Re: [PATCH] Fix skip.exp test failure observed with gcc-9.2.0

[Bernd Edlinger <bernd.edlinger@hotmail.de>]

On 12/15/19 2:05 PM, Simon Marchi wrote:
> On 2019-12-15 6:30 a.m., Bernd Edlinger wrote:
>> Hi,
>>
>> this is the split out patch on skip.exp which fixes a pre-existing
>> compatibilty issue with that test case and gcc-9.2.0 (and gcc-10 from
>> trunk of a few weeks ago at least, likely other versions too).
>>
>>
>> Is it OK for trunk?
>>
>>
>> Thanks
>> Bernd.
>>
>>
> 
> Hi Bernd,
> 
> Just wondering, were you able to figure out which change in debug info lead
> to this behavior change?  The behavior with gcc 9.2.0 seems better to be me,
> I think your patch is ok.
> 

Yes indeed.  The change started with gcc-8.1.0 when -gcolumn-info was enabled
by default.  -gcolumn-info was first implemented in gcc-7.1.0 but default-disabled,
so you can get the altered behavior already with gcc-7 if you manually enable
-gcolumn-info.

So previously there was just one point where line line 30 (of skip.c) started:

  [0x00000032]  Advance Line by 27 to 28
  [0x00000034]  Copy
  [0x00000035]  Special opcode 63: advance Address by 4 to 0x4004cb and Line by 2 to 30
  [0x00000036]  Advance PC by constant 17 to 0x4004dc
  [0x00000037]  Special opcode 7: advance Address by 0 to 0x4004dc and Line by 2 to 32

with column-info we have line 30 three times with different column:

  [0x00000034]  Advance Line by 27 to 28
  [0x00000036]  Copy
  [0x00000037]  Set column to 9
  [0x00000039]  Special opcode 63: advance Address by 4 to 0x4004c6 and Line by 2 to 30
  [0x0000003a]  Set column to 17
  [0x0000003c]  Special opcode 75: advance Address by 5 to 0x4004cb and Line by 0 to 30
  [0x0000003d]  Set column to 3
  [0x0000003f]  Special opcode 75: advance Address by 5 to 0x4004d0 and Line by 0 to 30
  [0x00000040]  Special opcode 105: advance Address by 7 to 0x4004d7 and Line by 2 to 32


That could probably be filtered in dwarf2read.c to keep the old behavior, but I agree
that the new behavior makes still sense, even if we cannot really use the column info
in the line number info.

> I would just remove the unrelated whitespace fix before merging.
> 

Okay, I just replicated you advice regarding 8-space tab columns on
skip-inline.exp in the other patch.  Exactly those 2 lines were copied
where the tabs were not used correctly.


Thanks
Bernd.

> Simon
>