// SPDX-License-Identifier: GPL-2.0
/*
 * Dynamic function tracer architecture backend.
 *
 * Copyright IBM Corp. 2009,2014
 *
 *   Author(s): Heiko Carstens <heiko.carstens@de.ibm.com>,
 *              Martin Schwidefsky <schwidefsky@de.ibm.com>
 */

#include <linux/moduleloader.h>
#include <linux/hardirq.h>
#include <linux/uaccess.h>
#include <linux/ftrace.h>
#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/kprobes.h>
#include <trace/syscall.h>
#include <asm/asm-offsets.h>
#include <asm/cacheflush.h>
#include <asm/set_memory.h>
#include "entry.h"

/*
 * To generate function prologue either gcc's hotpatch feature (since gcc 4.8)
 * or a combination of -pg -mrecord-mcount -mnop-mcount -mfentry flags
 * (since gcc 9 / clang 10) is used.
 * In both cases the original and also the disabled function prologue contains
 * only a single six byte instruction and looks like this:
 * >    brcl    0,0                     # offset 0
 * To enable ftrace the code gets patched like above and afterwards looks
 * like this:
 * >    brasl   %r0,ftrace_caller       # offset 0
 *
 * The instruction will be patched by ftrace_make_call / ftrace_make_nop.
 * The ftrace function gets called with a non-standard C function call ABI
 * where r0 contains the return address. It is also expected that the called
 * function only clobbers r0 and r1, but restores r2-r15.
 * For module code we can't directly jump to ftrace caller, but need a
 * trampoline (ftrace_plt), which clobbers also r1.
 */

void *ftrace_func __read_mostly = ftrace_stub;
unsigned long ftrace_plt;

int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
                       unsigned long addr)
{
        return 0;
}

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

        if (copy_from_kernel_nofault(&old, (void *) rec->ip, sizeof(old)))
                return -EFAULT;
        /* Replace ftrace call with a nop. */
        ftrace_generate_call_insn(&orig, rec->ip);
        ftrace_generate_nop_insn(&new);

        /* Verify that the to be replaced code matches what we expect. */
        if (memcmp(&orig, &old, sizeof(old)))
                return -EINVAL;
        s390_kernel_write((void *) rec->ip, &new, sizeof(new));
        return 0;
}

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

        if (copy_from_kernel_nofault(&old, (void *) rec->ip, sizeof(old)))
                return -EFAULT;
        /* Replace nop with an ftrace call. */
        ftrace_generate_nop_insn(&orig);
        ftrace_generate_call_insn(&new, rec->ip);

        /* Verify that the to be replaced code matches what we expect. */
        if (memcmp(&orig, &old, sizeof(old)))
                return -EINVAL;
        s390_kernel_write((void *) rec->ip, &new, sizeof(new));
        return 0;
}

int ftrace_update_ftrace_func(ftrace_func_t func)
{
        ftrace_func = func;
        return 0;
}

int __init ftrace_dyn_arch_init(void)
{
        return 0;
}

#ifdef CONFIG_MODULES

static int __init ftrace_plt_init(void)
{
        unsigned int *ip;

        ftrace_plt = (unsigned long) module_alloc(PAGE_SIZE);
        if (!ftrace_plt)
                panic("cannot allocate ftrace plt\n");
        ip = (unsigned int *) ftrace_plt;
        ip[0] = 0x0d10e310; /* basr 1,0; lg 1,10(1); br 1 */
        ip[1] = 0x100a0004;
        ip[2] = 0x07f10000;
        ip[3] = FTRACE_ADDR >> 32;
        ip[4] = FTRACE_ADDR & 0xffffffff;
        set_memory_ro(ftrace_plt, 1);
        return 0;
}
device_initcall(ftrace_plt_init);

#endif /* CONFIG_MODULES */

#ifdef CONFIG_FUNCTION_GRAPH_TRACER
/*
 * Hook the return address and push it in the stack of return addresses
 * in current thread info.
 */
unsigned long prepare_ftrace_return(unsigned long ra, unsigned long sp,
                                    unsigned long ip)
{
        if (unlikely(ftrace_graph_is_dead()))
                goto out;
        if (unlikely(atomic_read(&current->tracing_graph_pause)))
                goto out;
        ip -= MCOUNT_INSN_SIZE;
        if (!function_graph_enter(ra, ip, 0, (void *) sp))
                ra = (unsigned long) return_to_handler;
out:
        return ra;
}
NOKPROBE_SYMBOL(prepare_ftrace_return);

/*
 * Patch the kernel code at ftrace_graph_caller location. The instruction
 * there is branch relative on condition. To enable the ftrace graph code
 * block, we simply patch the mask field of the instruction to zero and
 * turn the instruction into a nop.
 * To disable the ftrace graph code the mask field will be patched to
 * all ones, which turns the instruction into an unconditional branch.
 */
int ftrace_enable_ftrace_graph_caller(void)
{
        u8 op = 0x04; /* set mask field to zero */

        s390_kernel_write(__va(ftrace_graph_caller)+1, &op, sizeof(op));
        return 0;
}

int ftrace_disable_ftrace_graph_caller(void)
{
        u8 op = 0xf4; /* set mask field to all ones */

        s390_kernel_write(__va(ftrace_graph_caller)+1, &op, sizeof(op));
        return 0;
}

#endif /* CONFIG_FUNCTION_GRAPH_TRACER */

#ifdef CONFIG_KPROBES_ON_FTRACE
void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
                struct ftrace_ops *ops, struct ftrace_regs *fregs)
{
        struct kprobe_ctlblk *kcb;
        struct pt_regs *regs;
        struct kprobe *p;
        int bit;

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

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

        if (kprobe_running()) {
                kprobes_inc_nmissed_count(p);
                goto out;
        }

        __this_cpu_write(current_kprobe, p);

        kcb = get_kprobe_ctlblk();
        kcb->kprobe_status = KPROBE_HIT_ACTIVE;

        instruction_pointer_set(regs, ip);

        if (!p->pre_handler || !p->pre_handler(p, regs)) {

                instruction_pointer_set(regs, ip + MCOUNT_INSN_SIZE);

                if (unlikely(p->post_handler)) {
                        kcb->kprobe_status = KPROBE_HIT_SSDONE;
                        p->post_handler(p, regs, 0);
                }
        }
        __this_cpu_write(current_kprobe, NULL);
out:
        preempt_enable_notrace();
        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