ll_union_merge(): pass name labels to ll_xdl_merge()

peff · gitster · commit 7f53f78b04b4 · 2021-06-11T12:37:07.000+09:00
Since cd1d61c (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 cd1d61c 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 <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git 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/t6406-merge-attr.sh b/t/t6406-merge-attr.sh
@@ -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
 '
 
 test_done

Original file line number	Diff line number	Diff line change
`@@ -151,7 +151,7 @@ static int ll_union_merge(const struct ll_merge_driver *drv_unused,`
`151`	`151`	`o = *opts;`
`152`	`152`	`o.variant = XDL_MERGE_FAVOR_UNION;`
`153`	`153`	`return ll_xdl_merge(drv_unused, result, path_unused,`
`154`		`- orig, NULL, src1, NULL, src2, NULL,`
	`154`	`+ orig, orig_name, src1, name1, src2, name2,`
`155`	`155`	`&o, marker_size);`
`156`	`156`	`}`
`157`	`157`
Original file line number	Diff line number	Diff line change
`@@ -221,7 +221,8 @@ test_expect_success 'binary files with union attribute' '`
`221`	`221`	`printf "two\0" >bin.txt &&`
`222`	`222`	`git commit -am two &&`
`223`	`223`
`224`		`- test_must_fail git merge bin-main`
	`224`	`+ test_must_fail git merge bin-main 2>stderr &&`
	`225`	`+ grep -i "warning.cannot merge.HEAD vs. bin-main" stderr`
`225`	`226`	`'`
`226`	`227`
`227`	`228`	`test_done`