ip (callsite's LR)
 	ldr	x2, [sp, #PT_REGS_SIZE]	   	// parent fp (callsite's FP)
 	bl	prepare_ftrace_return
+SYM_INNER_LABEL(ftrace_graph_caller_entry, SYM_L_GLOBAL)
+	UNWIND_HINT_REGS PT_REGS_SIZE
 	b	ftrace_common_return
 SYM_CODE_END(ftrace_graph_caller)
 #endif
 
+/*
+ * ftrace_regs_entry() sets up two stackframes - one for the callsite and
+ * one for the ftrace entry code. Unwind hints have been placed for the
+ * ftrace entry code above. We need an unwind hint for the callsite. Callsites
+ * are numerous. But the unwind hint required for all the callsites is the
+ * same. Define a dummy function here with the callsite unwind hint for the
+ * benefit of the unwinder.
+ */
+SYM_CODE_START(ftrace_callsite)
+	UNWIND_HINT_FTRACE 16		// for the callsite
+	ret
+SYM_CODE_END(ftrace_callsite)
+
 #else /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
 
 /*
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index ede028dee81b..95d5f3c08aa1 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -28,6 +28,7 @@
 #include <asm/thread_info.h>
 #include <asm/asm-uaccess.h>
 #include <asm/unistd.h>
+#include <asm/unwind_hints.h>
 
 	.macro	clear_gp_regs
 	.irp	n,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29
@@ -560,6 +561,7 @@ SYM_CODE_START_LOCAL(el\el\ht\()_\regsize\()_\label)
 	.if \el == 0
 	b	ret_to_user
 	.else
+	UNWIND_HINT_REGS PT_REGS_SIZE
 	b	ret_to_kernel
 	.endif
 SYM_CODE_END(el\el\ht\()_\regsize\()_\label)
@@ -894,6 +896,7 @@ SYM_FUNC_START(call_on_irq_stack)
 	/* Move to the new stack and call the function there */
 	mov	sp, x16
 	blr	x1
+	UNWIND_HINT_IRQ 16
 
 	/*
 	 * Restore the SP from the FP, and restore the FP and LR from the frame
diff --git a/arch/arm64/kernel/probes/kprobes_trampoline.S b/arch/arm64/kernel/probes/kprobes_trampoline.S
index 9a6499bed58b..847cbb81ca33 100644
--- a/arch/arm64/kernel/probes/kprobes_trampoline.S
+++ b/arch/arm64/kernel/probes/kprobes_trampoline.S
@@ -6,6 +6,7 @@
 #include <linux/linkage.h>
 #include <asm/asm-offsets.h>
 #include <asm/assembler.h>
+#include <asm/unwind_hints.h>
 
 	.text
 
@@ -71,6 +72,8 @@ SYM_CODE_START(__kretprobe_trampoline)
 
 	mov x0, sp
 	bl trampoline_probe_handler
+	UNWIND_HINT_REGS PT_REGS_SIZE
+
 	/*
 	 * Replace trampoline address in lr with actual orig_ret_addr return
 	 * address.
-- 
2.25.1