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git-commit-vandalism/builtin/worktree.c
Jeff King 0e5bba53af add UNLEAK annotation for reducing leak false positives 
It's a common pattern in git commands to allocate some
memory that should last for the lifetime of the program and
then not bother to free it, relying on the OS to throw it
away.

This keeps the code simple, and it's fast (we don't waste
time traversing structures or calling free at the end of the
program). But it also triggers warnings from memory-leak
checkers like valgrind or LSAN. They know that the memory
was still allocated at program exit, but they don't know
_when_ the leaked memory stopped being useful. If it was
early in the program, then it's probably a real and
important leak. But if it was used right up until program
exit, it's not an interesting leak and we'd like to suppress
it so that we can see the real leaks.

This patch introduces an UNLEAK() macro that lets us do so.
To understand its design, let's first look at some of the
alternatives.

Unfortunately the suppression systems offered by
leak-checking tools don't quite do what we want. A
leak-checker basically knows two things:

  1. Which blocks were allocated via malloc, and the
     callstack during the allocation.

  2. Which blocks were left un-freed at the end of the
     program (and which are unreachable, but more on that
     later).

Their suppressions work by mentioning the function or
callstack of a particular allocation, and marking it as OK
to leak.  So imagine you have code like this:

  int cmd_foo(...)
  {
	/* this allocates some memory */
	char *p = some_function();
	printf("%s", p);
	return 0;
  }

You can say "ignore allocations from some_function(),
they're not leaks". But that's not right. That function may
be called elsewhere, too, and we would potentially want to
know about those leaks.

So you can say "ignore the callstack when main calls
some_function".  That works, but your annotations are
brittle. In this case it's only two functions, but you can
imagine that the actual allocation is much deeper. If any of
the intermediate code changes, you have to update the
suppression.

What we _really_ want to say is that "the value assigned to
p at the end of the function is not a real leak". But
leak-checkers can't understand that; they don't know about
"p" in the first place.

However, we can do something a little bit tricky if we make
some assumptions about how leak-checkers work. They
generally don't just report all un-freed blocks. That would
report even globals which are still accessible when the
leak-check is run.  Instead they take some set of memory
(like BSS) as a root and mark it as "reachable". Then they
scan the reachable blocks for anything that looks like a
pointer to a malloc'd block, and consider that block
reachable. And then they scan those blocks, and so on,
transitively marking anything reachable from a global as
"not leaked" (or at least leaked in a different category).

So we can mark the value of "p" as reachable by putting it
into a variable with program lifetime. One way to do that is
to just mark "p" as static. But that actually affects the
run-time behavior if the function is called twice (you
aren't likely to call main() twice, but some of our cmd_*()
functions are called from other commands).

Instead, we can trick the leak-checker by putting the value
into _any_ reachable bytes. This patch keeps a global
linked-list of bytes copied from "unleaked" variables. That
list is reachable even at program exit, which confers
recursive reachability on whatever values we unleak.

In other words, you can do:

  int cmd_foo(...)
  {
	char *p = some_function();
	printf("%s", p);
	UNLEAK(p);
	return 0;
  }

to annotate "p" and suppress the leak report.

But wait, couldn't we just say "free(p)"? In this toy
example, yes. But UNLEAK()'s byte-copying strategy has
several advantages over actually freeing the memory:

  1. It's recursive across structures. In many cases our "p"
     is not just a pointer, but a complex struct whose
     fields may have been allocated by a sub-function. And
     in some cases (e.g., dir_struct) we don't even have a
     function which knows how to free all of the struct
     members.

     By marking the struct itself as reachable, that confers
     reachability on any pointers it contains (including those
     found in embedded structs, or reachable by walking
     heap blocks recursively.

  2. It works on cases where we're not sure if the value is
     allocated or not. For example:

       char *p = argc > 1 ? argv[1] : some_function();

     It's safe to use UNLEAK(p) here, because it's not
     freeing any memory. In the case that we're pointing to
     argv here, the reachability checker will just ignore
     our bytes.

  3. Likewise, it works even if the variable has _already_
     been freed. We're just copying the pointer bytes. If
     the block has been freed, the leak-checker will skip
     over those bytes as uninteresting.

  4. Because it's not actually freeing memory, you can
     UNLEAK() before we are finished accessing the variable.
     This is helpful in cases like this:

       char *p = some_function();
       return another_function(p);

     Writing this with free() requires:

       int ret;
       char *p = some_function();
       ret = another_function(p);
       free(p);
       return ret;

     But with unleak we can just write:

       char *p = some_function();
       UNLEAK(p);
       return another_function(p);

This patch adds the UNLEAK() macro and enables it
automatically when Git is compiled with SANITIZE=leak.  In
normal builds it's a noop, so we pay no runtime cost.

It also adds some UNLEAK() annotations to show off how the
feature works. On top of other recent leak fixes, these are
enough to get t0000 and t0001 to pass when compiled with
LSAN.

Note the case in commit.c which actually converts a
strbuf_release() into an UNLEAK. This code was already
non-leaky, but the free didn't do anything useful, since
we're exiting. Converting it to an annotation means that
non-leak-checking builds pay no runtime cost. The cost is
minimal enough that it's probably not worth going on a
crusade to convert these kinds of frees to UNLEAKS. I did it
here for consistency with the "sb" leak (though it would
have been equally correct to go the other way, and turn them
both into strbuf_release() calls).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-09-08 15:43:17 +09:00

560 lines
14 KiB
C
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#include "cache.h"
#include "config.h"
#include "builtin.h"
#include "dir.h"
#include "parse-options.h"
#include "argv-array.h"
#include "branch.h"
#include "refs.h"
#include "run-command.h"
#include "sigchain.h"
#include "refs.h"
#include "utf8.h"
#include "worktree.h"
static const char * const worktree_usage[] = {
N_("git worktree add [<options>] <path> [<branch>]"),
N_("git worktree list [<options>]"),
N_("git worktree lock [<options>] <path>"),
N_("git worktree prune [<options>]"),
N_("git worktree unlock <path>"),
NULL
};
struct add_opts {
int force;
int detach;
int checkout;
int keep_locked;
const char *new_branch;
int force_new_branch;
};
static int show_only;
static int verbose;
static timestamp_t expire;
static int prune_worktree(const char *id, struct strbuf *reason)
{
struct stat st;
char *path;
int fd, len;
if (!is_directory(git_path("worktrees/%s", id))) {
strbuf_addf(reason, _("Removing worktrees/%s: not a valid directory"), id);
return 1;
}
if (file_exists(git_path("worktrees/%s/locked", id)))
return 0;
if (stat(git_path("worktrees/%s/gitdir", id), &st)) {
strbuf_addf(reason, _("Removing worktrees/%s: gitdir file does not exist"), id);
return 1;
}
fd = open(git_path("worktrees/%s/gitdir", id), O_RDONLY);
if (fd < 0) {
strbuf_addf(reason, _("Removing worktrees/%s: unable to read gitdir file (%s)"),
id, strerror(errno));
return 1;
}
len = st.st_size;
path = xmallocz(len);
read_in_full(fd, path, len);
close(fd);
while (len && (path[len - 1] == '\n' || path[len - 1] == '\r'))
len--;
if (!len) {
strbuf_addf(reason, _("Removing worktrees/%s: invalid gitdir file"), id);
free(path);
return 1;
}
path[len] = '\0';
if (!file_exists(path)) {
struct stat st_link;
free(path);
/*
* the repo is moved manually and has not been
* accessed since?
*/
if (!stat(git_path("worktrees/%s/link", id), &st_link) &&
st_link.st_nlink > 1)
return 0;
if (st.st_mtime <= expire) {
strbuf_addf(reason, _("Removing worktrees/%s: gitdir file points to non-existent location"), id);
return 1;
} else {
return 0;
}
}
free(path);
return 0;
}
static void prune_worktrees(void)
{
struct strbuf reason = STRBUF_INIT;
struct strbuf path = STRBUF_INIT;
DIR *dir = opendir(git_path("worktrees"));
struct dirent *d;
int ret;
if (!dir)
return;
while ((d = readdir(dir)) != NULL) {
if (is_dot_or_dotdot(d->d_name))
continue;
strbuf_reset(&reason);
if (!prune_worktree(d->d_name, &reason))
continue;
if (show_only || verbose)
printf("%s\n", reason.buf);
if (show_only)
continue;
git_path_buf(&path, "worktrees/%s", d->d_name);
ret = remove_dir_recursively(&path, 0);
if (ret < 0 && errno == ENOTDIR)
ret = unlink(path.buf);
if (ret)
error_errno(_("failed to remove '%s'"), path.buf);
}
closedir(dir);
if (!show_only)
rmdir(git_path("worktrees"));
strbuf_release(&reason);
strbuf_release(&path);
}
static int prune(int ac, const char **av, const char *prefix)
{
struct option options[] = {
OPT__DRY_RUN(&show_only, N_("do not remove, show only")),
OPT__VERBOSE(&verbose, N_("report pruned working trees")),
OPT_EXPIRY_DATE(0, "expire", &expire,
N_("expire working trees older than <time>")),
OPT_END()
};
expire = TIME_MAX;
ac = parse_options(ac, av, prefix, options, worktree_usage, 0);
if (ac)
usage_with_options(worktree_usage, options);
prune_worktrees();
return 0;
}
static char *junk_work_tree;
static char *junk_git_dir;
static int is_junk;
static pid_t junk_pid;
static void remove_junk(void)
{
struct strbuf sb = STRBUF_INIT;
if (!is_junk || getpid() != junk_pid)
return;
if (junk_git_dir) {
strbuf_addstr(&sb, junk_git_dir);
remove_dir_recursively(&sb, 0);
strbuf_reset(&sb);
}
if (junk_work_tree) {
strbuf_addstr(&sb, junk_work_tree);
remove_dir_recursively(&sb, 0);
}
strbuf_release(&sb);
}
static void remove_junk_on_signal(int signo)
{
remove_junk();
sigchain_pop(signo);
raise(signo);
}
static const char *worktree_basename(const char *path, int *olen)
{
const char *name;
int len;
len = strlen(path);
while (len && is_dir_sep(path[len - 1]))
len--;
for (name = path + len - 1; name > path; name--)
if (is_dir_sep(*name)) {
name++;
break;
}
*olen = len;
return name;
}
static int add_worktree(const char *path, const char *refname,
const struct add_opts *opts)
{
struct strbuf sb_git = STRBUF_INIT, sb_repo = STRBUF_INIT;
struct strbuf sb = STRBUF_INIT;
const char *name;
struct stat st;
struct child_process cp = CHILD_PROCESS_INIT;
struct argv_array child_env = ARGV_ARRAY_INIT;
int counter = 0, len, ret;
struct strbuf symref = STRBUF_INIT;
struct commit *commit = NULL;
if (file_exists(path) && !is_empty_dir(path))
die(_("'%s' already exists"), path);
/* is 'refname' a branch or commit? */
if (!opts->detach && !strbuf_check_branch_ref(&symref, refname) &&
ref_exists(symref.buf)) { /* it's a branch */
if (!opts->force)
die_if_checked_out(symref.buf, 0);
} else { /* must be a commit */
commit = lookup_commit_reference_by_name(refname);
if (!commit)
die(_("invalid reference: %s"), refname);
}
name = worktree_basename(path, &len);
git_path_buf(&sb_repo, "worktrees/%.*s", (int)(path + len - name), name);
len = sb_repo.len;
if (safe_create_leading_directories_const(sb_repo.buf))
die_errno(_("could not create leading directories of '%s'"),
sb_repo.buf);
while (!stat(sb_repo.buf, &st)) {
counter++;
strbuf_setlen(&sb_repo, len);
strbuf_addf(&sb_repo, "%d", counter);
}
name = strrchr(sb_repo.buf, '/') + 1;
junk_pid = getpid();
atexit(remove_junk);
sigchain_push_common(remove_junk_on_signal);
if (mkdir(sb_repo.buf, 0777))
die_errno(_("could not create directory of '%s'"), sb_repo.buf);
junk_git_dir = xstrdup(sb_repo.buf);
is_junk = 1;
/*
* lock the incomplete repo so prune won't delete it, unlock
* after the preparation is over.
*/
strbuf_addf(&sb, "%s/locked", sb_repo.buf);
if (!opts->keep_locked)
write_file(sb.buf, "initializing");
else
write_file(sb.buf, "added with --lock");
strbuf_addf(&sb_git, "%s/.git", path);
if (safe_create_leading_directories_const(sb_git.buf))
die_errno(_("could not create leading directories of '%s'"),
sb_git.buf);
junk_work_tree = xstrdup(path);
strbuf_reset(&sb);
strbuf_addf(&sb, "%s/gitdir", sb_repo.buf);
write_file(sb.buf, "%s", real_path(sb_git.buf));
write_file(sb_git.buf, "gitdir: %s/worktrees/%s",
real_path(get_git_common_dir()), name);
/*
* This is to keep resolve_ref() happy. We need a valid HEAD
* or is_git_directory() will reject the directory. Any value which
* looks like an object ID will do since it will be immediately
* replaced by the symbolic-ref or update-ref invocation in the new
* worktree.
*/
strbuf_reset(&sb);
strbuf_addf(&sb, "%s/HEAD", sb_repo.buf);
write_file(sb.buf, "%s", sha1_to_hex(null_sha1));
strbuf_reset(&sb);
strbuf_addf(&sb, "%s/commondir", sb_repo.buf);
write_file(sb.buf, "../..");
fprintf_ln(stderr, _("Preparing %s (identifier %s)"), path, name);
argv_array_pushf(&child_env, "%s=%s", GIT_DIR_ENVIRONMENT, sb_git.buf);
argv_array_pushf(&child_env, "%s=%s", GIT_WORK_TREE_ENVIRONMENT, path);
cp.git_cmd = 1;
if (commit)
argv_array_pushl(&cp.args, "update-ref", "HEAD",
oid_to_hex(&commit->object.oid), NULL);
else
argv_array_pushl(&cp.args, "symbolic-ref", "HEAD",
symref.buf, NULL);
cp.env = child_env.argv;
ret = run_command(&cp);
if (ret)
goto done;
if (opts->checkout) {
cp.argv = NULL;
argv_array_clear(&cp.args);
argv_array_pushl(&cp.args, "reset", "--hard", NULL);
cp.env = child_env.argv;
ret = run_command(&cp);
if (ret)
goto done;
}
is_junk = 0;
FREE_AND_NULL(junk_work_tree);
FREE_AND_NULL(junk_git_dir);
done:
if (ret || !opts->keep_locked) {
strbuf_reset(&sb);
strbuf_addf(&sb, "%s/locked", sb_repo.buf);
unlink_or_warn(sb.buf);
}
argv_array_clear(&child_env);
strbuf_release(&sb);
strbuf_release(&symref);
strbuf_release(&sb_repo);
strbuf_release(&sb_git);
return ret;
}
static int add(int ac, const char **av, const char *prefix)
{
struct add_opts opts;
const char *new_branch_force = NULL;
char *path;
const char *branch;
struct option options[] = {
OPT__FORCE(&opts.force, N_("checkout <branch> even if already checked out in other worktree")),
OPT_STRING('b', NULL, &opts.new_branch, N_("branch"),
N_("create a new branch")),
OPT_STRING('B', NULL, &new_branch_force, N_("branch"),
N_("create or reset a branch")),
OPT_BOOL(0, "detach", &opts.detach, N_("detach HEAD at named commit")),
OPT_BOOL(0, "checkout", &opts.checkout, N_("populate the new working tree")),
OPT_BOOL(0, "lock", &opts.keep_locked, N_("keep the new working tree locked")),
OPT_END()
};
memset(&opts, 0, sizeof(opts));
opts.checkout = 1;
ac = parse_options(ac, av, prefix, options, worktree_usage, 0);
if (!!opts.detach + !!opts.new_branch + !!new_branch_force > 1)
die(_("-b, -B, and --detach are mutually exclusive"));
if (ac < 1 || ac > 2)
usage_with_options(worktree_usage, options);
path = prefix_filename(prefix, av[0]);
branch = ac < 2 ? "HEAD" : av[1];
if (!strcmp(branch, "-"))
branch = "@{-1}";
opts.force_new_branch = !!new_branch_force;
if (opts.force_new_branch) {
struct strbuf symref = STRBUF_INIT;
opts.new_branch = new_branch_force;
if (!opts.force &&
!strbuf_check_branch_ref(&symref, opts.new_branch) &&
ref_exists(symref.buf))
die_if_checked_out(symref.buf, 0);
strbuf_release(&symref);
}
if (ac < 2 && !opts.new_branch && !opts.detach) {
int n;
const char *s = worktree_basename(path, &n);
opts.new_branch = xstrndup(s, n);
}
if (opts.new_branch) {
struct child_process cp = CHILD_PROCESS_INIT;
cp.git_cmd = 1;
argv_array_push(&cp.args, "branch");
if (opts.force_new_branch)
argv_array_push(&cp.args, "--force");
argv_array_push(&cp.args, opts.new_branch);
argv_array_push(&cp.args, branch);
if (run_command(&cp))
return -1;
branch = opts.new_branch;
}
UNLEAK(path);
UNLEAK(opts);
return add_worktree(path, branch, &opts);
}
static void show_worktree_porcelain(struct worktree *wt)
{
printf("worktree %s\n", wt->path);
if (wt->is_bare)
printf("bare\n");
else {
printf("HEAD %s\n", sha1_to_hex(wt->head_sha1));
if (wt->is_detached)
printf("detached\n");
else if (wt->head_ref)
printf("branch %s\n", wt->head_ref);
}
printf("\n");
}
static void show_worktree(struct worktree *wt, int path_maxlen, int abbrev_len)
{
struct strbuf sb = STRBUF_INIT;
int cur_path_len = strlen(wt->path);
int path_adj = cur_path_len - utf8_strwidth(wt->path);
strbuf_addf(&sb, "%-*s ", 1 + path_maxlen + path_adj, wt->path);
if (wt->is_bare)
strbuf_addstr(&sb, "(bare)");
else {
strbuf_addf(&sb, "%-*s ", abbrev_len,
find_unique_abbrev(wt->head_sha1, DEFAULT_ABBREV));
if (wt->is_detached)
strbuf_addstr(&sb, "(detached HEAD)");
else if (wt->head_ref) {
char *ref = shorten_unambiguous_ref(wt->head_ref, 0);
strbuf_addf(&sb, "[%s]", ref);
free(ref);
} else
strbuf_addstr(&sb, "(error)");
}
printf("%s\n", sb.buf);
strbuf_release(&sb);
}
static void measure_widths(struct worktree **wt, int *abbrev, int *maxlen)
{
int i;
for (i = 0; wt[i]; i++) {
int sha1_len;
int path_len = strlen(wt[i]->path);
if (path_len > *maxlen)
*maxlen = path_len;
sha1_len = strlen(find_unique_abbrev(wt[i]->head_sha1, *abbrev));
if (sha1_len > *abbrev)
*abbrev = sha1_len;
}
}
static int list(int ac, const char **av, const char *prefix)
{
int porcelain = 0;
struct option options[] = {
OPT_BOOL(0, "porcelain", &porcelain, N_("machine-readable output")),
OPT_END()
};
ac = parse_options(ac, av, prefix, options, worktree_usage, 0);
if (ac)
usage_with_options(worktree_usage, options);
else {
struct worktree **worktrees = get_worktrees(GWT_SORT_LINKED);
int path_maxlen = 0, abbrev = DEFAULT_ABBREV, i;
if (!porcelain)
measure_widths(worktrees, &abbrev, &path_maxlen);
for (i = 0; worktrees[i]; i++) {
if (porcelain)
show_worktree_porcelain(worktrees[i]);
else
show_worktree(worktrees[i], path_maxlen, abbrev);
}
free_worktrees(worktrees);
}
return 0;
}
static int lock_worktree(int ac, const char **av, const char *prefix)
{
const char *reason = "", *old_reason;
struct option options[] = {
OPT_STRING(0, "reason", &reason, N_("string"),
N_("reason for locking")),
OPT_END()
};
struct worktree **worktrees, *wt;
ac = parse_options(ac, av, prefix, options, worktree_usage, 0);
if (ac != 1)
usage_with_options(worktree_usage, options);
worktrees = get_worktrees(0);
wt = find_worktree(worktrees, prefix, av[0]);
if (!wt)
die(_("'%s' is not a working tree"), av[0]);
if (is_main_worktree(wt))
die(_("The main working tree cannot be locked or unlocked"));
old_reason = is_worktree_locked(wt);
if (old_reason) {
if (*old_reason)
die(_("'%s' is already locked, reason: %s"),
av[0], old_reason);
die(_("'%s' is already locked"), av[0]);
}
write_file(git_common_path("worktrees/%s/locked", wt->id),
"%s", reason);
free_worktrees(worktrees);
return 0;
}
static int unlock_worktree(int ac, const char **av, const char *prefix)
{
struct option options[] = {
OPT_END()
};
struct worktree **worktrees, *wt;
int ret;
ac = parse_options(ac, av, prefix, options, worktree_usage, 0);
if (ac != 1)
usage_with_options(worktree_usage, options);
worktrees = get_worktrees(0);
wt = find_worktree(worktrees, prefix, av[0]);
if (!wt)
die(_("'%s' is not a working tree"), av[0]);
if (is_main_worktree(wt))
die(_("The main working tree cannot be locked or unlocked"));
if (!is_worktree_locked(wt))
die(_("'%s' is not locked"), av[0]);
ret = unlink_or_warn(git_common_path("worktrees/%s/locked", wt->id));
free_worktrees(worktrees);
return ret;
}
int cmd_worktree(int ac, const char **av, const char *prefix)
{
struct option options[] = {
OPT_END()
};
git_config(git_default_config, NULL);
if (ac < 2)
usage_with_options(worktree_usage, options);
if (!prefix)
prefix = "";
if (!strcmp(av[1], "add"))
return add(ac - 1, av + 1, prefix);
if (!strcmp(av[1], "prune"))
return prune(ac - 1, av + 1, prefix);
if (!strcmp(av[1], "list"))
return list(ac - 1, av + 1, prefix);
if (!strcmp(av[1], "lock"))
return lock_worktree(ac - 1, av + 1, prefix);
if (!strcmp(av[1], "unlock"))
return unlock_worktree(ac - 1, av + 1, prefix);
usage_with_options(worktree_usage, options);
}
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