common-main.c: move non-trace2 exit() behavior out of trace2.c

Change the exit() wrapper added in ee4512ed481 (trace2: create new
combined trace facility, 2019-02-22) so that we'll split up the trace2
logging concerns from wanting to wrap the "exit()" function itself for
other purposes.

This makes more sense structurally, as we won't seem to conflate
non-trace2 behavior with the trace2 code. I'd previously added an
explanation for this in 368b5843158 (common-main.c: call exit(), don't
return, 2021-12-07), that comment is being adjusted here.

Now the only thing we'll do if we're not using trace2 is to truncate
the "code" argument to the lowest 8 bits.

We only need to do that truncation on non-POSIX systems, but in
ee4512ed481 that "if defined(__MINGW32__)" code added in
47e3de0e796 (MinGW: truncate exit()'s argument to lowest 8 bits,
2009-07-05) was made to run everywhere. It might be good for clarify
to narrow that down by an "ifdef" again, but I'm not certain that in
the interim we haven't had some other non-POSIX systems rely the
behavior. On a POSIX system taking the lowest 8 bits is implicit, see
exit(3)[1] and wait(2)[2]. Let's leave a comment about that instead.

1. https://man7.org/linux/man-pages/man3/exit.3.html
2. https://man7.org/linux/man-pages/man2/wait.2.html

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 16 insertions, 4 deletions

diff --git a/common-main.c b/common-main.c
index 29fb7452f8..b6124dd2c2 100644
--- a/common-main.c
+++ b/common-main.c
@@ -55,10 +55,22 @@ int main(int argc, const char **argv)
 
 	result = cmd_main(argc, argv);
 
+	/* Not exit(3), but a wrapper calling our common_exit() */
+	exit(result);
+}
+
+/* We wrap exit() to call common_exit() in git-compat-util.h */
+int common_exit(const char *file, int line, int code)
+{
 	/*
-	 * We define exit() to call trace2_cmd_exit_fl() in
-	 * git-compat-util.h. Whether we reach this or exit()
-	 * elsewhere we'll always run our trace2 exit handler.
+	 * For non-POSIX systems: Take the lowest 8 bits of the "code"
+	 * to e.g. turn -1 into 255. On a POSIX system this is
+	 * redundant, see exit(3) and wait(2), but as it doesn't harm
+	 * anything there we don't need to guard this with an "ifdef".
 	 */
-	exit(result);
+	code &= 0xff;
+
+	trace2_cmd_exit_fl(file, line, code);
+
+	return code;
 }