Documentation: make me less confused

[smatch.git] / smatch_implied.c

/*
 * Copyright (C) 2008 Dan Carpenter.
 *
 * 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
 */

/*
 * Imagine we have this code:
 * foo = 1;
 * if (bar)
 *         foo = 99;
 * else
 *         frob();
 *                   //  <-- point #1
 * if (foo == 99)    //  <-- point #2
 *         bar->baz; //  <-- point #3
 *
 *
 * At point #3 bar is non null and can be dereferenced.
 *
 * It's smatch_implied.c which sets bar to non null at point #2.
 *
 * At point #1 merge_slist() stores the list of states from both
 * the true and false paths.  On the true path foo == 99 and on
 * the false path foo == 1.  merge_slist() sets their pool
 * list to show the other states which were there when foo == 99.
 *
 * When it comes to the if (foo == 99) the smatch implied hook
 * looks for all the pools where foo was not 99.  It makes a list
 * of those.
 *
 * Then for bar (and all the other states) it says, ok bar is a
 * merged state that came from these previous states.  We'll
 * chop out all the states where it came from a pool where
 * foo != 99 and merge it all back together.
 *
 * That is the implied state of bar.
 *
 * merge_slist() sets up ->pool.  An sm_state only has one ->pool and
 *    that is the pool where it was first set.  The my pool gets set when
 *    code paths merge.  States that have been set since the last merge do
 *    not have a ->pool.
 * merge_sm_state() sets ->left and ->right.  (These are the states which were
 *    merged to form the current state.)
 * a pool:  a pool is an slist that has been merged with another slist.
 */

#include <sys/time.h>
#include <time.h>
#include "smatch.h"
#include "smatch_slist.h"
#include "smatch_extra.h"

char *implied_debug_msg;
#define DIMPLIED(msg...) do { if (option_debug_implied) printf(msg); } while (0)

int option_debug_implied = 0;
int option_no_implied = 0;

#define RIGHT 0
#define LEFT  1

/*
 * tmp_range_list():
 * It messes things up to free range list allocations.  This helper fuction
 * lets us reuse memory instead of doing new allocations.
 */
static struct range_list *tmp_range_list(long long num)
{
        static struct range_list *my_list = NULL;
        static struct data_range *my_range;

        __free_ptr_list((struct ptr_list **)&my_list);
        my_range = alloc_range(ll_to_sval(num), ll_to_sval(num));
        add_ptr_list(&my_list, my_range);
        return my_list;
}

static void print_debug_tf(struct sm_state *s, int istrue, int isfalse)
{
        if (!option_debug_implied && !option_debug)
                return;

        if (istrue && isfalse) {
                printf("'%s = %s' from %d does not exist.\n", s->name,
                        show_state(s->state), s->line);
        } else if (istrue) {
                printf("'%s = %s' from %d is true. [stree %d]\n", s->name, show_state(s->state),
                        s->line, get_stree_id(s->pool));
        } else if (isfalse) {
                printf("'%s = %s' from %d is false. [stree %d]\n", s->name, show_state(s->state),
                        s->line, get_stree_id(s->pool));
        } else {
                printf("'%s = %s' from %d could be true or false. [stree %d]\n", s->name,
                        show_state(s->state), s->line, get_stree_id(s->pool));
        }
}

/*
 * add_pool() adds a slist to *pools. If the slist has already been
 * added earlier then it doesn't get added a second time.
 */
void add_pool(struct stree_stack **pools, struct stree *new)
{
        struct stree *tmp;

        FOR_EACH_PTR(*pools, tmp) {
                if (tmp < new)
                        continue;
                else if (tmp == new) {
                        return;
                } else {
                        INSERT_CURRENT(new, tmp);
                        return;
                }
        } END_FOR_EACH_PTR(tmp);
        add_ptr_list(pools, new);
}

/*
 * If 'foo' == 99 add it that pool to the true pools.  If it's false, add it to
 * the false pools.  If we're not sure, then we don't add it to either.
 */
static void do_compare(struct sm_state *sm_state, int comparison, struct range_list *vals,
                        int lr,
                        struct stree_stack **true_stack,
                        struct stree_stack **false_stack)
{
        struct sm_state *s;
        int istrue;
        int isfalse;

        if (!sm_state->pool)
                return;

        if (is_implied(sm_state)) {
                s = get_sm_state_stree(sm_state->pool,
                                sm_state->owner, sm_state->name,
                                sm_state->sym);
        } else {
                s = sm_state;
        }

        if (!s) {
                if (option_debug_implied || option_debug)
                        sm_msg("%s from %d, has borrowed implications.",
                                sm_state->name, sm_state->line);
                return;
        }

        if (lr == LEFT) {
                istrue = !possibly_false_rl(estate_rl(s->state), comparison, vals);
                isfalse = !possibly_true_rl(estate_rl(s->state), comparison, vals);
        } else {
                istrue = !possibly_false_rl(vals, comparison, estate_rl(s->state));
                isfalse = !possibly_true_rl(vals, comparison, estate_rl(s->state));
        }

        print_debug_tf(s, istrue, isfalse);

        if (istrue)
                add_pool(true_stack, s->pool);

        if (isfalse)
                add_pool(false_stack, s->pool);
}

static int pool_in_pools(struct stree *pool,
                        struct stree_stack *pools)
{
        struct stree *tmp;

        FOR_EACH_PTR(pools, tmp) {
                if (tmp == pool)
                        return 1;
                if (tmp > pool)
                        return 0;
        } END_FOR_EACH_PTR(tmp);
        return 0;
}

static int is_checked(struct state_list *checked, struct sm_state *sm)
{
        struct sm_state *tmp;

        FOR_EACH_PTR(checked, tmp) {
                if (tmp == sm)
                        return 1;
        } END_FOR_EACH_PTR(tmp);
        return 0;
}

/*
 * separate_pools():
 * Example code:  if (foo == 99) {
 *
 * Say 'foo' is a merged state that has many possible values.  It is the combination
 * of merges.  separate_pools() iterates through the pools recursively and calls
 * do_compare() for each time 'foo' was set.
 */
static void separate_pools(struct sm_state *sm_state, int comparison, struct range_list *vals,
                        int lr,
                        struct stree_stack **true_stack,
                        struct stree_stack **false_stack,
                        struct state_list **checked)
{
        int free_checked = 0;
        struct state_list *checked_states = NULL;

        if (!sm_state)
                return;

        /*
           Sometimes the implications are just too big to deal with
           so we bail.  Theoretically, bailing out here can cause more false
           positives but won't hide actual bugs.
        */
        if (sm_state->nr_children > 4000) {
                static char buf[1028];
                snprintf(buf, sizeof(buf), "debug: separate_pools: nr_children over 4000 (%d). (%s %s)",
                         sm_state->nr_children, sm_state->name, show_state(sm_state->state));
                implied_debug_msg = buf;
                return;
        }

        if (checked == NULL) {
                checked = &checked_states;
                free_checked = 1;
        }
        if (is_checked(*checked, sm_state))
                return;
        add_ptr_list(checked, sm_state);

        do_compare(sm_state, comparison, vals, lr, true_stack, false_stack);

        separate_pools(sm_state->left, comparison, vals, lr, true_stack, false_stack, checked);
        separate_pools(sm_state->right, comparison, vals, lr, true_stack, false_stack, checked);
        if (free_checked)
                free_slist(checked);
}

struct sm_state *filter_pools(struct sm_state *sm,
                              struct stree_stack *remove_stack,
                              struct stree_stack *keep_stack,
                              int *modified)
{
        struct sm_state *ret = NULL;
        struct sm_state *left;
        struct sm_state *right;
        int removed = 0;

        if (!sm)
                return NULL;

        if (sm->nr_children > 4000) {
                static char buf[1028];
                snprintf(buf, sizeof(buf), "debug: %s: nr_children over 4000 (%d). (%s %s)",
                         __func__, sm->nr_children, sm->name, show_state(sm->state));
                implied_debug_msg = buf;
                return NULL;
        }

        if (pool_in_pools(sm->pool, remove_stack)) {
                DIMPLIED("removed %s from %d [stree %d]\n", show_sm(sm), sm->line, get_stree_id(sm->pool));
                *modified = 1;
                return NULL;
        }

        if (!is_merged(sm) || pool_in_pools(sm->pool, keep_stack)) {
                DIMPLIED("kept %s from %d [stree %d]\n", show_sm(sm), sm->line, get_stree_id(sm->pool));
                return sm;
        }

        DIMPLIED("checking %s from %d (%d) [stree %d] left = %s [stree %d] right = %s [stree %d]\n",
                 show_sm(sm), sm->line, sm->nr_children, get_stree_id(sm->pool),
                 sm->left ? show_sm(sm->left) : "<none>", sm->left ? get_stree_id(sm->left->pool) : -1,
                 sm->right ? show_sm(sm->right) : "<none>", sm->right ? get_stree_id(sm->right->pool) : -1);
        left = filter_pools(sm->left, remove_stack, keep_stack, &removed);
        right = filter_pools(sm->right, remove_stack, keep_stack, &removed);
        if (!removed) {
                DIMPLIED("kept %s from %d [stree %d]\n", show_sm(sm), sm->line, get_stree_id(sm->pool));
                return sm;
        }
        *modified = 1;
        if (!left && !right) {
                DIMPLIED("removed %s from %d <none> [stree %d]\n", show_sm(sm), sm->line, get_stree_id(sm->pool));
                return NULL;
        }

        if (!left) {
                ret = clone_sm(right);
                ret->merged = 1;
                ret->right = right;
                ret->left = NULL;
                ret->pool = sm->pool;
        } else if (!right) {
                ret = clone_sm(left);
                ret->merged = 1;
                ret->left = left;
                ret->right = NULL;
                ret->pool = sm->pool;
        } else {
                ret = merge_sm_states(left, right);
                ret->pool = sm->pool;
        }
        ret->implied = 1;
        DIMPLIED("partial %s => ", show_sm(sm));
        DIMPLIED("%s from %d [stree %d]\n", show_sm(ret), sm->line, get_stree_id(sm->pool));
        return ret;
}

static int highest_stree_id(struct sm_state *sm)
{
        int left = 0;
        int right = 0;

        if (!sm->left && !sm->right)
                return 0;

        if (sm->left)
                left = get_stree_id(sm->left->pool);
        if (sm->right)
                right = get_stree_id(sm->right->pool);

        if (right > left)
                return right;
        return left;
}

static struct stree *filter_stack(struct sm_state *gate_sm,
                                       struct stree *pre_stree,
                                       struct stree_stack *remove_stack,
                                       struct stree_stack *keep_stack)
{
        struct stree *ret = NULL;
        struct sm_state *tmp;
        struct sm_state *filtered_sm;
        int modified;

        if (!remove_stack)
                return NULL;

        FOR_EACH_SM(pre_stree, tmp) {
                if (highest_stree_id(tmp) < highest_stree_id(gate_sm)) {
                        DIMPLIED("skipping %s.  set before.  %d vs %d\n",
                                        tmp->name, highest_stree_id(tmp),
                                        highest_stree_id(gate_sm));
                        continue;
                }
                modified = 0;
                filtered_sm = filter_pools(tmp, remove_stack, keep_stack, &modified);
                if (filtered_sm && modified) {
                        /* the assignments here are for borrowed implications */
                        filtered_sm->name = tmp->name;
                        filtered_sm->sym = tmp->sym;
                        avl_insert(&ret, filtered_sm);
                        if (out_of_memory())
                                return NULL;

                }
        } END_FOR_EACH_SM(tmp);
        return ret;
}

static void separate_and_filter(struct sm_state *sm_state, int comparison, struct range_list *vals,
                int lr,
                struct stree *pre_stree,
                struct stree **true_states,
                struct stree **false_states)
{
        struct stree_stack *true_stack = NULL;
        struct stree_stack *false_stack = NULL;
        struct timeval time_before;
        struct timeval time_after;

        gettimeofday(&time_before, NULL);

        if (!is_merged(sm_state)) {
                DIMPLIED("%d '%s' is not merged.\n", get_lineno(), sm_state->name);
                return;
        }

        if (option_debug_implied || option_debug) {
                if (lr == LEFT)
                        sm_msg("checking implications: (%s %s %s)",
                                sm_state->name, show_special(comparison), show_rl(vals));
                else
                        sm_msg("checking implications: (%s %s %s)",
                                show_rl(vals), show_special(comparison), sm_state->name);
        }

        separate_pools(sm_state, comparison, vals, lr, &true_stack, &false_stack, NULL);

        DIMPLIED("filtering true stack.\n");
        *true_states = filter_stack(sm_state, pre_stree, false_stack, true_stack);
        DIMPLIED("filtering false stack.\n");
        *false_states = filter_stack(sm_state, pre_stree, true_stack, false_stack);
        free_stree_stack(&true_stack);
        free_stree_stack(&false_stack);
        if (option_debug_implied || option_debug) {
                printf("These are the implied states for the true path:\n");
                __print_stree(*true_states);
                printf("These are the implied states for the false path:\n");
                __print_stree(*false_states);
        }

        gettimeofday(&time_after, NULL);
        if (time_after.tv_sec - time_before.tv_sec > 7)
                __bail_on_rest_of_function = 1;
}

static struct expression *get_left_most_expr(struct expression *expr)
{
        expr = strip_expr(expr);
        if (expr->type == EXPR_ASSIGNMENT)
                return get_left_most_expr(expr->left);
        return expr;
}

static int is_merged_expr(struct expression  *expr)
{
        struct sm_state *sm;
        sval_t dummy;

        if (get_value(expr, &dummy))
                return 0;
        sm = get_sm_state_expr(SMATCH_EXTRA, expr);
        if (!sm)
                return 0;
        if (is_merged(sm))
                return 1;
        return 0;
}

static void delete_equiv_stree(struct stree **stree, const char *name, struct symbol *sym)
{
        struct smatch_state *state;
        struct relation *rel;

        state = get_state(SMATCH_EXTRA, name, sym);
        if (!estate_related(state)) {
                delete_state_stree(stree, SMATCH_EXTRA, name, sym);
                return;
        }

        FOR_EACH_PTR(estate_related(state), rel) {
                delete_state_stree(stree, SMATCH_EXTRA, rel->name, rel->sym);
        } END_FOR_EACH_PTR(rel);
}

static void handle_comparison(struct expression *expr,
                              struct stree **implied_true,
                              struct stree **implied_false)
{
        struct sm_state *sm = NULL;
        struct range_list *ranges = NULL;
        struct expression *left;
        struct expression *right;
        int lr;

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

        if (is_merged_expr(left)) {
                lr = LEFT;
                sm = get_sm_state_expr(SMATCH_EXTRA, left);
                get_implied_rl(right, &ranges);
        } else if (is_merged_expr(right)) {
                lr = RIGHT;
                sm = get_sm_state_expr(SMATCH_EXTRA, right);
                get_implied_rl(left, &ranges);
        }

        if (!ranges || !sm) {
                free_rl(&ranges);
                return;
        }

        separate_and_filter(sm, expr->op, ranges, lr, __get_cur_stree(), implied_true, implied_false);
        free_rl(&ranges);
        delete_equiv_stree(implied_true, sm->name, sm->sym);
        delete_equiv_stree(implied_false, sm->name, sm->sym);
}

static void handle_zero_comparison(struct expression *expr,
                                struct stree **implied_true,
                                struct stree **implied_false)
{
        struct symbol *sym;
        char *name;
        struct sm_state *sm;

        if (expr->type == EXPR_POSTOP)
                expr = strip_expr(expr->unop);

        if (expr->type == EXPR_ASSIGNMENT) {
                /* most of the time ->pools will be empty here because we
                   just set the state, but if have assigned a conditional
                   function there are implications. */
                expr = expr->left;
        }

        name = expr_to_var_sym(expr, &sym);
        if (!name || !sym)
                goto free;
        sm = get_sm_state(SMATCH_EXTRA, name, sym);
        if (!sm)
                goto free;

        separate_and_filter(sm, SPECIAL_NOTEQUAL, tmp_range_list(0), LEFT, __get_cur_stree(), implied_true, implied_false);
        delete_equiv_stree(implied_true, name, sym);
        delete_equiv_stree(implied_false, name, sym);
free:
        free_string(name);
}

static int handled_by_implied_hook(struct expression *expr,
                                   struct stree **implied_true,
                                   struct stree **implied_false)
{
        struct stree_stack *true_stack = NULL;
        struct stree_stack *false_stack = NULL;
        struct stree *pre_stree;
        struct sm_state *sm;

        sm = comparison_implication_hook(expr, &true_stack, &false_stack);
        if (!sm)
                return 0;

        pre_stree = clone_stree(__get_cur_stree());

        *implied_true = filter_stack(sm, pre_stree, false_stack, true_stack);
        *implied_false = filter_stack(sm, pre_stree, true_stack, false_stack);

        free_stree(&pre_stree);
        free_stree_stack(&true_stack);
        free_stree_stack(&false_stack);

        return 1;
}

static void get_tf_states(struct expression *expr,
                          struct stree **implied_true,
                          struct stree **implied_false)
{
        if (handled_by_implied_hook(expr, implied_true, implied_false))
                return;

        if (expr->type == EXPR_COMPARE)
                handle_comparison(expr, implied_true, implied_false);
        else
                handle_zero_comparison(expr, implied_true, implied_false);
}

static struct stree *saved_implied_true;
static struct stree *saved_implied_false;

static void save_implications_hook(struct expression *expr)
{
        if (option_no_implied)
                return;
        get_tf_states(expr, &saved_implied_true, &saved_implied_false);
}

static void set_implied_states(struct expression *expr)
{
        struct sm_state *sm;

        FOR_EACH_SM(saved_implied_true, sm) {
                __set_true_false_sm(sm, NULL);
        } END_FOR_EACH_SM(sm);
        free_stree(&saved_implied_true);

        FOR_EACH_SM(saved_implied_false, sm) {
                __set_true_false_sm(NULL, sm);
        } END_FOR_EACH_SM(sm);
        free_stree(&saved_implied_false);
}

struct range_list *__get_implied_values(struct expression *switch_expr)
{
        char *name;
        struct symbol *sym;
        struct smatch_state *state;
        struct range_list *ret = NULL;

        name = expr_to_var_sym(switch_expr, &sym);
        if (!name || !sym)
                goto free;
        state = get_state(SMATCH_EXTRA, name, sym);
        if (!state)
                goto free;
        ret = clone_rl(estate_rl(state));
free:
        free_string(name);
        if (!ret) {
                struct symbol *type;

                type = get_type(switch_expr);
                ret = alloc_rl(sval_type_min(type), sval_type_max(type));
        }
        return ret;
}

struct stree *__implied_case_stree(struct expression *switch_expr,
                                        struct expression *case_expr,
                                        struct range_list_stack **remaining_cases,
                                        struct stree **raw_stree)
{
        char *name = NULL;
        struct symbol *sym;
        struct sm_state *sm;
        struct stree *true_states = NULL;
        struct stree *false_states = NULL;
        struct stree *extra_states = NULL;
        struct stree *ret = clone_stree(*raw_stree);
        sval_t sval;
        struct range_list *vals = NULL;

        name = expr_to_var_sym(switch_expr, &sym);
        if (!name || !sym)
                goto free;
        sm = get_sm_state_stree(*raw_stree, SMATCH_EXTRA, name, sym);

        if (case_expr) {
                if (get_value(case_expr, &sval)) {
                        filter_top_rl(remaining_cases, sval);
                        add_range(&vals, sval, sval);
                } else {
                        vals = clone_rl(top_rl(*remaining_cases));
                }
        } else {
                vals = top_rl(*remaining_cases);
        }

        if (sm)
                separate_and_filter(sm, SPECIAL_EQUAL, vals, LEFT, *raw_stree, &true_states, &false_states);

        __push_fake_cur_stree();
        __unnullify_path();
        set_extra_nomod(name, sym, alloc_estate_rl(vals));
        extra_states = __pop_fake_cur_stree();
        overwrite_stree(extra_states, &true_states);
        overwrite_stree(true_states, &ret);
        free_stree(&extra_states);
        free_stree(&true_states);
        free_stree(&false_states);
free:
        free_string(name);
        return ret;
}

static void match_end_func(struct symbol *sym)
{
        if (__inline_fn)
                return;
        implied_debug_msg = NULL;
}

static int sm_state_in_slist(struct sm_state *sm, struct state_list *slist)
{
        struct sm_state *tmp;

        FOR_EACH_PTR(slist, tmp) {
                if (tmp == sm)
                        return 1;
        } END_FOR_EACH_PTR(tmp);
        return 0;
}

/*
 * The situation is we have a SMATCH_EXTRA state and we want to break it into
 * each of the ->possible states and find the implications of each.  The caller
 * has to use __push_fake_cur_stree() to preserve the correct states so they
 * can be restored later.
 */
void overwrite_states_using_pool(struct sm_state *sm)
{
        struct sm_state *old;
        struct sm_state *new;

        if (!sm->pool)
                return;

        FOR_EACH_SM(sm->pool, old) {
                new = get_sm_state(old->owner, old->name, old->sym);
                if (!new)  /* the variable went out of scope */
                        continue;
                if (sm_state_in_slist(old, new->possible))
                        set_state(old->owner, old->name, old->sym, old->state);
        } END_FOR_EACH_SM(old);
}

void __extra_match_condition(struct expression *expr);
void __comparison_match_condition(struct expression *expr);
void register_implications(int id)
{
        add_hook(&save_implications_hook, CONDITION_HOOK);
        add_hook(&__extra_match_condition, CONDITION_HOOK);
        add_hook(&__comparison_match_condition, CONDITION_HOOK);
        add_hook(&set_implied_states, CONDITION_HOOK);
        add_hook(&match_end_func, END_FUNC_HOOK);
}