[c++] Improve error message when using libstdcxx without SDT probes

  On 26-08-19 16:11, Sergio Durigan Junior wrote:
> On Thursday, July 25 2019, Tom de Vries wrote:
> 
>> Hi,
>>
>> When using catch catch/rethrow/catch, a libstdcxx with SDT probes is required
>> for both the regexp argument, and the convenience variable $_exception (
>> https://sourceware.org/gdb/current/onlinedocs/gdb/Set-Catchpoints.html ).
>>
>> Currently, when using these features with a libstdcxx without SDT probes, we
>> get the cryptic error message:
>> ...
>> not stopped at a C++ exception catchpoint
>> ...
>>
>> Improve this by instead emitting the more helpful:
>> ...
>> did not find exception probe (does libstdcxx have SDT probes?)
>> ...
>>
>> Tested on x86_64-linux.
>>
>> OK for trunk?
> 
> Thanks for the patch.
> 
>> Thanks,
>> - Tom
>>
>> [gdb, c++] Improve error message when using libstdcxx without SDT probes
>>
>> gdb/ChangeLog:
>>
>> 2019-07-25  Tom de Vries  <tdevries@suse.de>
>>
>> 	PR c++/24852
>> 	* break-catch-throw.c (fetch_probe_arguments): Improve error mesage
>> 	when pc_probe.prob == NULL.
>>
>> gdb/testsuite/ChangeLog:
>>
>> 2019-07-25  Tom de Vries  <tdevries@suse.de>
>>
>> 	PR c++/24852
>> 	* gdb.cp/no-libstdcxx-probe.exp: New test.
>>
>> ---
>>  gdb/break-catch-throw.c                     |  6 ++-
>>  gdb/testsuite/gdb.cp/no-libstdcxx-probe.exp | 58 +++++++++++++++++++++++++++++
>>  2 files changed, 62 insertions(+), 2 deletions(-)
>>
>> diff --git a/gdb/break-catch-throw.c b/gdb/break-catch-throw.c
>> index 0677a55ee5..2d91285312 100644
>> --- a/gdb/break-catch-throw.c
>> +++ b/gdb/break-catch-throw.c
>> @@ -106,8 +106,10 @@ fetch_probe_arguments (struct value **arg0, struct value **arg1)
>>    unsigned n_args;
>>  
>>    pc_probe = find_probe_by_pc (pc);
>> -  if (pc_probe.prob == NULL
>> -      || pc_probe.prob->get_provider () != "libstdcxx"
>> +  if (pc_probe.prob == NULL)
>> +    error (_("did not find exception probe (does libstdcxx have SDT probes?)"));
>> +
>> +  if (pc_probe.prob->get_provider () != "libstdcxx"
>>        || (pc_probe.prob->get_name () != "catch"
>>  	  && pc_probe.prob->get_name () != "throw"
>>  	  && pc_probe.prob->get_name () != "rethrow"))
>> diff --git a/gdb/testsuite/gdb.cp/no-libstdcxx-probe.exp b/gdb/testsuite/gdb.cp/no-libstdcxx-probe.exp
>> new file mode 100644
>> index 0000000000..4c1a706ae0
>> --- /dev/null
>> +++ b/gdb/testsuite/gdb.cp/no-libstdcxx-probe.exp
>> @@ -0,0 +1,58 @@
>> +# Copyright 2019 Free Software Foundation, Inc.
>> +
>> +# This program is free software; you can redistribute it and/or modify
>> +# it under the terms of the GNU General Public License as published by
>> +# the Free Software Foundation; either version 3 of the License, or
>> +# (at your option) any later version.
>> +#
>> +# This program is distributed in the hope that it will be useful,
>> +# but WITHOUT ANY WARRANTY; without even the implied warranty of
>> +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>> +# GNU General Public License for more details.
>> +#
>> +# You should have received a copy of the GNU General Public License
>> +# along with this program.  If not, see <http://www.gnu.org/licenses/>.
>> +
>> +standard_testfile exceptprint.cc
>> +
>> +if {[skip_cplus_tests]} {
>> +    return -1
>> +}
>> +
>> +if {[prepare_for_testing "failed to prepare" $testfile $srcfile {debug c++}]} {
>> +    return -1
>> +}
>> +
>> +if {![runto_main]} {
>> +    return -1
>> +}
>> +
>> +set libstdcxx_probe_tests_supported [skip_libstdcxx_probe_tests]
> 
> Not your fault, but this reversed logic (skip_libstdcxx_probe_tests
> returns 0 if the tests should be skipped) is kinda confusing.
> 

[ FTR, dealt with here (
https://sourceware.org/ml/gdb-patches/2019-08/msg00595.html ). ]

>> +
>> +if { $libstdcxx_probe_tests_supported == 1 } {
>> +    untested "Have libstdc++ stap probe"
>> +    return -1
>> +}
>> +
>> +proc do_continue_to_catchpoint {name} {
>> +    global gdb_prompt
>> +
>> +    gdb_test_multiple "continue" $name {
>> +	-re "Continuing.*Catchpoint \[0-9\].*\r\n$gdb_prompt $" {
> 
> You can use $decimal instead of \[0-9\] if you want.
> 

Done.

>> +	    pass $name
>> +	}
>> +    }
>> +}
>> +
>> +proc do_exceptprint_tests {prefix output} {
>> +    with_test_prefix $prefix {
>> +	do_continue_to_catchpoint "continue to throw"
>> +	gdb_test "print \$_exception" \
>> +	    "did not find exception probe \\(does libstdcxx have SDT probes\\?\\).*"
>> +    }
>> +}
> 
> You don't seem to use $output here.
> 

Hmm, and also prefix doesn't make much sense. In fact, the code becomes
more clear if I just inline the procs, and replace the gdb_test_multiple
with gdb_test.

>> +
>> +gdb_test "catch throw" "Catchpoint \[0-9\]+ \\(throw\\)" \
>> +    "catch throw"
> 
> $decimal if you want.
> 

Done.

>> +
>> +do_exceptprint_tests string "$hex \"hi bob\""
> 
> The patch looks good to me.  Thanks for doing this.

Committed as below.

Thanks,
- Tom