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git/builtin/init-db.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

587 lines
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/*
* GIT - The information manager from hell
*
* Copyright (C) Linus Torvalds, 2005
*/
#include "cache.h"
#include "config.h"
#include "refs.h"
#include "builtin.h"
#include "exec_cmd.h"
#include "parse-options.h"
#ifndef DEFAULT_GIT_TEMPLATE_DIR
#define DEFAULT_GIT_TEMPLATE_DIR "/usr/share/git-core/templates"
#endif
#ifdef NO_TRUSTABLE_FILEMODE
#define TEST_FILEMODE 0
#else
#define TEST_FILEMODE 1
#endif
static int init_is_bare_repository = 0;
static int init_shared_repository = -1;
static const char *init_db_template_dir;
static void copy_templates_1(struct strbuf *path, struct strbuf *template,
DIR *dir)
{
size_t path_baselen = path->len;
size_t template_baselen = template->len;
struct dirent *de;
/* Note: if ".git/hooks" file exists in the repository being
* re-initialized, /etc/core-git/templates/hooks/update would
* cause "git init" to fail here. I think this is sane but
* it means that the set of templates we ship by default, along
* with the way the namespace under .git/ is organized, should
* be really carefully chosen.
*/
safe_create_dir(path->buf, 1);
while ((de = readdir(dir)) != NULL) {
struct stat st_git, st_template;
int exists = 0;
strbuf_setlen(path, path_baselen);
strbuf_setlen(template, template_baselen);
if (de->d_name[0] == '.')
continue;
strbuf_addstr(path, de->d_name);
strbuf_addstr(template, de->d_name);
if (lstat(path->buf, &st_git)) {
if (errno != ENOENT)
die_errno(_("cannot stat '%s'"), path->buf);
}
else
exists = 1;
if (lstat(template->buf, &st_template))
die_errno(_("cannot stat template '%s'"), template->buf);
if (S_ISDIR(st_template.st_mode)) {
DIR *subdir = opendir(template->buf);
if (!subdir)
die_errno(_("cannot opendir '%s'"), template->buf);
strbuf_addch(path, '/');
strbuf_addch(template, '/');
copy_templates_1(path, template, subdir);
closedir(subdir);
}
else if (exists)
continue;
else if (S_ISLNK(st_template.st_mode)) {
struct strbuf lnk = STRBUF_INIT;
if (strbuf_readlink(&lnk, template->buf, 0) < 0)
die_errno(_("cannot readlink '%s'"), template->buf);
if (symlink(lnk.buf, path->buf))
die_errno(_("cannot symlink '%s' '%s'"),
lnk.buf, path->buf);
strbuf_release(&lnk);
}
else if (S_ISREG(st_template.st_mode)) {
if (copy_file(path->buf, template->buf, st_template.st_mode))
die_errno(_("cannot copy '%s' to '%s'"),
template->buf, path->buf);
}
else
error(_("ignoring template %s"), template->buf);
}
}
static void copy_templates(const char *template_dir)
{
struct strbuf path = STRBUF_INIT;
struct strbuf template_path = STRBUF_INIT;
size_t template_len;
struct repository_format template_format;
struct strbuf err = STRBUF_INIT;
DIR *dir;
char *to_free = NULL;
if (!template_dir)
template_dir = getenv(TEMPLATE_DIR_ENVIRONMENT);
if (!template_dir)
template_dir = init_db_template_dir;
if (!template_dir)
template_dir = to_free = system_path(DEFAULT_GIT_TEMPLATE_DIR);
if (!template_dir[0]) {
free(to_free);
return;
}
strbuf_addstr(&template_path, template_dir);
strbuf_complete(&template_path, '/');
template_len = template_path.len;
dir = opendir(template_path.buf);
if (!dir) {
warning(_("templates not found %s"), template_dir);
goto free_return;
}
/* Make sure that template is from the correct vintage */
strbuf_addstr(&template_path, "config");
read_repository_format(&template_format, template_path.buf);
strbuf_setlen(&template_path, template_len);
/*
* No mention of version at all is OK, but anything else should be
* verified.
*/
if (template_format.version >= 0 &&
verify_repository_format(&template_format, &err) < 0) {
warning(_("not copying templates from '%s': %s"),
template_dir, err.buf);
strbuf_release(&err);
goto close_free_return;
}
strbuf_addstr(&path, get_git_common_dir());
strbuf_complete(&path, '/');
copy_templates_1(&path, &template_path, dir);
close_free_return:
closedir(dir);
free_return:
free(to_free);
strbuf_release(&path);
strbuf_release(&template_path);
}
static int git_init_db_config(const char *k, const char *v, void *cb)
{
if (!strcmp(k, "init.templatedir"))
return git_config_pathname(&init_db_template_dir, k, v);
return 0;
}
/*
* If the git_dir is not directly inside the working tree, then git will not
* find it by default, and we need to set the worktree explicitly.
*/
static int needs_work_tree_config(const char *git_dir, const char *work_tree)
{
if (!strcmp(work_tree, "/") && !strcmp(git_dir, "/.git"))
return 0;
if (skip_prefix(git_dir, work_tree, &git_dir) &&
!strcmp(git_dir, "/.git"))
return 0;
return 1;
}
static int create_default_files(const char *template_path,
const char *original_git_dir)
{
struct stat st1;
struct strbuf buf = STRBUF_INIT;
char *path;
char repo_version_string[10];
char junk[2];
int reinit;
int filemode;
struct strbuf err = STRBUF_INIT;
/* Just look for `init.templatedir` */
git_config(git_init_db_config, NULL);
/*
* First copy the templates -- we might have the default
* config file there, in which case we would want to read
* from it after installing.
*
* Before reading that config, we also need to clear out any cached
* values (since we've just potentially changed what's available on
* disk).
*/
copy_templates(template_path);
git_config_clear();
reset_shared_repository();
git_config(git_default_config, NULL);
/*
* We must make sure command-line options continue to override any
* values we might have just re-read from the config.
*/
is_bare_repository_cfg = init_is_bare_repository;
if (init_shared_repository != -1)
set_shared_repository(init_shared_repository);
/*
* We would have created the above under user's umask -- under
* shared-repository settings, we would need to fix them up.
*/
if (get_shared_repository()) {
adjust_shared_perm(get_git_dir());
}
/*
* We need to create a "refs" dir in any case so that older
* versions of git can tell that this is a repository.
*/
safe_create_dir(git_path("refs"), 1);
adjust_shared_perm(git_path("refs"));
if (refs_init_db(&err))
die("failed to set up refs db: %s", err.buf);
/*
* Create the default symlink from ".git/HEAD" to the "master"
* branch, if it does not exist yet.
*/
path = git_path_buf(&buf, "HEAD");
reinit = (!access(path, R_OK)
|| readlink(path, junk, sizeof(junk)-1) != -1);
if (!reinit) {
if (create_symref("HEAD", "refs/heads/master", NULL) < 0)
exit(1);
}
/* This forces creation of new config file */
xsnprintf(repo_version_string, sizeof(repo_version_string),
"%d", GIT_REPO_VERSION);
git_config_set("core.repositoryformatversion", repo_version_string);
/* Check filemode trustability */
path = git_path_buf(&buf, "config");
filemode = TEST_FILEMODE;
if (TEST_FILEMODE && !lstat(path, &st1)) {
struct stat st2;
filemode = (!chmod(path, st1.st_mode ^ S_IXUSR) &&
!lstat(path, &st2) &&
st1.st_mode != st2.st_mode &&
!chmod(path, st1.st_mode));
if (filemode && !reinit && (st1.st_mode & S_IXUSR))
filemode = 0;
}
git_config_set("core.filemode", filemode ? "true" : "false");
if (is_bare_repository())
git_config_set("core.bare", "true");
else {
const char *work_tree = get_git_work_tree();
git_config_set("core.bare", "false");
/* allow template config file to override the default */
if (log_all_ref_updates == LOG_REFS_UNSET)
git_config_set("core.logallrefupdates", "true");
if (needs_work_tree_config(original_git_dir, work_tree))
git_config_set("core.worktree", work_tree);
}
if (!reinit) {
/* Check if symlink is supported in the work tree */
path = git_path_buf(&buf, "tXXXXXX");
if (!close(xmkstemp(path)) &&
!unlink(path) &&
!symlink("testing", path) &&
!lstat(path, &st1) &&
S_ISLNK(st1.st_mode))
unlink(path); /* good */
else
git_config_set("core.symlinks", "false");
/* Check if the filesystem is case-insensitive */
path = git_path_buf(&buf, "CoNfIg");
if (!access(path, F_OK))
git_config_set("core.ignorecase", "true");
probe_utf8_pathname_composition();
}
strbuf_release(&buf);
return reinit;
}
static void create_object_directory(void)
{
struct strbuf path = STRBUF_INIT;
size_t baselen;
strbuf_addstr(&path, get_object_directory());
baselen = path.len;
safe_create_dir(path.buf, 1);
strbuf_setlen(&path, baselen);
strbuf_addstr(&path, "/pack");
safe_create_dir(path.buf, 1);
strbuf_setlen(&path, baselen);
strbuf_addstr(&path, "/info");
safe_create_dir(path.buf, 1);
strbuf_release(&path);
}
static void separate_git_dir(const char *git_dir, const char *git_link)
{
struct stat st;
if (!stat(git_link, &st)) {
const char *src;
if (S_ISREG(st.st_mode))
src = read_gitfile(git_link);
else if (S_ISDIR(st.st_mode))
src = git_link;
else
die(_("unable to handle file type %d"), (int)st.st_mode);
if (rename(src, git_dir))
die_errno(_("unable to move %s to %s"), src, git_dir);
}
write_file(git_link, "gitdir: %s", git_dir);
}
int init_db(const char *git_dir, const char *real_git_dir,
const char *template_dir, unsigned int flags)
{
int reinit;
int exist_ok = flags & INIT_DB_EXIST_OK;
char *original_git_dir = real_pathdup(git_dir, 1);
if (real_git_dir) {
struct stat st;
if (!exist_ok && !stat(git_dir, &st))
die(_("%s already exists"), git_dir);
if (!exist_ok && !stat(real_git_dir, &st))
die(_("%s already exists"), real_git_dir);
set_git_dir(real_path(real_git_dir));
git_dir = get_git_dir();
separate_git_dir(git_dir, original_git_dir);
}
else {
set_git_dir(real_path(git_dir));
git_dir = get_git_dir();
}
startup_info->have_repository = 1;
safe_create_dir(git_dir, 0);
init_is_bare_repository = is_bare_repository();
/* Check to see if the repository version is right.
* Note that a newly created repository does not have
* config file, so this will not fail. What we are catching
* is an attempt to reinitialize new repository with an old tool.
*/
check_repository_format();
reinit = create_default_files(template_dir, original_git_dir);
create_object_directory();
if (get_shared_repository()) {
char buf[10];
/* We do not spell "group" and such, so that
* the configuration can be read by older version
* of git. Note, we use octal numbers for new share modes,
* and compatibility values for PERM_GROUP and
* PERM_EVERYBODY.
*/
if (get_shared_repository() < 0)
/* force to the mode value */
xsnprintf(buf, sizeof(buf), "0%o", -get_shared_repository());
else if (get_shared_repository() == PERM_GROUP)
xsnprintf(buf, sizeof(buf), "%d", OLD_PERM_GROUP);
else if (get_shared_repository() == PERM_EVERYBODY)
xsnprintf(buf, sizeof(buf), "%d", OLD_PERM_EVERYBODY);
else
die("BUG: invalid value for shared_repository");
git_config_set("core.sharedrepository", buf);
git_config_set("receive.denyNonFastforwards", "true");
}
if (!(flags & INIT_DB_QUIET)) {
int len = strlen(git_dir);
if (reinit)
printf(get_shared_repository()
? _("Reinitialized existing shared Git repository in %s%s\n")
: _("Reinitialized existing Git repository in %s%s\n"),
git_dir, len && git_dir[len-1] != '/' ? "/" : "");
else
printf(get_shared_repository()
? _("Initialized empty shared Git repository in %s%s\n")
: _("Initialized empty Git repository in %s%s\n"),
git_dir, len && git_dir[len-1] != '/' ? "/" : "");
}
free(original_git_dir);
return 0;
}
static int guess_repository_type(const char *git_dir)
{
const char *slash;
char *cwd;
int cwd_is_git_dir;
/*
* "GIT_DIR=. git init" is always bare.
* "GIT_DIR=`pwd` git init" too.
*/
if (!strcmp(".", git_dir))
return 1;
cwd = xgetcwd();
cwd_is_git_dir = !strcmp(git_dir, cwd);
free(cwd);
if (cwd_is_git_dir)
return 1;
/*
* "GIT_DIR=.git or GIT_DIR=something/.git is usually not.
*/
if (!strcmp(git_dir, ".git"))
return 0;
slash = strrchr(git_dir, '/');
if (slash && !strcmp(slash, "/.git"))
return 0;
/*
* Otherwise it is often bare. At this point
* we are just guessing.
*/
return 1;
}
static int shared_callback(const struct option *opt, const char *arg, int unset)
{
*((int *) opt->value) = (arg) ? git_config_perm("arg", arg) : PERM_GROUP;
return 0;
}
static const char *const init_db_usage[] = {
N_("git init [-q | --quiet] [--bare] [--template=<template-directory>] [--shared[=<permissions>]] [<directory>]"),
NULL
};
/*
* If you want to, you can share the DB area with any number of branches.
* That has advantages: you can save space by sharing all the SHA1 objects.
* On the other hand, it might just make lookup slower and messier. You
* be the judge. The default case is to have one DB per managed directory.
*/
int cmd_init_db(int argc, const char **argv, const char *prefix)
{
const char *git_dir;
const char *real_git_dir = NULL;
const char *work_tree;
const char *template_dir = NULL;
unsigned int flags = 0;
const struct option init_db_options[] = {
OPT_STRING(0, "template", &template_dir, N_("template-directory"),
N_("directory from which templates will be used")),
OPT_SET_INT(0, "bare", &is_bare_repository_cfg,
N_("create a bare repository"), 1),
{ OPTION_CALLBACK, 0, "shared", &init_shared_repository,
N_("permissions"),
N_("specify that the git repository is to be shared amongst several users"),
PARSE_OPT_OPTARG | PARSE_OPT_NONEG, shared_callback, 0},
OPT_BIT('q', "quiet", &flags, N_("be quiet"), INIT_DB_QUIET),
OPT_STRING(0, "separate-git-dir", &real_git_dir, N_("gitdir"),
N_("separate git dir from working tree")),
OPT_END()
};
argc = parse_options(argc, argv, prefix, init_db_options, init_db_usage, 0);
if (real_git_dir && !is_absolute_path(real_git_dir))
real_git_dir = real_pathdup(real_git_dir, 1);
if (argc == 1) {
int mkdir_tried = 0;
retry:
if (chdir(argv[0]) < 0) {
if (!mkdir_tried) {
int saved;
/*
* At this point we haven't read any configuration,
* and we know shared_repository should always be 0;
* but just in case we play safe.
*/
saved = get_shared_repository();
set_shared_repository(0);
switch (safe_create_leading_directories_const(argv[0])) {
case SCLD_OK:
case SCLD_PERMS:
break;
case SCLD_EXISTS:
errno = EEXIST;
/* fallthru */
default:
die_errno(_("cannot mkdir %s"), argv[0]);
break;
}
set_shared_repository(saved);
if (mkdir(argv[0], 0777) < 0)
die_errno(_("cannot mkdir %s"), argv[0]);
mkdir_tried = 1;
goto retry;
}
die_errno(_("cannot chdir to %s"), argv[0]);
}
} else if (0 < argc) {
usage(init_db_usage[0]);
}
if (is_bare_repository_cfg == 1) {
char *cwd = xgetcwd();
setenv(GIT_DIR_ENVIRONMENT, cwd, argc > 0);
free(cwd);
}
if (init_shared_repository != -1)
set_shared_repository(init_shared_repository);
/*
* GIT_WORK_TREE makes sense only in conjunction with GIT_DIR
* without --bare. Catch the error early.
*/
git_dir = getenv(GIT_DIR_ENVIRONMENT);
work_tree = getenv(GIT_WORK_TREE_ENVIRONMENT);
if ((!git_dir || is_bare_repository_cfg == 1) && work_tree)
die(_("%s (or --work-tree=<directory>) not allowed without "
"specifying %s (or --git-dir=<directory>)"),
GIT_WORK_TREE_ENVIRONMENT,
GIT_DIR_ENVIRONMENT);
/*
* Set up the default .git directory contents
*/
if (!git_dir)
git_dir = DEFAULT_GIT_DIR_ENVIRONMENT;
if (is_bare_repository_cfg < 0)
is_bare_repository_cfg = guess_repository_type(git_dir);
if (!is_bare_repository_cfg) {
const char *git_dir_parent = strrchr(git_dir, '/');
if (git_dir_parent) {
char *rel = xstrndup(git_dir, git_dir_parent - git_dir);
git_work_tree_cfg = real_pathdup(rel, 1);
free(rel);
}
if (!git_work_tree_cfg)
git_work_tree_cfg = xgetcwd();
if (work_tree)
set_git_work_tree(work_tree);
else
set_git_work_tree(git_work_tree_cfg);
if (access(get_git_work_tree(), X_OK))
die_errno (_("Cannot access work tree '%s'"),
get_git_work_tree());
}
else {
if (work_tree)
set_git_work_tree(work_tree);
}
UNLEAK(real_git_dir);
flags |= INIT_DB_EXIST_OK;
return init_db(git_dir, real_git_dir, template_dir, flags);
}
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