Re: [PATCH 3/3] gdb/testsuite: Handle targets with lots of registers

[Pedro Alves <palves at redhat dot com>]

On 04/13/2018 12:39 AM, Maciej W. Rozycki wrote:
> On Mon, 9 Apr 2018, Andrew Burgess wrote:
> 
>>  # Test for a regression where this command would internal-error if the
>> -# program wasn't running.
>> -gdb_test "maint print registers" "Name.*Nr.*Rel.*Offset.*Size.*Type.*"
>> +# program wasn't running.  If there's a lot of registers then this
>> +# might overflow expect's buffers, so process the output line at a
>> +# time.
>> +send_gdb "maint print registers\n"
>> +gdb_expect {
>> +    -re "^\[^\n\r\]+\[0-9\]+\[^\n\r\]+\[0-9\]+\[^\n\r\]+\[0-9\]+\[^\n\r\]+\[0-9\]+\[^\n\r\]+\[\n\r\]+" {
>> +	exp_continue
>> +    }
> 
>  I think this changes the meaning of the test; you want to preserve the 
> heading match pattern at the very least.  Also `gdb_test' handles various 
> error cases gracefully (which matters for the avoidance of excessive 
> timeouts with some test boards), whereas your simple matcher does not.

Yeah, there's no good reason to use gdb_expect directly here, AFAICT.
You can do the same thing with gdb_test_multiple, which handles
the timeout already, as well as other error conditions, including
the internal-error the comment the test above mentions.

> 
>  Also how many is "a lot"?  Perhaps you could take the path of least 
> resistance instead and simply increase the size of the buffer, like with 
> commit ff604a674771 ("gdb/testsuite: Bump up `match_max'").  This could be 
> done temporarily for this test only, so as to avoid slowing down `expect' 
> throughout the test suite.

I think the exp_continue trick is better for getting rid of the
problem for good.  We can still use it, with gdb_test_multiple.

A few comments more:

> +    -re "^\[^\n\r\]+\[0-9\]+\[^\n\r\]+\[0-9\]+\[^\n\r\]+\[0-9\]+\[^\n\r\]+\[0-9\]+\[^\n\r\]+\[\n\r\]+" {

Nit: \n\r instead of \r\n kind of reads like a typo to me:

$ grep -rn "\\\\r\\\\n\\\\]" | wc -l
1036
$ grep -rn "\\\\n\\\\r\\\\]" | wc -l
28

I'd suggest flipping it around to the more usual form
just to avoid causing pause when people read the regexp.

> +	exp_continue
> +    }
> +    -re ".*$gdb_prompt $" {

No need for leading .*, it's implied.

> +	pass "maint print registers"
> +    }
> +    timeout {
> +	fail "maint print registers (timeout)"
> +    }
> +}
> +

So I'd suggest something like this:

set saw_registers 0
set test "maint print registers"
gdb_test_multiple $test $test {
    -re "^\[^\r\n\]+\[0-9\]+\[^\r\n\]+\[0-9\]+\[^\r\n\]+\[0-9\]+\[^\r\n\]+\[0-9\]+\[^\r\n\]+\[\r\n\]+" {
        set saw_registers 1
	exp_continue
    }
    -re "$gdb_prompt $" {
	gdb_assert $saw_registers $test
    }
}

The "saw_registers" bit ends up serving as replacement for
seeing the heading, though you can also add a pattern to 
match the heading and check it in the gdb_assert instead if
you'd like.

Thanks,
Pedro Alves