From patchwork Wed Aug 30 16:43:47 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jonathan Tan X-Patchwork-Id: 13370383 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 02233C83F1C for ; Wed, 30 Aug 2023 18:29:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232003AbjH3S3g (ORCPT ); Wed, 30 Aug 2023 14:29:36 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39150 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1343748AbjH3QoQ (ORCPT ); Wed, 30 Aug 2023 12:44:16 -0400 Received: from mail-yw1-x114a.google.com (mail-yw1-x114a.google.com [IPv6:2607:f8b0:4864:20::114a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6094619A for ; Wed, 30 Aug 2023 09:44:13 -0700 (PDT) Received: by mail-yw1-x114a.google.com with SMTP id 00721157ae682-592210fe8easo81776507b3.3 for ; Wed, 30 Aug 2023 09:44:13 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20221208; t=1693413852; x=1694018652; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=Q4mL2tbF3LkDJjowa2ynLMPhz+LsGJJ2c/Y7IBxmQhE=; b=NMujZADngW52aEeQOLiUY7v3SDL39xAQ7re8x0eQsd2Y+nomUfmLfxrLPI49gdBHJl W/t2HKXr5KSjhV1wMAG3xWtnDsxxcsMpGyZQokTB7U5LUsB2k7xx5npd95nHF+XBWFDp SuDT1U4KxXeuf4DkIdqRxzQ+NoH/LJikQVko5au4QSJKGBFH36jR92ElDECosjNPdUc6 yvjPOzk30zPtNgbXXbxL6/dbdDpXSix2apxYwCsmTr1WqgX0II5hu1eI6o6FOodMmop2 sKYxLSDNijinpb/RmfaYlkvJDOcoy6rdJg/7fYFMkRgWzYgdG2OS9mLzJd+VydRXO/aE B5Qw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1693413852; x=1694018652; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=Q4mL2tbF3LkDJjowa2ynLMPhz+LsGJJ2c/Y7IBxmQhE=; b=j/+jlDvzx3dxQKoSrQ7mAPG9EgMsBKE7ay2C9yyaqLumZqSsC9cXUKmzyBpfOx3ePj 1DhU7f2hGY6Sxhg18v0xyk8fKZmd556RC9+dgEevGw7BnhkK21rOxaDPQZw70JFQnd1j rjWnn/7EWwZXAsYhZiVvlJ5sQ4RRoc7+7//KPZL3SZvfmcrs1U6h5d0j9Nyw/idmhq2E a2Qp+0P+LxY3y7lNRH350mGOhzAlPqzD8JkyeWZL8h50pXwUyipwOes63I9lUHVhof40 BMGB8caLrkMTpj+oLBhL1gqzUK012A/8g2RH4AVq/JKI1GYPkC1XlemyRmwrDNdG7Msx zkAQ== X-Gm-Message-State: AOJu0Yydk9ctqbXKbyxTLbsIgxa2FOfVdWebjJc9CvFUqv4rkv9sSY6+ m8CjlDZtZeCW41MxANNX9KwiJP3t92OTIQcuIelDPbN1vQX1eqo/9wny+5zM6oOVGDt0wrqZNSk 22YPFcA9OrNt+FqFIq78PTFP8VpKPHDUBDfFAcI/XxSiyWoRtPVO9Wojn95dL02wCw7nPwhrJtZ DM X-Google-Smtp-Source: AGHT+IHTp32lagjGIi1p/FktkkT+IZLHgNOxzNDDe95aqFt8yrWRuoNch+wI5cwpQ6Yp1yo562upuaPJqJccJnC1JYzM X-Received: from jonathantanmy0.svl.corp.google.com ([2620:15c:2d3:204:2899:32d6:b7e3:8e6e]) (user=jonathantanmy job=sendgmr) by 2002:a25:b323:0:b0:d4b:df05:3500 with SMTP id l35-20020a25b323000000b00d4bdf053500mr81859ybj.11.1693413852635; Wed, 30 Aug 2023 09:44:12 -0700 (PDT) Date: Wed, 30 Aug 2023 09:43:47 -0700 In-Reply-To: Mime-Version: 1.0 References: X-Mailer: git-send-email 2.42.0.rc2.253.gd59a3bf2b4-goog Message-ID: <44d3163125026843d75ec609401d96acc3387f28.1693413637.git.jonathantanmy@google.com> Subject: [PATCH v2 07/15] commit-graph: new filter ver. that fixes murmur3 From: Jonathan Tan To: git@vger.kernel.org Cc: Jonathan Tan , Junio C Hamano , "SZEDER =?utf-8?b?R8OhYm9y?= " , Taylor Blau Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org The murmur3 implementation in bloom.c has a bug when converting series of 4 bytes into network-order integers when char is signed (which is controllable by a compiler option, and the default signedness of char is platform-specific). When a string contains characters with the high bit set, this bug causes results that, although internally consistent within Git, does not accord with other implementations of murmur3 (thus, the changed path filters wouldn't be readable by other off-the-shelf implementatios of murmur3) and even with Git binaries that were compiled with different signedness of char. This bug affects both how Git writes changed path filters to disk and how Git interprets changed path filters on disk. Therefore, introduce a new version (2) of changed path filters that corrects this problem. The existing version (1) is still supported and is still the default, but users should migrate away from it as soon as possible. Because this bug only manifests with characters that have the high bit set, it may be possible that some (or all) commits in a given repo would have the same changed path filter both before and after this fix is applied. However, in order to determine whether this is the case, the changed paths would first have to be computed, at which point it is not much more expensive to just compute a new changed path filter. So this patch does not include any mechanism to "salvage" changed path filters from repositories. There is also no "mixed" mode - for each invocation of Git, reading and writing changed path filters are done with the same version number; this version number may be explicitly stated (typically if the user knows which version they need) or automatically determined from the version of the existing changed path filters in the repository. There is a change in write_commit_graph(). graph_read_bloom_data() makes it possible for chunk_bloom_data to be non-NULL but bloom_filter_settings to be NULL, which causes a segfault later on. I produced such a segfault while developing this patch, but couldn't find a way to reproduce it neither after this complete patch (or before), but in any case it seemed like a good thing to include that might help future patch authors. The value in t0095 was obtained from another murmur3 implementation using the following Go source code: package main import "fmt" import "github.com/spaolacci/murmur3" func main() { fmt.Printf("%x\n", murmur3.Sum32([]byte("Hello world!"))) fmt.Printf("%x\n", murmur3.Sum32([]byte{0x99, 0xaa, 0xbb, 0xcc, 0xdd, 0xee, 0xff})) } Signed-off-by: Jonathan Tan Signed-off-by: Junio C Hamano Signed-off-by: Taylor Blau Signed-off-by: Junio C Hamano --- Documentation/config/commitgraph.txt | 5 +- bloom.c | 69 +++++++++++++++++- bloom.h | 8 +- commit-graph.c | 32 ++++++-- t/helper/test-bloom.c | 9 ++- t/t0095-bloom.sh | 8 ++ t/t4216-log-bloom.sh | 105 +++++++++++++++++++++++++++ 7 files changed, 223 insertions(+), 13 deletions(-) diff --git a/Documentation/config/commitgraph.txt b/Documentation/config/commitgraph.txt index 2dc9170622..acc74a2f27 100644 --- a/Documentation/config/commitgraph.txt +++ b/Documentation/config/commitgraph.txt @@ -15,7 +15,7 @@ commitGraph.readChangedPaths:: commitGraph.changedPathsVersion:: Specifies the version of the changed-path Bloom filters that Git will read and - write. May be -1, 0 or 1. + write. May be -1, 0, 1, or 2. + Defaults to -1. + @@ -28,4 +28,7 @@ filters when instructed to write. If 1, Git will only read version 1 Bloom filters, and will write version 1 Bloom filters. + +If 2, Git will only read version 2 Bloom filters, and will write version 2 +Bloom filters. ++ See linkgit:git-commit-graph[1] for more information. diff --git a/bloom.c b/bloom.c index 3e78cfe79d..ebef5cfd2f 100644 --- a/bloom.c +++ b/bloom.c @@ -66,7 +66,64 @@ int load_bloom_filter_from_graph(struct commit_graph *g, * Not considered to be cryptographically secure. * Implemented as described in https://en.wikipedia.org/wiki/MurmurHash#Algorithm */ -uint32_t murmur3_seeded(uint32_t seed, const char *data, size_t len) +uint32_t murmur3_seeded_v2(uint32_t seed, const char *data, size_t len) +{ + const uint32_t c1 = 0xcc9e2d51; + const uint32_t c2 = 0x1b873593; + const uint32_t r1 = 15; + const uint32_t r2 = 13; + const uint32_t m = 5; + const uint32_t n = 0xe6546b64; + int i; + uint32_t k1 = 0; + const char *tail; + + int len4 = len / sizeof(uint32_t); + + uint32_t k; + for (i = 0; i < len4; i++) { + uint32_t byte1 = (uint32_t)(unsigned char)data[4*i]; + uint32_t byte2 = ((uint32_t)(unsigned char)data[4*i + 1]) << 8; + uint32_t byte3 = ((uint32_t)(unsigned char)data[4*i + 2]) << 16; + uint32_t byte4 = ((uint32_t)(unsigned char)data[4*i + 3]) << 24; + k = byte1 | byte2 | byte3 | byte4; + k *= c1; + k = rotate_left(k, r1); + k *= c2; + + seed ^= k; + seed = rotate_left(seed, r2) * m + n; + } + + tail = (data + len4 * sizeof(uint32_t)); + + switch (len & (sizeof(uint32_t) - 1)) { + case 3: + k1 ^= ((uint32_t)(unsigned char)tail[2]) << 16; + /*-fallthrough*/ + case 2: + k1 ^= ((uint32_t)(unsigned char)tail[1]) << 8; + /*-fallthrough*/ + case 1: + k1 ^= ((uint32_t)(unsigned char)tail[0]) << 0; + k1 *= c1; + k1 = rotate_left(k1, r1); + k1 *= c2; + seed ^= k1; + break; + } + + seed ^= (uint32_t)len; + seed ^= (seed >> 16); + seed *= 0x85ebca6b; + seed ^= (seed >> 13); + seed *= 0xc2b2ae35; + seed ^= (seed >> 16); + + return seed; +} + +static uint32_t murmur3_seeded_v1(uint32_t seed, const char *data, size_t len) { const uint32_t c1 = 0xcc9e2d51; const uint32_t c2 = 0x1b873593; @@ -131,8 +188,14 @@ void fill_bloom_key(const char *data, int i; const uint32_t seed0 = 0x293ae76f; const uint32_t seed1 = 0x7e646e2c; - const uint32_t hash0 = murmur3_seeded(seed0, data, len); - const uint32_t hash1 = murmur3_seeded(seed1, data, len); + uint32_t hash0, hash1; + if (settings->hash_version == 2) { + hash0 = murmur3_seeded_v2(seed0, data, len); + hash1 = murmur3_seeded_v2(seed1, data, len); + } else { + hash0 = murmur3_seeded_v1(seed0, data, len); + hash1 = murmur3_seeded_v1(seed1, data, len); + } key->hashes = (uint32_t *)xcalloc(settings->num_hashes, sizeof(uint32_t)); for (i = 0; i < settings->num_hashes; i++) diff --git a/bloom.h b/bloom.h index 1e4f612d2c..138d57a86b 100644 --- a/bloom.h +++ b/bloom.h @@ -8,9 +8,11 @@ struct commit_graph; struct bloom_filter_settings { /* * The version of the hashing technique being used. - * We currently only support version = 1 which is + * The newest version is 2, which is * the seeded murmur3 hashing technique implemented - * in bloom.c. + * in bloom.c. Bloom filters of version 1 were created + * with prior versions of Git, which had a bug in the + * implementation of the hash function. */ uint32_t hash_version; @@ -80,7 +82,7 @@ int load_bloom_filter_from_graph(struct commit_graph *g, * Not considered to be cryptographically secure. * Implemented as described in https://en.wikipedia.org/wiki/MurmurHash#Algorithm */ -uint32_t murmur3_seeded(uint32_t seed, const char *data, size_t len); +uint32_t murmur3_seeded_v2(uint32_t seed, const char *data, size_t len); void fill_bloom_key(const char *data, size_t len, diff --git a/commit-graph.c b/commit-graph.c index da99f15fdf..f7322c4fff 100644 --- a/commit-graph.c +++ b/commit-graph.c @@ -304,17 +304,26 @@ static int graph_read_oid_lookup(const unsigned char *chunk_start, return 0; } +struct graph_read_bloom_data_context { + struct commit_graph *g; + int *commit_graph_changed_paths_version; +}; + static int graph_read_bloom_data(const unsigned char *chunk_start, size_t chunk_size, void *data) { - struct commit_graph *g = data; + struct graph_read_bloom_data_context *c = data; + struct commit_graph *g = c->g; uint32_t hash_version; - g->chunk_bloom_data = chunk_start; hash_version = get_be32(chunk_start); - if (hash_version != 1) + if (*c->commit_graph_changed_paths_version == -1) { + *c->commit_graph_changed_paths_version = hash_version; + } else if (hash_version != *c->commit_graph_changed_paths_version) { return 0; + } + g->chunk_bloom_data = chunk_start; g->bloom_filter_settings = xmalloc(sizeof(struct bloom_filter_settings)); g->bloom_filter_settings->hash_version = hash_version; g->bloom_filter_settings->num_hashes = get_be32(chunk_start + 4); @@ -402,10 +411,14 @@ struct commit_graph *parse_commit_graph(struct repo_settings *s, } if (s->commit_graph_changed_paths_version) { + struct graph_read_bloom_data_context context = { + .g = graph, + .commit_graph_changed_paths_version = &s->commit_graph_changed_paths_version + }; pair_chunk(cf, GRAPH_CHUNKID_BLOOMINDEXES, &graph->chunk_bloom_indexes); read_chunk(cf, GRAPH_CHUNKID_BLOOMDATA, - graph_read_bloom_data, graph); + graph_read_bloom_data, &context); } if (graph->chunk_bloom_indexes && graph->chunk_bloom_data) { @@ -2376,6 +2389,13 @@ int write_commit_graph(struct object_directory *odb, } if (!commit_graph_compatible(r)) return 0; + if (r->settings.commit_graph_changed_paths_version < -1 + || r->settings.commit_graph_changed_paths_version > 2) { + warning(_("attempting to write a commit-graph, but " + "'commitgraph.changedPathsVersion' (%d) is not supported"), + r->settings.commit_graph_changed_paths_version); + return 0; + } CALLOC_ARRAY(ctx, 1); ctx->r = r; @@ -2388,6 +2408,8 @@ int write_commit_graph(struct object_directory *odb, ctx->write_generation_data = (get_configured_generation_version(r) == 2); ctx->num_generation_data_overflows = 0; + bloom_settings.hash_version = r->settings.commit_graph_changed_paths_version == 2 + ? 2 : 1; bloom_settings.bits_per_entry = git_env_ulong("GIT_TEST_BLOOM_SETTINGS_BITS_PER_ENTRY", bloom_settings.bits_per_entry); bloom_settings.num_hashes = git_env_ulong("GIT_TEST_BLOOM_SETTINGS_NUM_HASHES", @@ -2417,7 +2439,7 @@ int write_commit_graph(struct object_directory *odb, g = ctx->r->objects->commit_graph; /* We have changed-paths already. Keep them in the next graph */ - if (g && g->chunk_bloom_data) { + if (g && g->bloom_filter_settings) { ctx->changed_paths = 1; ctx->bloom_settings = g->bloom_filter_settings; } diff --git a/t/helper/test-bloom.c b/t/helper/test-bloom.c index aabe31d724..3cbc0a5b50 100644 --- a/t/helper/test-bloom.c +++ b/t/helper/test-bloom.c @@ -50,6 +50,7 @@ static void get_bloom_filter_for_commit(const struct object_id *commit_oid) static const char *bloom_usage = "\n" " test-tool bloom get_murmur3 \n" +" test-tool bloom get_murmur3_seven_highbit\n" " test-tool bloom generate_filter [...]\n" " test-tool bloom get_filter_for_commit \n"; @@ -64,7 +65,13 @@ int cmd__bloom(int argc, const char **argv) uint32_t hashed; if (argc < 3) usage(bloom_usage); - hashed = murmur3_seeded(0, argv[2], strlen(argv[2])); + hashed = murmur3_seeded_v2(0, argv[2], strlen(argv[2])); + printf("Murmur3 Hash with seed=0:0x%08x\n", hashed); + } + + if (!strcmp(argv[1], "get_murmur3_seven_highbit")) { + uint32_t hashed; + hashed = murmur3_seeded_v2(0, "\x99\xaa\xbb\xcc\xdd\xee\xff", 7); printf("Murmur3 Hash with seed=0:0x%08x\n", hashed); } diff --git a/t/t0095-bloom.sh b/t/t0095-bloom.sh index b567383eb8..c8d84ab606 100755 --- a/t/t0095-bloom.sh +++ b/t/t0095-bloom.sh @@ -29,6 +29,14 @@ test_expect_success 'compute unseeded murmur3 hash for test string 2' ' test_cmp expect actual ' +test_expect_success 'compute unseeded murmur3 hash for test string 3' ' + cat >expect <<-\EOF && + Murmur3 Hash with seed=0:0xa183ccfd + EOF + test-tool bloom get_murmur3_seven_highbit >actual && + test_cmp expect actual +' + test_expect_success 'compute bloom key for empty string' ' cat >expect <<-\EOF && Hashes:0x5615800c|0x5b966560|0x61174ab4|0x66983008|0x6c19155c|0x7199fab0|0x771ae004| diff --git a/t/t4216-log-bloom.sh b/t/t4216-log-bloom.sh index 0aa9719934..1d0e11d7c1 100755 --- a/t/t4216-log-bloom.sh +++ b/t/t4216-log-bloom.sh @@ -456,4 +456,109 @@ test_expect_success 'version 1 changed-path used when version 1 requested' ' ) ' +test_expect_success 'version 1 changed-path not used when version 2 requested' ' + ( + cd highbit1 && + git config --add commitgraph.changedPathsVersion 2 && + test_bloom_filters_not_used "-- another$CENT" + ) +' + +test_expect_success 'version 1 changed-path used when autodetect requested' ' + ( + cd highbit1 && + git config --add commitgraph.changedPathsVersion -1 && + test_bloom_filters_used "-- another$CENT" + ) +' + +test_expect_success 'when writing another commit graph, preserve existing version 1 of changed-path' ' + test_commit -C highbit1 c1double "$CENT$CENT" && + git -C highbit1 commit-graph write --reachable --changed-paths && + ( + cd highbit1 && + git config --add commitgraph.changedPathsVersion -1 && + echo "options: bloom(1,10,7) read_generation_data" >expect && + test-tool read-graph >full && + grep options full >actual && + test_cmp expect actual + ) +' + +test_expect_success 'set up repo with high bit path, version 2 changed-path' ' + git init highbit2 && + git -C highbit2 config --add commitgraph.changedPathsVersion 2 && + test_commit -C highbit2 c2 "$CENT" && + git -C highbit2 commit-graph write --reachable --changed-paths +' + +test_expect_success 'check value of version 2 changed-path' ' + ( + cd highbit2 && + echo "c01f" >expect && + get_first_changed_path_filter >actual && + test_cmp expect actual + ) +' + +test_expect_success 'setup make another commit' ' + # "git log" does not use Bloom filters for root commits - see how, in + # revision.c, rev_compare_tree() (the only code path that eventually calls + # get_bloom_filter()) is only called by try_to_simplify_commit() when the commit + # has one parent. Therefore, make another commit so that we perform the tests on + # a non-root commit. + test_commit -C highbit2 anotherc2 "another$CENT" +' + +test_expect_success 'version 2 changed-path used when version 2 requested' ' + ( + cd highbit2 && + test_bloom_filters_used "-- another$CENT" + ) +' + +test_expect_success 'version 2 changed-path not used when version 1 requested' ' + ( + cd highbit2 && + git config --add commitgraph.changedPathsVersion 1 && + test_bloom_filters_not_used "-- another$CENT" + ) +' + +test_expect_success 'version 2 changed-path used when autodetect requested' ' + ( + cd highbit2 && + git config --add commitgraph.changedPathsVersion -1 && + test_bloom_filters_used "-- another$CENT" + ) +' + +test_expect_success 'when writing another commit graph, preserve existing version 2 of changed-path' ' + test_commit -C highbit2 c2double "$CENT$CENT" && + git -C highbit2 commit-graph write --reachable --changed-paths && + ( + cd highbit2 && + git config --add commitgraph.changedPathsVersion -1 && + echo "options: bloom(2,10,7) read_generation_data" >expect && + test-tool read-graph >full && + grep options full >actual && + test_cmp expect actual + ) +' + +test_expect_success 'when writing commit graph, do not reuse changed-path of another version' ' + git init doublewrite && + test_commit -C doublewrite c "$CENT" && + git -C doublewrite config --add commitgraph.changedPathsVersion 1 && + git -C doublewrite commit-graph write --reachable --changed-paths && + git -C doublewrite config --add commitgraph.changedPathsVersion 2 && + git -C doublewrite commit-graph write --reachable --changed-paths && + ( + cd doublewrite && + echo "c01f" >expect && + get_first_changed_path_filter >actual && + test_cmp expect actual + ) +' + test_done