[PATCHv4 5/5] arm64: Trace emulation of AArch32 legacy instructions

[Punit Agrawal]

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.

Cc: Steven Rostedt <rostedt at goodmis.org>
Signed-off-by: Punit Agrawal <punit.agrawal at arm.com>
---
 arch/arm64/kernel/Makefile                 |  1 +
 arch/arm64/kernel/armv8_deprecated.c       | 19 ++++++++++++--
 arch/arm64/kernel/trace-events-emulation.h | 40 ++++++++++++++++++++++++++++++
 3 files changed, 58 insertions(+), 2 deletions(-)
 create mode 100644 arch/arm64/kernel/trace-events-emulation.h

diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
index 84e9e51..b36ebd0 100644
--- a/arch/arm64/kernel/Makefile
+++ b/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
diff --git a/arch/arm64/kernel/armv8_deprecated.c b/arch/arm64/kernel/armv8_deprecated.c
index 248b222..62d0672 100644
--- a/arch/arm64/kernel/armv8_deprecated.c
+++ b/arch/arm64/kernel/armv8_deprecated.c
@@ -15,6 +15,9 @@
 #include <linux/slab.h>
 #include <linux/sysctl.h>
 
+#define CREATE_TRACE_POINTS
+#include "trace-events-emulation.h"
+
 #include <asm/insn.h>
 #include <asm/opcodes.h>
 #include <asm/system_misc.h>
@@ -203,6 +206,11 @@ 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);
 
@@ -260,10 +268,15 @@ 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:
 		/*
@@ -272,6 +285,8 @@ 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;
 	}
 
diff --git a/arch/arm64/kernel/trace-events-emulation.h b/arch/arm64/kernel/trace-events-emulation.h
new file mode 100644
index 0000000..2ba3882
--- /dev/null
+++ b/arch/arm64/kernel/trace-events-emulation.h
@@ -0,0 +1,40 @@
+#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(
+		__array(char, comm, TASK_COMM_LEN)
+		__field(pid_t, pid)
+		__string(instr, instr)
+		__field(u64, addr)
+	),
+
+	TP_fast_assign(
+		memcpy(__entry->comm, current->comm, TASK_COMM_LEN);
+		__entry->pid = current->pid;
+		__assign_str(instr, instr);
+		__entry->addr = addr;
+	),
+
+	TP_printk("instr=\"%s\" comm=%s pid=%d addr=0x%llx", __get_str(instr),
+		__entry->comm, __entry->pid, __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>
-- 
2.1.1