[RFC PATCH v3 5/5] ntdll: Properly parse UDF instruction in ARM.

[Jinoh Kang]

Today, the UDF instruction handler code assumes Thumb mode code, and
cannot recognise the UDF.W form or equivalent instructions in ARM mode
encoding.

Fix this by generalising the UDF instruction parser code.

Signed-off-by: Jinoh Kang 
---
 dlls/ntdll/unix/signal_arm.c | 35 ++++++++++++++++++++++++++++++++---
 1 file changed, 32 insertions(+), 3 deletions(-)

diff --git a/dlls/ntdll/unix/signal_arm.c b/dlls/ntdll/unix/signal_arm.c
index 1816e210644..f4987f902e0 100644
--- a/dlls/ntdll/unix/signal_arm.c
+++ b/dlls/ntdll/unix/signal_arm.c
@@ -359,6 +359,35 @@ static inline WORD get_error_code( const ucontext_t *sigcontext )
 }

+/***********************************************************************
+ *           get_udf_immediate
+ *
+ * Get the immediate operand if the PC is at a UDF instruction.
+ */
+static inline int get_udf_immediate( const ucontext_t *sigcontext )
+{
+    if (CPSR_sig(sigcontext) & 0x20)
+    {
+        WORD thumb_insn = *(WORD *)PC_sig(sigcontext);
+        if ((thumb_insn >> 8) == 0xde) return thumb_insn & 0xff;
+        if ((thumb_insn & 0xfff0) == 0xf7f0)  /* udf.w */
+        {
+            WORD ext = *(WORD *)(PC_sig(sigcontext) + 2);
+            if ((ext & 0xf000) == 0xa000) return ((thumb_insn & 0xf) << 12) | (ext & 0x0fff);
+        }
+    }
+    else
+    {
+        DWORD arm_insn = *(DWORD *)PC_sig(sigcontext);
+        if ((arm_insn & 0xfff000f0) == 0xe7f000f0)
+        {
+            return ((arm_insn >> 4) & 0xfff0) | (arm_insn & 0xf);
+        }
+    }
+    return -1;
+}
+
+
 /***********************************************************************
  *           save_context
  *
@@ -809,16 +838,16 @@ static void segv_handler( int signal, siginfo_t *siginfo, void *sigcontext )
     switch (get_trap_code(signal, context))
     {
     case TRAP_ARM_PRIVINFLT:   /* Invalid opcode exception */
-        switch (*(WORD *)PC_sig(context))
+        switch (get_udf_immediate( context ))
         {
-        case 0xdefb:  /* __fastfail */
+        case 0xfb:  /* __fastfail */
             rec.ExceptionCode = STATUS_STACK_BUFFER_OVERRUN;
             rec.ExceptionFlags = EH_NONCONTINUABLE;
             rec.NumberParameters = 1;
             rec.ExceptionInformation[0] = REGn_sig(0, context);
             setup_exception( context, &rec, FALSE );
             return;
-        case 0xdefe:  /* breakpoint */
+        case 0xfe:  /* breakpoint */
             rec.ExceptionCode = EXCEPTION_BREAKPOINT;
             rec.NumberParameters = 1;
             break;