Change BKPT and UDF encodings on ARM.

src/include/arm_sandbox.h

Index: src/include/arm_sandbox.h
diff --git a/src/include/arm_sandbox.h b/src/include/arm_sandbox.h
new file mode 100644
index 0000000000000000000000000000000000000000..0519f7af284504eb8f75cece60a4e1e6d3f2d81d
--- /dev/null
+++ b/src/include/arm_sandbox.h
@@ -0,0 +1,32 @@
+/*
+ * Copyright (c) 2012 The Native Client Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+/* Minimal ARM sandbox constants.

[Mark Seaborn, 2012/10/19 18:08:43]

Nit: NaCl comment style is
/*
 * blah...
 */

i.e. First line is '/*' on its own.

+ *
+ * These constants are used in C code as well as assembly, hence the use of
+ * the preprocessor.
+ */
+
+#ifndef NATIVE_CLIENT_SRC_INCLUDE_ARM_SANDBOX_H_
+#define NATIVE_CLIENT_SRC_INCLUDE_ARM_SANDBOX_H_ 1
+
+/*
+ * Specially chosen BKPT and UDF instructions that also correspond to
+ * BKPT and UDF when decoded as Thumb instructions.
+ *  - BKPT #0x5BE0 is used as literal pool head.
+ *  - BKPT #0x5BEF is used as generic breakpoint.
+ *  - UDF #0xEDEF is used as halt-fill.
+ *  - UDF #0xEDE0 is used as abort-now (such as __builtin_trap).

[Mark Seaborn, 2012/10/19 18:08:43]

Why do you want to distinguish between abort-now and halt-fill?  Can you add
comments to explain when the differences are for debugging purposes, and when
they affect safety?

+ *  - UDF #0xEDE1 is used to always fail validation.

[Mark Seaborn, 2012/10/19 18:08:43]

Please comment that this is one of many, but it's the one we are guaranteeing.

+ * All other BKPT/UDF values are disallowed by the validator out of paranoia.
+ */
+#define NACL_INSTR_LITERAL_POOL_HEAD 0xE125BE70
+#define NACL_INSTR_BREAKPOINT        0xE125BE7F
+#define NACL_INSTR_HALT_FILL         0xE7FEDEFF
+#define NACL_INSTR_ABORT_NOW         0xE7FEDEF0
+#define NACL_INSTR_FAIL_VALIDATION   0xE7FEDEF1
+
+#endif  /* NATIVE_CLIENT_SRC_INCLUDE_ARM_SANDBOX_H_ */