Re: [PATCH] gdb/testsuite: Bump up 'match_max'

[Thiago Jung Bauermann <thiago.bauermann@linaro.org>]

Hello Andrew,

Andrew Burgess <aburgess@redhat.com> writes:

> Thiago Jung Bauermann via Gdb-patches <gdb-patches@sourceware.org>
> writes:
>
>> Simon Marchi <simark@simark.ca> writes:
>>
>>> On 2023-10-04 18:43, Thiago Jung Bauermann wrote:
>>>> 
>>>> Hello Simon,
>>>> 
>>>> Thanks for looking into this.
>>>> 
>>>> Simon Marchi <simark@simark.ca> writes:
>>>> 
>>> The "maint info line-table" test is specifically written in a way to
>>> deal with large output.  It uses gdb_test_multiple with different -re
>>> patterns to match the different expected lines.  expect reads some
>>> output from GDB, then tries to match any -re line.  If there's a match,
>>> the text that matched is removed from the expect buffer.  When there
>>> isn't enough data in the buffer, expect reads more GDB output.  This
>>> way, we consume the GDB output line by line and avoid having all the
>>> huge output of the command in the buffer at the same time.
>>>
>>> See this commit:
>>>
>>> https://gitlab.com/gnutools/binutils-gdb/-/commit/f610ab6d3cbab5d8b8ef3f3a93dd81a800ec5725
>>>
>>> I added some "puts" in each -re clause, to see which matched (see diff
>>> at the end).  With "make check", it looks fine, this -re (which matches
>>> table entries) gets matched often:
>>>
>>>   -re "^$decimal\[ \t\]+$decimal\[ \t\]+$hex\[ \t\]+$hex\[^\r\n\]*\r\n"
>>>
>>> But with "make check-read1", it doesn't get matched and we accumulate
>>> lots of output in the buffer.  I follow the test execution with `tail -F
>>> testsuite/gdb.log` on another terminal, and I see the output coming in
>>> slower and slower (presumably because expect tries to match our patterns
>>> on an ever growing buffer).
>>>
>>> So I think this is what you should dig into, why doesn't this -re get
>>> matched with read1.  Note that the ^ at the beginning of the regex means
>>> that this regex will match only against some output at the very
>>> beginning of the buffer.  So if there is some unmatched output in the
>>> buffer before what this line intends to match, it won't match.
>>>
>>> The culprits are likely the regexes that finish with an unbounded
>>> repetition like [^\r\n]*.  When characters are read one by one in the
>>> buffer, the regex can match early and leave something in the buffer that
>>> it would have otherwise matched, if the reads were done in big chunks as
>>> usual (this is precisely the kind of issue that read1 means to uncover).
>>> Those regexes would need to be modified to consume the entire line, even
>>> with read1.
>>
>> Thank you for the detailed explanation and for the debug patch! I'll dig
>> further into it and see if I can fix the testcase.
>
> The patch below is what you are looking for.

Indeed it is! I was just going to start digging into this issue. Thank
you very much for fixing it.

I tested it on the machines I mentioned before, and all tests pass in
all of them. It even runs a lot faster now, too.

Tested-by: Thiago Jung Bauermann <thiago.bauermann@linaro.org>

-- 
Thiago