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From: Jeff King <>
Cc: Junio C Hamano <>
Subject: [PATCH 2/2] ll_union_merge(): pass name labels to ll_xdl_merge()
Date: Thu, 10 Jun 2021 08:58:43 -0400	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

Since cd1d61c44f (make union merge an xdl merge favor, 2010-03-01), we
pass NULL to ll_xdl_merge() for the "name" labels of the ancestor, ours
and theirs buffers. We usually use these for annotating conflict markers
left in a file. For a union merge, these shouldn't matter; the point of
it is that we'd never leave conflict markers in the first place.

But there is one code path where we may dereference them: if the file
contents appear to be binary, ll_binary_merge() will give up and pass
them to warning() to generate a message for the user (that was true even
when cd1d61c44f was written, though the warning was in ll_xdl_merge()
back then).

That can result in a segfault, though on many systems (including glibc),
the printf routines will helpfully just say "(null)" instead. We can
extend our binary-union test in t6406 to check stderr, which catches the
problem on all systems.

This also fixes a warning from "gcc -O3". Unlike lower optimization
levels, it inlines enough to see that the NULL can make it to warning()
and complains:

  In function ‘ll_binary_merge’,
      inlined from ‘ll_xdl_merge’ at ll-merge.c:115:10,
      inlined from ‘ll_union_merge’ at ll-merge.c:151:9:
  ll-merge.c:74:4: warning: ‘%s’ directive argument is null [-Wformat-overflow=]
     74 |    warning("Cannot merge binary files: %s (%s vs. %s)",
        |    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     75 |     path, name1, name2);
        |     ~~~~~~~~~~~~~~~~~~~

Signed-off-by: Jeff King <>
 ll-merge.c            | 2 +-
 t/ | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/ll-merge.c b/ll-merge.c
index 145deb12fa..0ee34d8a01 100644
--- a/ll-merge.c
+++ b/ll-merge.c
@@ -151,7 +151,7 @@ static int ll_union_merge(const struct ll_merge_driver *drv_unused,
 	o = *opts;
 	o.variant = XDL_MERGE_FAVOR_UNION;
 	return ll_xdl_merge(drv_unused, result, path_unused,
-			    orig, NULL, src1, NULL, src2, NULL,
+			    orig, orig_name, src1, name1, src2, name2,
 			    &o, marker_size);
diff --git a/t/ b/t/
index c1c458d933..8494645837 100755
--- a/t/
+++ b/t/
@@ -221,7 +221,8 @@ test_expect_success 'binary files with union attribute' '
 	printf "two\0" >bin.txt &&
 	git commit -am two &&
-	test_must_fail git merge bin-main
+	test_must_fail git merge bin-main 2>stderr &&
+	grep -i "warning.*cannot merge.*HEAD vs. bin-main" stderr

  parent reply	other threads:[~2021-06-10 12:58 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-10 12:51 [PATCH 0/2] fix union merge with binary files Jeff King
2021-06-10 12:57 ` [PATCH 1/2] ll_binary_merge(): handle XDL_MERGE_FAVOR_UNION Jeff King
2021-06-11  3:36   ` Junio C Hamano
2021-06-10 12:58 ` Jeff King [this message]
2021-06-10 15:19   ` [PATCH 2/2] ll_union_merge(): pass name labels to ll_xdl_merge() Elijah Newren
2021-06-10 16:14     ` [PATCH 3/2] ll_union_merge(): rename path_unused parameter Jeff King
2021-06-10 15:19 ` [PATCH 0/2] fix union merge with binary files Elijah Newren

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