From: Johannes Schindelin <Johannes.Schindelin@gmx.de>
To: Junio C Hamano <gitster@pobox.com>
Cc: "René Scharfe" <l.s.r@web.de>,
git@vger.kernel.org, "Rohit Ashiwal" <rohit.ashiwal265@gmail.com>,
"Ævar Arnfjörð Bjarmason" <avarab@gmail.com>,
"Jeff King" <peff@peff.net>,
"brian m . carlson" <sandals@crustytoothpaste.net>
Subject: Re: [PATCH v3 5/5] archive-tar: use internal gzip by default
Date: Tue, 14 Jun 2022 13:27:37 +0200 (CEST) [thread overview]
Message-ID: <nycvar.QRO.7.76.6.2206141109270.353@tvgsbejvaqbjf.bet> (raw)
In-Reply-To: <xmqqk09k449y.fsf@gitster.g>
[-- Attachment #1: Type: text/plain, Size: 4352 bytes --]
Hi Junio,
On Mon, 13 Jun 2022, Junio C Hamano wrote:
> René Scharfe <l.s.r@web.de> writes:
>
> > -test_expect_success GZIP 'git archive --format=tar.gz' '
> > +test_expect_success 'git archive --format=tar.gz' '
> > git archive --format=tar.gz HEAD >j1.tar.gz &&
> > test_cmp_bin j.tgz j1.tar.gz
> > '
>
> Curiously, this breaks for me. It is understandable if we are not
> producing byte-for-byte identical output with internal gzip.
Indeed, I can reproduce this, too. In particular, `j.tgz` and `j1.tar.gz`
differ like this in my test run:
-00000000 1f 8b 08 1a 00 2e ca 09 00 03 04 00 89 45 fc 83 |.............E..|
+00000000 1f 8b 08 1a 00 35 2a 10 00 03 04 00 89 45 fc 83 |.....5*......E..|
and
-00000010 7d fc 00 f1 d0 ec b7 63 8c 30 cc 9b e6 db b6 6d |}......c.0.....m|
+00000010 7d fc 00 54 ff ec b7 63 8c 30 cc 9b e6 db b6 6d |}..T...c.0.....m|
According to https://datatracker.ietf.org/doc/html/rfc1952#page-5, the
difference in the first line is the mtime. For reference, this is the
version with `git -c tar.tgz.command="gzip -cn" archive --format=tgz
HEAD`:
00000000 1f 8b 08 00 00 00 00 00 00 03 ec b7 63 8c 30 cc |............c.0.|
In other words, `gzip` forces the `mtim` member to all zeros, which makes
sense.
The recorded mtimes are a bit funny, according to
https://wolf-tungsten.github.io/gzip-analyzer/, they are 1975-03-17
00:36:32 and 1978-08-05 22:45:36, respectively...
And the mtime actually changes all the time.
What's even more funny: if I comment out the `deflateSetHeader()`, the
mtime header field is left at all-zeros. This is on Ubuntu 18.04 with
zlib1g 1:1.2.11.dfsg-0ubuntu2.
So I dug in a bit deeper and what do you know, the `deflateHeader()`
function is implemented like this
(https://github.com/madler/zlib/blob/21767c654d31/deflate.c#L557-L565):
int ZEXPORT deflateSetHeader (strm, head)
z_streamp strm;
gz_headerp head;
{
if (deflateStateCheck(strm) || strm->state->wrap != 2)
return Z_STREAM_ERROR;
strm->state->gzhead = head;
return Z_OK;
}
Now, the caller is implemented like this:
static void tgz_set_os(git_zstream *strm, int os)
{
#if ZLIB_VERNUM >= 0x1221
struct gz_header_s gzhead = { .os = os };
deflateSetHeader(&strm->z, &gzhead);
#endif
}
The biggest problem is not that the return value of `deflateSetHeader()`
is ignored. The biggest problem is that it passes the address of a heap
variable to the `deflateSetHeader()` function, which then stores it away
in another struct that lives beyond the point when we return from
`tgz_set_os()`.
In other words, this is the very issue I pointed out as GCC not catching:
https://lore.kernel.org/git/nycvar.QRO.7.76.6.2205272235220.349@tvgsbejvaqbjf.bet/
The solution is to move the heap variable back into a scope that matches
the lifetime of the compression:
-- snip --
diff --git a/archive-tar.c b/archive-tar.c
index 60669eb7b9c..3d77e0f7509 100644
--- a/archive-tar.c
+++ b/archive-tar.c
@@ -460,17 +460,12 @@ static void tgz_write_block(const void *data)
static const char internal_gzip_command[] = "git archive gzip";
-static void tgz_set_os(git_zstream *strm, int os)
-{
-#if ZLIB_VERNUM >= 0x1221
- struct gz_header_s gzhead = { .os = os };
- deflateSetHeader(&strm->z, &gzhead);
-#endif
-}
-
static int write_tar_filter_archive(const struct archiver *ar,
struct archiver_args *args)
{
+#if ZLIB_VERNUM >= 0x1221
+ struct gz_header_s gzhead = { .os = 3 }; /* Unix, for reproducibility */
+#endif
struct strbuf cmd = STRBUF_INIT;
struct child_process filter = CHILD_PROCESS_INIT;
int r;
@@ -481,7 +476,10 @@ static int write_tar_filter_archive(const struct archiver *ar,
if (!strcmp(ar->filter_command, internal_gzip_command)) {
write_block = tgz_write_block;
git_deflate_init_gzip(&gzstream, args->compression_level);
- tgz_set_os(&gzstream, 3); /* Unix, for reproducibility */
+#if ZLIB_VERNUM >= 0x1221
+ if (deflateSetHeader(&gzstream.z, &gzhead) != Z_OK)
+ BUG("deflateSetHeader() called too late");
+#endif
gzstream.next_out = outbuf;
gzstream.avail_out = sizeof(outbuf);
-- snap --
With this, the test passes for me.
René, would you mind squashing this into your patch series?
Thank you,
Dscho
next prev parent reply other threads:[~2022-06-14 11:28 UTC|newest]
Thread overview: 74+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-12 23:04 [PATCH 0/2] Avoid spawning gzip in git archive Johannes Schindelin via GitGitGadget
2019-04-12 23:04 ` [PATCH 1/2] archive: replace write_or_die() calls with write_block_or_die() Rohit Ashiwal via GitGitGadget
2019-04-13 1:34 ` Jeff King
2019-04-13 5:51 ` Junio C Hamano
2019-04-14 4:36 ` Rohit Ashiwal
2019-04-26 14:29 ` Johannes Schindelin
2019-04-26 23:44 ` Junio C Hamano
2019-04-29 21:32 ` Johannes Schindelin
2019-05-01 18:09 ` Jeff King
2019-05-02 20:29 ` René Scharfe
2019-05-05 5:25 ` Junio C Hamano
2019-05-06 5:07 ` Jeff King
2019-04-14 4:34 ` Rohit Ashiwal
2019-04-14 10:33 ` Junio C Hamano
2019-04-26 14:28 ` Johannes Schindelin
2019-05-01 18:07 ` Jeff King
2019-04-12 23:04 ` [PATCH 2/2] archive: avoid spawning `gzip` Rohit Ashiwal via GitGitGadget
2019-04-13 1:51 ` Jeff King
2019-04-13 22:01 ` René Scharfe
2019-04-15 21:35 ` Jeff King
2019-04-26 14:51 ` Johannes Schindelin
2019-04-27 9:59 ` René Scharfe
2019-04-27 17:39 ` René Scharfe
2019-04-29 21:25 ` Johannes Schindelin
2019-05-01 17:45 ` René Scharfe
2019-05-01 18:18 ` Jeff King
2019-06-10 10:44 ` René Scharfe
2019-06-13 19:16 ` Jeff King
2019-04-13 22:16 ` brian m. carlson
2019-04-15 21:36 ` Jeff King
2019-04-26 14:54 ` Johannes Schindelin
2019-05-02 20:20 ` Ævar Arnfjörð Bjarmason
2019-05-03 20:49 ` Johannes Schindelin
2019-05-03 20:52 ` Jeff King
2019-04-26 14:47 ` Johannes Schindelin
[not found] ` <pull.145.v2.git.gitgitgadget@gmail.com>
[not found] ` <4ea94a8784876c3a19e387537edd81a957fc692c.1556321244.git.gitgitgadget@gmail.com>
2019-05-02 20:29 ` [PATCH v2 3/4] archive: optionally use zlib directly for gzip compression René Scharfe
[not found] ` <ac2b2488a1b42b3caf8a84594c48eca796748e59.1556321244.git.gitgitgadget@gmail.com>
2019-05-02 20:30 ` [PATCH v2 2/4] archive-tar: mark RECORDSIZE/BLOCKSIZE as unsigned René Scharfe
2019-05-08 11:45 ` Johannes Schindelin
2019-05-08 23:04 ` Jeff King
2019-05-09 14:06 ` Johannes Schindelin
2019-05-09 18:38 ` Jeff King
2019-05-10 17:18 ` René Scharfe
2019-05-10 21:20 ` Jeff King
2022-06-12 6:00 ` [PATCH v3 0/5] Avoid spawning gzip in git archive René Scharfe
2022-06-12 6:03 ` [PATCH v3 1/5] archive: rename archiver data field to filter_command René Scharfe
2022-06-12 6:05 ` [PATCH v3 2/5] archive-tar: factor out write_block() René Scharfe
2022-06-12 6:08 ` [PATCH v3 3/5] archive-tar: add internal gzip implementation René Scharfe
2022-06-13 19:10 ` Junio C Hamano
2022-06-12 6:18 ` [PATCH v3 4/5] archive-tar: use OS_CODE 3 (Unix) for internal gzip René Scharfe
2022-06-12 6:19 ` [PATCH v3 5/5] archive-tar: use internal gzip by default René Scharfe
2022-06-13 21:55 ` Junio C Hamano
2022-06-14 11:27 ` Johannes Schindelin [this message]
2022-06-14 15:47 ` René Scharfe
2022-06-14 15:56 ` René Scharfe
2022-06-14 16:29 ` Johannes Schindelin
2022-06-14 20:04 ` René Scharfe
2022-06-15 16:41 ` Junio C Hamano
2022-06-14 11:28 ` [PATCH v3 0/5] Avoid spawning gzip in git archive Johannes Schindelin
2022-06-14 20:05 ` René Scharfe
2022-06-30 18:55 ` Johannes Schindelin
2022-07-01 16:05 ` Johannes Schindelin
2022-07-01 16:27 ` Jeff King
2022-07-01 17:47 ` Junio C Hamano
2022-06-15 16:53 ` [PATCH v4 0/6] " René Scharfe
2022-06-15 16:58 ` [PATCH v4 1/6] archive: update format documentation René Scharfe
2022-06-15 16:59 ` [PATCH v4 2/6] archive: rename archiver data field to filter_command René Scharfe
2022-06-15 17:01 ` [PATCH v4 3/6] archive-tar: factor out write_block() René Scharfe
2022-06-15 17:02 ` [PATCH v4 4/6] archive-tar: add internal gzip implementation René Scharfe
2022-06-15 20:32 ` Ævar Arnfjörð Bjarmason
2022-06-16 18:55 ` René Scharfe
2022-06-24 11:13 ` Ævar Arnfjörð Bjarmason
2022-06-24 20:24 ` René Scharfe
2022-06-15 17:04 ` [PATCH v4 5/6] archive-tar: use OS_CODE 3 (Unix) for internal gzip René Scharfe
2022-06-15 17:05 ` [PATCH v4 6/6] archive-tar: use internal gzip by default René Scharfe
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