[PATCH] [Arm] Fix endianness handling for arm record self tests

[Luis Machado via Gdb-patches <gdb-patches@sourceware.org>]

The arm record tests handle 16-bit and 32-bit thumb instructions, but the
code is laid out in a way that handles the 32-bit thumb instructions as
two 16-bit parts.

This is fine, but it is prone to host-endianness issues given how the two
16-bit parts are stored and how they are accessed later on. Arm is
little-endian by default, so running this test with a GDB built with
--enable-targets=all and on a big endian host will run into the following:

Running selftest arm-record.
Process record and replay target doesn't support syscall number -2036195
Process record does not support instruction 0x7f70ee1d at address 0x0.
Self test failed: self-test failed at ../../binutils-gdb/gdb/arm-tdep.c:14482

Investigating this a bit further, there seems to be a chance to do a simple
fix through a type template, using uint16_t for 16-bit thumb instructions
and uint32_t for 32-bit thumb instructions.

This patch implements this.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29432
---
 gdb/arm-tdep.c | 32 ++++++++++++++++++--------------
 1 file changed, 18 insertions(+), 14 deletions(-)

diff --git a/gdb/arm-tdep.c b/gdb/arm-tdep.c
index cf8b610a381..57b865a0819 100644
--- a/gdb/arm-tdep.c
+++ b/gdb/arm-tdep.c
@@ -14387,14 +14387,18 @@ decode_insn (abstract_memory_reader &reader,
 #if GDB_SELF_TEST
 namespace selftests {
 
-/* Provide both 16-bit and 32-bit thumb instructions.  */
+/* Provide both 16-bit and 32-bit thumb instructions.
 
+   For 16-bit Thumb instructions, an array of uint16_t should be used.
+   For 32-bit Thumb instructions, an array of uint32_t should be used.  */
+
+template<typename T>
 class instruction_reader_thumb : public abstract_memory_reader
 {
 public:
   template<size_t SIZE>
   instruction_reader_thumb (enum bfd_endian endian,
-			    const uint16_t (&insns)[SIZE])
+			    const T (&insns)[SIZE])
     : m_endian (endian), m_insns (insns), m_insns_size (SIZE)
   {}
 
@@ -14404,18 +14408,14 @@ class instruction_reader_thumb : public abstract_memory_reader
     SELF_CHECK (memaddr % 2 == 0);
     SELF_CHECK ((memaddr / 2) < m_insns_size);
 
-    store_unsigned_integer (buf, 2, m_endian, m_insns[memaddr / 2]);
-    if (len == 4)
-      {
-	store_unsigned_integer (&buf[2], 2, m_endian,
-				m_insns[memaddr / 2 + 1]);
-      }
+    store_unsigned_integer (buf, sizeof (T), m_endian, m_insns[memaddr / 2]);
+
     return true;
   }
 
 private:
   enum bfd_endian m_endian;
-  const uint16_t *m_insns;
+  const T *m_insns;
   size_t m_insns_size;
 };
 
@@ -14436,6 +14436,8 @@ arm_record_test (void)
     memset (&arm_record, 0, sizeof (arm_insn_decode_record));
     arm_record.gdbarch = gdbarch;
 
+    /* Use the endian-free representation of the instructions here.  The test
+       will handle endianness conversions.  */
     static const uint16_t insns[] = {
       /* db b2	uxtb	r3, r3 */
       0xb2db,
@@ -14444,7 +14446,7 @@ arm_record_test (void)
     };
 
     enum bfd_endian endian = gdbarch_byte_order_for_code (arm_record.gdbarch);
-    instruction_reader_thumb reader (endian, insns);
+    instruction_reader_thumb<uint16_t> reader (endian, insns);
     int ret = decode_insn (reader, &arm_record, THUMB_RECORD,
 			   THUMB_INSN_SIZE_BYTES);
 
@@ -14470,13 +14472,15 @@ arm_record_test (void)
     memset (&arm_record, 0, sizeof (arm_insn_decode_record));
     arm_record.gdbarch = gdbarch;
 
-    static const uint16_t insns[] = {
-      /* 1d ee 70 7f	 mrc	15, 0, r7, cr13, cr0, {3} */
-      0xee1d, 0x7f70,
+    /* Use the endian-free representation of the instruction here.  The test
+       will handle endianness conversions.  */
+    static const uint32_t insns[] = {
+      /* mrc	15, 0, r7, cr13, cr0, {3} */
+      0x7f70ee1d,
     };
 
     enum bfd_endian endian = gdbarch_byte_order_for_code (arm_record.gdbarch);
-    instruction_reader_thumb reader (endian, insns);
+    instruction_reader_thumb<uint32_t> reader (endian, insns);
     int ret = decode_insn (reader, &arm_record, THUMB2_RECORD,
 			   THUMB2_INSN_SIZE_BYTES);
 
-- 
2.25.1