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GeezerVison is showing github.com — gh-150467: Fix linking python3.dll and python3t.dll with ASan on Windows by ck0i · Pull Request #160992 · python/cpython

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@ck0i

@ck0i ck0i commented Oct 31, 2026 •
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Fixes gh-150467.

Root cause

python3.dll and python3t.dll only contain /EXPORT forwarders and are linked with /NOENTRY, so the CRT is never pulled in. With ASan enabled, the linker adds clang_rt.asan_dynamic_runtime_thunk, which needs the CRT (_initterm, abort, __vcrt_*, __acrt_*), so the link fails with LNK2001.

python3.dll also fails this way at the parent of GH-149218, so the bug is older. That change added python3t.dll, a second forwarder built with the same settings.

Fix

python3dll.vcxproj and python3tdll.vcxproj now set NoEntryPoint only when EnableASAN isn't true, so ASan builds keep the default CRT entry point. ASan turned on only through _CL_/_LINK_ is not detected; use /p:EnableASAN=true.

Non-ASan builds are unchanged: both DLLs still have no entry point and no imports.

Testing

x64 Release, VS 2026 (MSVC 14.51), building python3dll.vcxproj and python3tdll.vcxproj on their own:

  • /p:EnableASAN=true: both failed with LNK2001 before, and link now. dumpbin shows _DllMainCRTStartup as the entry point and an import of clang_rt.asan_dynamic-x86_64.dll.
  • Without ASan: both still have no entry point and no imports, and export the same 964 forwarders.

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@ck0i
pythongh-150467: Fix linking python3.dll and python3t.dll with ASan o…
0fd9307 
…n Windows

The stable ABI forwarder DLLs are linked with /NOENTRY, so nothing pulls
in the CRT. With AddressSanitizer enabled, the linker adds the ASan
runtime thunk library, which needs the CRT, and the link fails with
unresolved symbols. Keep the default CRT entry point for these DLLs
when building with ASan.
@ck0i
ck0i requested a review from a team as a code owner October 31, 2026 03:32
@bedevere-app bedevere-app Bot added the awaiting review label Oct 31, 2026
@python-cla-bot

python-cla-bot Bot commented Oct 31, 2026 •
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All commit authors signed the Contributor License Agreement.

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@bedevere-app bedevere-app Bot mentioned this pull request Oct 31, 2026
[Asan + msvc] Cpython build failed with error LNK2001: unresolved external symbol on windows #150467
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@chatgpt-codex-connector

chatgpt-codex-connector Bot commented Oct 31, 2026 •
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Codex Review Summary

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Review Status Commit Review trigger
📝 Code Review ⚠️ Failed 2026-10-31T03:33:16.126766Z
We couldn’t complete this review. Comment @codex review to try again.		 0fd9307 PR opened
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@picnixz picnixz added the AI-needs-explanation AI-assisted work that needs further explanation and follow up from the contributor label Oct 31, 2026
@bedevere-app

bedevere-app Bot commented Oct 31, 2026

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Thank you for your interest in contributing to Python. This is a community-driven project, and we want it to be a welcoming place to learn and collaborate.

Contributors are responsible for reviewing and understanding what they submit, checking its claims, and being able to explain changes in their own words. This helps reviewers focus on the contribution and leaves more time to support other contributors.

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@picnixz
picnixz requested a review from chris-eibl October 31, 2026 14:18
@chris-eibl

chris-eibl commented Oct 31, 2026

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LGTM, but see my earlier #150467 (comment) before we proceed here.
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@ck0i
Drive the python3 DLL entry point from EnableASAN only
d04b81a
@ck0i

ck0i commented Oct 31, 2026

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Agreed, made some changes regarding the comment you linked. Thanks.
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@chris-eibl chris-eibl Awaiting requested review from chris-eibl

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[Asan + msvc] Cpython build failed with error LNK2001: unresolved external symbol on windows

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@ck0i @chris-eibl @picnixz
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