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From:   Mao Han <han_mao@c-sky.com>
To:     linux-kernel@vger.kernel.org
Cc:     Mao Han <han_mao@c-sky.com>, Palmer Dabbelt <palmer@sifive.com>
Subject: [PATCH 1/3] riscv: Add perf callchain support
Date:   Thu, 11 Apr 2019 15:53:48 +0800
Message-Id: <195185ea63240ed396026505d96d1f6449963482.1554961908.git.han_mao@c-sky.com>
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In-Reply-To: <cover.1554961908.git.han_mao@c-sky.com>
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This patch add support for perf callchain sampling on riscv platform.
The return address of leaf function is retrieved from pt_regs as
it is not saved in the outmost frame.

Signed-off-by: Mao Han <han_mao@c-sky.com>

CC: Palmer Dabbelt <palmer@sifive.com>
---
 arch/riscv/kernel/Makefile         |   3 +-
 arch/riscv/kernel/perf_callchain.c | 122 +++++++++++++++++++++++++++++++++++++
 2 files changed, 124 insertions(+), 1 deletion(-)
 create mode 100644 arch/riscv/kernel/perf_callchain.c

diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
index 5985681..dd2ba44 100644
--- a/arch/riscv/kernel/Makefile
+++ b/arch/riscv/kernel/Makefile
@@ -37,6 +37,7 @@ obj-$(CONFIG_MODULE_SECTIONS)	+= module-sections.o
 obj-$(CONFIG_FUNCTION_TRACER)	+= mcount.o ftrace.o
 obj-$(CONFIG_DYNAMIC_FTRACE)	+= mcount-dyn.o
 
-obj-$(CONFIG_PERF_EVENTS)      += perf_event.o
+obj-$(CONFIG_PERF_EVENTS)	+= perf_event.o
+obj-$(CONFIG_PERF_EVENTS)	+= perf_callchain.o
 
 clean:
diff --git a/arch/riscv/kernel/perf_callchain.c b/arch/riscv/kernel/perf_callchain.c
new file mode 100644
index 0000000..eb3ddbb
--- /dev/null
+++ b/arch/riscv/kernel/perf_callchain.c
@@ -0,0 +1,122 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (C) 2019 Hangzhou C-SKY Microsystems co.,ltd.
+
+#include <linux/perf_event.h>
+#include <linux/uaccess.h>
+
+/* Kernel callchain */
+struct stackframe {
+	unsigned long fp;
+	unsigned long ra;
+};
+
+static int unwind_frame_kernel(struct stackframe *frame)
+{
+	int graph = 0;
+
+	/* 0x3 means misalignment */
+	if (!kstack_end((void *)frame->fp) &&
+	    !((unsigned long)frame->fp & 0x3) &&
+	    ((unsigned long)frame->fp >= TASK_SIZE)) {
+		frame->ra = ((struct stackframe *)frame->fp - 1)->ra;
+		frame->fp = ((struct stackframe *)frame->fp - 1)->fp;
+		/* make sure CONFIG_FUNCTION_GRAPH_TRACER is turned on */
+		if (__kernel_text_address(frame->ra))
+			frame->ra = ftrace_graph_ret_addr(NULL, &graph,
+							frame->ra, NULL);
+		return 0;
+	} else {
+		return -EPERM;
+	}
+}
+
+static void notrace walk_stackframe(struct stackframe *fr,
+			struct perf_callchain_entry_ctx *entry)
+{
+	while (1) {
+		int ret;
+
+		perf_callchain_store(entry, fr->ra);
+
+		ret = unwind_frame_kernel(fr);
+		if (ret < 0)
+			break;
+	}
+}
+
+/*
+ * Get the return address for a single stackframe and return a pointer to the
+ * next frame tail.
+ */
+static unsigned long user_backtrace(struct perf_callchain_entry_ctx *entry,
+			unsigned long fp, unsigned long reg_ra)
+{
+	struct stackframe buftail;
+	unsigned long ra = 0;
+	unsigned long *user_frame_tail = (unsigned long *)(fp - sizeof(struct stackframe));
+
+	/* Check accessibility of one struct frame_tail beyond */
+	if (!access_ok(user_frame_tail, sizeof(buftail)))
+		return 0;
+	if (__copy_from_user_inatomic(&buftail, user_frame_tail,
+				      sizeof(buftail)))
+		return 0;
+
+	if (reg_ra != 0)
+		ra = reg_ra;
+	else
+		ra = buftail.ra;
+
+	fp = buftail.fp;
+	perf_callchain_store(entry, ra);
+
+	return fp;
+}
+
+/*
+ * This will be called when the target is in user mode
+ * This function will only be called when we use
+ * "PERF_SAMPLE_CALLCHAIN" in
+ * kernel/events/core.c:perf_prepare_sample()
+ *
+ * How to trigger perf_callchain_[user/kernel] :
+ * $ perf record -e cpu-clock --call-graph fp ./program
+ * $ perf report --call-graph
+ *
+ * On RISC-V platform, the program being sampled and the C library
+ * need to be compiled with * -mbacktrace, otherwise the user
+ * stack will not contain function frame.
+ */
+void perf_callchain_user(struct perf_callchain_entry_ctx *entry,
+			 struct pt_regs *regs)
+{
+	unsigned long fp = 0;
+
+	/* RISC-V does not support virtualization. */
+	if (perf_guest_cbs && perf_guest_cbs->is_in_guest())
+		return;
+
+	fp = regs->s0;
+	perf_callchain_store(entry, regs->sepc);
+
+	fp = user_backtrace(entry, fp, regs->ra);
+	while ((entry->nr < entry->max_stack) &&
+		fp && !((unsigned long)fp & 0x3))
+		fp = user_backtrace(entry, fp, 0);
+}
+
+void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
+			   struct pt_regs *regs)
+{
+	struct stackframe fr;
+
+	/* RISC-V does not support virtualization. */
+	if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) {
+		pr_warn("RISC-V does not support perf in guest mode!");
+		return;
+	}
+
+	fr.fp = regs->s0;
+	fr.ra = regs->ra;
+	walk_stackframe(&fr, entry);
+}
-- 
2.7.4