// SPDX-License-Identifier: GPL-2.0
/*
 * Based on arch/arm64/kernel/ftrace.c
 *
 * Copyright (C) 2022 Loongson Technology Corporation Limited
 */

#include <linux/ftrace.h>
#include <linux/kprobes.h>
#include <linux/uaccess.h>

#include <asm/inst.h>
#include <asm/module.h>

static int ftrace_modify_code(unsigned long pc, u32 old, u32 new, bool validate)
{
        u32 replaced;

        if (validate) {
                if (larch_insn_read((void *)pc, &replaced))
                        return -EFAULT;

                if (replaced != old)
                        return -EINVAL;
        }

        if (larch_insn_patch_text((void *)pc, new))
                return -EPERM;

        return 0;
}

#ifdef CONFIG_MODULES
static bool reachable_by_bl(unsigned long addr, unsigned long pc)
{
        long offset = (long)addr - (long)pc;

        return offset >= -SZ_128M && offset < SZ_128M;
}

static struct plt_entry *get_ftrace_plt(struct module *mod, unsigned long addr)
{
        struct plt_entry *plt = mod->arch.ftrace_trampolines;

        if (addr == FTRACE_ADDR)
                return &plt[FTRACE_PLT_IDX];
        if (addr == FTRACE_REGS_ADDR &&
                        IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_REGS))
                return &plt[FTRACE_REGS_PLT_IDX];

        return NULL;
}

/*
 * Find the address the callsite must branch to in order to reach '*addr'.
 *
 * Due to the limited range of 'bl' instruction, modules may be placed too far
 * away to branch directly and we must use a PLT.
 *
 * Returns true when '*addr' contains a reachable target address, or has been
 * modified to contain a PLT address. Returns false otherwise.
 */
static bool ftrace_find_callable_addr(struct dyn_ftrace *rec, struct module *mod, unsigned long *addr)
{
        unsigned long pc = rec->ip + LOONGARCH_INSN_SIZE;
        struct plt_entry *plt;

        /*
         * If a custom trampoline is unreachable, rely on the ftrace_regs_caller
         * trampoline which knows how to indirectly reach that trampoline through
         * ops->direct_call.
         */
        if (*addr != FTRACE_ADDR && *addr != FTRACE_REGS_ADDR && !reachable_by_bl(*addr, pc))
                *addr = FTRACE_REGS_ADDR;

        /*
         * When the target is within range of the 'bl' instruction, use 'addr'
         * as-is and branch to that directly.
         */
        if (reachable_by_bl(*addr, pc))
                return true;

        /*
         * 'mod' is only set at module load time, but if we end up
         * dealing with an out-of-range condition, we can assume it
         * is due to a module being loaded far away from the kernel.
         *
         * NOTE: __module_text_address() must be called within a RCU read
         * section, but we can rely on ftrace_lock to ensure that 'mod'
         * retains its validity throughout the remainder of this code.
         */
        if (!mod) {
                scoped_guard(rcu)
                        mod = __module_text_address(pc);
        }

        if (WARN_ON(!mod))
                return false;

        plt = get_ftrace_plt(mod, *addr);
        if (!plt) {
                pr_err("ftrace: no module PLT for %ps\n", (void *)*addr);
                return false;
        }

        *addr = (unsigned long)plt;
        return true;
}
#else /* !CONFIG_MODULES */
static bool ftrace_find_callable_addr(struct dyn_ftrace *rec, struct module *mod, unsigned long *addr)
{
        return true;
}
#endif

#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr, unsigned long addr)
{
        u32 old, new;
        unsigned long pc;

        pc = rec->ip + LOONGARCH_INSN_SIZE;

        if (!ftrace_find_callable_addr(rec, NULL, &addr))
                return -EINVAL;

        if (!ftrace_find_callable_addr(rec, NULL, &old_addr))
                return -EINVAL;

        new = larch_insn_gen_bl(pc, addr);
        old = larch_insn_gen_bl(pc, old_addr);

        return ftrace_modify_code(pc, old, new, true);
}
#endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */

int ftrace_update_ftrace_func(ftrace_func_t func)
{
        u32 new;
        unsigned long pc;

        pc = (unsigned long)&ftrace_call;
        new = larch_insn_gen_bl(pc, (unsigned long)func);

        return ftrace_modify_code(pc, 0, new, false);
}

/*
 * The compiler has inserted 2 NOPs before the regular function prologue.
 * T series registers are available and safe because of LoongArch's psABI.
 *
 * At runtime, we can replace nop with bl to enable ftrace call and replace bl
 * with nop to disable ftrace call. The bl requires us to save the original RA
 * value, so it saves RA at t0 here.
 *
 * Details are:
 *
 * | Compiled   |       Disabled         |        Enabled         |
 * +------------+------------------------+------------------------+
 * | nop        | move     t0, ra        | move     t0, ra        |
 * | nop        | nop                    | bl       ftrace_caller |
 * | func_body  | func_body              | func_body              |
 *
 * The RA value will be recovered by ftrace_regs_entry, and restored into RA
 * before returning to the regular function prologue. When a function is not
 * being traced, the "move t0, ra" is not harmful.
 */

int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
{
        u32 old, new;
        unsigned long pc;

        pc = rec->ip;
        old = larch_insn_gen_nop();
        new = larch_insn_gen_move(LOONGARCH_GPR_T0, LOONGARCH_GPR_RA);

        return ftrace_modify_code(pc, old, new, true);
}

int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
{
        u32 old, new;
        unsigned long pc;

        pc = rec->ip + LOONGARCH_INSN_SIZE;

        if (!ftrace_find_callable_addr(rec, NULL, &addr))
                return -EINVAL;

        old = larch_insn_gen_nop();
        new = larch_insn_gen_bl(pc, addr);

        return ftrace_modify_code(pc, old, new, true);
}

int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, unsigned long addr)
{
        u32 old, new;
        unsigned long pc;

        pc = rec->ip + LOONGARCH_INSN_SIZE;

        if (!ftrace_find_callable_addr(rec, NULL, &addr))
                return -EINVAL;

        new = larch_insn_gen_nop();
        old = larch_insn_gen_bl(pc, addr);

        return ftrace_modify_code(pc, old, new, true);
}

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

int __init ftrace_dyn_arch_init(void)
{
        return 0;
}

#ifdef CONFIG_FUNCTION_GRAPH_TRACER
void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent)
{
        unsigned long old;
        unsigned long return_hooker = (unsigned long)&return_to_handler;

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

        old = *parent;

        if (!function_graph_enter(old, self_addr, 0, parent))
                *parent = return_hooker;
}

#ifdef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS
void ftrace_graph_func(unsigned long ip, unsigned long parent_ip,
                       struct ftrace_ops *op, struct ftrace_regs *fregs)
{
        struct pt_regs *regs = &arch_ftrace_regs(fregs)->regs;
        unsigned long *parent = (unsigned long *)&regs->regs[1];
        unsigned long return_hooker = (unsigned long)&return_to_handler;
        unsigned long old;

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

        old = *parent;

        if (!function_graph_enter_regs(old, ip, 0, parent, fregs))
                *parent = return_hooker;
}
#else
static int ftrace_modify_graph_caller(bool enable)
{
        u32 branch, nop;
        unsigned long pc, func;
        extern void ftrace_graph_call(void);

        pc = (unsigned long)&ftrace_graph_call;
        func = (unsigned long)&ftrace_graph_caller;

        nop = larch_insn_gen_nop();
        branch = larch_insn_gen_b(pc, func);

        if (enable)
                return ftrace_modify_code(pc, nop, branch, true);
        else
                return ftrace_modify_code(pc, branch, nop, true);
}

int ftrace_enable_ftrace_graph_caller(void)
{
        return ftrace_modify_graph_caller(true);
}

int ftrace_disable_ftrace_graph_caller(void)
{
        return ftrace_modify_graph_caller(false);
}
#endif /* CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS */
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */

#ifdef CONFIG_KPROBES_ON_FTRACE
/* Ftrace callback handler for kprobes -- called under preepmt disabled */
void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
                           struct ftrace_ops *ops, struct ftrace_regs *fregs)
{
        int bit;
        struct pt_regs *regs;
        struct kprobe *p;
        struct kprobe_ctlblk *kcb;

        if (unlikely(kprobe_ftrace_disabled))
                return;

        bit = ftrace_test_recursion_trylock(ip, parent_ip);
        if (bit < 0)
                return;

        p = get_kprobe((kprobe_opcode_t *)ip);
        if (unlikely(!p) || kprobe_disabled(p))
                goto out;

        regs = ftrace_get_regs(fregs);
        if (!regs)
                goto out;

        kcb = get_kprobe_ctlblk();
        if (kprobe_running()) {
                kprobes_inc_nmissed_count(p);
        } else {
                unsigned long orig_ip = instruction_pointer(regs);

                instruction_pointer_set(regs, ip);

                __this_cpu_write(current_kprobe, p);
                kcb->kprobe_status = KPROBE_HIT_ACTIVE;
                if (!p->pre_handler || !p->pre_handler(p, regs)) {
                        /*
                         * Emulate singlestep (and also recover regs->csr_era)
                         * as if there is a nop
                         */
                        instruction_pointer_set(regs, (unsigned long)p->addr + MCOUNT_INSN_SIZE);
                        if (unlikely(p->post_handler)) {
                                kcb->kprobe_status = KPROBE_HIT_SSDONE;
                                p->post_handler(p, regs, 0);
                        }
                        instruction_pointer_set(regs, orig_ip);
                }

                /*
                 * If pre_handler returns !0, it changes regs->csr_era. We have to
                 * skip emulating post_handler.
                 */
                __this_cpu_write(current_kprobe, NULL);
        }
out:
        ftrace_test_recursion_unlock(bit);
}
NOKPROBE_SYMBOL(kprobe_ftrace_handler);

int arch_prepare_kprobe_ftrace(struct kprobe *p)
{
        p->ainsn.insn = NULL;
        return 0;
}
#endif /* CONFIG_KPROBES_ON_FTRACE */