linux/arch/riscv/kernel/ftrace.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2013 Linaro Limited
 * Author: AKASHI Takahiro <takahiro.akashi@linaro.org>
 * Copyright (C) 2017 Andes Technology Corporation
 */

#include <linux/ftrace.h>
#include <linux/uaccess.h>
#include <linux/memory.h>
#include <linux/irqflags.h>
#include <linux/stop_machine.h>
#include <asm/cacheflush.h>
#include <asm/text-patching.h>

#ifdef CONFIG_DYNAMIC_FTRACE
void ftrace_arch_code_modify_prepare(void)
	__acquires(&text_mutex)
{
	mutex_lock(&text_mutex);
}

void ftrace_arch_code_modify_post_process(void)
	__releases(&text_mutex)
{
	mutex_unlock(&text_mutex);
}

unsigned long ftrace_call_adjust(unsigned long addr)
{
	if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_CALL_OPS))
		return addr + 8 + MCOUNT_AUIPC_SIZE;

	return addr + MCOUNT_AUIPC_SIZE;
}

unsigned long arch_ftrace_get_symaddr(unsigned long fentry_ip)
{
	return fentry_ip - MCOUNT_AUIPC_SIZE;
}

void arch_ftrace_update_code(int command)
{
	command |= FTRACE_MAY_SLEEP;
	ftrace_modify_all_code(command);
	flush_icache_all();
}

static int __ftrace_modify_call(unsigned long source, unsigned long target, bool validate)
{
	unsigned int call[2], offset;
	unsigned int replaced[2];

	offset = target - source;
	call[1] = to_jalr_t0(offset);

	if (validate) {
		call[0] = to_auipc_t0(offset);
		/*
		 * Read the text we want to modify;
		 * return must be -EFAULT on read error
		 */
		if (copy_from_kernel_nofault(replaced, (void *)source, 2 * MCOUNT_INSN_SIZE))
			return -EFAULT;

		if (replaced[0] != call[0]) {
			pr_err("%p: expected (%08x) but got (%08x)\n",
			       (void *)source, call[0], replaced[0]);
			return -EINVAL;
		}
	}

	/* Replace the jalr at once. Return -EPERM on write error. */
	if (patch_insn_write((void *)(source + MCOUNT_AUIPC_SIZE), call + 1, MCOUNT_JALR_SIZE))
		return -EPERM;

	return 0;
}

#ifdef CONFIG_DYNAMIC_FTRACE_WITH_CALL_OPS
static const struct ftrace_ops *riscv64_rec_get_ops(struct dyn_ftrace *rec)
{
	const struct ftrace_ops *ops = NULL;

	if (rec->flags & FTRACE_FL_CALL_OPS_EN) {
		ops = ftrace_find_unique_ops(rec);
		WARN_ON_ONCE(!ops);
	}

	if (!ops)
		ops = &ftrace_list_ops;

	return ops;
}

static int ftrace_rec_set_ops(const struct dyn_ftrace *rec, const struct ftrace_ops *ops)
{
	unsigned long literal = ALIGN_DOWN(rec->ip - 12, 8);

	return patch_text_nosync((void *)literal, &ops, sizeof(ops));
}

static int ftrace_rec_set_nop_ops(struct dyn_ftrace *rec)
{
	return ftrace_rec_set_ops(rec, &ftrace_nop_ops);
}

static int ftrace_rec_update_ops(struct dyn_ftrace *rec)
{
	return ftrace_rec_set_ops(rec, riscv64_rec_get_ops(rec));
}
#else
static int ftrace_rec_set_nop_ops(struct dyn_ftrace *rec) { return 0; }
static int ftrace_rec_update_ops(struct dyn_ftrace *rec) { return 0; }
#endif

int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
{
	unsigned long distance, orig_addr, pc = rec->ip - MCOUNT_AUIPC_SIZE;
	int ret;

	ret = ftrace_rec_update_ops(rec);
	if (ret)
		return ret;

	orig_addr = (unsigned long)&ftrace_caller;
	distance = addr > orig_addr ? addr - orig_addr : orig_addr - addr;
	if (distance > JALR_RANGE)
		addr = FTRACE_ADDR;

	return __ftrace_modify_call(pc, addr, false);
}

int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, unsigned long addr)
{
	u32 nop4 = RISCV_INSN_NOP4;
	int ret;

	ret = ftrace_rec_set_nop_ops(rec);
	if (ret)
		return ret;

	if (patch_insn_write((void *)rec->ip, &nop4, MCOUNT_NOP4_SIZE))
		return -EPERM;

	return 0;
}

/*
 * This is called early on, and isn't wrapped by
 * ftrace_arch_code_modify_{prepare,post_process}() and therefore doesn't hold
 * text_mutex, which triggers a lockdep failure.  SMP isn't running so we could
 * just directly poke the text, but it's simpler to just take the lock
 * ourselves.
 */
int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
{
	unsigned long pc = rec->ip - MCOUNT_AUIPC_SIZE;
	unsigned int nops[2], offset;
	int ret;

	guard(mutex)(&text_mutex);

	ret = ftrace_rec_set_nop_ops(rec);
	if (ret)
		return ret;

	offset = (unsigned long) &ftrace_caller - pc;
	nops[0] = to_auipc_t0(offset);
	nops[1] = RISCV_INSN_NOP4;

	ret = patch_insn_write((void *)pc, nops, 2 * MCOUNT_INSN_SIZE);

	return ret;
}

ftrace_func_t ftrace_call_dest = ftrace_stub;
int ftrace_update_ftrace_func(ftrace_func_t func)
{
	/*
	 * When using CALL_OPS, the function to call is associated with the
	 * call site, and we don't have a global function pointer to update.
	 */
	if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_CALL_OPS))
		return 0;

	WRITE_ONCE(ftrace_call_dest, func);
	/*
	 * The data fence ensure that the update to ftrace_call_dest happens
	 * before the write to function_trace_op later in the generic ftrace.
	 * If the sequence is not enforced, then an old ftrace_call_dest may
	 * race loading a new function_trace_op set in ftrace_modify_all_code
	 */
	smp_wmb();
	/*
	 * Updating ftrace dpes not take stop_machine path, so irqs should not
	 * be disabled.
	 */
	WARN_ON(irqs_disabled());
	smp_call_function(ftrace_sync_ipi, NULL, 1);
	return 0;
}

#else /* CONFIG_DYNAMIC_FTRACE */
unsigned long ftrace_call_adjust(unsigned long addr)
{
	return addr;
}
#endif /* CONFIG_DYNAMIC_FTRACE */

#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
		       unsigned long addr)
{
	unsigned long caller = rec->ip - MCOUNT_AUIPC_SIZE;
	int ret;

	ret = ftrace_rec_update_ops(rec);
	if (ret)
		return ret;

	return __ftrace_modify_call(caller, FTRACE_ADDR, true);
}
#endif

#ifdef CONFIG_FUNCTION_GRAPH_TRACER
/*
 * Most of this function is copied from arm64.
 */
void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
			   unsigned long frame_pointer)
{
	unsigned long return_hooker = (unsigned long)&return_to_handler;
	unsigned long old;

	if (unlikely(atomic_read(&current->tracing_graph_pause)))
		return;

	/*
	 * We don't suffer access faults, so no extra fault-recovery assembly
	 * is needed here.
	 */
	old = *parent;

	if (!function_graph_enter(old, self_addr, frame_pointer, parent))
		*parent = return_hooker;
}

#ifdef CONFIG_DYNAMIC_FTRACE
void ftrace_graph_func(unsigned long ip, unsigned long parent_ip,
		       struct ftrace_ops *op, struct ftrace_regs *fregs)
{
	unsigned long return_hooker = (unsigned long)&return_to_handler;
	unsigned long frame_pointer = arch_ftrace_regs(fregs)->s0;
	unsigned long *parent = &arch_ftrace_regs(fregs)->ra;
	unsigned long old;

	if (unlikely(atomic_read(&current->tracing_graph_pause)))
		return;

	/*
	 * We don't suffer access faults, so no extra fault-recovery assembly
	 * is needed here.
	 */
	old = *parent;

	if (!function_graph_enter_regs(old, ip, frame_pointer, parent, fregs))
		*parent = return_hooker;
}
#endif /* CONFIG_DYNAMIC_FTRACE */
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */