Subject: [PATCH v2 00/11] Handle cloning of objects larger than 4GB on Windows

From: "Johannes Schindelin via GitGitGadget" <[email-masked]>
Date: Mon, 04 May 2026 17:08:17 +0000

On Windows, unsigned long is 32-bit even on 64-bit systems. This causes
multiple problems when Git handles objects larger than 4GB. This patch
series is a very targeted fix for a very early part of the problem: it
addresses the most fundamental truncation points that prevent a >4GB object
from surviving a clone at all.

Specifically, this fixes:

 * zlib's uLong wrapping and triggering BUG() assertions in the git_zstream
   wrapper
 * Object sizes being truncated in pack streaming, delta headers, and
   index-pack/unpack-objects
 * pack-objects re-encoding reused pack entries with a truncated size,
   producing corrupt packs on the wire

Many other code paths still use unsigned long for object sizes (e.g.,
cat-file -s, object_info.sizep, the delta machinery) and will need their own
conversions. This series does not attempt to fix those.

Based on work by @LordKiRon in git-for-windows/git#6076.

The last two commits add a test helper that synthesizes a pack with a >4GB
blob and regression tests that clone it via both the unpack-objects and
index-pack code paths using file:// transport.

Changes since v1:

 * dramatically accelerated the test helper that generates 4GB pack files,
   via two separate strategies:
   1. using the "unsafe" SHA-1 for the blob OID computation.
   2. using pre-computed "Lego blocks" to construct the 4GB packs needed in
      the test cases, where the size (and therefore the involved OIDs) are
      well-known in advance.
 * even with these improvements, the actual git clone is still slow (of
   course, because it cannot use any of those shortcuts), therefore the
   tests are marked as EXPENSIVE.
 * to exercise those tests nevertheless, the last patch lets all EXPENSIVE
   test cases be run for the integration branches other than seen.

Johannes Schindelin (11):
  index-pack, unpack-objects: use size_t for object size
  git-zlib: handle data streams larger than 4GB
  odb, packfile: use size_t for streaming object sizes
  delta, packfile: use size_t for delta header sizes
  test-tool: add a helper to synthesize large packfiles
  t5608: add regression test for >4GB object clone
  test-tool synthesize: use the unsafe hash for speed
  test-tool synthesize: precompute pack for 4 GiB + 1
  test-tool synthesize: add precomputed SHA-256 pack for 4 GiB + 1
  t5608: mark >4GB tests as EXPENSIVE
  ci: run expensive tests on push builds to integration branches

 Makefile                     |   1 +
 builtin/index-pack.c         |   9 +-
 builtin/pack-objects.c       |  23 +-
 builtin/unpack-objects.c     |   5 +-
 ci/lib.sh                    |   9 +
 compat/zlib-compat.h         |   2 +
 delta.h                      |  14 +-
 git-zlib.c                   |  25 +-
 git-zlib.h                   |   4 +-
 object-file.c                |  12 +-
 odb/streaming.c              |  13 +-
 odb/streaming.h              |   2 +-
 oss-fuzz/fuzz-pack-headers.c |   2 +-
 pack-bitmap.c                |   2 +-
 pack-check.c                 |   6 +-
 packfile.c                   |  57 ++--
 packfile.h                   |   4 +-
 t/helper/meson.build         |   1 +
 t/helper/test-synthesize.c   | 541 +++++++++++++++++++++++++++++++++++
 t/helper/test-tool.c         |   1 +
 t/helper/test-tool.h         |   1 +
 t/t5608-clone-2gb.sh         |  37 +++
 22 files changed, 718 insertions(+), 53 deletions(-)
 create mode 100644 t/helper/test-synthesize.c

base-commit: 94f057755b7941b321fd11fec1b2e3ca5313a4e0
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-2102%2Fdscho%2Ffix-large-clones-on-windows-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-2102/dscho/fix-large-clones-on-windows-v2
Pull-Request: https://github.com/gitgitgadget/git/pull/2102

Range-diff vs v1:

  1:  dc660106ea =  1:  dc660106ea index-pack, unpack-objects: use size_t for object size
  2:  92f4327b1f =  2:  92f4327b1f git-zlib: handle data streams larger than 4GB
  3:  3a539061c5 =  3:  3a539061c5 odb, packfile: use size_t for streaming object sizes
  4:  3274cba862 =  4:  3274cba862 delta, packfile: use size_t for delta header sizes
  5:  afa74a3a2b =  5:  afa74a3a2b test-tool: add a helper to synthesize large packfiles
  6:  a3019888d8 =  6:  a3019888d8 t5608: add regression test for >4GB object clone
  -:  ---------- >  7:  859e93e7a9 test-tool synthesize: use the unsafe hash for speed
  -:  ---------- >  8:  29b9a74e91 test-tool synthesize: precompute pack for 4 GiB + 1
  -:  ---------- >  9:  8e6e720804 test-tool synthesize: add precomputed SHA-256 pack for 4 GiB + 1
  -:  ---------- > 10:  5b44410b2f t5608: mark >4GB tests as EXPENSIVE
  -:  ---------- > 11:  1eaaa7fad7 ci: run expensive tests on push builds to integration branches

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