Re: [PATCH][gdb, c++] Improve error message when using libstdcxx without SDT probes

[Sergio Durigan Junior <sergiodj@redhat.com>]

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.

> +
> +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.

> +	    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.

> +
> +gdb_test "catch throw" "Catchpoint \[0-9\]+ \\(throw\\)" \
> +    "catch throw"

$decimal if you want.

> +
> +do_exceptprint_tests string "$hex \"hi bob\""

The patch looks good to me.  Thanks for doing this.

-- 
Sergio
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