Fix macOS floating point corruption (#75467)

There is a race condition between activation signal handling and returning
from a hardware exception handler on macOS. It shows up intermittently in
the Regression/coreclr/GitHub_16833 test in the CI and I am able to repro
it on my local mac once in several thousands of iterations of the test when
running with GC stress C.

It turned out the issue is caused by the order in which we set parts of the
context in the thread when returning from the hardware exception handler.
MacOS can only set the floating point and control / integer portions separately.
We were setting the control / integer portion first and the floating point
portion after that. In the race condition, the signal handling code in the
macOS extracts the context that contains the new control registers, but the
old floating point ones (which is the state of those in the PAL_DispatchException).
The signal handler for the activation injection then gets executed and when it
returns later to our managed code, the floating point registers get restored
to the wrong values.

The fix is to change the context setting to first set the floating point
registers and then the control / integer portion of the context.

Close #66568

Co-authored-by: Jan Vorlicek <janvorli@microsoft.com>

Author: github-actions[bot]

src/coreclr/pal/src/thread/context.cpp

@@ -1398,68 +1398,6 @@ CONTEXT_SetThreadContextOnPort(
     mach_msg_type_number_t StateCount;
     thread_state_flavor_t StateFlavor;
 
-    if (lpContext->ContextFlags & (CONTEXT_CONTROL|CONTEXT_INTEGER) & CONTEXT_AREA_MASK)
-    {
-#ifdef HOST_AMD64
-        x86_thread_state64_t State;
-        StateFlavor = x86_THREAD_STATE64;
-
-        State.__rax = lpContext->Rax;
-        State.__rbx = lpContext->Rbx;
-        State.__rcx = lpContext->Rcx;
-        State.__rdx = lpContext->Rdx;
-        State.__rdi = lpContext->Rdi;
-        State.__rsi = lpContext->Rsi;
-        State.__rbp = lpContext->Rbp;
-        State.__rsp = lpContext->Rsp;
-        State.__r8 = lpContext->R8;
-        State.__r9 = lpContext->R9;
-        State.__r10 = lpContext->R10;
-        State.__r11 = lpContext->R11;
-        State.__r12 = lpContext->R12;
-        State.__r13 = lpContext->R13;
-        State.__r14 = lpContext->R14;
-        State.__r15 = lpContext->R15;
-//        State.ss = lpContext->SegSs;
-        State.__rflags = lpContext->EFlags;
-        State.__rip = lpContext->Rip;
-        State.__cs = lpContext->SegCs;
-//        State.ds = lpContext->SegDs_PAL_Undefined;
-//        State.es = lpContext->SegEs_PAL_Undefined;
-        State.__fs = lpContext->SegFs;
-        State.__gs = lpContext->SegGs;
-#elif defined(HOST_ARM64)
-        arm_thread_state64_t State;
-        StateFlavor = ARM_THREAD_STATE64;
-
-        memcpy(&State.__x[0], &lpContext->X0, 29 * 8);
-        State.__cpsr = lpContext->Cpsr;
-        arm_thread_state64_set_fp(State, lpContext->Fp);
-        arm_thread_state64_set_sp(State, lpContext->Sp);
-        arm_thread_state64_set_lr_fptr(State, lpContext->Lr);
-        arm_thread_state64_set_pc_fptr(State, lpContext->Pc);
-#else
-#error Unexpected architecture.
-#endif
-
-        StateCount = sizeof(State) / sizeof(natural_t);
-
-        do
-        {
-            MachRet = thread_set_state(Port,
-                                       StateFlavor,
-                                       (thread_state_t)&State,
-                                       StateCount);
-        }
-        while (MachRet == KERN_ABORTED);
-
-        if (MachRet != KERN_SUCCESS)
-        {
-            ASSERT("thread_set_state(THREAD_STATE) failed: %d\n", MachRet);
-            goto EXIT;
-        }
-    }
-
     if (lpContext->ContextFlags & CONTEXT_ALL_FLOATING & CONTEXT_AREA_MASK)
     {
 
@@ -1496,26 +1434,6 @@ CONTEXT_SetThreadContextOnPort(
 #error Unexpected architecture.
 #endif
 
-        // If we're setting only one of the floating point or extended registers (of which Mach supports only
-        // the xmm values) then we don't have values for the other set. This is a problem since Mach only
-        // supports setting both groups as a single unit. So in this case we'll need to fetch the current
-        // values first.
-        if ((lpContext->ContextFlags & CONTEXT_ALL_FLOATING) !=
-            CONTEXT_ALL_FLOATING)
-        {
-            mach_msg_type_number_t StateCountGet = StateCount;
-            MachRet = thread_get_state(Port,
-                                       StateFlavor,
-                                       (thread_state_t)&State,
-                                       &StateCountGet);
-            if (MachRet != KERN_SUCCESS)
-            {
-                ASSERT("thread_get_state(FLOAT_STATE) failed: %d\n", MachRet);
-                goto EXIT;
-            }
-            _ASSERTE(StateCountGet == StateCount);
-        }
-
         if (lpContext->ContextFlags & CONTEXT_FLOATING_POINT & CONTEXT_AREA_MASK)
         {
 #ifdef HOST_AMD64
@@ -1569,6 +1487,65 @@ CONTEXT_SetThreadContextOnPort(
         }
     }
 
+    if (lpContext->ContextFlags & (CONTEXT_CONTROL|CONTEXT_INTEGER) & CONTEXT_AREA_MASK)
+    {
+#ifdef HOST_AMD64
+        x86_thread_state64_t State;
+        StateFlavor = x86_THREAD_STATE64;
+
+        State.__rax = lpContext->Rax;
+        State.__rbx = lpContext->Rbx;
+        State.__rcx = lpContext->Rcx;
+        State.__rdx = lpContext->Rdx;
+        State.__rdi = lpContext->Rdi;
+        State.__rsi = lpContext->Rsi;
+        State.__rbp = lpContext->Rbp;
+        State.__rsp = lpContext->Rsp;
+        State.__r8 = lpContext->R8;
+        State.__r9 = lpContext->R9;
+        State.__r10 = lpContext->R10;
+        State.__r11 = lpContext->R11;
+        State.__r12 = lpContext->R12;
+        State.__r13 = lpContext->R13;
+        State.__r14 = lpContext->R14;
+        State.__r15 = lpContext->R15;
+        State.__rflags = lpContext->EFlags;
+        State.__rip = lpContext->Rip;
+        State.__cs = lpContext->SegCs;
+        State.__fs = lpContext->SegFs;
+        State.__gs = lpContext->SegGs;
+#elif defined(HOST_ARM64)
+        arm_thread_state64_t State;
+        StateFlavor = ARM_THREAD_STATE64;
+
+        memcpy(&State.__x[0], &lpContext->X0, 29 * 8);
+        State.__cpsr = lpContext->Cpsr;
+        arm_thread_state64_set_fp(State, lpContext->Fp);
+        arm_thread_state64_set_sp(State, lpContext->Sp);
+        arm_thread_state64_set_lr_fptr(State, lpContext->Lr);
+        arm_thread_state64_set_pc_fptr(State, lpContext->Pc);
+#else
+#error Unexpected architecture.
+#endif
+
+        StateCount = sizeof(State) / sizeof(natural_t);
+
+        do
+        {
+            MachRet = thread_set_state(Port,
+                                       StateFlavor,
+                                       (thread_state_t)&State,
+                                       StateCount);
+        }
+        while (MachRet == KERN_ABORTED);
+
+        if (MachRet != KERN_SUCCESS)
+        {
+            ASSERT("thread_set_state(THREAD_STATE) failed: %d\n", MachRet);
+            goto EXIT;
+        }
+    }
+
 EXIT:
     return MachRet;
 }