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

  In gdb.base/maint.exp a test calls 'maint print registers'.  If the
target has lots of registers this may overflow expect's buffers,
causing the test to fail.

After this commit we process the output line at a time until we get back
to the GDB prompt, this should prevent buffer overrun while still
testing that the command works as required.

gdb/testsuite/ChangeLog:

	* gdb.base/maint.exp: Process output from 'maint print registers'
	line at a time.
---
 gdb/testsuite/ChangeLog          |  5 +++++
 gdb/testsuite/gdb.base/maint.exp | 18 ++++++++++++++++--
 2 files changed, 21 insertions(+), 2 deletions(-)
  

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.

 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.

  Maciej
  

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
  

On Fri, 13 Apr 2018, Pedro Alves wrote:

> 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.

 FWIW I think we should keep the heading check.

  Maciej