/*
 * 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 "entry.h"

/*
 * The mcount code looks like this:
 *      stg     %r14,8(%r15)            # offset 0
 *      larl    %r1,<&counter>          # offset 6
 *      brasl   %r14,_mcount            # offset 12
 *      lg      %r14,8(%r15)            # offset 18
 * Total length is 24 bytes. Only the first instruction will be patched
 * by ftrace_make_call / ftrace_make_nop.
 * The enabled ftrace code block looks like this:
 * >    brasl   %r0,ftrace_caller       # offset 0
 *      larl    %r1,<&counter>          # offset 6
 *      brasl   %r14,_mcount            # offset 12
 *      lg      %r14,8(%r15)            # offset 18
 * 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.
 * The return point of the ftrace function has offset 24, so execution
 * continues behind the mcount block.
 * The disabled ftrace code block looks like this:
 * >    jg      .+24                    # offset 0
 *      larl    %r1,<&counter>          # offset 6
 *      brasl   %r14,_mcount            # offset 12
 *      lg      %r14,8(%r15)            # offset 18
 * The jg instruction branches to offset 24 to skip as many instructions
 * as possible.
 * In case we use gcc's hotpatch feature 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
 */

unsigned long ftrace_plt;

static inline void ftrace_generate_orig_insn(struct ftrace_insn *insn)
{
#ifdef CC_USING_HOTPATCH
        /* brcl 0,0 */
        insn->opc = 0xc004;
        insn->disp = 0;
#else
        /* stg r14,8(r15) */
        insn->opc = 0xe3e0;
        insn->disp = 0xf0080024;
#endif
}

static inline int is_kprobe_on_ftrace(struct ftrace_insn *insn)
{
#ifdef CONFIG_KPROBES
        if (insn->opc == BREAKPOINT_INSTRUCTION)
                return 1;
#endif
        return 0;
}

static inline void ftrace_generate_kprobe_nop_insn(struct ftrace_insn *insn)
{
#ifdef CONFIG_KPROBES
        insn->opc = BREAKPOINT_INSTRUCTION;
        insn->disp = KPROBE_ON_FTRACE_NOP;
#endif
}

static inline void ftrace_generate_kprobe_call_insn(struct ftrace_insn *insn)
{
#ifdef CONFIG_KPROBES
        insn->opc = BREAKPOINT_INSTRUCTION;
        insn->disp = KPROBE_ON_FTRACE_CALL;
#endif
}

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 (probe_kernel_read(&old, (void *) rec->ip, sizeof(old)))
                return -EFAULT;
        if (addr == MCOUNT_ADDR) {
                /* Initial code replacement */
                ftrace_generate_orig_insn(&orig);
                ftrace_generate_nop_insn(&new);
        } else if (is_kprobe_on_ftrace(&old)) {
                /*
                 * If we find a breakpoint instruction, a kprobe has been
                 * placed at the beginning of the function. We write the
                 * constant KPROBE_ON_FTRACE_NOP into the remaining four
                 * bytes of the original instruction so that the kprobes
                 * handler can execute a nop, if it reaches this breakpoint.
                 */
                ftrace_generate_kprobe_call_insn(&orig);
                ftrace_generate_kprobe_nop_insn(&new);
        } else {
                /* 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 (probe_kernel_read(&old, (void *) rec->ip, sizeof(old)))
                return -EFAULT;
        if (is_kprobe_on_ftrace(&old)) {
                /*
                 * If we find a breakpoint instruction, a kprobe has been
                 * placed at the beginning of the function. We write the
                 * constant KPROBE_ON_FTRACE_CALL into the remaining four
                 * bytes of the original instruction so that the kprobes
                 * handler can execute a brasl if it reaches this breakpoint.
                 */
                ftrace_generate_kprobe_nop_insn(&orig);
                ftrace_generate_kprobe_call_insn(&new);
        } else {
                /* 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)
{
        return 0;
}

int __init ftrace_dyn_arch_init(void)
{
        return 0;
}

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);

#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 parent, unsigned long ip)
{
        struct ftrace_graph_ent trace;

        if (unlikely(ftrace_graph_is_dead()))
                goto out;
        if (unlikely(atomic_read(&current->tracing_graph_pause)))
                goto out;
        ip -= MCOUNT_INSN_SIZE;
        trace.func = ip;
        trace.depth = current->curr_ret_stack + 1;
        /* Only trace if the calling function expects to. */
        if (!ftrace_graph_entry(&trace))
                goto out;
        if (ftrace_push_return_trace(parent, ip, &trace.depth, 0) == -EBUSY)
                goto out;
        parent = (unsigned long) return_to_handler;
out:
        return parent;
}
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 */