#include "include/trace.bpf.h"

#define STRING_KIND 24

// parse_string_param will parse a string parameter. The parsed value of the string
// will be put into param->deref_val. This function expects the string struct
// which contains a pointer to the string and the length of the string to have
// already been read from memory and passed in as param->val.
__always_inline
int parse_string_param(struct pt_regs *ctx, function_parameter_t *param) {
    u64 str_len;
    size_t str_addr;

    __builtin_memcpy(&str_addr, param->val, sizeof(str_addr));
    __builtin_memcpy(&str_len, param->val + sizeof(str_addr), sizeof(str_len));
    param->daddr = str_addr;

    if (str_addr != 0) {
        if (str_len > 0x30) {
            str_len = 0x30;
        }
        int ret = bpf_probe_read_user(&param->deref_val, str_len, (void *)(str_addr));
        if (ret < 0) {
            return 1;
        }
    }
    return 0;
}

__always_inline
int parse_param_stack(struct pt_regs *ctx, function_parameter_t *param) {
    long ret;
    size_t addr = ctx->sp + param->offset;
    ret = bpf_probe_read_user(&param->val, param->size, (void *)(addr));
    if (ret < 0) {
        return 1;
    }
    return 0;
}

__always_inline
void get_value_from_register(struct pt_regs *ctx, void *dest, int reg_num) {
    switch (reg_num) {
    case 0: // RAX
        __builtin_memcpy(dest, &ctx->ax, sizeof(ctx->ax));
        break;
    case 1: // RDX
        __builtin_memcpy(dest, &ctx->dx, sizeof(ctx->dx));
        break;
    case 2: // RCX
        __builtin_memcpy(dest, &ctx->cx, sizeof(ctx->cx));
        break;
    case 3: // RBX
        __builtin_memcpy(dest, &ctx->bx, sizeof(ctx->bx));
        break;
    case 4: // RSI
        __builtin_memcpy(dest, &ctx->si, sizeof(ctx->si));
        break;
    case 5: // RDI
        __builtin_memcpy(dest, &ctx->di, sizeof(ctx->di));
        break;
    case 6: // RBP
        __builtin_memcpy(dest, &ctx->bp, sizeof(ctx->bp));
        break;
    case 7: // RSP
        __builtin_memcpy(dest, &ctx->sp, sizeof(ctx->sp));
        break;
    case 8: // R8
        __builtin_memcpy(dest, &ctx->r8, sizeof(ctx->r8));
        break;
    case 9: // R9
        __builtin_memcpy(dest, &ctx->r9, sizeof(ctx->r9));
        break;
    case 10: // R10
        __builtin_memcpy(dest, &ctx->r10, sizeof(ctx->r10));
        break;
    case 11: // R11
        __builtin_memcpy(dest, &ctx->r11, sizeof(ctx->r11));
        break;
    case 12: // R12
        __builtin_memcpy(dest, &ctx->r12, sizeof(ctx->r12));
        break;
    case 13: // R13
        __builtin_memcpy(dest, &ctx->r13, sizeof(ctx->r13));
        break;
    case 14: // R14
        __builtin_memcpy(dest, &ctx->r14, sizeof(ctx->r14));
        break;
    case 15: // R15
        __builtin_memcpy(dest, &ctx->r15, sizeof(ctx->r15));
        break;
    }
}

__always_inline
int parse_param_registers(struct pt_regs *ctx, function_parameter_t *param) {
    switch (param->n_pieces) {
    case 6:
        get_value_from_register(ctx, param->val+40, param->reg_nums[5]);
    case 5:
        get_value_from_register(ctx, param->val+32, param->reg_nums[4]);
    case 4:
        get_value_from_register(ctx, param->val+24, param->reg_nums[3]);
    case 3:
        get_value_from_register(ctx, param->val+16, param->reg_nums[2]);
    case 2:
        get_value_from_register(ctx, param->val+8, param->reg_nums[1]);
    case 1:
        get_value_from_register(ctx, param->val, param->reg_nums[0]);
    }
    return 0;
}

__always_inline
int parse_param(struct pt_regs *ctx, function_parameter_t *param) {
    if (param->size > 0x30) {
        return 0;
    }

    // Parse the initial value of the parameter.
    // If the parameter is a basic type, we will be finished here.
    // If the parameter is a more complex type such as a string or
    // a slice we will need some further processing below.
    int ret = 0;
    if (param->in_reg) {
        ret = parse_param_registers(ctx, param);
    } else {
        ret = parse_param_stack(ctx, param);
    }
    if (ret != 0) {
        return ret;
    }

    switch (param->kind) {
        case STRING_KIND:
            return parse_string_param(ctx, param);
    }

    return 0;
}

__always_inline
int get_goroutine_id(function_parameter_list_t *parsed_args) {
    struct task_struct *task;
    size_t g_addr;
    __u64  goid;

    // Get the current task.
    task = (struct task_struct *)bpf_get_current_task();
    // Get the Goroutine ID which is stored in thread local storage.
    bpf_probe_read_user(&g_addr, sizeof(void *), (void*)(BPF_CORE_READ(task, thread.fsbase)+parsed_args->g_addr_offset));
    bpf_probe_read_user(&goid, sizeof(void *), (void*)(g_addr+parsed_args->goid_offset));
    parsed_args->goroutine_id = goid;

    return 1;
}

__always_inline
void parse_params(struct pt_regs *ctx, unsigned int n_params, function_parameter_t params[6]) {
    // Since we cannot loop in eBPF programs let's take adavantage of the
    // fact that in C switch cases will pass through automatically.
    switch (n_params) {
    case 6:
        parse_param(ctx, &params[5]);
    case 5:
        parse_param(ctx, &params[4]);
    case 4:
        parse_param(ctx, &params[3]);
    case 3:
        parse_param(ctx, &params[2]);
    case 2:
        parse_param(ctx, &params[1]);
    case 1:
        parse_param(ctx, &params[0]);
    }
}

SEC("uprobe/dlv_trace")
int uprobe__dlv_trace(struct pt_regs *ctx) {
    function_parameter_list_t *args;
    function_parameter_list_t *parsed_args;
    uint64_t key = ctx->ip;

    args = bpf_map_lookup_elem(&arg_map, &key);
    if (!args) {
        return 1;
    }

    parsed_args = bpf_ringbuf_reserve(&events, sizeof(function_parameter_list_t), 0);
    if (!parsed_args) {
        return 1;
    }

    // Initialize the parsed_args struct.
    parsed_args->goid_offset = args->goid_offset;
    parsed_args->g_addr_offset = args->g_addr_offset;
    parsed_args->goroutine_id = args->goroutine_id;
    parsed_args->fn_addr = args->fn_addr;
    parsed_args->n_parameters = args->n_parameters;
    parsed_args->n_ret_parameters = args->n_ret_parameters;
    parsed_args->is_ret = args->is_ret;
    __builtin_memcpy(parsed_args->params, args->params, sizeof(args->params));
    __builtin_memcpy(parsed_args->ret_params, args->ret_params, sizeof(args->ret_params));

    if (!get_goroutine_id(parsed_args)) {
        bpf_ringbuf_discard(parsed_args, 0);
        return 1;
    }

    if (!args->is_ret) {
        // In uprobe at function entry.

        // Parse input parameters.
        parse_params(ctx, args->n_parameters, parsed_args->params);
    } else {
        // We are now stopped at the RET instruction for this function.

        // Parse output parameters.
        parse_params(ctx, args->n_ret_parameters, parsed_args->ret_params);
    }

    bpf_ringbuf_submit(parsed_args, BPF_RB_FORCE_WAKEUP);

    return 0;
}

char _license[] SEC("license") = "Dual MIT/GPL";
