[PATCH v46 0/2] MR10291: Fix GetModuleFileName string termination

[Trent Waddington (＠trent.waddington)]

After Windows XP the string termination behavior of GetModuleFileName was changed to always terminate the path returned, even if  the buffer is insufficient to contain the null terminator.

--
  v46: kernel32: Fix string termination of GetModuleFileName
 
https://gitlab.winehq.org/wine/wine/-/merge_requests/10291

[PATCH v46 1/2] Add tests for GetModuleFileName string termination.

[Trent Waddington]

From: Trent Waddington <[e-mail]>

---
 dlls/kernel32/tests/loader.c | 48 ++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)

diff --git a/dlls/kernel32/tests/loader.c b/dlls/kernel32/tests/loader.c
index 529b9de870d..2ea83147296 100644
--- a/dlls/kernel32/tests/loader.c
+++ b/dlls/kernel32/tests/loader.c
@@ -1552,6 +1552,52 @@ static void test_filenames(void)
     DeleteFileA( long_path );
 }
 
+static void test_getmodulefilenamew_string_termination(void)
+{
+    WCHAR dll_name[MAX_PATH];
+    size_t dll_name_len, dll_name_term;
+    DWORD rv, err;
+
+    GetModuleFileNameW(NULL, dll_name, MAX_PATH);
+    err = GetLastError();
+    ok(err == ERROR_SUCCESS, "error getting path for NULL module: %lu\n", err);
+    dll_name_len = wcslen(dll_name);
+    ok(dll_name_len > 0, "can't get path for NULL module\n");
+
+    memset(dll_name, '*', sizeof(dll_name));
+    rv = GetModuleFileNameW(NULL, dll_name, dll_name_len);
+    err = GetLastError();
+    ok(err == ERROR_INSUFFICIENT_BUFFER, "didn't get expected error getting path for NULL module with short buffer: %lu\n", err);
+    dll_name_term = wcsnlen(dll_name, MAX_PATH);
+    ok(dll_name_term > 0, "can't get path for NULL module with short buffer, dll_name_term=%llu\n", dll_name_term);
+    todo_wine {
+        ok(dll_name_term == dll_name_len - 1, "incorrect path termination for NULL module with short buffer. Expected %llu got %llu. rv=%lu\n", dll_name_len - 1, dll_name_term, rv);
+    }
+}
+
+static void test_getmodulefilenamea_string_termination(void)
+{
+    char dll_name[MAX_PATH];
+    size_t dll_name_len, dll_name_term;
+    DWORD rv, err;
+
+    GetModuleFileNameA(NULL, dll_name, MAX_PATH);
+    err = GetLastError();
+    ok(err == ERROR_SUCCESS, "error getting path for NULL module: %d\n", (int)err);
+    dll_name_len = strlen(dll_name);
+    ok(dll_name_len > 0, "can't get path for NULL module\n");
+
+    memset(dll_name, '*', sizeof(dll_name));
+    rv = GetModuleFileNameA(NULL, dll_name, dll_name_len);
+    err = GetLastError();
+    ok(err == ERROR_INSUFFICIENT_BUFFER, "didn't get expected error getting path for NULL module with short buffer: %lu\n", err);
+    dll_name_term = strnlen(dll_name, MAX_PATH);
+    ok(dll_name_term > 0, "can't get path for NULL module with short buffer, dll_name_term=%llu\n", dll_name_term);
+    todo_wine {
+        ok(dll_name_term == dll_name_len - 1, "incorrect path termination for NULL module with short buffer. Expected %llu got %llu. rv=%lu\n", dll_name_len - 1, dll_name_term, rv);
+    }
+}
+
 /* Verify linking style of import descriptors */
 static void test_ImportDescriptors(void)
 {
@@ -4859,6 +4905,8 @@ START_TEST(loader)
     }
 
     test_filenames();
+    test_getmodulefilenamew_string_termination();
+    test_getmodulefilenamea_string_termination();
     test_ResolveDelayLoadedAPI();
     test_ImportDescriptors();
     test_section_access();
-- 
GitLab


https://gitlab.winehq.org/wine/wine/-/merge_requests/10291

[PATCH v46 2/2] kernel32: Fix string termination of GetModuleFileName

[Trent Waddington]

From: Trent Waddington <[e-mail]>

---
 dlls/kernel32/tests/loader.c | 8 ++------
 dlls/kernelbase/loader.c     | 9 ++++++++-
 2 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/dlls/kernel32/tests/loader.c b/dlls/kernel32/tests/loader.c
index 2ea83147296..9daf09a4310 100644
--- a/dlls/kernel32/tests/loader.c
+++ b/dlls/kernel32/tests/loader.c
@@ -1570,9 +1570,7 @@ static void test_getmodulefilenamew_string_termination(void)
     ok(err == ERROR_INSUFFICIENT_BUFFER, "didn't get expected error getting path for NULL module with short buffer: %lu\n", err);
     dll_name_term = wcsnlen(dll_name, MAX_PATH);
     ok(dll_name_term > 0, "can't get path for NULL module with short buffer, dll_name_term=%llu\n", dll_name_term);
-    todo_wine {
-        ok(dll_name_term == dll_name_len - 1, "incorrect path termination for NULL module with short buffer. Expected %llu got %llu. rv=%lu\n", dll_name_len - 1, dll_name_term, rv);
-    }
+    ok(dll_name_term == dll_name_len - 1, "incorrect path termination for NULL module with short buffer. Expected %llu got %llu. rv=%lu\n", dll_name_len - 1, dll_name_term, rv);
 }
 
 static void test_getmodulefilenamea_string_termination(void)
@@ -1593,9 +1591,7 @@ static void test_getmodulefilenamea_string_termination(void)
     ok(err == ERROR_INSUFFICIENT_BUFFER, "didn't get expected error getting path for NULL module with short buffer: %lu\n", err);
     dll_name_term = strnlen(dll_name, MAX_PATH);
     ok(dll_name_term > 0, "can't get path for NULL module with short buffer, dll_name_term=%llu\n", dll_name_term);
-    todo_wine {
-        ok(dll_name_term == dll_name_len - 1, "incorrect path termination for NULL module with short buffer. Expected %llu got %llu. rv=%lu\n", dll_name_len - 1, dll_name_term, rv);
-    }
+    ok(dll_name_term == dll_name_len - 1, "incorrect path termination for NULL module with short buffer. Expected %llu got %llu. rv=%lu\n", dll_name_len - 1, dll_name_term, rv);
 }
 
 /* Verify linking style of import descriptors */
diff --git a/dlls/kernelbase/loader.c b/dlls/kernelbase/loader.c
index f4e1ca2e23a..aeac1c3ec77 100644
--- a/dlls/kernelbase/loader.c
+++ b/dlls/kernelbase/loader.c
@@ -315,7 +315,14 @@ DWORD WINAPI DECLSPEC_HOTPATCH GetModuleFileNameW( HMODULE module, LPWSTR filena
     name.Buffer = filename;
     name.MaximumLength = min( size, UNICODE_STRING_MAX_CHARS ) * sizeof(WCHAR);
     status = LdrGetDllFullName( module, &name );
-    if (!status || status == STATUS_BUFFER_TOO_SMALL) len = name.Length / sizeof(WCHAR);
+    if (!status || status == STATUS_BUFFER_TOO_SMALL)
+    {
+        len = name.Length / sizeof(WCHAR);
+        if (len < size)
+            filename[len] = 0;
+        else if (size > 0)
+            filename[size - 1] = 0;
+    }
     SetLastError( RtlNtStatusToDosError( status ));
 done:
     TRACE( "%s\n", debugstr_wn(filename, len) );
-- 
GitLab

https://gitlab.winehq.org/wine/wine/-/merge_requests/10291

[eric pouech (＠epo)]

eric pouech (@epo) commented about dlls/kernel32/tests/loader.c:
> +    WCHAR dll_name[MAX_PATH];
> +    size_t dll_name_len, dll_name_term;
> +    DWORD rv, err;
> +
> +    GetModuleFileNameW(NULL, dll_name, MAX_PATH);
> +    err = GetLastError();
> +    ok(err == ERROR_SUCCESS, "error getting path for NULL module: %lu\n", err);
> +    dll_name_len = wcslen(dll_name);
> +    ok(dll_name_len > 0, "can't get path for NULL module\n");
> +
> +    memset(dll_name, '*', sizeof(dll_name));
> +    rv = GetModuleFileNameW(NULL, dll_name, dll_name_len);
> +    err = GetLastError();
> +    ok(err == ERROR_INSUFFICIENT_BUFFER, "didn't get expected error getting path for NULL module with short buffer: %lu\n", err);
> +    dll_name_term = wcsnlen(dll_name, MAX_PATH);
> +    ok(dll_name_term > 0, "can't get path for NULL module with short buffer, dll_name_term=%llu\n", dll_name_term);
> you need `%Iu `for size_t

-- 
https://gitlab.winehq.org/wine/wine/-/merge_requests/10291#note_134029

[eric pouech (＠epo)]

eric pouech (@epo) commented about dlls/kernel32/tests/loader.c:
> +    dll_name_term = wcsnlen(dll_name, MAX_PATH);
> +    ok(dll_name_term > 0, "can't get path for NULL module with short buffer, dll_name_term=%llu\n", dll_name_term);
> +    todo_wine {
> +        ok(dll_name_term == dll_name_len - 1, "incorrect path termination for NULL module with short buffer. Expected %llu got %llu. rv=%lu\n", dll_name_len - 1, dll_name_term, rv);
> +    }
> +}
> +
> +static void test_getmodulefilenamea_string_termination(void)
> +{
> +    char dll_name[MAX_PATH];
> +    size_t dll_name_len, dll_name_term;
> +    DWORD rv, err;
> +
> +    GetModuleFileNameA(NULL, dll_name, MAX_PATH);
> +    err = GetLastError();
> +    ok(err == ERROR_SUCCESS, "error getting path for NULL module: %d\n", (int)err);
> please remove the cast

-- 
https://gitlab.winehq.org/wine/wine/-/merge_requests/10291#note_134030

[eric pouech (＠epo)]

eric pouech (@epo) commented about dlls/kernel32/tests/loader.c:
> DeleteFileA( long_path );
>  }
>
> +static void test_getmodulefilenamew_string_termination(void)
> +{
> +    WCHAR dll_name[MAX_PATH];
> +    size_t dll_name_len, dll_name_term;
> +    DWORD rv, err;
> +
> +    GetModuleFileNameW(NULL, dll_name, MAX_PATH);

sorry for not advising for this earlier on, but we usually insert `SetLastError(0xdeadbeef); `before calling the APIs

it turns out that some APIs don't set last error in case of success; so this ensures that we check against the value set in the API call

(shall be done before all the calls to GetModuleFileNameW)

-- 
https://gitlab.winehq.org/wine/wine/-/merge_requests/10291#note_134031

[eric pouech (＠epo)]

On Fri Mar 27 12:50:22 2026 +0000, Trent Waddington wrote:
> I've moved the code from the done section but kept the `filename[len] =
> 0` in this function so the termination semantics are explicit in this API.
> if it's purely semantics, a comment would do

-- 
https://gitlab.winehq.org/wine/wine/-/merge_requests/10291#note_134032