MIPS: kernel: Support extracting off-line stack traces from user-space with perf

Add perf_event_mips_regs/perf_reg_value/perf_reg_validate to support
features HAVE_PERF_REGS/HAVE_PERF_USER_STACK_DUMP in kernel.

[[e-mail]: Repick this patch for unwinding userstack backtrace
by perf and libunwind on MIPS based CPU.]

[[e-mail]: Add perf_get_regs_user() which is required after
'commit 88a7c26af8da ("perf: Move task_pt_regs sampling into arch code")'.]

[[e-mail]: Fix build error about perf_get_regs_user() after
commit 76a4efa80900 ("perf/arch: Remove perf_sample_data::regs_user_copy"),
and also separate the original patches into two parts (MIPS kernel and perf
tools) to merge easily.]

The original patches:
https://lore.kernel.org/patchwork/patch/1126521/
https://lore.kernel.org/patchwork/patch/1126520/

Signed-off-by: David Daney <[e-mail]>
Signed-off-by: Ralf Baechle <[e-mail]>
Signed-off-by: Archer Yan <[e-mail]>
Signed-off-by: Tiezhu Yang <[e-mail]>
Signed-off-by: Thomas Bogendoerfer <[e-mail]>

arch/mips/Kconfig

···
 	select HAVE_NMI
 	select HAVE_OPROFILE
 	select HAVE_PERF_EVENTS
+	select HAVE_PERF_REGS
+	select HAVE_PERF_USER_STACK_DUMP
 	select HAVE_REGS_AND_STACK_ACCESS_API
 	select HAVE_RSEQ
 	select HAVE_SPARSE_SYSCALL_NR

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

···
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef _ASM_MIPS_PERF_REGS_H
+#define _ASM_MIPS_PERF_REGS_H
+
+enum perf_event_mips_regs {
+	PERF_REG_MIPS_PC,
+	PERF_REG_MIPS_R1,
+	PERF_REG_MIPS_R2,
+	PERF_REG_MIPS_R3,
+	PERF_REG_MIPS_R4,
+	PERF_REG_MIPS_R5,
+	PERF_REG_MIPS_R6,
+	PERF_REG_MIPS_R7,
+	PERF_REG_MIPS_R8,
+	PERF_REG_MIPS_R9,
+	PERF_REG_MIPS_R10,
+	PERF_REG_MIPS_R11,
+	PERF_REG_MIPS_R12,
+	PERF_REG_MIPS_R13,
+	PERF_REG_MIPS_R14,
+	PERF_REG_MIPS_R15,
+	PERF_REG_MIPS_R16,
+	PERF_REG_MIPS_R17,
+	PERF_REG_MIPS_R18,
+	PERF_REG_MIPS_R19,
+	PERF_REG_MIPS_R20,
+	PERF_REG_MIPS_R21,
+	PERF_REG_MIPS_R22,
+	PERF_REG_MIPS_R23,
+	PERF_REG_MIPS_R24,
+	PERF_REG_MIPS_R25,
+	PERF_REG_MIPS_R26,
+	PERF_REG_MIPS_R27,
+	PERF_REG_MIPS_R28,
+	PERF_REG_MIPS_R29,
+	PERF_REG_MIPS_R30,
+	PERF_REG_MIPS_R31,
+	PERF_REG_MIPS_MAX = PERF_REG_MIPS_R31 + 1,
+};
+#endif /* _ASM_MIPS_PERF_REGS_H */

arch/mips/kernel/Makefile

···
 
 CFLAGS_cpu-bugs64.o	= $(shell if $(CC) $(KBUILD_CFLAGS) -Wa,-mdaddi -c -o /dev/null -x c /dev/null >/dev/null 2>&1; then echo "-DHAVE_AS_SET_DADDI"; fi)
 
-obj-$(CONFIG_PERF_EVENTS)	+= perf_event.o
+obj-$(CONFIG_PERF_EVENTS)	+= perf_event.o perf_regs.o
 obj-$(CONFIG_HW_PERF_EVENTS)	+= perf_event_mipsxx.o
 
 obj-$(CONFIG_JUMP_LABEL)	+= jump_label.o

arch/mips/kernel/perf_regs.c

···
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ *
+ * Some parts derived from x86 version of this file.
+ *
+ * Copyright (C) 2013 Cavium, Inc.
+ */
+
+#include <linux/perf_event.h>
+
+#include <asm/ptrace.h>
+
+#ifdef CONFIG_32BIT
+u64 perf_reg_abi(struct task_struct *tsk)
+{
+	return PERF_SAMPLE_REGS_ABI_32;
+}
+#else /* Must be CONFIG_64BIT */
+u64 perf_reg_abi(struct task_struct *tsk)
+{
+	if (test_tsk_thread_flag(tsk, TIF_32BIT_REGS))
+		return PERF_SAMPLE_REGS_ABI_32;
+	else
+		return PERF_SAMPLE_REGS_ABI_64;
+}
+#endif /* CONFIG_32BIT */
+
+int perf_reg_validate(u64 mask)
+{
+	if (!mask)
+		return -EINVAL;
+	if (mask & ~((1ull << PERF_REG_MIPS_MAX) - 1))
+		return -EINVAL;
+	return 0;
+}
+
+u64 perf_reg_value(struct pt_regs *regs, int idx)
+{
+	long v;
+
+	switch (idx) {
+	case PERF_REG_MIPS_PC:
+		v = regs->cp0_epc;
+		break;
+	case PERF_REG_MIPS_R1 ... PERF_REG_MIPS_R25:
+		v = regs->regs[idx - PERF_REG_MIPS_R1 + 1];
+		break;
+	case PERF_REG_MIPS_R28 ... PERF_REG_MIPS_R31:
+		v = regs->regs[idx - PERF_REG_MIPS_R28 + 28];
+		break;
+
+	default:
+		WARN_ON_ONCE(1);
+		return 0;
+	}
+
+	return (s64)v; /* Sign extend if 32-bit. */
+}
+
+void perf_get_regs_user(struct perf_regs *regs_user,
+			struct pt_regs *regs)
+{
+	regs_user->regs = task_pt_regs(current);
+	regs_user->abi = perf_reg_abi(current);
+}