ARM: perf: add support for perf registers API

This patch implements the functions required for the perf registers API,
allowing the perf tool to interface kernel register dumps with libunwind
in order to provide userspace backtracing.

Cc: Jean Pihet <jean.pihet@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm/Kconfig

@@ -51,6 +51,8 @@ config ARM
 	select HAVE_MOD_ARCH_SPECIFIC if ARM_UNWIND
 	select HAVE_OPROFILE if (HAVE_PERF_EVENTS)
 	select HAVE_PERF_EVENTS
+	select HAVE_PERF_REGS
+	select HAVE_PERF_USER_STACK_DUMP
 	select HAVE_REGS_AND_STACK_ACCESS_API
 	select HAVE_SYSCALL_TRACEPOINTS
 	select HAVE_UID16

arch/arm/include/uapi/asm/Kbuild

@@ -7,6 +7,7 @@ header-y += hwcap.h
 header-y += ioctls.h
 header-y += kvm_para.h
 header-y += mman.h
+header-y += perf_regs.h
 header-y += posix_types.h
 header-y += ptrace.h
 header-y += setup.h

arch/arm/include/uapi/asm/perf_regs.h

@@ -0,0 +1,23 @@
+#ifndef _ASM_ARM_PERF_REGS_H
+#define _ASM_ARM_PERF_REGS_H
+
+enum perf_event_arm_regs {
+	PERF_REG_ARM_R0,
+	PERF_REG_ARM_R1,
+	PERF_REG_ARM_R2,
+	PERF_REG_ARM_R3,
+	PERF_REG_ARM_R4,
+	PERF_REG_ARM_R5,
+	PERF_REG_ARM_R6,
+	PERF_REG_ARM_R7,
+	PERF_REG_ARM_R8,
+	PERF_REG_ARM_R9,
+	PERF_REG_ARM_R10,
+	PERF_REG_ARM_FP,
+	PERF_REG_ARM_IP,
+	PERF_REG_ARM_SP,
+	PERF_REG_ARM_LR,
+	PERF_REG_ARM_PC,
+	PERF_REG_ARM_MAX,
+};
+#endif /* _ASM_ARM_PERF_REGS_H */

arch/arm/kernel/Makefile

@@ -78,6 +78,7 @@ obj-$(CONFIG_CPU_XSC3)		+= xscale-cp0.o
 obj-$(CONFIG_CPU_MOHAWK)	+= xscale-cp0.o
 obj-$(CONFIG_CPU_PJ4)		+= pj4-cp0.o
 obj-$(CONFIG_IWMMXT)		+= iwmmxt.o
+obj-$(CONFIG_PERF_EVENTS)	+= perf_regs.o
 obj-$(CONFIG_HW_PERF_EVENTS)	+= perf_event.o perf_event_cpu.o
 AFLAGS_iwmmxt.o			:= -Wa,-mcpu=iwmmxt
 obj-$(CONFIG_ARM_CPU_TOPOLOGY)  += topology.o

arch/arm/kernel/perf_regs.c

@@ -0,0 +1,30 @@
+
+#include <linux/errno.h>
+#include <linux/kernel.h>
+#include <linux/perf_event.h>
+#include <linux/bug.h>
+#include <asm/perf_regs.h>
+#include <asm/ptrace.h>
+
+u64 perf_reg_value(struct pt_regs *regs, int idx)
+{
+	if (WARN_ON_ONCE((u32)idx >= PERF_REG_ARM_MAX))
+		return 0;
+
+	return regs->uregs[idx];
+}
+
+#define REG_RESERVED (~((1ULL << PERF_REG_ARM_MAX) - 1))
+
+int perf_reg_validate(u64 mask)
+{
+	if (!mask || mask & REG_RESERVED)
+		return -EINVAL;
+
+	return 0;
+}
+
+u64 perf_reg_abi(struct task_struct *task)
+{
+	return PERF_SAMPLE_REGS_ABI_32;
+}