Re: [PATCH 2/2] arm-tdep.c: Refactor displaced stepping relocation functions

[Luis Machado <lgustavo at codesourcery dot com>]

On 02/26/2016 01:23 PM, Simon Marchi wrote:
> > > diff --git a/gdb/arm-tdep.c b/gdb/arm-tdep.c
> > > index 43b61c2..ef48a90 100644
> > > --- a/gdb/arm-tdep.c
> > > +++ b/gdb/arm-tdep.c
> > > @@ -7111,9 +7111,8 @@ thumb_copy_pop_pc_16bit (uint16_t insn1, struct arm_insn_reloc_data *data)
> > >      return 0;
> > >    }
> > >
> > > -static void
> > > -thumb_process_displaced_16bit_insn (uint16_t insn1,
> > > -				    struct arm_insn_reloc_data *data)
> > > +static int
> > > +arm_relocate_insn_thumb_16bit (uint16_t insn1, struct arm_insn_reloc_data *data)
> > >    {
> > >      unsigned short op_bit_12_15 = bits (insn1, 12, 15);
> > >      unsigned short op_bit_10_11 = bits (insn1, 10, 11);
> > > @@ -7202,9 +7201,7 @@ thumb_process_displaced_16bit_insn (uint16_t insn1,
> > >          err = 1;
> > >        }
> > >
> > > -  if (err)
> > > -    internal_error (__FILE__, __LINE__,
> > > -		    _("thumb_process_displaced_16bit_insn: Instruction decode error"));
> > > +  return err;
> >
> > Should we keep this internal error message under a different context
> > instead of exporting just an error code? Maybe the error code should
> > trigger this internal error for GDB?
>
> I am not sure I understand your comment. Given this call tree:
>
> - arm_process_displaced_insn
>    - arm_relocate_insn_arm
>      ...
>    - arm_relocate_insn_thumb_32bit
>      ...
>    - arm_relocate_insn_thumb_16bit
>      ...
>
> my patch makes it so that the arm_relocate_insn* functions return an error code, and
> arm_process_displaced_insn calls internal_error if an error is returned.  Do you suggest
> putting the internal_error calls in the arm_relocate_insn_* functions directly?

No. If we want them shared, i don't think we'd want them to throw 
internal errors.

I was just pointing out the fact that we're losing the function name 
information from arm_relocate_insn_thumb_16bit's and 
thumb_process_displaced_32bit_insn's internal error messages. This 
information may make debugging easier. We would need to throw errors 
with custom messages from within arm_process_displaced_insn in order to 
maintain those names. For example:

"thumb_process_displaced_16bit_insn: Instruction decode error"
"thumb_process_displaced_32bit_insn: Instruction decode error"

Instead of:

"arm_process_displaced_insn: Instruction decode error"

I see the regular non-thumb functions don't throw internal errors 
themselves though. So i'm fine if others think the more specific error 
message is not needed.

Luis