MIPS: Perf-events: Add callchain support

Adds callchain support for MIPS Perf-events. For more info on this feature,
please refer to tools/perf/Documentation/perf-report.txt and
tools/perf/design.txt.

Currently userspace callchain data is not recorded, because we do not have
a safe way to do this.

Signed-off-by: Deng-Cheng Zhu <dengcheng.zhu@gmail.com>
Acked-by: David Daney <ddaney@caviumnetworks.com>
To: linux-mips@linux-mips.org
Cc: a.p.zijlstra@chello.nl
Cc: paulus@samba.org
Cc: mingo@elte.hu
Cc: acme@redhat.com
Cc: jamie.iles@picochip.com
Cc: matt@console-pimps.org
Patchwork: https://patchwork.linux-mips.org/patch/1690/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/kernel/perf_event.c

@@ -6,7 +6,8 @@
  *
  * This code is based on the implementation for ARM, which is in turn
  * based on the sparc64 perf event code and the x86 code. Performance
- * counter access is based on the MIPS Oprofile code.
+ * counter access is based on the MIPS Oprofile code. And the callchain
+ * support references the code of MIPS stacktrace.c.
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2 as
@@ -486,3 +487,108 @@ handle_associated_event(struct cpu_hw_events *cpuc,
 	if (perf_event_overflow(event, 0, data, regs))
 		mipspmu->disable_event(idx);
 }
+
+/* Callchain handling code. */
+static inline void
+callchain_store(struct perf_callchain_entry *entry,
+		u64 ip)
+{
+	if (entry->nr < PERF_MAX_STACK_DEPTH)
+		entry->ip[entry->nr++] = ip;
+}
+
+/*
+ * Leave userspace callchain empty for now. When we find a way to trace
+ * the user stack callchains, we add here.
+ */
+static void
+perf_callchain_user(struct pt_regs *regs,
+		    struct perf_callchain_entry *entry)
+{
+}
+
+static void save_raw_perf_callchain(struct perf_callchain_entry *entry,
+	unsigned long reg29)
+{
+	unsigned long *sp = (unsigned long *)reg29;
+	unsigned long addr;
+
+	while (!kstack_end(sp)) {
+		addr = *sp++;
+		if (__kernel_text_address(addr)) {
+			callchain_store(entry, addr);
+			if (entry->nr >= PERF_MAX_STACK_DEPTH)
+				break;
+		}
+	}
+}
+
+static void
+perf_callchain_kernel(struct pt_regs *regs,
+		      struct perf_callchain_entry *entry)
+{
+	unsigned long sp = regs->regs[29];
+#ifdef CONFIG_KALLSYMS
+	unsigned long ra = regs->regs[31];
+	unsigned long pc = regs->cp0_epc;
+
+	callchain_store(entry, PERF_CONTEXT_KERNEL);
+	if (raw_show_trace || !__kernel_text_address(pc)) {
+		unsigned long stack_page =
+			(unsigned long)task_stack_page(current);
+		if (stack_page && sp >= stack_page &&
+		    sp <= stack_page + THREAD_SIZE - 32)
+			save_raw_perf_callchain(entry, sp);
+		return;
+	}
+	do {
+		callchain_store(entry, pc);
+		if (entry->nr >= PERF_MAX_STACK_DEPTH)
+			break;
+		pc = unwind_stack(current, &sp, pc, &ra);
+	} while (pc);
+#else
+	callchain_store(entry, PERF_CONTEXT_KERNEL);
+	save_raw_perf_callchain(entry, sp);
+#endif
+}
+
+static void
+perf_do_callchain(struct pt_regs *regs,
+		  struct perf_callchain_entry *entry)
+{
+	int is_user;
+
+	if (!regs)
+		return;
+
+	is_user = user_mode(regs);
+
+	if (!current || !current->pid)
+		return;
+
+	if (is_user && current->state != TASK_RUNNING)
+		return;
+
+	if (!is_user) {
+		perf_callchain_kernel(regs, entry);
+		if (current->mm)
+			regs = task_pt_regs(current);
+		else
+			regs = NULL;
+	}
+	if (regs)
+		perf_callchain_user(regs, entry);
+}
+
+static DEFINE_PER_CPU(struct perf_callchain_entry, pmc_irq_entry);
+
+struct perf_callchain_entry *
+perf_callchain(struct pt_regs *regs)
+{
+	struct perf_callchain_entry *entry = &__get_cpu_var(pmc_irq_entry);
+
+	entry->nr = 0;
+	perf_do_callchain(regs, entry);
+	return entry;
+}