Re: [PATCH v7.1] Support software single step on ARM in GDBServer.

Yao Qi
2015-12-11T15:38:30Z

Antoine Tremblay <antoine.tremblay@ericsson.com> writes:

>
> I'm not sure a macro is a good thing, it often makes the code harder
> to parse for ides/emacs etc...

Why macro is bad?

>
> And I don't think shortening the lines is a good justification in
> general for a macro.

It is! Supposing we have a macro like this ...

#define ARM_READ_UINT(MEMADDR, LEN, BYTE_ORDER) \
self->ops->read_memory_unsigned_integer ((MEMADDR), (LEN), (BYTE_ORDER))

>
> How about I use a function pointer variable like :
>
> ULONGEST (*read_memory_uint) (CORE_ADDR memaddr, int len, int byte_order);
>
> read_memory_uint = self->ops->read_memory_unsigned_integer;
>
> That would be already 23 shorter.
>
>>> + loc += 2;
>>> + if (!((insn1 & 0xfff0) == 0xe850
>>> + || ((insn1 & 0xfff0) == 0xe8d0 && (insn2 & 0x00c0) == 0x0040)))
>>> + return NULL;
>>> +
>>> + /* Assume that no atomic sequence is longer than "atomic_sequence_length"
>>> + instructions. */
>>> + for (insn_count = 0; insn_count < atomic_sequence_length; ++insn_count)
>>> + {
>>> + insn1
>>> + = self->ops->read_memory_unsigned_integer (loc, 2,byte_order_for_code);
>>> + loc += 2;
>>> +
>>> + if (thumb_insn_size (insn1) != 4)
>>> + {
>>> + /* Assume that there is at most one conditional branch in the
>>> + atomic sequence. If a conditional branch is found, put a
>>> + breakpoint in its destination address. */
>>> + if ((insn1 & 0xf000) == 0xd000 && bits (insn1, 8, 11) != 0x0f)
>>> + {
>>> + if (last_breakpoint > 0)
>>> + return NULL; /* More than one conditional branch found,
>>> + fallback to the standard code. */
>>> +
>>> + breaks[1] = loc + 2 + (sbits (insn1, 0, 7) << 1);
>>> + last_breakpoint++;
>>> + }
>>> +
>>> + /* We do not support atomic sequences that use any *other*
>>> + instructions but conditional branches to change the PC.
>>> + Fall back to standard code to avoid losing control of
>>> + execution. */
>>> + else if (thumb_instruction_changes_pc (insn1))
>>> + return NULL;
>>> + }
>>> + else
>>> + {
>>> + insn2 = self->ops->read_memory_unsigned_integer
>>> + (loc, 2, byte_order_for_code);
>>
>> Format looks wrong, multiple instances of this problem in the patch.
>>
>
> Yes actually I was not sure about that and discussed this with Pedro
> and he agreed this was ok. That's why I went with that.
>
> At some point when you have
> if
> if
> if
> long_function_name (long variable,
>
> And that does not fit you could have
>
> long_function_name (
> long variable, ... )
>
> or long_function_name
> (long variable, ...)
>
> or ?
>

... then, this problem doesn't exist at all. Isn't it better below?

insn2 = ARM_READ_UINT (loc, 2, byte_order_for_code);

--
Yao (齐尧)