ntdll: Fix unwinding functions that end with a branch instruction.

This happens with functions that aren't intended to return e.g. like _Unwind_Resume. In these cases, the return address is outside of the function (the first instruction in the next function). Set the flag CONTEXT_UNWOUND_TO_CALL after unwinding to a callsite, and if this flag is set, look up a RUNTIME_FUNCTION based on Control.Pc - 4. This isn't a complete (nor probably entirely correct) implementation of the flag CONTEXT_UNWOUND_TO_CALL, but it practically seems to work fine and fixes a large number of unwinding cases. Signed-off-by: Martin Storsjo <martin@martin.st> Signed-off-by: Alexandre Julliard <julliard@winehq.org>

ntdll: Fix unwinding functions that end with a branch instruction.
babbf352 · Martin Storsjo · Alexandre Julliard · 42a58856 · babbf352 · babbf352
Commit babbf352 authored May 28, 2020 by Martin Storsjo Committed by Alexandre Julliard May 28, 2020
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signal_arm64.c dlls/ntdll/signal_arm64.c +12 -1

winnt.h include/winnt.h +2 -0

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--- a/dlls/ntdll/signal_arm64.c
+++ b/dlls/ntdll/signal_arm64.c
@@ -527,6 +527,7 @@ static NTSTATUS libunwind_virtual_unwind( ULONG_PTR ip, ULONG_PTR *frame, CONTEX
        *frame = context->Sp;
        context->Pc = context->u.s.Lr;
        context->Sp = context->Sp + sizeof(ULONG64);
+        context->ContextFlags |= CONTEXT_UNWOUND_TO_CALL;
        return STATUS_SUCCESS;
    }

@@ -577,6 +578,7 @@ static NTSTATUS libunwind_virtual_unwind( ULONG_PTR ip, ULONG_PTR *frame, CONTEX
    unw_get_reg( &cursor, UNW_AARCH64_X30, (unw_word_t *)&context->u.s.Lr );
    unw_get_reg( &cursor, UNW_AARCH64_SP,  (unw_word_t *)&context->Sp );
    context->Pc = context->u.s.Lr;
+    context->ContextFlags |= CONTEXT_UNWOUND_TO_CALL;

    TRACE( "next function pc=%016lx%s\n", context->Pc, rc ? "" : " (last frame)" );
    TRACE("  x0=%016lx  x1=%016lx  x2=%016lx  x3=%016lx\n",
@@ -614,10 +616,17 @@ static NTSTATUS virtual_unwind( ULONG type, DISPATCHER_CONTEXT *dispatch, CONTEX
    dispatch->ScopeIndex       = 0;
    dispatch->EstablisherFrame = 0;
    dispatch->ControlPc        = context->Pc;
+    /*
+     * TODO: CONTEXT_UNWOUND_TO_CALL should be cleared if unwound past a
+     * signal frame.
+     */
+    dispatch->ControlPcIsUnwound = (context->ContextFlags & CONTEXT_UNWOUND_TO_CALL) != 0;

    /* first look for PE exception information */

-    if ((dispatch->FunctionEntry = lookup_function_info( context->Pc, &dispatch->ImageBase, &module )))
+    if ((dispatch->FunctionEntry = lookup_function_info(
+             context->Pc - (dispatch->ControlPcIsUnwound ? 4 : 0),
+             &dispatch->ImageBase, &module )))
    {
        dispatch->LanguageHandler = RtlVirtualUnwind( type, dispatch->ImageBase, context->Pc,
                                                      dispatch->FunctionEntry, context,
@@ -654,6 +663,7 @@ static NTSTATUS virtual_unwind( ULONG type, DISPATCHER_CONTEXT *dispatch, CONTEX
    dispatch->EstablisherFrame = context->u.s.Fp;
    dispatch->LanguageHandler = NULL;
    context->Pc = context->u.s.Lr;
+    context->ContextFlags |= CONTEXT_UNWOUND_TO_CALL;
    return STATUS_SUCCESS;
 }

@@ -1758,6 +1768,7 @@ PVOID WINAPI RtlVirtualUnwind( ULONG type, ULONG_PTR base, ULONG_PTR pc,

    TRACE( "ret: lr=%lx sp=%lx handler=%p\n", context->u.s.Lr, context->Sp, handler );
    context->Pc = context->u.s.Lr;
+    context->ContextFlags |= CONTEXT_UNWOUND_TO_CALL;
    *frame_ret = context->Sp;
    return handler;
 }

--- a/include/winnt.h
+++ b/include/winnt.h
@@ -1863,6 +1863,8 @@ NTSYSAPI PVOID WINAPI RtlVirtualUnwind(DWORD,DWORD,DWORD,RUNTIME_FUNCTION*,CONTE
 #define CONTEXT_FLOATING_POINT  (CONTEXT_ARM64 | 0x00000004)
 #define CONTEXT_DEBUG_REGISTERS (CONTEXT_ARM64 | 0x00000008)

+#define CONTEXT_UNWOUND_TO_CALL 0x20000000
+
 #define CONTEXT_FULL (CONTEXT_CONTROL | CONTEXT_INTEGER)
 #define CONTEXT_ALL  (CONTEXT_CONTROL | CONTEXT_INTEGER | CONTEXT_FLOATING_POINT | CONTEXT_DEBUG_REGISTERS)