ntdll: Avoid resetting x87 FPU state when saving context.

'FNSAVE' x87 instruction resets the FPU state to default values (like FINIT). This results in FPU state reset to default in any ntdll call which is getting x87 FPU state, e. g. obtaining context or raising an exception. Signed-off-by: Paul Gofman <gofmanp@gmail.com> Signed-off-by: Alexandre Julliard <julliard@winehq.org>

ntdll: Avoid resetting x87 FPU state when saving context.
c6cd92be · Paul Gofman · Alexandre Julliard · fddea78a · c6cd92be · c6cd92be
Commit c6cd92be authored Mar 04, 2019 by Paul Gofman Committed by Alexandre Julliard Mar 04, 2019
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Showing with 19 additions and 1 deletion

signal_i386.c dlls/ntdll/signal_i386.c +18 -0

exception.c dlls/ntdll/tests/exception.c +1 -1

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--- a/dlls/ntdll/signal_i386.c
+++ b/dlls/ntdll/signal_i386.c
@@ -860,8 +860,26 @@ static inline void *init_handler( const ucontext_t *sigcontext, WORD *fs, WORD *
 static inline void save_fpu( CONTEXT *context )
 {
 #ifdef __GNUC__
+    struct
+    {
+        DWORD ControlWord;
+        DWORD StatusWord;
+        DWORD TagWord;
+        DWORD ErrorOffset;
+        DWORD ErrorSelector;
+        DWORD DataOffset;
+        DWORD DataSelector;
+    }
+    float_status;
    context->ContextFlags |= CONTEXT_FLOATING_POINT;
    __asm__ __volatile__( "fnsave %0; fwait" : "=m" (context->FloatSave) );
+    /* Reset unmasked exceptions status to avoid firing an exception. */
+    memcpy(&float_status, &context->FloatSave, sizeof(float_status));
+    float_status.StatusWord &= float_status.ControlWord | 0xffffff80;
+    __asm__ __volatile__( "fldenv %0" : "=m" (float_status) );
 #endif
 }

--- a/dlls/ntdll/tests/exception.c
+++ b/dlls/ntdll/tests/exception.c
@@ -1642,7 +1642,7 @@ static void test_thread_context(void)
    ok( LOWORD(context.FloatSave.ControlWord) == LOWORD(expect.x87_control),
            "wrong x87 control word %#x/%#x.\n", context.FloatSave.ControlWord, expect.x87_control );
-    todo_wine ok( LOWORD(expect.x87_control) == LOWORD(new_x87_control),
+    ok( LOWORD(expect.x87_control) == LOWORD(new_x87_control),
            "x87 control word changed in NtGetContextThread() %#x/%#x.\n",
            LOWORD(expect.x87_control), LOWORD(new_x87_control) );