/*
 * Copyright (C) 2014 Oracle.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, see http://www.gnu.org/copyleft/gpl.txt
 */

/*
 * This file started out by saying that if you have:
 *
 *      struct foo one, two;
 *      ...
 *      one = two;
 *
 * That's equivalent to saying:
 *
 *      one.x = two.x;
 *      one.y = two.y;
 *
 * Turning an assignment like that into a bunch of small fake assignments is
 * really useful.
 *
 * The call to memcpy(&one, &two, sizeof(foo)); is the same as "one = two;" so
 * we can re-use the code.  And we may as well use it for memset() too.
 * Assigning pointers is almost the same:
 *
 *      p1 = p2;
 *
 * Is the same as:
 *
 *      p1->x = p2->x;
 *      p1->y = p2->y;
 *
 * The problem is that you can go a bit crazy with pointers to pointers.
 *
 *      p1->x->y->z->one->two->three = p2->x->y->z->one->two->three;
 *
 * I don't have a proper solution for this problem right now.  I just copy one
 * level and don't nest.  It should handle limitted nesting but intelligently.
 *
 * The other thing is that you end up with a lot of garbage assignments where
 * we record "x could be anything. x->y could be anything. x->y->z->a->b->c
 * could *also* be anything!".  There should be a better way to filter this
 * useless information.
 *
 */

#include "scope.h"
#include "smatch.h"
#include "smatch_slist.h"
#include "smatch_extra.h"

enum {
        COPY_NORMAL,
        COPY_MEMCPY,
        COPY_MEMSET,
};

static struct symbol *get_struct_type(struct expression *expr)
{
        struct symbol *type;

        type = get_type(expr);
        if (!type)
                return NULL;
        if (type->type == SYM_PTR) {
                type = get_real_base_type(type);
                if (!type)
                        return NULL;
        }
        if (type->type == SYM_STRUCT)
                return type;
        if (type->type == SYM_UNION)
                return type;
        return NULL;
}

static struct expression *get_right_base_expr(struct symbol *left_type, struct expression *right)
{
        struct symbol *struct_type;

        if (!right)
                return NULL;

        struct_type = get_struct_type(right);
        if (!struct_type)
                return NULL;
        if (struct_type != left_type)
                return NULL;

        if (right->type == EXPR_PREOP && right->op == '&')
                right = strip_expr(right->unop);

        if (right->type == EXPR_CALL)
                return NULL;

        if (is_pointer(right))
                right = deref_expression(right);

        return right;
}

static struct expression *remove_addr(struct expression *expr)
{
        struct symbol *type;

        expr = strip_expr(expr);
        if (!expr)
                return NULL;

        if (expr->type == EXPR_PREOP && expr->op == '&')
                return strip_expr(expr->unop);
        type = get_type(expr);
        if (!type)
                return expr;
        if (type->type != SYM_PTR && type->type != SYM_ARRAY)
                return expr;

        return deref_expression(expr);
}

static struct expression *faked_expression;
struct expression *get_faked_expression(void)
{
        if (!__in_fake_assign)
                return NULL;
        return faked_expression;
}

static void split_fake_expr(struct expression *expr)
{
        __in_fake_assign++;
        __in_fake_struct_assign++;
        __split_expr(expr);
        __in_fake_struct_assign--;
        __in_fake_assign--;
}

static void handle_non_struct_assignments(struct expression *left, struct expression *right)
{
        struct symbol *type;
        struct expression *assign;

        while (right && right->type == EXPR_ASSIGNMENT)
                right = strip_parens(right->left);

        type = get_type(left);
        if (!type)
                return;
        if (type->type == SYM_PTR) {
                left = deref_expression(left);
                if (right)
                        right = deref_expression(right);
                else
                        right = unknown_value_expression(left);
                assign = assign_expression(left, '=', right);
                split_fake_expr(assign);
                return;
        }
        if (type->type != SYM_BASETYPE)
                return;
        right = strip_expr(right);
        type = get_type(right);
        if (!right || !type || type->type == SYM_ARRAY)
                right = unknown_value_expression(left);
        assign = assign_expression(left, '=', right);
        split_fake_expr(assign);
}

static void set_inner_struct_members(int mode, struct expression *faked, struct expression *left, struct expression *right, struct symbol *member)
{
        struct expression *left_member;
        struct expression *right_member = NULL;  /* silence GCC */
        struct expression *assign;
        struct symbol *base = get_real_base_type(member);
        struct symbol *tmp;

        if (member->ident) {
                left = member_expression(left, '.', member->ident);
                if (mode != COPY_MEMSET && right)
                        right = member_expression(right, '.', member->ident);
        }

        FOR_EACH_PTR(base->symbol_list, tmp) {
                struct symbol *type;

                type = get_real_base_type(tmp);
                if (!type)
                        continue;

                if (type->type == SYM_ARRAY)
                        continue;
                if (type->type == SYM_UNION || type->type == SYM_STRUCT) {
                        set_inner_struct_members(mode, faked, left, right, tmp);
                        continue;
                }
                if (!tmp->ident)
                        continue;

                left_member = member_expression(left, '.', tmp->ident);

                switch (mode) {
                case COPY_NORMAL:
                case COPY_MEMCPY:
                        if (right)
                                right_member = member_expression(right, '.', tmp->ident);
                        else
                                right_member = unknown_value_expression(left_member);
                        break;
                case COPY_MEMSET:
                        right_member = right;
                        break;
                }

                assign = assign_expression(left_member, '=', right_member);
                split_fake_expr(assign);
        } END_FOR_EACH_PTR(tmp);
}

static void __struct_members_copy(int mode, struct expression *faked,
                                  struct expression *left,
                                  struct expression *right)
{
        struct symbol *struct_type, *tmp, *type;
        struct expression *left_member;
        struct expression *right_member;
        struct expression *assign;
        int op = '.';

        if (__in_fake_assign)
                return;
        faked_expression = faked;

        left = strip_expr(left);
        right = strip_expr(right);

        if (left->type == EXPR_PREOP && left->op == '*' && is_pointer(left))
                left = preop_expression(left, '(');

        struct_type = get_struct_type(left);
        if (!struct_type) {
                /*
                 * This is not a struct assignment obviously.  But this is where
                 * memcpy() is handled so it feels like a good place to add this
                 * code.
                 */
                handle_non_struct_assignments(left, right);
                goto done;
        }

        if (is_pointer(left)) {
                left = deref_expression(left);
                op = '*';
        }
        if (mode != COPY_MEMSET)
                right = get_right_base_expr(struct_type, right);

        FOR_EACH_PTR(struct_type->symbol_list, tmp) {
                type = get_real_base_type(tmp);
                if (!type)
                        continue;
                if (type->type == SYM_ARRAY)
                        continue;

                if (type->type == SYM_UNION || type->type == SYM_STRUCT) {
                        set_inner_struct_members(mode, faked, left, right, tmp);
                        continue;
                }

                if (!tmp->ident)
                        continue;

                left_member = member_expression(left, op, tmp->ident);
                right_member = NULL;

                switch (mode) {
                case COPY_NORMAL:
                case COPY_MEMCPY:
                        if (right)
                                right_member = member_expression(right, op, tmp->ident);
                        else
                                right_member = unknown_value_expression(left_member);
                        break;
                case COPY_MEMSET:
                        right_member = right;
                        break;
                }
                if (!right_member) {
                        sm_perror("No right member");
                        continue;
                }
                assign = assign_expression(left_member, '=', right_member);
                split_fake_expr(assign);
        } END_FOR_EACH_PTR(tmp);

done:
        faked_expression = NULL;
}

static int returns_zeroed_mem(struct expression *expr)
{
        char *fn;

        if (expr->type != EXPR_CALL || expr->fn->type != EXPR_SYMBOL)
                return 0;
        fn = expr_to_var(expr->fn);
        if (!fn)
                return 0;
        if (strcmp(fn, "kcalloc") == 0)
                return 1;
        if (option_project == PROJ_KERNEL && strstr(fn, "zalloc"))
                return 1;
        return 0;
}

static int copy_containter_states(struct expression *left, struct expression *right, int offset)
{
        char *left_name = NULL, *right_name = NULL;
        struct symbol *left_sym, *right_sym;
        struct sm_state *sm, *new_sm;
        int ret = 0;
        int len;
        char buf[64];
        char new_name[128];

        right_name = expr_to_var_sym(right, &right_sym);
        if (!right_name || !right_sym)
                goto free;
        left_name = expr_to_var_sym(left, &left_sym);
        if (!left_name || !left_sym)
                goto free;

        len = snprintf(buf, sizeof(buf), "%s(-%d)", right_name, offset);
        if (len >= sizeof(buf))
                goto free;

        FOR_EACH_SM(__get_cur_stree(), sm) {
                if (sm->sym != right_sym)
                        continue;
                if (strncmp(sm->name, buf, len) != 0)
                        continue;
                snprintf(new_name, sizeof(new_name), "%s%s", left_name, sm->name + len);
                new_sm = clone_sm(sm);
                new_sm->name = alloc_sname(new_name);
                new_sm->sym = left_sym;
                __set_sm(new_sm);
                ret = 1;
        } END_FOR_EACH_SM(sm);
free:
        free_string(left_name);
        free_string(right_name);
        return ret;
}

static int handle_param_offsets(struct expression *expr)
{
        struct expression *right;
        sval_t sval;

        right = strip_expr(expr->right);

        if (right->type != EXPR_BINOP || right->op != '-')
                return 0;

        if (!get_value(right->right, &sval))
                return 0;

        right = get_assigned_expr(right->left);
        if (!right)
                return 0;
        return copy_containter_states(expr->left, right, sval.value);
}

static void returns_container_of(struct expression *expr, int param, char *key, char *value)
{
        struct expression *call, *arg;
        int offset;

        if (expr->type != EXPR_ASSIGNMENT || expr->op != '=')
                return;
        call = strip_expr(expr->right);
        if (call->type != EXPR_CALL)
                return;
        if (param != -1)
                return;
        param = atoi(key);
        offset = atoi(value);

        arg = get_argument_from_call_expr(call->args, param);
        if (!arg)
                return;

        copy_containter_states(expr->left, arg, -offset);
}

void __fake_struct_member_assignments(struct expression *expr)
{
        struct symbol *left_type;

        if (expr->op != '=')
                return;

        if (expr_is_zero(expr->right))
                return;

        left_type = get_type(expr->left);
        if (!left_type ||
            (left_type->type != SYM_PTR &&
             left_type->type != SYM_STRUCT))
                return;

        if (handle_param_offsets(expr))
                return;

        if (returns_zeroed_mem(expr->right))
                __struct_members_copy(COPY_MEMSET, expr, expr->left, zero_expr());
        else
                __struct_members_copy(COPY_NORMAL, expr, expr->left, expr->right);
}

static void match_memset(const char *fn, struct expression *expr, void *_size_arg)
{
        struct expression *buf;
        struct expression *val;

        buf = get_argument_from_call_expr(expr->args, 0);
        val = get_argument_from_call_expr(expr->args, 1);

        buf = strip_expr(buf);
        __struct_members_copy(COPY_MEMSET, expr, remove_addr(buf), val);
}

static void match_memcpy(const char *fn, struct expression *expr, void *_arg)
{
        struct expression *dest;
        struct expression *src;

        dest = get_argument_from_call_expr(expr->args, 0);
        src = get_argument_from_call_expr(expr->args, 1);

        __struct_members_copy(COPY_MEMCPY, expr, remove_addr(dest), remove_addr(src));
}

static void match_memdup(const char *fn, struct expression *call_expr,
                        struct expression *expr, void *_unused)
{
        struct expression *left, *right, *arg;

        if (!expr || expr->type != EXPR_ASSIGNMENT)
                return;

        left = strip_expr(expr->left);
        right = strip_expr(expr->right);

        if (right->type != EXPR_CALL)
                return;
        arg = get_argument_from_call_expr(right->args, 0);
        __struct_members_copy(COPY_MEMCPY, expr, left, arg);
}

static void match_memcpy_unknown(const char *fn, struct expression *expr, void *_arg)
{
        struct expression *dest;

        dest = get_argument_from_call_expr(expr->args, 0);
        __struct_members_copy(COPY_MEMCPY, expr, remove_addr(dest), NULL);
}

static void match_sscanf(const char *fn, struct expression *expr, void *unused)
{
        struct expression *arg;
        int i;

        i = -1;
        FOR_EACH_PTR(expr->args, arg) {
                if (++i < 2)
                        continue;
                __struct_members_copy(COPY_MEMCPY, expr, remove_addr(arg), NULL);
        } END_FOR_EACH_PTR(arg);
}

static void unop_expr(struct expression *expr)
{
        if (expr->op != SPECIAL_INCREMENT &&
            expr->op != SPECIAL_DECREMENT)
                return;

        if (!is_pointer(expr))
                return;
        faked_expression = expr;
        __struct_members_copy(COPY_MEMCPY, expr, expr->unop, NULL);
        faked_expression = NULL;
}

static void register_clears_param(void)
{
        struct token *token;
        char name[256];
        const char *function;
        int param;

        if (option_project == PROJ_NONE)
                return;

        snprintf(name, 256, "%s.clears_argument", option_project_str);

        token = get_tokens_file(name);
        if (!token)
                return;
        if (token_type(token) != TOKEN_STREAMBEGIN)
                return;
        token = token->next;
        while (token_type(token) != TOKEN_STREAMEND) {
                if (token_type(token) != TOKEN_IDENT)
                        return;
                function = show_ident(token->ident);
                token = token->next;
                if (token_type(token) != TOKEN_NUMBER)
                        return;
                param = atoi(token->number);
                add_function_hook(function, &match_memcpy_unknown, INT_PTR(param));
                token = token->next;
        }
        clear_token_alloc();
}

static void db_param_cleared(struct expression *expr, int param, char *key, char *value)
{
        struct expression *arg;

        while (expr->type == EXPR_ASSIGNMENT)
                expr = strip_expr(expr->right);
        if (expr->type != EXPR_CALL)
                return;

        /*
         * FIXME:  __struct_members_copy() requires an expression but
         * get_variable_from_key() returns a name/sym pair so that doesn't
         * work here.
         */
        if (strcmp(key, "$") != 0)
                return;

        arg = get_argument_from_call_expr(expr->args, param);
        if (!arg)
                return;

        if (strcmp(value, "0") == 0)
                __struct_members_copy(COPY_MEMSET, expr, remove_addr(arg), zero_expr());
        else
                __struct_members_copy(COPY_MEMCPY, expr, remove_addr(arg), NULL);
}

void register_struct_assignment(int id)
{
        add_function_hook("memset", &match_memset, NULL);
        add_function_hook("__memset", &match_memset, NULL);

        add_function_hook("memcpy", &match_memcpy, INT_PTR(0));
        add_function_hook("memmove", &match_memcpy, INT_PTR(0));
        add_function_hook("__memcpy", &match_memcpy, INT_PTR(0));
        add_function_hook("__memmove", &match_memcpy, INT_PTR(0));

        if (option_project == PROJ_KERNEL)
                return_implies_state_sval("kmemdup", valid_ptr_min_sval, valid_ptr_max_sval, &match_memdup, NULL);

        add_function_hook("sscanf", &match_sscanf, NULL);

        add_hook(&unop_expr, OP_HOOK);
        register_clears_param();
        select_return_states_hook(PARAM_CLEARED, &db_param_cleared);

        select_return_states_hook(CONTAINER, &returns_container_of);
}