[PATCH v3 0/2] MR7312: msvcp: Avoid explicitly aligning fpos_mbstatet.

[Jacek Caban (＠jacek)]

Based on Piotr's findings.

On MSVC i386 targets, structs requiring alignment greater than 4 are never passed by value.
Clang follows the same behavior in MSVC mode (see [1] for details and [2] for a follow-up
that applies this logic when fields, not necessarily the entire struct, are aligned).

A number of ios functions take fpos_mbstatet as an argument and expect it to be passed by value.

[1] https://reviews.llvm.org/D72114
[2] https://github.com/llvm/llvm-project/issues/63257

Wine-Bug: https://bugs.winehq.org/show_bug.cgi?id=57817

--
  v3: msvcp60: Avoid explicitly aligning structs passed by value.
      msvcp: Avoid explicitly aligning structs passed by value.

https://gitlab.winehq.org/wine/wine/-/merge_requests/7312

[PATCH v3 1/2] msvcp: Avoid explicitly aligning structs passed by value.

[Jacek Caban]

From: Jacek Caban

Based on Piotr's findings.

On MSVC i386 targets, structs requiring alignment greater than 4 are never passed by value.
Clang follows the same behavior in MSVC mode (see [1] for details and [2] for a follow-up
that applies this logic when fields, not necessarily the entire struct, are aligned).

A number of ios functions take fpos_mbstatet as an argument and expect it to be passed by value.

[1] https://reviews.llvm.org/D72114
[2] https://github.com/llvm/llvm-project/issues/63257

Wine-Bug: https://bugs.winehq.org/show_bug.cgi?id=57817
---
 dlls/msvcp90/ios.c       | 2 +-
 dlls/msvcp90/msvcp90.h   | 4 ++--
 dlls/msvcp90/tests/ios.c | 2 +-
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/dlls/msvcp90/ios.c b/dlls/msvcp90/ios.c
index cb3e7573283..d7f25b559a8 100644
--- a/dlls/msvcp90/ios.c
+++ b/dlls/msvcp90/ios.c
@@ -41,7 +41,7 @@ bool ios_base_Sync = FALSE;

typedef struct {
     streamoff off;
-    __int64 DECLSPEC_ALIGN(8) pos;
+    INT64 pos;
     _Mbstatet state;
 } fpos_mbstatet;

diff --git a/dlls/msvcp90/msvcp90.h b/dlls/msvcp90/msvcp90.h
index 925af2eda73..b6e20826ff7 100644
--- a/dlls/msvcp90/msvcp90.h
+++ b/dlls/msvcp90/msvcp90.h
@@ -27,8 +27,8 @@
 #define ALIGNED_SIZE(size, alignment) (((size)+((alignment)-1))/(alignment)*(alignment))

#if _MSVCP_VER >= 100
-typedef __int64 DECLSPEC_ALIGN(8) streamoff;
-typedef __int64 DECLSPEC_ALIGN(8) streamsize;
+typedef INT64 streamoff;
+typedef INT64 streamsize;
 #else
 typedef SSIZE_T streamoff;
 typedef SSIZE_T streamsize;
diff --git a/dlls/msvcp90/tests/ios.c b/dlls/msvcp90/tests/ios.c
index 86bf78e21b4..91da0b91dd8 100644
--- a/dlls/msvcp90/tests/ios.c
+++ b/dlls/msvcp90/tests/ios.c
@@ -425,7 +425,7 @@ typedef struct

typedef struct {
     streamoff off;
-    __int64 DECLSPEC_ALIGN(8) pos;
+    INT64 pos;
     int state;
 } fpos_int;

[PATCH v3 2/2] msvcp60: Avoid explicitly aligning structs passed by value.

[Jacek Caban]

From: Jacek Caban

---
 dlls/msvcp60/ios.c       | 2 +-
 dlls/msvcp60/tests/ios.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/dlls/msvcp60/ios.c b/dlls/msvcp60/ios.c
index b94dba86062..b29a1f416d6 100644
--- a/dlls/msvcp60/ios.c
+++ b/dlls/msvcp60/ios.c
@@ -37,7 +37,7 @@ bool ios_base_Sync = FALSE;

typedef struct {
     streamoff off;
-    __int64 DECLSPEC_ALIGN(8) pos;
+    INT64 pos;
     int state;
 } fpos_int;

diff --git a/dlls/msvcp60/tests/ios.c b/dlls/msvcp60/tests/ios.c
index e6b79edcd11..3edd5fd4c81 100644
--- a/dlls/msvcp60/tests/ios.c
+++ b/dlls/msvcp60/tests/ios.c
@@ -406,7 +406,7 @@ typedef struct {

typedef struct {
     streamoff off;
-    __int64 DECLSPEC_ALIGN(8) pos;
+    INT64 pos;
     int state;
 } fpos_int;

[PATCH v3 0/2] MR7312: msvcp: Avoid explicitly aligning fpos_mbstatet. - approved

[Piotr Caban (＠piotr)]

This merge request was approved by Piotr Caban.

[Piotr Caban (＠piotr)]

On Wed Feb 12 10:45:08 2025 +0000, Jacek Caban wrote:
> I missed that, it should be fixed in the new version, thanks. I also
> fixed relevant tests.
> The only remaining explicit alignment in msvcp* DLLs is `ios_base`,
> which should not be a problem as it's not passed by value (although we
> could consider replacing it by an explicit padding).

`ios_base` has virtual functions. AFAIR such classes are always passed by pointer. I'm not opposed to adding explicit padding though.