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gh-126929: Retry extension loading with long Windows paths #156759

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gh-126929: Retry extension loading with long Windows paths #156759

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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Windows/2026-09-01-10-05-00.gh-issue-126929.long-path-dll.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Fix loading extension modules from long Windows paths by retrying with an extended-length path after the initial load fails and the target is confirmed to be a regular file.
30 changes: 30 additions & 0 deletions Python/dynload_win.c
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Expand Up @@ -307,6 +307,36 @@ dl_funcptr _PyImport_FindSharedFuncptrWindows(const char *prefix,
hDLL = LoadLibraryExW(wpathname, NULL,
LOAD_LIBRARY_SEARCH_DEFAULT_DIRS |
LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR);
if (hDLL == NULL) {
DWORD attributes = GetFileAttributesW(wpathname);
if (attributes != INVALID_FILE_ATTRIBUTES &&
!(attributes & FILE_ATTRIBUTE_DIRECTORY)) {
size_t path_length = wcslen(wpathname);
int is_unc = wpathname[0] == L'\\' && wpathname[1] == L'\\';
size_t prefix_length = is_unc ? 8 : 4;
wchar_t *extended_path = PyMem_RawMalloc(
(path_length + prefix_length + 1) * sizeof(wchar_t));
if (extended_path != NULL) {
if (is_unc) {
wcscpy_s(extended_path, path_length + prefix_length + 1,
L"\\\\?\\UNC\\");
wcscat_s(extended_path, path_length + prefix_length + 1,
wpathname + 2);
}
else {
wcscpy_s(extended_path, path_length + prefix_length + 1,
L"\\\\?\\");
wcscat_s(extended_path, path_length + prefix_length + 1,
wpathname);
}
hDLL = LoadLibraryExW(
extended_path, NULL,
LOAD_LIBRARY_SEARCH_DEFAULT_DIRS |
LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR);
PyMem_RawFree(extended_path);
}
}
}
Py_END_ALLOW_THREADS
PyMem_Free(wpathname);

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