refs/files: fix NULL pointer deref when releasing ref store

[git/gitster.git] / attr.c

/*
 * Handle git attributes.  See gitattributes(5) for a description of
 * the file syntax, and attr.h for a description of the API.
 *
 * One basic design decision here is that we are not going to support
 * an insanely large number of attributes.
 */

#include "git-compat-util.h"
#include "config.h"
#include "environment.h"
#include "exec-cmd.h"
#include "attr.h"
#include "dir.h"
#include "gettext.h"
#include "path.h"
#include "utf8.h"
#include "quote.h"
#include "read-cache-ll.h"
#include "refs.h"
#include "revision.h"
#include "object-store-ll.h"
#include "setup.h"
#include "thread-utils.h"
#include "tree-walk.h"
#include "object-name.h"

const char *git_attr_tree;

const char git_attr__true[] = "(builtin)true";
const char git_attr__false[] = "\0(builtin)false";
static const char git_attr__unknown[] = "(builtin)unknown";
#define ATTR__TRUE git_attr__true
#define ATTR__FALSE git_attr__false
#define ATTR__UNSET NULL
#define ATTR__UNKNOWN git_attr__unknown

struct git_attr {
        unsigned int attr_nr; /* unique attribute number */
        char name[FLEX_ARRAY]; /* attribute name */
};

const char *git_attr_name(const struct git_attr *attr)
{
        return attr->name;
}

struct attr_hashmap {
        struct hashmap map;
        pthread_mutex_t mutex;
};

static inline void hashmap_lock(struct attr_hashmap *map)
{
        pthread_mutex_lock(&map->mutex);
}

static inline void hashmap_unlock(struct attr_hashmap *map)
{
        pthread_mutex_unlock(&map->mutex);
}

/* The container for objects stored in "struct attr_hashmap" */
struct attr_hash_entry {
        struct hashmap_entry ent;
        const char *key; /* the key; memory should be owned by value */
        size_t keylen; /* length of the key */
        void *value; /* the stored value */
};

/* attr_hashmap comparison function */
static int attr_hash_entry_cmp(const void *cmp_data UNUSED,
                               const struct hashmap_entry *eptr,
                               const struct hashmap_entry *entry_or_key,
                               const void *keydata UNUSED)
{
        const struct attr_hash_entry *a, *b;

        a = container_of(eptr, const struct attr_hash_entry, ent);
        b = container_of(entry_or_key, const struct attr_hash_entry, ent);
        return (a->keylen != b->keylen) || strncmp(a->key, b->key, a->keylen);
}

/*
 * The global dictionary of all interned attributes.  This
 * is a singleton object which is shared between threads.
 * Access to this dictionary must be surrounded with a mutex.
 */
static struct attr_hashmap g_attr_hashmap = {
        .map = HASHMAP_INIT(attr_hash_entry_cmp, NULL),
};

/*
 * Retrieve the 'value' stored in a hashmap given the provided 'key'.
 * If there is no matching entry, return NULL.
 */
static void *attr_hashmap_get(struct attr_hashmap *map,
                              const char *key, size_t keylen)
{
        struct attr_hash_entry k;
        struct attr_hash_entry *e;

        hashmap_entry_init(&k.ent, memhash(key, keylen));
        k.key = key;
        k.keylen = keylen;
        e = hashmap_get_entry(&map->map, &k, ent, NULL);

        return e ? e->value : NULL;
}

/* Add 'value' to a hashmap based on the provided 'key'. */
static void attr_hashmap_add(struct attr_hashmap *map,
                             const char *key, size_t keylen,
                             void *value)
{
        struct attr_hash_entry *e;

        e = xmalloc(sizeof(struct attr_hash_entry));
        hashmap_entry_init(&e->ent, memhash(key, keylen));
        e->key = key;
        e->keylen = keylen;
        e->value = value;

        hashmap_add(&map->map, &e->ent);
}

struct all_attrs_item {
        const struct git_attr *attr;
        const char *value;
        /*
         * If 'macro' is non-NULL, indicates that 'attr' is a macro based on
         * the current attribute stack and contains a pointer to the match_attr
         * definition of the macro
         */
        const struct match_attr *macro;
};

/*
 * Reallocate and reinitialize the array of all attributes (which is used in
 * the attribute collection process) in 'check' based on the global dictionary
 * of attributes.
 */
static void all_attrs_init(struct attr_hashmap *map, struct attr_check *check)
{
        int i;
        unsigned int size;

        hashmap_lock(map);

        size = hashmap_get_size(&map->map);
        if (size < check->all_attrs_nr)
                BUG("interned attributes shouldn't be deleted");

        /*
         * If the number of attributes in the global dictionary has increased
         * (or this attr_check instance doesn't have an initialized all_attrs
         * field), reallocate the provided attr_check instance's all_attrs
         * field and fill each entry with its corresponding git_attr.
         */
        if (size != check->all_attrs_nr) {
                struct attr_hash_entry *e;
                struct hashmap_iter iter;

                REALLOC_ARRAY(check->all_attrs, size);
                check->all_attrs_nr = size;

                hashmap_for_each_entry(&map->map, &iter, e,
                                        ent /* member name */) {
                        const struct git_attr *a = e->value;
                        check->all_attrs[a->attr_nr].attr = a;
                }
        }

        hashmap_unlock(map);

        /*
         * Re-initialize every entry in check->all_attrs.
         * This re-initialization can live outside of the locked region since
         * the attribute dictionary is no longer being accessed.
         */
        for (i = 0; i < check->all_attrs_nr; i++) {
                check->all_attrs[i].value = ATTR__UNKNOWN;
                check->all_attrs[i].macro = NULL;
        }
}

/*
 * Atribute name cannot begin with "builtin_" which
 * is a reserved namespace for built in attributes values.
 */
static int attr_name_reserved(const char *name)
{
        return starts_with(name, "builtin_");
}

static int attr_name_valid(const char *name, size_t namelen)
{
        /*
         * Attribute name cannot begin with '-' and must consist of
         * characters from [-A-Za-z0-9_.].
         */
        if (namelen <= 0 || *name == '-')
                return 0;
        while (namelen--) {
                char ch = *name++;
                if (! (ch == '-' || ch == '.' || ch == '_' ||
                       ('0' <= ch && ch <= '9') ||
                       ('a' <= ch && ch <= 'z') ||
                       ('A' <= ch && ch <= 'Z')) )
                        return 0;
        }
        return 1;
}

static void report_invalid_attr(const char *name, size_t len,
                                const char *src, int lineno)
{
        struct strbuf err = STRBUF_INIT;
        strbuf_addf(&err, _("%.*s is not a valid attribute name"),
                    (int) len, name);
        fprintf(stderr, "%s: %s:%d\n", err.buf, src, lineno);
        strbuf_release(&err);
}

/*
 * Given a 'name', lookup and return the corresponding attribute in the global
 * dictionary.  If no entry is found, create a new attribute and store it in
 * the dictionary.
 */
static const struct git_attr *git_attr_internal(const char *name, size_t namelen)
{
        struct git_attr *a;

        if (!attr_name_valid(name, namelen))
                return NULL;

        hashmap_lock(&g_attr_hashmap);

        a = attr_hashmap_get(&g_attr_hashmap, name, namelen);

        if (!a) {
                FLEX_ALLOC_MEM(a, name, name, namelen);
                a->attr_nr = hashmap_get_size(&g_attr_hashmap.map);

                attr_hashmap_add(&g_attr_hashmap, a->name, namelen, a);
                if (a->attr_nr != hashmap_get_size(&g_attr_hashmap.map) - 1)
                        die(_("unable to add additional attribute"));
        }

        hashmap_unlock(&g_attr_hashmap);

        return a;
}

const struct git_attr *git_attr(const char *name)
{
        return git_attr_internal(name, strlen(name));
}

/* What does a matched pattern decide? */
struct attr_state {
        const struct git_attr *attr;
        const char *setto;
};

struct pattern {
        const char *pattern;
        int patternlen;
        int nowildcardlen;
        unsigned flags;         /* PATTERN_FLAG_* */
};

/*
 * One rule, as from a .gitattributes file.
 *
 * If is_macro is true, then u.attr is a pointer to the git_attr being
 * defined.
 *
 * If is_macro is false, then u.pat is the filename pattern to which the
 * rule applies.
 *
 * In either case, num_attr is the number of attributes affected by
 * this rule, and state is an array listing them.  The attributes are
 * listed as they appear in the file (macros unexpanded).
 */
struct match_attr {
        union {
                struct pattern pat;
                const struct git_attr *attr;
        } u;
        char is_macro;
        size_t num_attr;
        struct attr_state state[FLEX_ARRAY];
};

static const char blank[] = " \t\r\n";

/* Flags usable in read_attr() and parse_attr_line() family of functions. */
#define READ_ATTR_MACRO_OK (1<<0)
#define READ_ATTR_NOFOLLOW (1<<1)

/*
 * Parse a whitespace-delimited attribute state (i.e., "attr",
 * "-attr", "!attr", or "attr=value") from the string starting at src.
 * If e is not NULL, write the results to *e.  Return a pointer to the
 * remainder of the string (with leading whitespace removed), or NULL
 * if there was an error.
 */
static const char *parse_attr(const char *src, int lineno, const char *cp,
                              struct attr_state *e)
{
        const char *ep, *equals;
        size_t len;

        ep = cp + strcspn(cp, blank);
        equals = strchr(cp, '=');
        if (equals && ep < equals)
                equals = NULL;
        if (equals)
                len = equals - cp;
        else
                len = ep - cp;
        if (!e) {
                if (*cp == '-' || *cp == '!') {
                        cp++;
                        len--;
                }
                if (!attr_name_valid(cp, len) || attr_name_reserved(cp)) {
                        report_invalid_attr(cp, len, src, lineno);
                        return NULL;
                }
        } else {
                /*
                 * As this function is always called twice, once with
                 * e == NULL in the first pass and then e != NULL in
                 * the second pass, no need for attr_name_valid()
                 * check here.
                 */
                if (*cp == '-' || *cp == '!') {
                        e->setto = (*cp == '-') ? ATTR__FALSE : ATTR__UNSET;
                        cp++;
                        len--;
                }
                else if (!equals)
                        e->setto = ATTR__TRUE;
                else {
                        e->setto = xmemdupz(equals + 1, ep - equals - 1);
                }
                e->attr = git_attr_internal(cp, len);
        }
        return ep + strspn(ep, blank);
}

static struct match_attr *parse_attr_line(const char *line, const char *src,
                                          int lineno, unsigned flags)
{
        size_t namelen, num_attr, i;
        const char *cp, *name, *states;
        struct match_attr *res = NULL;
        int is_macro;
        struct strbuf pattern = STRBUF_INIT;

        cp = line + strspn(line, blank);
        if (!*cp || *cp == '#')
                return NULL;
        name = cp;

        if (strlen(line) >= ATTR_MAX_LINE_LENGTH) {
                warning(_("ignoring overly long attributes line %d"), lineno);
                return NULL;
        }

        if (*cp == '"' && !unquote_c_style(&pattern, name, &states)) {
                name = pattern.buf;
                namelen = pattern.len;
        } else {
                namelen = strcspn(name, blank);
                states = name + namelen;
        }

        if (strlen(ATTRIBUTE_MACRO_PREFIX) < namelen &&
            starts_with(name, ATTRIBUTE_MACRO_PREFIX)) {
                if (!(flags & READ_ATTR_MACRO_OK)) {
                        fprintf_ln(stderr, _("%s not allowed: %s:%d"),
                                   name, src, lineno);
                        goto fail_return;
                }
                is_macro = 1;
                name += strlen(ATTRIBUTE_MACRO_PREFIX);
                name += strspn(name, blank);
                namelen = strcspn(name, blank);
                if (!attr_name_valid(name, namelen) || attr_name_reserved(name)) {
                        report_invalid_attr(name, namelen, src, lineno);
                        goto fail_return;
                }
        }
        else
                is_macro = 0;

        states += strspn(states, blank);

        /* First pass to count the attr_states */
        for (cp = states, num_attr = 0; *cp; num_attr++) {
                cp = parse_attr(src, lineno, cp, NULL);
                if (!cp)
                        goto fail_return;
        }

        res = xcalloc(1, st_add3(sizeof(*res),
                                 st_mult(sizeof(struct attr_state), num_attr),
                                 is_macro ? 0 : namelen + 1));
        if (is_macro) {
                res->u.attr = git_attr_internal(name, namelen);
        } else {
                char *p = (char *)&(res->state[num_attr]);
                memcpy(p, name, namelen);
                res->u.pat.pattern = p;
                parse_path_pattern(&res->u.pat.pattern,
                                      &res->u.pat.patternlen,
                                      &res->u.pat.flags,
                                      &res->u.pat.nowildcardlen);
                if (res->u.pat.flags & PATTERN_FLAG_NEGATIVE) {
                        warning(_("Negative patterns are ignored in git attributes\n"
                                  "Use '\\!' for literal leading exclamation."));
                        goto fail_return;
                }
        }
        res->is_macro = is_macro;
        res->num_attr = num_attr;

        /* Second pass to fill the attr_states */
        for (cp = states, i = 0; *cp; i++) {
                cp = parse_attr(src, lineno, cp, &(res->state[i]));
        }

        strbuf_release(&pattern);
        return res;

fail_return:
        strbuf_release(&pattern);
        free(res);
        return NULL;
}

/*
 * Like info/exclude and .gitignore, the attribute information can
 * come from many places.
 *
 * (1) .gitattributes file of the same directory;
 * (2) .gitattributes file of the parent directory if (1) does not have
 *      any match; this goes recursively upwards, just like .gitignore.
 * (3) $GIT_DIR/info/attributes, which overrides both of the above.
 *
 * In the same file, later entries override the earlier match, so in the
 * global list, we would have entries from info/attributes the earliest
 * (reading the file from top to bottom), .gitattributes of the root
 * directory (again, reading the file from top to bottom) down to the
 * current directory, and then scan the list backwards to find the first match.
 * This is exactly the same as what is_excluded() does in dir.c to deal with
 * .gitignore file and info/excludes file as a fallback.
 */

struct attr_stack {
        struct attr_stack *prev;
        char *origin;
        size_t originlen;
        unsigned num_matches;
        unsigned alloc;
        struct match_attr **attrs;
};

static void attr_stack_free(struct attr_stack *e)
{
        unsigned i;
        free(e->origin);
        for (i = 0; i < e->num_matches; i++) {
                struct match_attr *a = e->attrs[i];
                size_t j;

                for (j = 0; j < a->num_attr; j++) {
                        const char *setto = a->state[j].setto;
                        if (setto == ATTR__TRUE ||
                            setto == ATTR__FALSE ||
                            setto == ATTR__UNSET ||
                            setto == ATTR__UNKNOWN)
                                ;
                        else
                                free((char *) setto);
                }
                free(a);
        }
        free(e->attrs);
        free(e);
}

static void drop_attr_stack(struct attr_stack **stack)
{
        while (*stack) {
                struct attr_stack *elem = *stack;
                *stack = elem->prev;
                attr_stack_free(elem);
        }
}

/* List of all attr_check structs; access should be surrounded by mutex */
static struct check_vector {
        size_t nr;
        size_t alloc;
        struct attr_check **checks;
        pthread_mutex_t mutex;
} check_vector;

static inline void vector_lock(void)
{
        pthread_mutex_lock(&check_vector.mutex);
}

static inline void vector_unlock(void)
{
        pthread_mutex_unlock(&check_vector.mutex);
}

static void check_vector_add(struct attr_check *c)
{
        vector_lock();

        ALLOC_GROW(check_vector.checks,
                   check_vector.nr + 1,
                   check_vector.alloc);
        check_vector.checks[check_vector.nr++] = c;

        vector_unlock();
}

static void check_vector_remove(struct attr_check *check)
{
        int i;

        vector_lock();

        /* Find entry */
        for (i = 0; i < check_vector.nr; i++)
                if (check_vector.checks[i] == check)
                        break;

        if (i >= check_vector.nr)
                BUG("no entry found");

        /* shift entries over */
        for (; i < check_vector.nr - 1; i++)
                check_vector.checks[i] = check_vector.checks[i + 1];

        check_vector.nr--;

        vector_unlock();
}

/* Iterate through all attr_check instances and drop their stacks */
static void drop_all_attr_stacks(void)
{
        int i;

        vector_lock();

        for (i = 0; i < check_vector.nr; i++) {
                drop_attr_stack(&check_vector.checks[i]->stack);
        }

        vector_unlock();
}

struct attr_check *attr_check_alloc(void)
{
        struct attr_check *c = xcalloc(1, sizeof(struct attr_check));

        /* save pointer to the check struct */
        check_vector_add(c);

        return c;
}

struct attr_check *attr_check_initl(const char *one, ...)
{
        struct attr_check *check;
        int cnt;
        va_list params;
        const char *param;

        va_start(params, one);
        for (cnt = 1; (param = va_arg(params, const char *)) != NULL; cnt++)
                ;
        va_end(params);

        check = attr_check_alloc();
        check->nr = cnt;
        check->alloc = cnt;
        CALLOC_ARRAY(check->items, cnt);

        check->items[0].attr = git_attr(one);
        va_start(params, one);
        for (cnt = 1; cnt < check->nr; cnt++) {
                const struct git_attr *attr;
                param = va_arg(params, const char *);
                if (!param)
                        BUG("counted %d != ended at %d",
                            check->nr, cnt);
                attr = git_attr(param);
                if (!attr)
                        BUG("%s: not a valid attribute name", param);
                check->items[cnt].attr = attr;
        }
        va_end(params);
        return check;
}

struct attr_check *attr_check_dup(const struct attr_check *check)
{
        struct attr_check *ret;

        if (!check)
                return NULL;

        ret = attr_check_alloc();

        ret->nr = check->nr;
        ret->alloc = check->alloc;
        DUP_ARRAY(ret->items, check->items, ret->nr);

        return ret;
}

struct attr_check_item *attr_check_append(struct attr_check *check,
                                          const struct git_attr *attr)
{
        struct attr_check_item *item;

        ALLOC_GROW(check->items, check->nr + 1, check->alloc);
        item = &check->items[check->nr++];
        item->attr = attr;
        return item;
}

void attr_check_reset(struct attr_check *check)
{
        check->nr = 0;
}

void attr_check_clear(struct attr_check *check)
{
        FREE_AND_NULL(check->items);
        check->alloc = 0;
        check->nr = 0;

        FREE_AND_NULL(check->all_attrs);
        check->all_attrs_nr = 0;

        drop_attr_stack(&check->stack);
}

void attr_check_free(struct attr_check *check)
{
        if (check) {
                /* Remove check from the check vector */
                check_vector_remove(check);

                attr_check_clear(check);
                free(check);
        }
}

static const char *builtin_attr[] = {
        "[attr]binary -diff -merge -text",
        NULL,
};

static void handle_attr_line(struct attr_stack *res,
                             const char *line,
                             const char *src,
                             int lineno,
                             unsigned flags)
{
        struct match_attr *a;

        a = parse_attr_line(line, src, lineno, flags);
        if (!a)
                return;
        ALLOC_GROW_BY(res->attrs, res->num_matches, 1, res->alloc);
        res->attrs[res->num_matches - 1] = a;
}

static struct attr_stack *read_attr_from_array(const char **list)
{
        struct attr_stack *res;
        const char *line;
        int lineno = 0;

        CALLOC_ARRAY(res, 1);
        while ((line = *(list++)) != NULL)
                handle_attr_line(res, line, "[builtin]", ++lineno,
                                 READ_ATTR_MACRO_OK);
        return res;
}

/*
 * Callers into the attribute system assume there is a single, system-wide
 * global state where attributes are read from and when the state is flipped by
 * calling git_attr_set_direction(), the stack frames that have been
 * constructed need to be discarded so that subsequent calls into the
 * attribute system will lazily read from the right place.  Since changing
 * direction causes a global paradigm shift, it should not ever be called while
 * another thread could potentially be calling into the attribute system.
 */
static enum git_attr_direction direction;

void git_attr_set_direction(enum git_attr_direction new_direction)
{
        if (is_bare_repository() && new_direction != GIT_ATTR_INDEX)
                BUG("non-INDEX attr direction in a bare repo");

        if (new_direction != direction)
                drop_all_attr_stacks();

        direction = new_direction;
}

static struct attr_stack *read_attr_from_file(const char *path, unsigned flags)
{
        struct strbuf buf = STRBUF_INIT;
        int fd;
        FILE *fp;
        struct attr_stack *res;
        int lineno = 0;
        struct stat st;

        if (flags & READ_ATTR_NOFOLLOW)
                fd = open_nofollow(path, O_RDONLY);
        else
                fd = open(path, O_RDONLY);

        if (fd < 0) {
                warn_on_fopen_errors(path);
                return NULL;
        }
        fp = xfdopen(fd, "r");
        if (fstat(fd, &st)) {
                warning_errno(_("cannot fstat gitattributes file '%s'"), path);
                fclose(fp);
                return NULL;
        }
        if (st.st_size >= ATTR_MAX_FILE_SIZE) {
                warning(_("ignoring overly large gitattributes file '%s'"), path);
                fclose(fp);
                return NULL;
        }

        CALLOC_ARRAY(res, 1);
        while (strbuf_getline(&buf, fp) != EOF) {
                if (!lineno && starts_with(buf.buf, utf8_bom))
                        strbuf_remove(&buf, 0, strlen(utf8_bom));
                handle_attr_line(res, buf.buf, path, ++lineno, flags);
        }

        fclose(fp);
        strbuf_release(&buf);
        return res;
}

static struct attr_stack *read_attr_from_buf(char *buf, size_t length,
                                             const char *path, unsigned flags)
{
        struct attr_stack *res;
        char *sp;
        int lineno = 0;

        if (!buf)
                return NULL;
        if (length >= ATTR_MAX_FILE_SIZE) {
                warning(_("ignoring overly large gitattributes blob '%s'"), path);
                free(buf);
                return NULL;
        }

        CALLOC_ARRAY(res, 1);
        for (sp = buf; *sp;) {
                char *ep;
                int more;

                ep = strchrnul(sp, '\n');
                more = (*ep == '\n');
                *ep = '\0';
                handle_attr_line(res, sp, path, ++lineno, flags);
                sp = ep + more;
        }
        free(buf);

        return res;
}

static struct attr_stack *read_attr_from_blob(struct index_state *istate,
                                              const struct object_id *tree_oid,
                                              const char *path, unsigned flags)
{
        struct object_id oid;
        unsigned long sz;
        enum object_type type;
        void *buf;
        unsigned short mode;

        if (!tree_oid)
                return NULL;

        if (get_tree_entry(istate->repo, tree_oid, path, &oid, &mode))
                return NULL;

        buf = repo_read_object_file(istate->repo, &oid, &type, &sz);
        if (!buf || type != OBJ_BLOB) {
                free(buf);
                return NULL;
        }

        return read_attr_from_buf(buf, sz, path, flags);
}

static struct attr_stack *read_attr_from_index(struct index_state *istate,
                                               const char *path, unsigned flags)
{
        struct attr_stack *stack = NULL;
        char *buf;
        unsigned long size;
        int sparse_dir_pos = -1;

        if (!istate)
                return NULL;

        /*
         * When handling sparse-checkouts, .gitattributes files
         * may reside within a sparse directory. We distinguish
         * whether a path exists directly in the index or not by
         * evaluating if 'pos' is negative.
         * If 'pos' is negative, the path is not directly present
         * in the index and is likely within a sparse directory.
         * For paths not in the index, The absolute value of 'pos'
         * minus 1 gives us the position where the path would be
         * inserted in lexicographic order within the index.
         * We then subtract another 1 from this value
         * (sparse_dir_pos = -pos - 2) to find the position of the
         * last index entry which is lexicographically smaller than
         * the path. This would be the sparse directory containing
         * the path. By identifying the sparse directory containing
         * the path, we can correctly read the attributes specified
         * in the .gitattributes file from the tree object of the
         * sparse directory.
         */
        if (!path_in_cone_mode_sparse_checkout(path, istate)) {
                int pos = index_name_pos_sparse(istate, path, strlen(path));

                if (pos < 0)
                        sparse_dir_pos = -pos - 2;
        }

        if (sparse_dir_pos >= 0 &&
            S_ISSPARSEDIR(istate->cache[sparse_dir_pos]->ce_mode) &&
            !strncmp(istate->cache[sparse_dir_pos]->name, path, ce_namelen(istate->cache[sparse_dir_pos]))) {
                const char *relative_path = path + ce_namelen(istate->cache[sparse_dir_pos]);
                stack = read_attr_from_blob(istate, &istate->cache[sparse_dir_pos]->oid, relative_path, flags);
        } else {
                buf = read_blob_data_from_index(istate, path, &size);
                stack = read_attr_from_buf(buf, size, path, flags);
        }
        return stack;
}

static struct attr_stack *read_attr(struct index_state *istate,
                                    const struct object_id *tree_oid,
                                    const char *path, unsigned flags)
{
        struct attr_stack *res = NULL;

        if (direction == GIT_ATTR_INDEX) {
                res = read_attr_from_index(istate, path, flags);
        } else if (tree_oid) {
                res = read_attr_from_blob(istate, tree_oid, path, flags);
        } else if (!is_bare_repository()) {
                if (direction == GIT_ATTR_CHECKOUT) {
                        res = read_attr_from_index(istate, path, flags);
                        if (!res)
                                res = read_attr_from_file(path, flags);
                } else if (direction == GIT_ATTR_CHECKIN) {
                        res = read_attr_from_file(path, flags);
                        if (!res)
                                /*
                                 * There is no checked out .gitattributes file
                                 * there, but we might have it in the index.
                                 * We allow operation in a sparsely checked out
                                 * work tree, so read from it.
                                 */
                                res = read_attr_from_index(istate, path, flags);
                }
        }

        if (!res)
                CALLOC_ARRAY(res, 1);
        return res;
}

const char *git_attr_system_file(void)
{
        static const char *system_wide;
        if (!system_wide)
                system_wide = system_path(ETC_GITATTRIBUTES);
        return system_wide;
}

const char *git_attr_global_file(void)
{
        if (!git_attributes_file)
                git_attributes_file = xdg_config_home("attributes");

        return git_attributes_file;
}

int git_attr_system_is_enabled(void)
{
        return !git_env_bool("GIT_ATTR_NOSYSTEM", 0);
}

static GIT_PATH_FUNC(git_path_info_attributes, INFOATTRIBUTES_FILE)

static void push_stack(struct attr_stack **attr_stack_p,
                       struct attr_stack *elem, char *origin, size_t originlen)
{
        if (elem) {
                elem->origin = origin;
                if (origin)
                        elem->originlen = originlen;
                elem->prev = *attr_stack_p;
                *attr_stack_p = elem;
        }
}

static void bootstrap_attr_stack(struct index_state *istate,
                                 const struct object_id *tree_oid,
                                 struct attr_stack **stack)
{
        struct attr_stack *e;
        unsigned flags = READ_ATTR_MACRO_OK;

        if (*stack)
                return;

        /* builtin frame */
        e = read_attr_from_array(builtin_attr);
        push_stack(stack, e, NULL, 0);

        /* system-wide frame */
        if (git_attr_system_is_enabled()) {
                e = read_attr_from_file(git_attr_system_file(), flags);
                push_stack(stack, e, NULL, 0);
        }

        /* home directory */
        if (git_attr_global_file()) {
                e = read_attr_from_file(git_attr_global_file(), flags);
                push_stack(stack, e, NULL, 0);
        }

        /* root directory */
        e = read_attr(istate, tree_oid, GITATTRIBUTES_FILE, flags | READ_ATTR_NOFOLLOW);
        push_stack(stack, e, xstrdup(""), 0);

        /* info frame */
        if (startup_info->have_repository)
                e = read_attr_from_file(git_path_info_attributes(), flags);
        else
                e = NULL;
        if (!e)
                CALLOC_ARRAY(e, 1);
        push_stack(stack, e, NULL, 0);
}

static void prepare_attr_stack(struct index_state *istate,
                               const struct object_id *tree_oid,
                               const char *path, int dirlen,
                               struct attr_stack **stack)
{
        struct attr_stack *info;
        struct strbuf pathbuf = STRBUF_INIT;

        /*
         * At the bottom of the attribute stack is the built-in
         * set of attribute definitions, followed by the contents
         * of $(prefix)/etc/gitattributes and a file specified by
         * core.attributesfile.  Then, contents from
         * .gitattributes files from directories closer to the
         * root to the ones in deeper directories are pushed
         * to the stack.  Finally, at the very top of the stack
         * we always keep the contents of $GIT_DIR/info/attributes.
         *
         * When checking, we use entries from near the top of the
         * stack, preferring $GIT_DIR/info/attributes, then
         * .gitattributes in deeper directories to shallower ones,
         * and finally use the built-in set as the default.
         */
        bootstrap_attr_stack(istate, tree_oid, stack);

        /*
         * Pop the "info" one that is always at the top of the stack.
         */
        info = *stack;
        *stack = info->prev;

        /*
         * Pop the ones from directories that are not the prefix of
         * the path we are checking. Break out of the loop when we see
         * the root one (whose origin is an empty string "") or the builtin
         * one (whose origin is NULL) without popping it.
         */
        while ((*stack)->origin) {
                int namelen = (*stack)->originlen;
                struct attr_stack *elem;

                elem = *stack;
                if (namelen <= dirlen &&
                    !strncmp(elem->origin, path, namelen) &&
                    (!namelen || path[namelen] == '/'))
                        break;

                *stack = elem->prev;
                attr_stack_free(elem);
        }

        /*
         * bootstrap_attr_stack() should have added, and the
         * above loop should have stopped before popping, the
         * root element whose attr_stack->origin is set to an
         * empty string.
         */
        assert((*stack)->origin);

        strbuf_addstr(&pathbuf, (*stack)->origin);
        /* Build up to the directory 'path' is in */
        while (pathbuf.len < dirlen) {
                size_t len = pathbuf.len;
                struct attr_stack *next;
                char *origin;

                /* Skip path-separator */
                if (len < dirlen && is_dir_sep(path[len]))
                        len++;
                /* Find the end of the next component */
                while (len < dirlen && !is_dir_sep(path[len]))
                        len++;

                if (pathbuf.len > 0)
                        strbuf_addch(&pathbuf, '/');
                strbuf_add(&pathbuf, path + pathbuf.len, (len - pathbuf.len));
                strbuf_addf(&pathbuf, "/%s", GITATTRIBUTES_FILE);

                next = read_attr(istate, tree_oid, pathbuf.buf, READ_ATTR_NOFOLLOW);

                /* reset the pathbuf to not include "/.gitattributes" */
                strbuf_setlen(&pathbuf, len);

                origin = xstrdup(pathbuf.buf);
                push_stack(stack, next, origin, len);
        }

        /*
         * Finally push the "info" one at the top of the stack.
         */
        push_stack(stack, info, NULL, 0);

        strbuf_release(&pathbuf);
}

static int path_matches(const char *pathname, int pathlen,
                        int basename_offset,
                        const struct pattern *pat,
                        const char *base, int baselen)
{
        const char *pattern = pat->pattern;
        int prefix = pat->nowildcardlen;
        int isdir = (pathlen && pathname[pathlen - 1] == '/');

        if ((pat->flags & PATTERN_FLAG_MUSTBEDIR) && !isdir)
                return 0;

        if (pat->flags & PATTERN_FLAG_NODIR) {
                return match_basename(pathname + basename_offset,
                                      pathlen - basename_offset - isdir,
                                      pattern, prefix,
                                      pat->patternlen, pat->flags);
        }
        return match_pathname(pathname, pathlen - isdir,
                              base, baselen,
                              pattern, prefix, pat->patternlen);
}

static int macroexpand_one(struct all_attrs_item *all_attrs, int nr, int rem);

static int fill_one(struct all_attrs_item *all_attrs,
                    const struct match_attr *a, int rem)
{
        size_t i;

        for (i = a->num_attr; rem > 0 && i > 0; i--) {
                const struct git_attr *attr = a->state[i - 1].attr;
                const char **n = &(all_attrs[attr->attr_nr].value);
                const char *v = a->state[i - 1].setto;

                if (*n == ATTR__UNKNOWN) {
                        *n = v;
                        rem--;
                        rem = macroexpand_one(all_attrs, attr->attr_nr, rem);
                }
        }
        return rem;
}

static int fill(const char *path, int pathlen, int basename_offset,
                const struct attr_stack *stack,
                struct all_attrs_item *all_attrs, int rem)
{
        for (; rem > 0 && stack; stack = stack->prev) {
                unsigned i;
                const char *base = stack->origin ? stack->origin : "";

                for (i = stack->num_matches; 0 < rem && 0 < i; i--) {
                        const struct match_attr *a = stack->attrs[i - 1];
                        if (a->is_macro)
                                continue;
                        if (path_matches(path, pathlen, basename_offset,
                                         &a->u.pat, base, stack->originlen))
                                rem = fill_one(all_attrs, a, rem);
                }
        }

        return rem;
}

static int macroexpand_one(struct all_attrs_item *all_attrs, int nr, int rem)
{
        const struct all_attrs_item *item = &all_attrs[nr];

        if (item->macro && item->value == ATTR__TRUE)
                return fill_one(all_attrs, item->macro, rem);
        else
                return rem;
}

/*
 * Marks the attributes which are macros based on the attribute stack.
 * This prevents having to search through the attribute stack each time
 * a macro needs to be expanded during the fill stage.
 */
static void determine_macros(struct all_attrs_item *all_attrs,
                             const struct attr_stack *stack)
{
        for (; stack; stack = stack->prev) {
                unsigned i;
                for (i = stack->num_matches; i > 0; i--) {
                        const struct match_attr *ma = stack->attrs[i - 1];
                        if (ma->is_macro) {
                                unsigned int n = ma->u.attr->attr_nr;
                                if (!all_attrs[n].macro) {
                                        all_attrs[n].macro = ma;
                                }
                        }
                }
        }
}

/*
 * Collect attributes for path into the array pointed to by check->all_attrs.
 * If check->check_nr is non-zero, only attributes in check[] are collected.
 * Otherwise all attributes are collected.
 */
static void collect_some_attrs(struct index_state *istate,
                               const struct object_id *tree_oid,
                               const char *path, struct attr_check *check)
{
        int pathlen, rem, dirlen;
        const char *cp, *last_slash = NULL;
        int basename_offset;

        for (cp = path; *cp; cp++) {
                if (*cp == '/' && cp[1])
                        last_slash = cp;
        }
        pathlen = cp - path;
        if (last_slash) {
                basename_offset = last_slash + 1 - path;
                dirlen = last_slash - path;
        } else {
                basename_offset = 0;
                dirlen = 0;
        }

        prepare_attr_stack(istate, tree_oid, path, dirlen, &check->stack);
        all_attrs_init(&g_attr_hashmap, check);
        determine_macros(check->all_attrs, check->stack);

        rem = check->all_attrs_nr;
        fill(path, pathlen, basename_offset, check->stack, check->all_attrs, rem);
}

static const char *default_attr_source_tree_object_name;
static int ignore_bad_attr_tree;

void set_git_attr_source(const char *tree_object_name)
{
        default_attr_source_tree_object_name = xstrdup(tree_object_name);
}

static void compute_default_attr_source(struct object_id *attr_source)
{
        if (!default_attr_source_tree_object_name)
                default_attr_source_tree_object_name = getenv(GIT_ATTR_SOURCE_ENVIRONMENT);

        if (!default_attr_source_tree_object_name && git_attr_tree) {
                default_attr_source_tree_object_name = git_attr_tree;
                ignore_bad_attr_tree = 1;
        }

        if (!default_attr_source_tree_object_name || !is_null_oid(attr_source))
                return;

        if (repo_get_oid_treeish(the_repository,
                                 default_attr_source_tree_object_name,
                                 attr_source) && !ignore_bad_attr_tree)
                die(_("bad --attr-source or GIT_ATTR_SOURCE"));
}

static struct object_id *default_attr_source(void)
{
        static struct object_id attr_source;

        if (is_null_oid(&attr_source))
                compute_default_attr_source(&attr_source);
        if (is_null_oid(&attr_source))
                return NULL;
        return &attr_source;
}

static const char *interned_mode_string(unsigned int mode)
{
        static struct {
                unsigned int val;
                char str[7];
        } mode_string[] = {
                { .val = 0040000 },
                { .val = 0100644 },
                { .val = 0100755 },
                { .val = 0120000 },
                { .val = 0160000 },
        };
        int i;

        for (i = 0; i < ARRAY_SIZE(mode_string); i++) {
                if (mode_string[i].val != mode)
                        continue;
                if (!*mode_string[i].str)
                        snprintf(mode_string[i].str, sizeof(mode_string[i].str),
                                 "%06o", mode);
                return mode_string[i].str;
        }
        BUG("Unsupported mode 0%o", mode);
}

static const char *builtin_object_mode_attr(struct index_state *istate, const char *path)
{
        unsigned int mode;

        if (direction == GIT_ATTR_CHECKIN) {
                struct object_id oid;
                struct stat st;
                if (lstat(path, &st))
                        die_errno(_("unable to stat '%s'"), path);
                mode = canon_mode(st.st_mode);
                if (S_ISDIR(mode)) {
                        /*
                         *`path` is either a directory or it is a submodule,
                         * in which case it is already indexed as submodule
                         * or it does not exist in the index yet and we need to
                         * check if we can resolve to a ref.
                        */
                        int pos = index_name_pos(istate, path, strlen(path));
                        if (pos >= 0) {
                                 if (S_ISGITLINK(istate->cache[pos]->ce_mode))
                                         mode = istate->cache[pos]->ce_mode;
                        } else if (repo_resolve_gitlink_ref(the_repository, path,
                                                            "HEAD", &oid) == 0) {
                                mode = S_IFGITLINK;
                        }
                }
        } else {
                /*
                 * For GIT_ATTR_CHECKOUT and GIT_ATTR_INDEX we only check
                 * for mode in the index.
                 */
                int pos = index_name_pos(istate, path, strlen(path));
                if (pos >= 0)
                        mode = istate->cache[pos]->ce_mode;
                else
                        return ATTR__UNSET;
        }

        return interned_mode_string(mode);
}


static const char *compute_builtin_attr(struct index_state *istate,
                                          const char *path,
                                          const struct git_attr *attr) {
        static const struct git_attr *object_mode_attr;

        if (!object_mode_attr)
                object_mode_attr = git_attr("builtin_objectmode");

        if (attr == object_mode_attr)
                return builtin_object_mode_attr(istate, path);
        return ATTR__UNSET;
}

void git_check_attr(struct index_state *istate,
                    const char *path,
                    struct attr_check *check)
{
        int i;
        const struct object_id *tree_oid = default_attr_source();

        collect_some_attrs(istate, tree_oid, path, check);

        for (i = 0; i < check->nr; i++) {
                unsigned int n = check->items[i].attr->attr_nr;
                const char *value = check->all_attrs[n].value;
                if (value == ATTR__UNKNOWN)
                        value = compute_builtin_attr(istate, path, check->all_attrs[n].attr);
                check->items[i].value = value;
        }
}

void git_all_attrs(struct index_state *istate,
                   const char *path, struct attr_check *check)
{
        int i;
        const struct object_id *tree_oid = default_attr_source();

        attr_check_reset(check);
        collect_some_attrs(istate, tree_oid, path, check);

        for (i = 0; i < check->all_attrs_nr; i++) {
                const char *name = check->all_attrs[i].attr->name;
                const char *value = check->all_attrs[i].value;
                struct attr_check_item *item;
                if (value == ATTR__UNSET || value == ATTR__UNKNOWN)
                        continue;
                item = attr_check_append(check, git_attr(name));
                item->value = value;
        }
}

void attr_start(void)
{
        pthread_mutex_init(&g_attr_hashmap.mutex, NULL);
        pthread_mutex_init(&check_vector.mutex, NULL);
}