diff mbox series

[2/3] commit-graph: use the hash version byte

Message ID 4bbfd345d16da4604dd20decda8ecb12372e4223.1597428440.git.gitgitgadget@gmail.com (mailing list archive)
State Superseded
Headers show
Series [1/3] t/README: document GIT_TEST_DEFAULT_HASH | expand

Commit Message

Philippe Blain via GitGitGadget Aug. 14, 2020, 6:07 p.m. UTC 
From: Derrick Stolee <dstolee@microsoft.com>

The commit-graph format reserved a byte among the header of the file to
store a "hash version". During the SHA-256 work, this was not modified
because file formats are not necessarily intended to work across hash
versions. If a repository has SHA-256 as its hash algorithm, it
automatically up-shifts the lengths of object names in all necessary
formats.

However, since we have this byte available for adjusting the version, we
can make the file formats more obviously incompatible instead of relying
on other context from the repository.

Update the oid_version() method in commit-graph.c to add a new value, 2,
for sha-256. This automatically writes the new value in a SHA-256
repository _and_ verifies the value is correct. This is a breaking
change relative to the current 'master' branch since 092b677 (Merge
branch 'bc/sha-256-cvs-svn-updates', 2020-08-13) but it is not breaking
relative to any released version of Git.

The test impact is relatively minor: the output of 'test-tool
read-graph' lists the header information, so those instances of '1' need
to be replaced with a variable determined by GIT_TEST_DEFAULT_HASH. A
more careful test is added that specifically creates a repository of
each type then swaps the commit-graph files. The important value here is
that the "git log" command succeeds while writing a message to stderr.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 .../technical/commit-graph-format.txt         |  9 ++++-
 commit-graph.c                                |  6 ++-
 t/t4216-log-bloom.sh                          |  8 +++-
 t/t5318-commit-graph.sh                       | 37 ++++++++++++++++++-
 t/t5324-split-commit-graph.sh                 |  8 +++-
 5 files changed, 62 insertions(+), 6 deletions(-)

Comments

Junio C Hamano Aug. 14, 2020, 7:05 p.m. UTC | #1 
"Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com> writes:

> From: Derrick Stolee <dstolee@microsoft.com>
>
> The commit-graph format reserved a byte among the header of the file to
> store a "hash version". During the SHA-256 work, this was not modified
> because file formats are not necessarily intended to work across hash
> versions. If a repository has SHA-256 as its hash algorithm, it
> automatically up-shifts the lengths of object names in all necessary
> formats.
>
> However, since we have this byte available for adjusting the version, we
> can make the file formats more obviously incompatible instead of relying
> on other context from the repository.

Very good idea.

> Update the oid_version() method in commit-graph.c to add a new value, 2,
> for sha-256. This automatically writes the new value in a SHA-256
> repository _and_ verifies the value is correct. This is a breaking
> change relative to the current 'master' branch since 092b677 (Merge
> branch 'bc/sha-256-cvs-svn-updates', 2020-08-13) but it is not breaking
> relative to any released version of Git.

That is perfectly fine.  I think any file and on-wire protocol that
uses anything but SHA-1 without identifying what it uses is a bug.

Will queue.  Thanks.

> +OID_VERSION=1
> +if [ "$GIT_DEFAULT_HASH" = "sha256" ]
> +then
> +	OID_VERSION=2
> +fi
> +
>  test_expect_success 'setup test - repo, commits, commit graph, log outputs' '
>  	git init &&
>  	mkdir A A/B A/B/C &&
> @@ -35,7 +41,7 @@ test_expect_success 'setup test - repo, commits, commit graph, log outputs' '
>  graph_read_expect () {
>  	NUM_CHUNKS=5
>  	cat >expect <<- EOF
> -	header: 43475048 1 1 $NUM_CHUNKS 0
> +	header: 43475048 1 $OID_VERSION $NUM_CHUNKS 0
>  	num_commits: $1
>  	chunks: oid_fanout oid_lookup commit_metadata bloom_indexes bloom_data
>  	EOF
> diff --git a/t/t5318-commit-graph.sh b/t/t5318-commit-graph.sh
> index 044cf8a3de..5b65017676 100755
> --- a/t/t5318-commit-graph.sh
> +++ b/t/t5318-commit-graph.sh
> @@ -5,6 +5,12 @@ test_description='commit graph'
>  
>  GIT_TEST_COMMIT_GRAPH_CHANGED_PATHS=0
>  
> +OID_VERSION=1
> +if [ "$GIT_DEFAULT_HASH" = "sha256" ]
> +then
> +	OID_VERSION=2
> +fi
> +
>  test_expect_success 'setup full repo' '
>  	mkdir full &&
>  	cd "$TRASH_DIRECTORY/full" &&
> @@ -77,7 +83,7 @@ graph_read_expect() {
>  		NUM_CHUNKS=$((3 + $(echo "$2" | wc -w)))
>  	fi
>  	cat >expect <<- EOF
> -	header: 43475048 1 1 $NUM_CHUNKS 0
> +	header: 43475048 1 $OID_VERSION $NUM_CHUNKS 0
>  	num_commits: $1
>  	chunks: oid_fanout oid_lookup commit_metadata$OPTIONAL
>  	EOF
> @@ -412,6 +418,35 @@ test_expect_success 'replace-objects invalidates commit-graph' '
>  	)
>  '
>  
> +test_expect_success 'warn on improper hash version' '
> +	git init --object-format=sha1 sha1 &&
> +	(
> +		cd sha1 &&
> +		test_commit 1 &&
> +		git commit-graph write --reachable &&
> +		mv .git/objects/info/commit-graph ../cg-sha1
> +	) &&
> +	git init --object-format=sha256 sha256 &&
> +	(
> +		cd sha256 &&
> +		test_commit 1 &&
> +		git commit-graph write --reachable &&
> +		mv .git/objects/info/commit-graph ../cg-sha256
> +	) &&
> +	(
> +		cd sha1 &&
> +		mv ../cg-sha256 .git/objects/info/commit-graph &&
> +		git log -1 2>err &&
> +		test_i18ngrep "commit-graph hash version 2 does not match version 1" err
> +	) &&
> +	(
> +		cd sha256 &&
> +		mv ../cg-sha1 .git/objects/info/commit-graph &&
> +		git log -1 2>err &&
> +		test_i18ngrep "commit-graph hash version 1 does not match version 2" err
> +	)
> +'
> +
>  # the verify tests below expect the commit-graph to contain
>  # exactly the commits reachable from the commits/8 branch.
>  # If the file changes the set of commits in the list, then the
> diff --git a/t/t5324-split-commit-graph.sh b/t/t5324-split-commit-graph.sh
> index ea28d522b8..6f1a324f4f 100755
> --- a/t/t5324-split-commit-graph.sh
> +++ b/t/t5324-split-commit-graph.sh
> @@ -6,6 +6,12 @@ test_description='split commit graph'
>  GIT_TEST_COMMIT_GRAPH=0
>  GIT_TEST_COMMIT_GRAPH_CHANGED_PATHS=0
>  
> +OID_VERSION=1
> +if [ "$GIT_DEFAULT_HASH" = "sha256" ]
> +then
> +	OID_VERSION=2
> +fi
> +
>  test_expect_success 'setup repo' '
>  	git init &&
>  	git config core.commitGraph true &&
> @@ -28,7 +34,7 @@ graph_read_expect() {
>  		NUM_BASE=$2
>  	fi
>  	cat >expect <<- EOF
> -	header: 43475048 1 1 3 $NUM_BASE
> +	header: 43475048 1 $OID_VERSION 3 $NUM_BASE
>  	num_commits: $1
>  	chunks: oid_fanout oid_lookup commit_metadata
>  	EOF
Taylor Blau Aug. 14, 2020, 8:05 p.m. UTC | #2 
On Fri, Aug 14, 2020 at 12:05:09PM -0700, Junio C Hamano wrote:
> "Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com> writes:
>
> > From: Derrick Stolee <dstolee@microsoft.com>
> >
> > The commit-graph format reserved a byte among the header of the file to
> > store a "hash version". During the SHA-256 work, this was not modified
> > because file formats are not necessarily intended to work across hash
> > versions. If a repository has SHA-256 as its hash algorithm, it
> > automatically up-shifts the lengths of object names in all necessary
> > formats.
> >
> > However, since we have this byte available for adjusting the version, we
> > can make the file formats more obviously incompatible instead of relying
> > on other context from the repository.
>
> Very good idea.
>
> > Update the oid_version() method in commit-graph.c to add a new value, 2,
> > for sha-256. This automatically writes the new value in a SHA-256
> > repository _and_ verifies the value is correct. This is a breaking
> > change relative to the current 'master' branch since 092b677 (Merge
> > branch 'bc/sha-256-cvs-svn-updates', 2020-08-13) but it is not breaking
> > relative to any released version of Git.
>
> That is perfectly fine.  I think any file and on-wire protocol that
> uses anything but SHA-1 without identifying what it uses is a bug.
>
> Will queue.  Thanks.

Great. I have nothing to add other than my 'ack' that this is a good
idea.

> > +OID_VERSION=1
> > +if [ "$GIT_DEFAULT_HASH" = "sha256" ]
> > +then
> > +	OID_VERSION=2
> > +fi
> > +
> >  test_expect_success 'setup test - repo, commits, commit graph, log outputs' '
> >  	git init &&
> >  	mkdir A A/B A/B/C &&
> > @@ -35,7 +41,7 @@ test_expect_success 'setup test - repo, commits, commit graph, log outputs' '
> >  graph_read_expect () {
> >  	NUM_CHUNKS=5
> >  	cat >expect <<- EOF
> > -	header: 43475048 1 1 $NUM_CHUNKS 0
> > +	header: 43475048 1 $OID_VERSION $NUM_CHUNKS 0
> >  	num_commits: $1
> >  	chunks: oid_fanout oid_lookup commit_metadata bloom_indexes bloom_data
> >  	EOF
> > diff --git a/t/t5318-commit-graph.sh b/t/t5318-commit-graph.sh
> > index 044cf8a3de..5b65017676 100755
> > --- a/t/t5318-commit-graph.sh
> > +++ b/t/t5318-commit-graph.sh
> > @@ -5,6 +5,12 @@ test_description='commit graph'
> >
> >  GIT_TEST_COMMIT_GRAPH_CHANGED_PATHS=0
> >
> > +OID_VERSION=1
> > +if [ "$GIT_DEFAULT_HASH" = "sha256" ]
> > +then
> > +	OID_VERSION=2
> > +fi
> > +
> >  test_expect_success 'setup full repo' '
> >  	mkdir full &&
> >  	cd "$TRASH_DIRECTORY/full" &&
> > @@ -77,7 +83,7 @@ graph_read_expect() {
> >  		NUM_CHUNKS=$((3 + $(echo "$2" | wc -w)))
> >  	fi
> >  	cat >expect <<- EOF
> > -	header: 43475048 1 1 $NUM_CHUNKS 0
> > +	header: 43475048 1 $OID_VERSION $NUM_CHUNKS 0
> >  	num_commits: $1
> >  	chunks: oid_fanout oid_lookup commit_metadata$OPTIONAL
> >  	EOF
> > @@ -412,6 +418,35 @@ test_expect_success 'replace-objects invalidates commit-graph' '
> >  	)
> >  '
> >
> > +test_expect_success 'warn on improper hash version' '
> > +	git init --object-format=sha1 sha1 &&
> > +	(
> > +		cd sha1 &&
> > +		test_commit 1 &&
> > +		git commit-graph write --reachable &&
> > +		mv .git/objects/info/commit-graph ../cg-sha1
> > +	) &&
> > +	git init --object-format=sha256 sha256 &&
> > +	(
> > +		cd sha256 &&
> > +		test_commit 1 &&
> > +		git commit-graph write --reachable &&
> > +		mv .git/objects/info/commit-graph ../cg-sha256
> > +	) &&
> > +	(
> > +		cd sha1 &&
> > +		mv ../cg-sha256 .git/objects/info/commit-graph &&
> > +		git log -1 2>err &&
> > +		test_i18ngrep "commit-graph hash version 2 does not match version 1" err
> > +	) &&
> > +	(
> > +		cd sha256 &&
> > +		mv ../cg-sha1 .git/objects/info/commit-graph &&
> > +		git log -1 2>err &&
> > +		test_i18ngrep "commit-graph hash version 1 does not match version 2" err
> > +	)
> > +'
> > +
> >  # the verify tests below expect the commit-graph to contain
> >  # exactly the commits reachable from the commits/8 branch.
> >  # If the file changes the set of commits in the list, then the
> > diff --git a/t/t5324-split-commit-graph.sh b/t/t5324-split-commit-graph.sh
> > index ea28d522b8..6f1a324f4f 100755
> > --- a/t/t5324-split-commit-graph.sh
> > +++ b/t/t5324-split-commit-graph.sh
> > @@ -6,6 +6,12 @@ test_description='split commit graph'
> >  GIT_TEST_COMMIT_GRAPH=0
> >  GIT_TEST_COMMIT_GRAPH_CHANGED_PATHS=0
> >
> > +OID_VERSION=1
> > +if [ "$GIT_DEFAULT_HASH" = "sha256" ]
> > +then
> > +	OID_VERSION=2
> > +fi
> > +
> >  test_expect_success 'setup repo' '
> >  	git init &&
> >  	git config core.commitGraph true &&
> > @@ -28,7 +34,7 @@ graph_read_expect() {
> >  		NUM_BASE=$2
> >  	fi
> >  	cat >expect <<- EOF
> > -	header: 43475048 1 1 3 $NUM_BASE
> > +	header: 43475048 1 $OID_VERSION 3 $NUM_BASE
> >  	num_commits: $1
> >  	chunks: oid_fanout oid_lookup commit_metadata
> >  	EOF
Thanks,
Taylor
brian m. carlson Aug. 14, 2020, 8:11 p.m. UTC | #3 
On 2020-08-14 at 18:07:19, Derrick Stolee via GitGitGadget wrote:
> diff --git a/commit-graph.c b/commit-graph.c
> index e51c91dd5b..d03328d64c 100644
> --- a/commit-graph.c
> +++ b/commit-graph.c
> @@ -179,7 +179,11 @@ static char *get_chain_filename(struct object_directory *odb)
>  
>  static uint8_t oid_version(void)
>  {
> -	return 1;
> +	if (the_hash_algo->rawsz == GIT_SHA1_RAWSZ)
> +		return 1;
> +	if (the_hash_algo->rawsz == GIT_SHA256_RAWSZ)
> +		return 2;
> +	die(_("invalid hash version"));
>  }

Can we maybe say something like this?

  switch (hash_algo_by_ptr(the_hash_algo)) {
    case GIT_HASH_SHA1:
      return 1;
    case GIT_HASH_SHA256:
      return 2;
    default:
      die(_("invalid hash version"));
  }

That way if SHA-256 gets broken and we switch to another 256-bit hash
(SHA-3-256?), we'll be forced to update this properly.

>  static struct commit_graph *alloc_commit_graph(void)
> diff --git a/t/t4216-log-bloom.sh b/t/t4216-log-bloom.sh
> index c21cc160f3..906af2799d 100755
> --- a/t/t4216-log-bloom.sh
> +++ b/t/t4216-log-bloom.sh
> @@ -6,6 +6,12 @@ test_description='git log for a path with Bloom filters'
>  GIT_TEST_COMMIT_GRAPH=0
>  GIT_TEST_COMMIT_GRAPH_CHANGED_PATHS=0
>  
> +OID_VERSION=1
> +if [ "$GIT_DEFAULT_HASH" = "sha256" ]
> +then
> +	OID_VERSION=2
> +fi

Can we do something like this in the setup test instead?

  test_oid_cache <<-EOF
  oid_version sha1:1
  oid_version sha256:2
  EOF

  OID_VERSION=$(test_oid oid_version)
  # or, inline
  $(test_oid oid_version)

That uses the existing test framework to ensure we produce the right
results if someone adds another hash algorithm and that we produce a BUG
if the value is missing.  It will also make it easier to write tests if
we end up creating SHA-1- or SHA-256-specific tests, since we can look
up those values directly with test_oid.

Since you're using this across several tests, you could even just add
this to t/oid-info/hash-info like so:

  commit_graph_oid_version sha1:1
  commit_graph_oid_version sha256:2

and then it's set in one place and can be used without any required
test_oid_cache invocations at all.  I think three tests is sufficient
basis for us to add an entry there.
Junio C Hamano Aug. 14, 2020, 8:22 p.m. UTC | #4 
"brian m. carlson" <sandals@crustytoothpaste.net> writes:

> Can we maybe say something like this?
>
>   switch (hash_algo_by_ptr(the_hash_algo)) {
>     case GIT_HASH_SHA1:
>       return 1;
>     case GIT_HASH_SHA256:
>       return 2;
>     default:
>       die(_("invalid hash version"));
>   }
>
> That way if SHA-256 gets broken and we switch to another 256-bit hash
> (SHA-3-256?), we'll be forced to update this properly.

Excellent.
Derrick Stolee Aug. 14, 2020, 8:36 p.m. UTC | #5 
On 8/14/2020 4:11 PM, brian m. carlson wrote:
> On 2020-08-14 at 18:07:19, Derrick Stolee via GitGitGadget wrote:
>> diff --git a/commit-graph.c b/commit-graph.c
>> index e51c91dd5b..d03328d64c 100644
>> --- a/commit-graph.c
>> +++ b/commit-graph.c
>> @@ -179,7 +179,11 @@ static char *get_chain_filename(struct object_directory *odb)
>>  
>>  static uint8_t oid_version(void)
>>  {
>> -	return 1;
>> +	if (the_hash_algo->rawsz == GIT_SHA1_RAWSZ)
>> +		return 1;
>> +	if (the_hash_algo->rawsz == GIT_SHA256_RAWSZ)
>> +		return 2;
>> +	die(_("invalid hash version"));
>>  }
> 
> Can we maybe say something like this?
> 
>   switch (hash_algo_by_ptr(the_hash_algo)) {
>     case GIT_HASH_SHA1:
>       return 1;
>     case GIT_HASH_SHA256:
>       return 2;
>     default:
>       die(_("invalid hash version"));
>   }
> 
> That way if SHA-256 gets broken and we switch to another 256-bit hash
> (SHA-3-256?), we'll be forced to update this properly.
> 
>>  static struct commit_graph *alloc_commit_graph(void)
>> diff --git a/t/t4216-log-bloom.sh b/t/t4216-log-bloom.sh
>> index c21cc160f3..906af2799d 100755
>> --- a/t/t4216-log-bloom.sh
>> +++ b/t/t4216-log-bloom.sh
>> @@ -6,6 +6,12 @@ test_description='git log for a path with Bloom filters'
>>  GIT_TEST_COMMIT_GRAPH=0
>>  GIT_TEST_COMMIT_GRAPH_CHANGED_PATHS=0
>>  
>> +OID_VERSION=1
>> +if [ "$GIT_DEFAULT_HASH" = "sha256" ]
>> +then
>> +	OID_VERSION=2
>> +fi
> 
> Can we do something like this in the setup test instead?
> 
>   test_oid_cache <<-EOF
>   oid_version sha1:1
>   oid_version sha256:2
>   EOF
> 
>   OID_VERSION=$(test_oid oid_version)
>   # or, inline
>   $(test_oid oid_version)
> 
> That uses the existing test framework to ensure we produce the right
> results if someone adds another hash algorithm and that we produce a BUG
> if the value is missing.  It will also make it easier to write tests if
> we end up creating SHA-1- or SHA-256-specific tests, since we can look
> up those values directly with test_oid.
> 
> Since you're using this across several tests, you could even just add
> this to t/oid-info/hash-info like so:
> 
>   commit_graph_oid_version sha1:1
>   commit_graph_oid_version sha256:2
> 
> and then it's set in one place and can be used without any required
> test_oid_cache invocations at all.  I think three tests is sufficient
> basis for us to add an entry there.

I appreciate the suggested improvements here. I'm happy to do
something more similar to other places in the code.

These will be part of my v2 to be re-rolled early next week.

Thanks,
-Stolee
Martin Ågren Aug. 15, 2020, 1:46 p.m. UTC | #6 
On Fri, 14 Aug 2020 at 22:36, Derrick Stolee <stolee@gmail.com> wrote:
>
> I appreciate the suggested improvements here. I'm happy to do
> something more similar to other places in the code.
>
> These will be part of my v2 to be re-rolled early next week.

I have nothing to add to brian's great suggestions. I'll be very happy
to see this patch instead of my patch 5/5 'commit-graph-format.txt: fix
"Hash Version" description'.

Martin
diff mbox series

Patch

diff --git a/Documentation/technical/commit-graph-format.txt b/Documentation/technical/commit-graph-format.txt
index 440541045d..6ddbceba15 100644
--- a/Documentation/technical/commit-graph-format.txt
+++ b/Documentation/technical/commit-graph-format.txt
@@ -42,8 +42,13 @@  HEADER:
   1-byte version number:
       Currently, the only valid version is 1.
 
-  1-byte Hash Version (1 = SHA-1)
-      We infer the hash length (H) from this value.
+  1-byte Hash Version
+      We infer the hash length (H) from this value:
+	1 => SHA-1
+	2 => SHA-256
+      If the hash type does not match the repository's hash algorithm, the
+      commit-graph file should be ignored with a warning presented to the
+      user.
 
   1-byte number (C) of "chunks"
 
diff --git a/commit-graph.c b/commit-graph.c
index e51c91dd5b..d03328d64c 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -179,7 +179,11 @@  static char *get_chain_filename(struct object_directory *odb)
 
 static uint8_t oid_version(void)
 {
-	return 1;
+	if (the_hash_algo->rawsz == GIT_SHA1_RAWSZ)
+		return 1;
+	if (the_hash_algo->rawsz == GIT_SHA256_RAWSZ)
+		return 2;
+	die(_("invalid hash version"));
 }
 
 static struct commit_graph *alloc_commit_graph(void)
diff --git a/t/t4216-log-bloom.sh b/t/t4216-log-bloom.sh
index c21cc160f3..906af2799d 100755
--- a/t/t4216-log-bloom.sh
+++ b/t/t4216-log-bloom.sh
@@ -6,6 +6,12 @@  test_description='git log for a path with Bloom filters'
 GIT_TEST_COMMIT_GRAPH=0
 GIT_TEST_COMMIT_GRAPH_CHANGED_PATHS=0
 
+OID_VERSION=1
+if [ "$GIT_DEFAULT_HASH" = "sha256" ]
+then
+	OID_VERSION=2
+fi
+
 test_expect_success 'setup test - repo, commits, commit graph, log outputs' '
 	git init &&
 	mkdir A A/B A/B/C &&
@@ -35,7 +41,7 @@  test_expect_success 'setup test - repo, commits, commit graph, log outputs' '
 graph_read_expect () {
 	NUM_CHUNKS=5
 	cat >expect <<- EOF
-	header: 43475048 1 1 $NUM_CHUNKS 0
+	header: 43475048 1 $OID_VERSION $NUM_CHUNKS 0
 	num_commits: $1
 	chunks: oid_fanout oid_lookup commit_metadata bloom_indexes bloom_data
 	EOF
diff --git a/t/t5318-commit-graph.sh b/t/t5318-commit-graph.sh
index 044cf8a3de..5b65017676 100755
--- a/t/t5318-commit-graph.sh
+++ b/t/t5318-commit-graph.sh
@@ -5,6 +5,12 @@  test_description='commit graph'
 
 GIT_TEST_COMMIT_GRAPH_CHANGED_PATHS=0
 
+OID_VERSION=1
+if [ "$GIT_DEFAULT_HASH" = "sha256" ]
+then
+	OID_VERSION=2
+fi
+
 test_expect_success 'setup full repo' '
 	mkdir full &&
 	cd "$TRASH_DIRECTORY/full" &&
@@ -77,7 +83,7 @@  graph_read_expect() {
 		NUM_CHUNKS=$((3 + $(echo "$2" | wc -w)))
 	fi
 	cat >expect <<- EOF
-	header: 43475048 1 1 $NUM_CHUNKS 0
+	header: 43475048 1 $OID_VERSION $NUM_CHUNKS 0
 	num_commits: $1
 	chunks: oid_fanout oid_lookup commit_metadata$OPTIONAL
 	EOF
@@ -412,6 +418,35 @@  test_expect_success 'replace-objects invalidates commit-graph' '
 	)
 '
 
+test_expect_success 'warn on improper hash version' '
+	git init --object-format=sha1 sha1 &&
+	(
+		cd sha1 &&
+		test_commit 1 &&
+		git commit-graph write --reachable &&
+		mv .git/objects/info/commit-graph ../cg-sha1
+	) &&
+	git init --object-format=sha256 sha256 &&
+	(
+		cd sha256 &&
+		test_commit 1 &&
+		git commit-graph write --reachable &&
+		mv .git/objects/info/commit-graph ../cg-sha256
+	) &&
+	(
+		cd sha1 &&
+		mv ../cg-sha256 .git/objects/info/commit-graph &&
+		git log -1 2>err &&
+		test_i18ngrep "commit-graph hash version 2 does not match version 1" err
+	) &&
+	(
+		cd sha256 &&
+		mv ../cg-sha1 .git/objects/info/commit-graph &&
+		git log -1 2>err &&
+		test_i18ngrep "commit-graph hash version 1 does not match version 2" err
+	)
+'
+
 # the verify tests below expect the commit-graph to contain
 # exactly the commits reachable from the commits/8 branch.
 # If the file changes the set of commits in the list, then the
diff --git a/t/t5324-split-commit-graph.sh b/t/t5324-split-commit-graph.sh
index ea28d522b8..6f1a324f4f 100755
--- a/t/t5324-split-commit-graph.sh
+++ b/t/t5324-split-commit-graph.sh
@@ -6,6 +6,12 @@  test_description='split commit graph'
 GIT_TEST_COMMIT_GRAPH=0
 GIT_TEST_COMMIT_GRAPH_CHANGED_PATHS=0
 
+OID_VERSION=1
+if [ "$GIT_DEFAULT_HASH" = "sha256" ]
+then
+	OID_VERSION=2
+fi
+
 test_expect_success 'setup repo' '
 	git init &&
 	git config core.commitGraph true &&
@@ -28,7 +34,7 @@  graph_read_expect() {
 		NUM_BASE=$2
 	fi
 	cat >expect <<- EOF
-	header: 43475048 1 1 3 $NUM_BASE
+	header: 43475048 1 $OID_VERSION 3 $NUM_BASE
 	num_commits: $1
 	chunks: oid_fanout oid_lookup commit_metadata
 	EOF