On x64, Clang/LLVM doesn't generate the correct scope table for exceptions thrown in the same frame

[cl91]

On x64, clang/llvm (version 13.0.1) doesn't seem to generate the correct scope table for the following example

VOID Test() {
    __try {
        asm { "ud2" }
    } __except (EXCEPTION_EXECUTE_HANDLER) {
        DbgPrint("Caught exception");
    }
}

The scope table for the unwind data of Test() is empty (it should have one entry corresponding to the __try block). However the following is OK:

VOID ExceptionalFunction() {
    asm { "ud2" }
}

VOID Test() {
    __try {
        ExceptionalFunction();
    } __except (EXCEPTION_EXECUTE_HANDLER) {
        DbgPrint("Caught exception");
    }
}

Clang correctly generates the scope table for Test() (it has one entry which points to the __try block with the exception filter EXCEPTION_EXECUTE_HANDLER).

Clang/LLVM documentation claims that LLVM does not model asynchronous exceptions so it is currently impossible to catch an asynchronous exception generated in the same frame as the catching __try (x86 uses frame-based SEH instead of table based exception handling so it is OK). Our code is correct (after fixing a bug in the ReactOS code RtlpUnwindInternal --- the leaf function case didn't update the context record correctly) and can correct catch and unwind the second example above.

[cl91]

This appears to happen on i386 release build as well.

** 891 		__try {

ntdll.dll`LdrpInitialize:
ntdll.dll[0x10012cc8] <+3272>: movl   $0x0, -0x10(%ebp)

** 892 		    asm { "ud2" }
   893 		    /* PCHAR p = (PCHAR)0x233; */
   894 		    /* *p = 0xd; */

ntdll.dll[0x10012ccf] <+3279>: nop    
ntdll.dll[0x10012cd0] <+3280>: movl   $0xffffffff, -0x10(%ebp) ; imm = 0xFFFFFFFF 
ntdll.dll[0x10012cd7] <+3287>: ud2    

** 895 		} __except(EXCEPTION_EXECUTE_HANDLER) {
   896 		    NtDisplayStringA("EEEEEEEEEEEEEEE\n");
   897 		}

ntdll.dll[0x10012cd9] <+3289>: movl   $0x0, -0x10(%ebp)

   898 	
** 899 		if (InitInfo.DriverProcess) {
   900 		    PLDR_DATA_TABLE_ENTRY WdmDllEntry = NULL;
   901 		    LdrpCheckForLoadedDll("wdm.dll", &WdmDllEntry);

ntdll.dll[0x10012ce0] <+3296>: nop    
ntdll.dll[0x10012ce1] <+3297>: cmpb   $0x0, -0x574(%ebp)

For some reason clang sets the try-scope to -1 before the ud instruction.

[cl91]

Appears to be a clang bug: llvm/llvm-project#62606