From 0fd93073c26b87a29ef76c36c7015f3116676610 Mon Sep 17 00:00:00 2001
From: Koi <helzky@proton.me>
Date: Fri, 30 Oct 2026 23:16:59 -0400
Subject: [PATCH 1/2] gh-150467: Fix linking python3.dll and python3t.dll with
 ASan on 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.
---
 .../Build/2026-10-30-23-16-35.gh-issue-150467.qMGY7M.rst  | 2 ++
 PCbuild/pyproject.props                                   | 8 ++++++++
 PCbuild/python3dll.vcxproj                                | 6 +++++-
 PCbuild/python3tdll.vcxproj                               | 6 +++++-
 4 files changed, 20 insertions(+), 2 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Build/2026-10-30-23-16-35.gh-issue-150467.qMGY7M.rst

diff --git a/Misc/NEWS.d/next/Build/2026-10-30-23-16-35.gh-issue-150467.qMGY7M.rst b/Misc/NEWS.d/next/Build/2026-10-30-23-16-35.gh-issue-150467.qMGY7M.rst
new file mode 100644
index 000000000000000..c1d63934f80a6ed
--- /dev/null
+++ b/Misc/NEWS.d/next/Build/2026-10-30-23-16-35.gh-issue-150467.qMGY7M.rst
@@ -0,0 +1,2 @@
+Fix linking ``python3.dll`` and ``python3t.dll`` on Windows when building with
+AddressSanitizer.
diff --git a/PCbuild/pyproject.props b/PCbuild/pyproject.props
index ca8330c004cccea..8e4f7dd8bebf778 100644
--- a/PCbuild/pyproject.props
+++ b/PCbuild/pyproject.props
@@ -25,6 +25,14 @@
     <SupportSigning Condition="'$(Configuration)' == 'Debug'">false</SupportSigning>
     <SupportSigning Condition="'$(ConfigurationType)' == 'StaticLibrary'">false</SupportSigning>
     <LinkIncremental Condition="$(Configuration) != 'Debug'">false</LinkIncremental>
+
+    <!--
+    AddressSanitizer may be enabled with the EnableASAN property or through the
+    _CL_ and _LINK_ environment variables, so check all of them.
+    -->
+    <PyUsingAsan Condition="'$(PyUsingAsan)' == '' and '$(EnableASAN)' == 'true'">true</PyUsingAsan>
+    <PyUsingAsan Condition="'$(PyUsingAsan)' == '' and $(_CL_.ToLowerInvariant().Contains('fsanitize=address'))">true</PyUsingAsan>
+    <PyUsingAsan Condition="'$(PyUsingAsan)' == '' and $(_LINK_.ToLowerInvariant().Contains('inferasanlibs'))">true</PyUsingAsan>
   </PropertyGroup>
 
   <PropertyGroup Condition="$(TargetExt) != ''">
diff --git a/PCbuild/python3dll.vcxproj b/PCbuild/python3dll.vcxproj
index 3d8ac1b23532c1d..604e75073e1d662 100644
--- a/PCbuild/python3dll.vcxproj
+++ b/PCbuild/python3dll.vcxproj
@@ -95,7 +95,11 @@
       <BufferSecurityCheck>false</BufferSecurityCheck>
     </ClCompile>
     <Link>
-      <NoEntryPoint>true</NoEntryPoint>
+      <!--
+      The ASan runtime thunks need the CRT to be initialized, so keep the
+      default entry point when building with AddressSanitizer.
+      -->
+      <NoEntryPoint Condition="$(PyUsingAsan) != 'true'">true</NoEntryPoint>
     </Link>
   </ItemDefinitionGroup>
   <ItemGroup>
diff --git a/PCbuild/python3tdll.vcxproj b/PCbuild/python3tdll.vcxproj
index 796712cca3146c4..49a123c1cf89631 100644
--- a/PCbuild/python3tdll.vcxproj
+++ b/PCbuild/python3tdll.vcxproj
@@ -95,7 +95,11 @@
       <BufferSecurityCheck>false</BufferSecurityCheck>
     </ClCompile>
     <Link>
-      <NoEntryPoint>true</NoEntryPoint>
+      <!--
+      The ASan runtime thunks need the CRT to be initialized, so keep the
+      default entry point when building with AddressSanitizer.
+      -->
+      <NoEntryPoint Condition="$(PyUsingAsan) != 'true'">true</NoEntryPoint>
     </Link>
   </ItemDefinitionGroup>
   <ItemGroup>

From d04b81a9ee02eae2a09e2bee186247c26afbcfa4 Mon Sep 17 00:00:00 2001
From: Koi <helzky@proton.me>
Date: Sat, 31 Oct 2026 10:59:04 -0400
Subject: [PATCH 2/2] Drive the python3 DLL entry point from EnableASAN only

---
 PCbuild/pyproject.props     | 8 --------
 PCbuild/python3dll.vcxproj  | 2 +-
 PCbuild/python3tdll.vcxproj | 2 +-
 3 files changed, 2 insertions(+), 10 deletions(-)

diff --git a/PCbuild/pyproject.props b/PCbuild/pyproject.props
index 8e4f7dd8bebf778..ca8330c004cccea 100644
--- a/PCbuild/pyproject.props
+++ b/PCbuild/pyproject.props
@@ -25,14 +25,6 @@
     <SupportSigning Condition="'$(Configuration)' == 'Debug'">false</SupportSigning>
     <SupportSigning Condition="'$(ConfigurationType)' == 'StaticLibrary'">false</SupportSigning>
     <LinkIncremental Condition="$(Configuration) != 'Debug'">false</LinkIncremental>
-
-    <!--
-    AddressSanitizer may be enabled with the EnableASAN property or through the
-    _CL_ and _LINK_ environment variables, so check all of them.
-    -->
-    <PyUsingAsan Condition="'$(PyUsingAsan)' == '' and '$(EnableASAN)' == 'true'">true</PyUsingAsan>
-    <PyUsingAsan Condition="'$(PyUsingAsan)' == '' and $(_CL_.ToLowerInvariant().Contains('fsanitize=address'))">true</PyUsingAsan>
-    <PyUsingAsan Condition="'$(PyUsingAsan)' == '' and $(_LINK_.ToLowerInvariant().Contains('inferasanlibs'))">true</PyUsingAsan>
   </PropertyGroup>
 
   <PropertyGroup Condition="$(TargetExt) != ''">
diff --git a/PCbuild/python3dll.vcxproj b/PCbuild/python3dll.vcxproj
index 604e75073e1d662..f6f1d0d8f95ed96 100644
--- a/PCbuild/python3dll.vcxproj
+++ b/PCbuild/python3dll.vcxproj
@@ -99,7 +99,7 @@
       The ASan runtime thunks need the CRT to be initialized, so keep the
       default entry point when building with AddressSanitizer.
       -->
-      <NoEntryPoint Condition="$(PyUsingAsan) != 'true'">true</NoEntryPoint>
+      <NoEntryPoint Condition="$(EnableASAN) != 'true'">true</NoEntryPoint>
     </Link>
   </ItemDefinitionGroup>
   <ItemGroup>
diff --git a/PCbuild/python3tdll.vcxproj b/PCbuild/python3tdll.vcxproj
index 49a123c1cf89631..9ccc71ce4a40a81 100644
--- a/PCbuild/python3tdll.vcxproj
+++ b/PCbuild/python3tdll.vcxproj
@@ -99,7 +99,7 @@
       The ASan runtime thunks need the CRT to be initialized, so keep the
       default entry point when building with AddressSanitizer.
       -->
-      <NoEntryPoint Condition="$(PyUsingAsan) != 'true'">true</NoEntryPoint>
+      <NoEntryPoint Condition="$(EnableASAN) != 'true'">true</NoEntryPoint>
     </Link>
   </ItemDefinitionGroup>
   <ItemGroup>