[NativeAOT/x86] Fix funclet unwinding (#100732)

* Guard ABI changes necessary for funclet unwinding with UsesFunclets()/FEATURE_EH_FUNCLETS instead of UNIX_X86_ABI

* Fix the emitFullArgInfo condition.

* Update comments, add test case

src/coreclr/gcdump/i386/gcdumpx86.cpp

@@ -456,10 +456,10 @@ size_t              GCDump::DumpGCTable(PTR_CBYTE      table,
                     /* non-ptr arg push */
 
                     curOffs += (val & 0x07);
-#ifndef UNIX_X86_ABI
-                    // For x86/Linux, non-ptr arg pushes can be reported even for EBP frames
+#ifndef FEATURE_EH_FUNCLETS
+                    // For funclets, non-ptr arg pushes can be reported even for EBP frames
                     _ASSERTE(!header.ebpFrame);
-#endif // UNIX_X86_ABI
+#endif // FEATURE_EH_FUNCLETS
                     argCnt++;
 
                     DumpEncoding(bp, table-bp); bp = table;

src/coreclr/jit/emit.cpp

@@ -6680,11 +6680,11 @@ unsigned emitter::emitEndCodeGen(Compiler*         comp,
 
     emitFullyInt   = fullyInt;
     emitFullGCinfo = fullPtrMap;
-
-#ifndef UNIX_X86_ABI
-    emitFullArgInfo = !emitHasFramePtr;
+#if TARGET_X86
+    // On x86 with funclets we emit full ptr map even for EBP frames
+    emitFullArgInfo = comp->UsesFunclets() ? fullPtrMap : !emitHasFramePtr;
 #else
-    emitFullArgInfo = fullPtrMap;
+    emitFullArgInfo = !emitHasFramePtr;
 #endif
 
 #if EMITTER_STATS

src/coreclr/jit/gcencode.cpp

@@ -2584,9 +2584,7 @@ size_t GCInfo::gcMakeRegPtrTable(BYTE* dest, int mask, const InfoHdr& header, un
 
                     assert((codeDelta & 0x7) == codeDelta);
                     *dest++ = 0xB0 | (BYTE)codeDelta;
-#ifndef UNIX_X86_ABI
-                    assert(!compiler->isFramePointerUsed());
-#endif
+                    assert(compiler->UsesFunclets() || !compiler->isFramePointerUsed());
 
                     /* Remember the new 'last' offset */
 

src/coreclr/jit/morph.cpp

@@ -14236,6 +14236,13 @@ void Compiler::fgSetOptions()
     if (info.compXcptnsCount > 0)
     {
         codeGen->setFramePointerRequiredEH(true);
+
+        if (UsesFunclets())
+        {
+            assert(!codeGen->isGCTypeFixed());
+            // Enforce fully interruptible codegen for funclet unwinding
+            SetInterruptible(true);
+        }
     }
 
 #else // !TARGET_X86
@@ -14247,15 +14254,6 @@ void Compiler::fgSetOptions()
 
 #endif // TARGET_X86
 
-#ifdef UNIX_X86_ABI
-    if (info.compXcptnsCount > 0)
-    {
-        assert(!codeGen->isGCTypeFixed());
-        // Enforce fully interruptible codegen for funclet unwinding
-        SetInterruptible(true);
-    }
-#endif // UNIX_X86_ABI
-
     if (compMethodRequiresPInvokeFrame())
     {
         codeGen->setFramePointerRequired(true); // Setup of Pinvoke frame currently requires an EBP style frame

src/coreclr/vm/gc_unwind_x86.inl

@@ -1519,10 +1519,10 @@ unsigned scanArgRegTableI(PTR_CBYTE    table,
 
     bool      hasPartialArgInfo;
 
-#ifndef UNIX_X86_ABI
+#ifndef FEATURE_EH_FUNCLETS
     hasPartialArgInfo = info->ebpFrame;
 #else
-    // For x86/Linux, interruptible code always has full arg info
+    // For funclets, interruptible code always has full arg info
     //
     // This should be aligned with emitFullArgInfo setting at
     // emitter::emitEndCodeGen (in JIT)

src/tests/nativeaot/SmokeTests/Exceptions/Exceptions.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Diagnostics;
+using System.Runtime.CompilerServices;
 using System.Runtime.ExceptionServices;
 using System.Text;
 
@@ -160,6 +161,8 @@ public static int Main()
 
         TestFirstChanceExceptionEvent();
 
+        TestUnwindInFunclet();
+
         throw new Exception("UnhandledException");
 
         return Fail;
@@ -300,5 +303,27 @@ static bool FilterWithGC()
         CreateSomeGarbage();
         return true;
     }
+
+    static void TestUnwindInFunclet()
+    {
+        try
+        {
+            throw new Exception();
+        }
+        catch (Exception e)
+        {
+            // x86 pushes the call arguments on the stack and moves the stack pointer.
+            // We use a non-inlined call with enough parameters to force this to happen,
+            // so we can verify that the unwinder can walk through this funclet. The
+            // unwinding is triggered by the GC.Collect call.
+            MultiparameterCallWithGC(0, 1, 2, 3, 4);
+        }
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    static void MultiparameterCallWithGC(nint a, nint b, nint c, nint d, nint f)
+    {
+        GC.Collect();
+    }
 }