arm64: Trace emulation of AArch32 legacy instructions

Introduce an event to trace the usage of emulated instructions. The
trace event is intended to help identify and encourage the migration
of legacy software using the emulation features.

Use this event to trace usage of swp and CP15 barrier emulation.

Acked-by: Steven Rostedt <rostedt@goodmis.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Punit Agrawal <punit.agrawal@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/kernel/Makefile

@@ -5,6 +5,7 @@
 CPPFLAGS_vmlinux.lds	:= -DTEXT_OFFSET=$(TEXT_OFFSET)
 AFLAGS_head.o		:= -DTEXT_OFFSET=$(TEXT_OFFSET)
 CFLAGS_efi-stub.o 	:= -DTEXT_OFFSET=$(TEXT_OFFSET)
+CFLAGS_armv8_deprecated.o := -I$(src)
 
 CFLAGS_REMOVE_ftrace.o = -pg
 CFLAGS_REMOVE_insn.o = -pg

arch/arm64/kernel/armv8_deprecated.c

@@ -20,6 +20,9 @@
 #include <asm/traps.h>
 #include <asm/uaccess.h>
 
+#define CREATE_TRACE_POINTS
+#include "trace-events-emulation.h"
+
 /*
  * The runtime support for deprecated instruction support can be in one of
  * following three states -
@@ -358,6 +361,11 @@ static int swp_handler(struct pt_regs *regs, u32 instr)
 		regs->user_regs.regs[destreg] = data;
 
 ret:
+	if (type == TYPE_SWPB)
+		trace_instruction_emulation("swpb", regs->pc);
+	else
+		trace_instruction_emulation("swp", regs->pc);
+
 	pr_warn_ratelimited("\"%s\" (%ld) uses obsolete SWP{B} instruction at 0x%llx\n",
 			current->comm, (unsigned long)current->pid, regs->pc);
 
@@ -415,10 +423,15 @@ static int cp15barrier_handler(struct pt_regs *regs, u32 instr)
 		 * dmb - mcr p15, 0, Rt, c7, c10, 5
 		 * dsb - mcr p15, 0, Rt, c7, c10, 4
 		 */
-		if (aarch32_insn_mcr_extract_opc2(instr) == 5)
+		if (aarch32_insn_mcr_extract_opc2(instr) == 5) {
 			dmb(sy);
-		else
+			trace_instruction_emulation(
+				"mcr p15, 0, Rt, c7, c10, 5 ; dmb", regs->pc);
+		} else {
 			dsb(sy);
+			trace_instruction_emulation(
+				"mcr p15, 0, Rt, c7, c10, 4 ; dsb", regs->pc);
+		}
 		break;
 	case 5:
 		/*
@@ -427,6 +440,8 @@ static int cp15barrier_handler(struct pt_regs *regs, u32 instr)
 		 * Taking an exception or returning from one acts as an
 		 * instruction barrier. So no explicit barrier needed here.
 		 */
+		trace_instruction_emulation(
+			"mcr p15, 0, Rt, c7, c5, 4 ; isb", regs->pc);
 		break;
 	}
 

arch/arm64/kernel/trace-events-emulation.h

@@ -0,0 +1,35 @@
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM emulation
+
+#if !defined(_TRACE_EMULATION_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_EMULATION_H
+
+#include <linux/tracepoint.h>
+
+TRACE_EVENT(instruction_emulation,
+
+	TP_PROTO(const char *instr, u64 addr),
+	TP_ARGS(instr, addr),
+
+	TP_STRUCT__entry(
+		__string(instr, instr)
+		__field(u64, addr)
+	),
+
+	TP_fast_assign(
+		__assign_str(instr, instr);
+		__entry->addr = addr;
+	),
+
+	TP_printk("instr=\"%s\" addr=0x%llx", __get_str(instr), __entry->addr)
+);
+
+#endif /* _TRACE_EMULATION_H */
+
+/* This part must be outside protection */
+#undef TRACE_INCLUDE_PATH
+#undef TRACE_INCLUDE_FILE
+#define TRACE_INCLUDE_PATH .
+
+#define TRACE_INCLUDE_FILE trace-events-emulation
+#include <trace/define_trace.h>