Re: [PING][PATCH,v2] [Arm] Fix endianness handling for arm record self tests

[Tom de Vries via Gdb-patches <gdb-patches@sourceware.org>]

On 9/1/22 11:29, Luis Machado wrote:
> On 8/23/22 21:32, Luis Machado via Gdb-patches wrote:
>> v2:
>>
>> - Add 32-bit Arm instruction selftest
>> - Refactored abstract memory reader into abstract instruction reader
>> - Adjusted code to use templated type and to use host endianness as
>>    opposed to target endianness.
>>
>> 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
>>
>> It turns out the abstract memory reader class is more generic than it 
>> needs to
>> be, and we can simplify the code a bit by assuming we have a simple 
>> instruction
>> reader that only reads up to 4 bytes, which is the length of a 32-bit
>> instruction.
>>
>> Instead of returning a bool, we return instead the instruction that 
>> has been
>> read. This way we avoid having to deal with the endianness conversion, 
>> and use
>> the host endianness instead. The Arm selftests can be executed on non-Arm
>> hosts.
>>

LGTM.

Thanks,
- Tom

>> While at it, Tom suggested adding a 32-bit Arm instruction selftest to 
>> increase
>> the coverage of the selftests.
>>
>> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29432
>>
>> Co-authored-by: Tom de Vries <tdevries@suse.de>
>> ---
>>   gdb/arm-tdep.c | 150 ++++++++++++++++++++++---------------------------
>>   1 file changed, 68 insertions(+), 82 deletions(-)
>>
>> diff --git a/gdb/arm-tdep.c b/gdb/arm-tdep.c
>> index 0091d14708f..ead9bbf46c5 100644
>> --- a/gdb/arm-tdep.c
>> +++ b/gdb/arm-tdep.c
>> @@ -14252,59 +14252,39 @@ thumb2_record_decode_insn_handler 
>> (arm_insn_decode_record *thumb2_insn_r)
>>   }
>>   namespace {
>> -/* Abstract memory reader.  */
>> +/* Abstract instruction reader.  */
>> -class abstract_memory_reader
>> +class abstract_instruction_reader
>>   {
>>   public:
>> -  /* Read LEN bytes of target memory at address MEMADDR, placing the
>> -     results in GDB's memory at BUF.  Return true on success.  */
>> +  /* Read one instruction of size LEN from address MEMADDR and using
>> +     BYTE_ORDER endianness.  */
>> -  virtual bool read (CORE_ADDR memaddr, gdb_byte *buf, const size_t 
>> len) = 0;
>> +  virtual ULONGEST read (CORE_ADDR memaddr, const size_t len,
>> +             enum bfd_endian byte_order) = 0;
>>   };
>>   /* Instruction reader from real target.  */
>> -class instruction_reader : public abstract_memory_reader
>> +class instruction_reader : public abstract_instruction_reader
>>   {
>>    public:
>> -  bool read (CORE_ADDR memaddr, gdb_byte *buf, const size_t len) 
>> override
>> +  ULONGEST read (CORE_ADDR memaddr, const size_t len,
>> +         enum bfd_endian byte_order) override
>>     {
>> -    if (target_read_memory (memaddr, buf, len))
>> -      return false;
>> -    else
>> -      return true;
>> +    return read_code_unsigned_integer (memaddr, len, byte_order);
>>     }
>>   };
>>   } // namespace
>> -/* Extracts arm/thumb/thumb2 insn depending on the size, and returns 
>> 0 on success
>> -and positive val on failure.  */
>> -
>> -static int
>> -extract_arm_insn (abstract_memory_reader& reader,
>> -          arm_insn_decode_record *insn_record, uint32_t insn_size)
>> -{
>> -  gdb_byte buf[insn_size];
>> -
>> -  memset (&buf[0], 0, insn_size);
>> -
>> -  if (!reader.read (insn_record->this_addr, buf, insn_size))
>> -    return 1;
>> -  insn_record->arm_insn = (uint32_t) extract_unsigned_integer (&buf[0],
>> -               insn_size,
>> -               gdbarch_byte_order_for_code (insn_record->gdbarch));
>> -  return 0;
>> -}
>> -
>>   typedef int (*sti_arm_hdl_fp_t) (arm_insn_decode_record*);
>>   /* Decode arm/thumb insn depending on condition cods and opcodes; and
>>      dispatch it.  */
>>   static int
>> -decode_insn (abstract_memory_reader &reader,
>> +decode_insn (abstract_instruction_reader &reader,
>>            arm_insn_decode_record *arm_record,
>>            record_type_t record_type, uint32_t insn_size)
>>   {
>> @@ -14339,20 +14319,12 @@ decode_insn (abstract_memory_reader &reader,
>>     uint32_t ret = 0;    /* return value: negative:failure   
>> 0:success.  */
>>     uint32_t insn_id = 0;
>> +  enum bfd_endian code_endian
>> +    = gdbarch_byte_order_for_code (arm_record->gdbarch);
>> +  arm_record->arm_insn
>> +    = reader.read (arm_record->this_addr, insn_size, code_endian);
>> -  if (extract_arm_insn (reader, arm_record, insn_size))
>> -    {
>> -      if (record_debug)
>> -    {
>> -      gdb_printf (gdb_stdlog,
>> -              _("Process record: error reading memory at "
>> -            "addr %s len = %d.\n"),
>> -              paddress (arm_record->gdbarch,
>> -                arm_record->this_addr), insn_size);
>> -    }
>> -      return -1;
>> -    }
>> -  else if (ARM_RECORD == record_type)
>> +  if (ARM_RECORD == record_type)
>>       {
>>         arm_record->cond = bits (arm_record->arm_insn, 28, 31);
>>         insn_id = bits (arm_record->arm_insn, 25, 27);
>> @@ -14412,36 +14384,35 @@ decode_insn (abstract_memory_reader &reader,
>>   #if GDB_SELF_TEST
>>   namespace selftests {
>> -/* Provide both 16-bit and 32-bit thumb instructions.  */
>> +/* Instruction reader class for selftests.
>> +
>> +   For 16-bit Thumb instructions, an array of uint16_t should be used.
>> -class instruction_reader_thumb : public abstract_memory_reader
>> +   For 32-bit Thumb instructions and regular 32-bit Arm instructions, 
>> an array
>> +   of uint32_t should be used.  */
>> +
>> +template<typename T>
>> +class instruction_reader_selftest : public abstract_instruction_reader
>>   {
>>   public:
>>     template<size_t SIZE>
>> -  instruction_reader_thumb (enum bfd_endian endian,
>> -                const uint16_t (&insns)[SIZE])
>> -    : m_endian (endian), m_insns (insns), m_insns_size (SIZE)
>> +  instruction_reader_selftest (const T (&insns)[SIZE])
>> +    : m_insns (insns), m_insns_size (SIZE)
>>     {}
>> -  bool read (CORE_ADDR memaddr, gdb_byte *buf, const size_t len) 
>> override
>> +  ULONGEST read (CORE_ADDR memaddr, const size_t length,
>> +         enum bfd_endian byte_order) override
>>     {
>> -    SELF_CHECK (len == 4 || len == 2);
>> -    SELF_CHECK (memaddr % 2 == 0);
>> -    SELF_CHECK ((memaddr / 2) < m_insns_size);
>> +    SELF_CHECK (length == sizeof (T));
>> +    SELF_CHECK (memaddr % sizeof (T) == 0);
>> +    SELF_CHECK ((memaddr / sizeof (T)) < 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]);
>> -      }
>> -    return true;
>> +    return m_insns[memaddr / sizeof (T)];
>>     }
>>   private:
>> -  enum bfd_endian m_endian;
>> -  const uint16_t *m_insns;
>> -  size_t m_insns_size;
>> +  const T *m_insns;
>> +  const size_t m_insns_size;
>>   };
>>   static void
>> @@ -14461,6 +14432,8 @@ 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,
>> @@ -14468,8 +14441,7 @@ arm_record_test (void)
>>         0x58cd,
>>       };
>> -    enum bfd_endian endian = gdbarch_byte_order_for_code 
>> (arm_record.gdbarch);
>> -    instruction_reader_thumb reader (endian, insns);
>> +    instruction_reader_selftest<uint16_t> reader (insns);
>>       int ret = decode_insn (reader, &arm_record, THUMB_RECORD,
>>                  THUMB_INSN_SIZE_BYTES);
>> @@ -14495,13 +14467,14 @@ 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_selftest<uint32_t> reader (insns);
>>       int ret = decode_insn (reader, &arm_record, THUMB2_RECORD,
>>                  THUMB2_INSN_SIZE_BYTES);
>> @@ -14510,6 +14483,27 @@ arm_record_test (void)
>>       SELF_CHECK (arm_record.reg_rec_count == 1);
>>       SELF_CHECK (arm_record.arm_regs[0] == 7);
>>     }
>> +
>> +  /* 32-bit instructions.  */
>> +  {
>> +    arm_insn_decode_record arm_record;
>> +
>> +    memset (&arm_record, 0, sizeof (arm_insn_decode_record));
>> +    arm_record.gdbarch = gdbarch;
>> +
>> +    /* Use the endian-free representation of the instruction here.  
>> The test
>> +       will handle endianness conversions.  */
>> +    static const uint32_t insns[] = {
>> +      /* mov     r5, r0 */
>> +      0xe1a05000,
>> +    };
>> +
>> +    instruction_reader_selftest<uint32_t> reader (insns);
>> +    int ret = decode_insn (reader, &arm_record, ARM_RECORD,
>> +               ARM_INSN_SIZE_BYTES);
>> +
>> +    SELF_CHECK (ret == 0);
>> +  }
>>   }
>>   /* Instruction reader from manually cooked instruction sequences.  */
>> @@ -14609,18 +14603,10 @@ arm_process_record (struct gdbarch *gdbarch, 
>> struct regcache *regcache,
>>       }
>>     instruction_reader reader;
>> -  if (extract_arm_insn (reader, &arm_record, 2))
>> -    {
>> -      if (record_debug)
>> -    {
>> -      gdb_printf (gdb_stdlog,
>> -              _("Process record: error reading memory at "
>> -            "addr %s len = %d.\n"),
>> -              paddress (arm_record.gdbarch,
>> -                arm_record.this_addr), 2);
>> -    }
>> -      return -1;
>> -    }
>> +  enum bfd_endian code_endian
>> +    = gdbarch_byte_order_for_code (arm_record.gdbarch);
>> +  arm_record.arm_insn
>> +    = reader.read (arm_record.this_addr, 2, code_endian);
>>     /* Check the insn, whether it is thumb or arm one.  */
>