From 6854a8f5c9ecf32f5bd85020e77d48d3ffdf48fc Mon Sep 17 00:00:00 2001
From: Jeff King <peff@peff.net>
Date: Sat, 26 Nov 2016 23:31:13 -0500
Subject: common-main: stop munging argv[0] path

Since 650c44925 (common-main: call git_extract_argv0_path(),
2016-07-01), the argv[0] that is seen in cmd_main() of
individual programs is always the basename of the
executable, as common-main strips off the full path. This
can produce confusing results for git-daemon, which wants to
re-exec itself.

For instance, if the program was originally run as
"/usr/lib/git/git-daemon", it will try just re-execing
"git-daemon", which will find the first instance in $PATH.
If git's exec-path has not been prepended to $PATH, we may
find the git-daemon from a different version (or no
git-daemon at all).

Normally this isn't a problem. Git commands are run as "git
daemon", the git wrapper puts the exec-path at the front of
$PATH, and argv[0] is already "daemon" anyway. But running
git-daemon via its full exec-path, while not really a
recommended method, did work prior to 650c44925. Let's make
it work again.

The real goal of 650c44925 was not to munge argv[0], but to
reliably set the argv0_path global. The only reason it
munges at all is that one caller, the git.c wrapper,
piggy-backed on that computation to find the command
basename.  Instead, let's leave argv[0] untouched in
common-main, and have git.c do its own basename computation.

While we're at it, let's drop the return value from
git_extract_argv0_path(). It was only ever used in this one
callsite, and its dual purposes is what led to this
confusion in the first place.

Note that by changing the interface, the compiler can
confirm for us that there are no other callers storing the
return value. But the compiler can't tell us whether any of
the cmd_main() functions (besides git.c) were relying on the
basename munging. However, we can observe that prior to
650c44925, no other cmd_main() functions did that munging,
and no new cmd_main() functions have been introduced since
then. So we can't be regressing any of those cases.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/common-main.c b/common-main.c
index 44a29e8..c654f95 100644
--- a/common-main.c
+++ b/common-main.c
@@ -33,7 +33,7 @@ int main(int argc, const char **argv)
 
 	git_setup_gettext();
 
-	argv[0] = git_extract_argv0_path(argv[0]);
+	git_extract_argv0_path(argv[0]);
 
 	restore_sigpipe_to_default();
 
diff --git a/exec_cmd.c b/exec_cmd.c
index 9d5703a..19ac214 100644
--- a/exec_cmd.c
+++ b/exec_cmd.c
@@ -38,21 +38,17 @@ char *system_path(const char *path)
 	return strbuf_detach(&d, NULL);
 }
 
-const char *git_extract_argv0_path(const char *argv0)
+void git_extract_argv0_path(const char *argv0)
 {
 	const char *slash;
 
 	if (!argv0 || !*argv0)
-		return NULL;
+		return;
 
 	slash = find_last_dir_sep(argv0);
 
-	if (slash) {
+	if (slash)
 		argv0_path = xstrndup(argv0, slash - argv0);
-		return slash + 1;
-	}
-
-	return argv0;
 }
 
 void git_set_argv_exec_path(const char *exec_path)
diff --git a/exec_cmd.h b/exec_cmd.h
index 1f6b433..ff0b480 100644
--- a/exec_cmd.h
+++ b/exec_cmd.h
@@ -4,7 +4,7 @@
 struct argv_array;
 
 extern void git_set_argv_exec_path(const char *exec_path);
-extern const char *git_extract_argv0_path(const char *path);
+extern void git_extract_argv0_path(const char *path);
 extern const char *git_exec_path(void);
 extern void setup_path(void);
 extern const char **prepare_git_cmd(struct argv_array *out, const char **argv);
diff --git a/git.c b/git.c
index 0f1937f..5e50a41 100644
--- a/git.c
+++ b/git.c
@@ -617,6 +617,11 @@ int cmd_main(int argc, const char **argv)
 	cmd = argv[0];
 	if (!cmd)
 		cmd = "git-help";
+	else {
+		const char *slash = find_last_dir_sep(cmd);
+		if (slash)
+			cmd = slash + 1;
+	}
 
 	trace_command_performance(argv);
 
-- 
cgit v0.10.2-6-g49f6