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Reproducible snapshot error #304

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Closed
Reproducible snapshot error#304

Description

@targos
targos
opened on Nov 9, 2025

Seems arm-specific: https://github.com/nodejs/node-v8/actions/runs/19205829620/job/54900847817

@joyeecheung

=== release test-snapshot-reproducible ===
Path: parallel/test-snapshot-reproducible
Error: --- stderr ---
node:internal/assert/utils:146
  throw error;
  ^

AssertionError [ERR_ASSERTION]: Expected values to be strictly deep-equal:
+ actual - expected

+ [
+   {
+     offset: '0x2ffec0',
+     slice1: '06000400000000000300000059ab0000',
+     slice2: '060004000000000003000000b8aa0000'
+   },
+   {
+     offset: '0x476eb0',
+     slice1: '00000059ab0000580701106100000000',
+     slice2: '000000b8aa0000580701106100000000'
+   }
+ ]
- []

    at Object.<anonymous> (/home/runner/work/node-v8/node-v8/node/test/parallel/test-snapshot-reproducible.js:69:8)
    at Module._compile (node:internal/modules/cjs/loader:1760:14)
    at Object..js (node:internal/modules/cjs/loader:1892:10)
    at Module.load (node:internal/modules/cjs/loader:1480:32)
    at Module._load (node:internal/modules/cjs/loader:1299:12)
    at TracingChannel.traceSync (node:diagnostics_channel:328:14)
    at wrapModuleLoad (node:internal/modules/cjs/loader:245:24)
    at Module.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:154:5)
    at node:internal/main/run_main_module:33:47 {
  generatedMessage: true,
  code: 'ERR_ASSERTION',
  actual: [
    {
      offset: '0x2ffec0',
      slice1: '06000400000000000300000059ab0000',
      slice2: '060004000000000003000000b8aa0000'
    },
    {
      offset: '0x476eb0',
      slice1: '00000059ab0000580701106100000000',
      slice2: '000000b8aa0000580701106100000000'
    }
  ],
  expected: [],
  operator: 'deepStrictEqual',
  diff: 'simple'
}

Node.js v26.0.0-pre
--- stdout ---
0x0: Write magic 143da19
0x4: Write metadata
0x35: Write snapshot blob
0x258bfc: Write IsolateDataSerializeInfo
0x25a299: Write EnvSerializeInfo
0x25b1c0: Write CodeCacheInfo
0x0: Write magic 143da19
0x4: Write metadata
0x35: Write snapshot blob
0x258bfc: Write IsolateDataSerializeInfo
0x25a299: Write EnvSerializeInfo
0x25b1c0: Write CodeCacheInfo
Command: out/Release/node /home/runner/work/node-v8/node-v8/node/test/parallel/test-snapshot-reproducible.js

===
=== 1 tests failed
===

Failed tests:
out/Release/node /home/runner/work/node-v8/node-v8/node/test/parallel/test-snapshot-reproducible.js

Activity

  1. targos commented on Nov 15, 2025

    @targos
    targos
    on Nov 15, 2025
    MemberAuthor

    Still happening.
    Looking at https://github.com/nodejs/node-v8/actions/workflows/test-linux.yml:

  2. targos commented on Nov 15, 2025

    @targos
    targos
    on Nov 15, 2025
    MemberAuthor

    I suspect v8/v8@db44401
    It was relanded on Oct 28, reverted on Oct 29, and relanded again on Oct 30.

  3. targos commented on Dec 2, 2025

    @targos
    targos
    on Dec 2, 2025
    MemberAuthor

    Still failing: https://github.com/nodejs/node-v8/actions/runs/19816998138/job/56770380628

  4. joyeecheung commented on Dec 2, 2025

    @joyeecheung
    joyeecheung
    on Dec 2, 2025
    Member

    Looks like the code cache reproducibility is altered by some recent change, going to take a look when I get back to a powerful enough build machine..

  5. targos commented on Dec 13, 2025

    @targos
    targos
    on Dec 13, 2025
    MemberAuthor

    I bisected it to https://chromium-review.googlesource.com/c/v8/v8/+/7139418

  6. joyeecheung commented on Dec 16, 2025

    @joyeecheung
    joyeecheung
    on Dec 16, 2025
    Member

    Looks like it broke the code cache reproducibility somehow

    < Write<builtins::CodeCacheInfo>() id = internal/errors, length=97160, hash=3258954470
> Write<builtins::CodeCacheInfo>() id = internal/errors, length=97160, hash=2884610497

  7. targos commented on Dec 17, 2025

    @targos
    targos
    on Dec 17, 2025
    MemberAuthor

    It's more complex than this. If I revert that commit on the V8 14.4 update branch, the test still fails.

  8. joyeecheung commented on Dec 17, 2025

    @joyeecheung
    joyeecheung
    on Dec 17, 2025
    Member

    I noticed that the debug build has been failing on canary, this gyp change should fix it: https://github.com/joyeecheung/node/tree/fix-debug - where should I submit this?

  9. joyeecheung commented on Dec 17, 2025

    @joyeecheung
    joyeecheung
    on Dec 17, 2025
    Member

    Also opened nodejs/node#61101 to help diffing the snapshots

  10. joyeecheung commented on Dec 17, 2025

    @joyeecheung
    joyeecheung
    on Dec 17, 2025
    Member

    It seems the diffing object is a class boilerplate, or it appears to be its static_properties_template

    0x224633025a69: [ClassBoilerplate] in OldSpace
 - map: 0x0ec5791c1f89 <Map[64](CLASS_BOILERPLATE_TYPE)>
 - arguments_count: 3
 - static_properties_template: 0x224633025969 <DescriptorArray[4]>
 - static_elements_template: 0x0ec5791c8f99 <NumberDictionary[7]>
 - static_computed_properties: 0x0ec5791c0dd1 <FixedArray[0]>
 - instance_properties_template: 0x224633025a31 <DescriptorArray[1]>
 - instance_elements_template: 0x0ec5791c8f99 <NumberDictionary[7]>
 - instance_computed_properties: 0x0ec5791c0dd1 <FixedArray[0]>

    I have a feeling that it might be the same as the bug fixed by https://chromium-review.googlesource.com/c/v8/v8/+/7252791, only that this happens to the descriptor array instead of transition array. Looknig..

  11. joyeecheung commented on Dec 17, 2025

    @joyeecheung
    joyeecheung
    on Dec 17, 2025
    Member

    I can fix it locally with this:

    diff --git a/deps/v8/src/objects/objects.cc b/deps/v8/src/objects/objects.cc
index aa3c306212..5e8a1ed3c9 100644
--- a/deps/v8/src/objects/objects.cc
+++ b/deps/v8/src/objects/objects.cc
@@ -3997,6 +3997,9 @@ void DescriptorArray::Initialize(Tagged<EnumCache> empty_enum_cache,
   set_enum_cache(empty_enum_cache, SKIP_WRITE_BARRIER);
   set_flags(FastIterableBits::encode(FastIterableState::kUnknown),
             kRelaxedStore);
+#if TAGGED_SIZE_8_BYTES
+  set_optional_padding(0);
+#endif
   MemsetTagged(GetDescriptorSlot(0), undefined_value,
                number_of_all_descriptors() * kEntrySize);
 }

    Going to upstream it

  12. targos commented on Dec 18, 2025

    @targos
    targos
    on Dec 18, 2025
    MemberAuthor

    I noticed that the debug build has been failing on canary, this gyp change should fix it: https://github.com/joyeecheung/node/tree/fix-debug - where should I submit this?

    You can directly cherry-pick and push it to canary-base

  13. joyeecheung commented on Dec 18, 2025

    @joyeecheung
    joyeecheung
    on Dec 18, 2025
    Member

    You can directly cherry-pick and push it to canary-base

    Done, thanks for the pointer

  14. joyeecheung commented on Dec 18, 2025

    @joyeecheung
    joyeecheung
    on Dec 18, 2025
    Member

    Upstream CL: https://chromium-review.googlesource.com/c/v8/v8/+/7271645

  15. hubot
    added a commit that references this issue on Dec 19, 2025

    [runtime] zero-initialize descriptor array padding

    6eff00a
  16. targos
    added a commit that references this issue on Dec 22, 2025

    deps: V8: cherry-pick 6eff00a342cb

    24f92ec

  17. targos commented on Dec 22, 2025

    @targos
    targos
    on Dec 22, 2025
    MemberAuthor

    Thanks for the investigation and fix @joyeecheung !

  18. targos
    closed this as completedon Dec 22, 2025
  19. targos
    added a commit that references this issue on Feb 11, 2026

    deps: V8: cherry-pick 6eff00a342cb

    5b658e7
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