csky: Add perf callchain support

obj-$(CONFIG_FUNCTION_TRACER)		+= ftrace.o

obj-$(CONFIG_STACKTRACE)		+= stacktrace.o

obj-$(CONFIG_CSKY_PMU_V1)		+= perf_event.o

obj-$(CONFIG_PERF_EVENTS)		+= perf_callchain.o

ifdef CONFIG_FUNCTION_TRACER

CFLAGS_REMOVE_ftrace.o = $(CC_FLAGS_FTRACE)

// 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 lr;

};

static int unwind_frame_kernel(struct stackframe *frame)

{

	if (kstack_end((void *)frame->fp))

		return -EPERM;

	if (frame->fp & 0x3 || frame->fp < TASK_SIZE)

		return -EPERM;

	*frame = *(struct stackframe *)frame->fp;

	if (__kernel_text_address(frame->lr)) {

		int graph = 0;

		frame->lr = ftrace_graph_ret_addr(NULL, &graph, frame->lr,

				NULL);

	}

	return 0;

}

static void notrace walk_stackframe(struct stackframe *fr,

			struct perf_callchain_entry_ctx *entry)

{

	do {

		perf_callchain_store(entry, fr->lr);

	} while (unwind_frame_kernel(fr) >= 0);

}

/*

 * 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_lr)

{

	struct stackframe buftail;

	unsigned long lr = 0;

	unsigned long *user_frame_tail = (unsigned long *)fp;

	/* 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_lr != 0)

		lr = reg_lr;

	else

		lr = buftail.lr;

	fp = buftail.fp;

	perf_callchain_store(entry, lr);

	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 C-SKY 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;

	/* C-SKY does not support virtualization. */

	if (perf_guest_cbs && perf_guest_cbs->is_in_guest())

		return;

	fp = regs->regs[4];

	perf_callchain_store(entry, regs->pc);

	/*

	 * While backtrace from leaf function, lr is normally

	 * not saved inside frame on C-SKY, so get lr from pt_regs

	 * at the sample point. However, lr value can be incorrect if

	 * lr is used as temp register

	 */

	fp = user_backtrace(entry, fp, regs->lr);

	while (fp && !(fp & 0x3) && entry->nr < entry->max_stack)

		fp = user_backtrace(entry, fp, 0);

}

void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,

			   struct pt_regs *regs)

{

	struct stackframe fr;

	/* C-SKY does not support virtualization. */

	if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) {

		pr_warn("C-SKY does not support perf in guest mode!");

		return;

	}

	fr.fp = regs->regs[4];

	fr.lr = regs->lr;

	walk_stackframe(&fr, entry);

}