[PATCH 0/6] MR8481: Improve compiler detection for Clang in MSVC mode

[Jacek Caban (＠jacek)]

Clang doesn't define `__GNUC__` in MSVC compatibility mode, but it still provides the functionality typically associated with it.

[PATCH 1/6] krnl386: Use inline assembly in get_idtr for Clang.

[Jacek Caban]

From: Jacek Caban

---
 dlls/krnl386.exe16/instr.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/dlls/krnl386.exe16/instr.c b/dlls/krnl386.exe16/instr.c
index 666ef71363f..8e4a0ac65d4 100644
--- a/dlls/krnl386.exe16/instr.c
+++ b/dlls/krnl386.exe16/instr.c
@@ -72,7 +72,7 @@ static LDT_ENTRY idt[256];
 static inline struct idtr get_idtr(void)
 {
     struct idtr ret;
-#if defined(__i386__) && defined(__GNUC__)
+#if defined(__i386__) && (defined(__GNUC__) || defined(__clang__))
     __asm__( "sidtl %0" : "=m" (ret) );
 #else
     ret.base = (BYTE *)idt;

[PATCH 2/6] ntdll: Use inline assembly in RtlEnlargedUnsignedDivide for Clang.

[Jacek Caban]

From: Jacek Caban

---
 dlls/ntdll/large_int.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/dlls/ntdll/large_int.c b/dlls/ntdll/large_int.c
index 0973888d654..3ef3aa70dd9 100644
--- a/dlls/ntdll/large_int.c
+++ b/dlls/ntdll/large_int.c
@@ -256,7 +256,7 @@ ULONGLONG WINAPI RtlEnlargedUnsignedMultiply( UINT a, UINT b )
  */
 UINT WINAPI RtlEnlargedUnsignedDivide( ULONGLONG a, UINT b, UINT *remptr )
 {
-#if defined(__i386__) && defined(__GNUC__)
+#if defined(__i386__) && (defined(__GNUC__) || defined(__clang__))
     UINT ret, rem;

__asm__("divl %4"

[PATCH 3/6] ntdll: Use inline assembly in save_fpu and save_fpux for Clang.

[Jacek Caban]

From: Jacek Caban

---
 dlls/ntdll/signal_i386.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/dlls/ntdll/signal_i386.c b/dlls/ntdll/signal_i386.c
index 4446a9b1f3d..22364938ae4 100644
--- a/dlls/ntdll/signal_i386.c
+++ b/dlls/ntdll/signal_i386.c
@@ -215,7 +215,7 @@ void WINAPI KiUserCallbackDispatcher( ULONG id, void *args, ULONG len )
  */
 static inline void save_fpu( CONTEXT *context )
 {
-#ifdef __GNUC__
+#if defined(__GNUC__) || defined(__clang__)
     struct
     {
         DWORD ControlWord;
@@ -247,7 +247,7 @@ static inline void save_fpu( CONTEXT *context )
  */
 static inline void save_fpux( CONTEXT *context )
 {
-#ifdef __GNUC__
+#if defined(__GNUC__) || defined(__clang__)
     /* we have to enforce alignment by hand */
     char buffer[sizeof(XSAVE_FORMAT) + 16];
     XSAVE_FORMAT *state = (XSAVE_FORMAT *)(((ULONG_PTR)buffer + 15) & ~15);

[PATCH 4/6] ntdll/tests: Use inline assembly in exception tests for Clang.

[Jacek Caban]

From: Jacek Caban

---
 dlls/ntdll/tests/exception.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/dlls/ntdll/tests/exception.c b/dlls/ntdll/tests/exception.c
index 025923b7d8e..25f83ee5a8f 100644
--- a/dlls/ntdll/tests/exception.c
+++ b/dlls/ntdll/tests/exception.c
@@ -1072,7 +1072,7 @@ static const BYTE direction_flag_code[] = {
 static DWORD direction_flag_handler( EXCEPTION_RECORD *rec, EXCEPTION_REGISTRATION_RECORD *frame,
                                      CONTEXT *context, EXCEPTION_REGISTRATION_RECORD **dispatcher )
 {
-#ifdef __GNUC__
+#if defined(__GNUC__) || defined(__clang__)
     unsigned int flags;
     __asm__("pushfl; popl %0; cld" : "=r" (flags) );
     /* older windows versions don't clear DF properly so don't test */
@@ -3175,7 +3175,7 @@ static const BYTE align_check_code[] =
 static DWORD WINAPI align_check_handler( EXCEPTION_RECORD *rec, ULONG64 frame,
                                          CONTEXT *context, DISPATCHER_CONTEXT *dispatcher )
 {
-#ifdef __GNUC__
+#if defined(__GNUC__) || defined(__clang__)
     __asm__ volatile( "pushfq; andl $~0x40000,(%rsp); popfq" );
 #endif
     ok (context->EFlags & 0x40000, "eflags has AC bit unset\n");
@@ -3199,7 +3199,7 @@ static const BYTE direction_flag_code[] =
 static DWORD WINAPI direction_flag_handler( EXCEPTION_RECORD *rec, ULONG64 frame,
                                             CONTEXT *context, DISPATCHER_CONTEXT *dispatcher )
 {
-#ifdef __GNUC__
+#if defined(__GNUC__) || defined(__clang__)
     ULONG_PTR flags;
     __asm__("pushfq; popq %0; cld" : "=r" (flags) );
     /* older windows versions don't clear DF properly so don't test */
@@ -5199,7 +5199,7 @@ static void test_KiUserExceptionDispatcher(void)
         test_kiuserexceptiondispatcher_saved_r12 = ctx.R12;
         ctx.R12 = (ULONG64)0xdeadbeeffeedcafe;

-#ifdef __GNUC__
+#if defined(__GNUC__) || defined(__clang__)
         /* Spoil r12 value to make sure it doesn't come from the current userspace registers. */
         __asm__ volatile("movq $0xdeadcafe, %%r12" : : : "%r12");
 #endif
@@ -10014,7 +10014,7 @@ static DWORD test_extended_context_handler(EXCEPTION_RECORD *rec, EXCEPTION_REGI
     }

done:
-#ifdef __GNUC__
+#if defined(__GNUC__) || defined(__clang__)
     __asm__ volatile("vmovups (%0),%%ymm0" : : "r"(test_extended_context_spoil_data2));
 #endif
 #ifdef __x86_64__

[PATCH 5/6] ntoskrnl: Use inline assembly in get_idtr for Clang.

[Jacek Caban]

From: Jacek Caban

---
 dlls/ntoskrnl.exe/instr.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/dlls/ntoskrnl.exe/instr.c b/dlls/ntoskrnl.exe/instr.c
index 20fce992fcc..5af24eed0d1 100644
--- a/dlls/ntoskrnl.exe/instr.c
+++ b/dlls/ntoskrnl.exe/instr.c
@@ -64,7 +64,7 @@ static LDT_ENTRY idt[256];
 static inline struct idtr get_idtr(void)
 {
     struct idtr ret;
-#ifdef __GNUC__
+#if defined(__GNUC__) || defined(__clang__)
     __asm__( "sidtl %0" : "=m" (ret) );
 #else
     ret.base = (BYTE *)idt;

[PATCH 6/6] oleaut32: Use inline assembly in VarCyFromR8 for Clang.

[Jacek Caban]

From: Jacek Caban

---
 dlls/oleaut32/vartype.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/dlls/oleaut32/vartype.c b/dlls/oleaut32/vartype.c
index 747705f94e2..86a3f8b5950 100644
--- a/dlls/oleaut32/vartype.c
+++ b/dlls/oleaut32/vartype.c
@@ -3496,7 +3496,7 @@ HRESULT WINAPI VarCyFromR4(FLOAT fltIn, CY* pCyOut)
  */
 HRESULT WINAPI VarCyFromR8(double dblIn, CY* pCyOut)
 {
-#if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
+#if (defined(__GNUC__) || defined(__clang__)) && (defined(__i386__) || defined(__x86_64__))
   /* This code gives identical results to Win32 on Intel.
    * Here we use fp exceptions to catch overflows when storing the value.
    */

[Alexandre Julliard (＠julliard)]

This breaks the arm64ec build, because several places lack the required `&& !defined(__arm64ec__)`.

[Jacek Caban (＠jacek)]

On Tue Jul  1 20:02:22 2025 +0000, Alexandre Julliard wrote:
> This breaks the arm64ec build, because several places lack the required
> `&& !defined(__arm64ec__)`.

I missed that, sorry about that. Fixed in the new version.

[Alexandre Julliard (＠julliard)]

On Tue Jul  1 20:02:22 2025 +0000, Jacek Caban wrote:
> I missed that, sorry about that. Fixed in the new version.

You never pushed the new version... But I think we might just as well get rid of the `__GNUC__` checks, these dlls won't build with MSVC anyway.