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From: sergiodj+buildbot@redhat.com To: gdb-testers@sourceware.org Subject: [binutils-gdb] [Ada] GDB crash during "finish" of function with out parameters Date: Mon, 09 Nov 2015 18:08:00 -0000 [thread overview] Message-ID: <dddc0e16ef5d77e4f97d02ee0e2d4234c97dae0e@gdb-build> (raw) *** TEST RESULTS FOR COMMIT dddc0e16ef5d77e4f97d02ee0e2d4234c97dae0e *** Author: Joel Brobecker <brobecker@adacore.com> Branch: master Commit: dddc0e16ef5d77e4f97d02ee0e2d4234c97dae0e [Ada] GDB crash during "finish" of function with out parameters Consider a function with the following signature... function F (R : out Rec_Type) return Enum_Type; ... where Rec_Type is a simple record: type Rec_Type is record Cur : Integer; end record; Trying to "finish" from that function causes GDB to SEGV: (gdb) fin Run till exit from #0 bar.f (r=...) at bar.adb:5 0x00000000004022fe in foo () at foo.adb:5 5 I : Enum_Type := F (R); [1] 18949 segmentation fault (core dumped) /[..]/gdb This is related to the fact that funtion F has a parameter (R) which is an "out" parameter being passed by copy. For those, GNAT transforms the return value to be a record with multiple fields: The first one is called "RETVAL" and contains the return value shown in the source, and the remaining fields have the same name as the "out" or "in out" parameters which are passed by copy. So, in the example above, function F returns a struct that has one field who name is "r". Because "RETVAL" starts with "R", GDB thinks it's a wrapper field, because it looks like the encoding used for variant records: -- member_name ::= {choice} | others_choice -- choice ::= simple_choice | range_choice -- simple_choice ::= S number -- range_choice ::= R number T number <<<<<----- here -- number ::= {decimal_digit} [m] -- others_choice ::= O (upper case letter O) See ada_is_wrapper_field: return (name != NULL && (startswith (name, "PARENT") || strcmp (name, "REP") == 0 || startswith (name, "_parent") || name[0] == 'S' || name[0] == 'R' || name[0] == 'O')); As a result of this, when trying to print the RETURN value, we think that RETVAL is a wrapper, and thus recurse into print_field_values... if (ada_is_wrapper_field (type, i)) { comma_needed = print_field_values (TYPE_FIELD_TYPE (type, i), valaddr, (offset + TYPE_FIELD_BITPOS (type, i) / HOST_CHAR_BIT), stream, recurse, val, options, comma_needed, type, offset, language); ... which is a problem since print_field_values assumes that the type it is given ("TYPE_FIELD_TYPE (type, i)" here), is also a record type. However, that's not the case, since RETVAL is an enum. That eventually leads GDB to a NULL type when trying to extract fields out of the enum, which then leads to a SEGV when trying to dereference it. Ideally, we'd want to be a little more careful in identifying wrapper fields, by enhancing ada_is_wrapper_field to be a little more complete in its analysis of the field name before declaring it a variant record wrapper. However, it's not super easy to do so, considering that the choices can be combined together when complex choices are used. Eg: -- [...] the choice 1 .. 4 | 7 | -10 would be represented by -- R1T4S7S10m Given that we are working towards getting rid of GNAT encodings, which means that the above will eventually disappear, we took the more pragmatic approach is just treating RETVAL as a special case. gdb/ChangeLog: * ada-lang.c (ada_is_wrapper_field): Add special handling for fields called "RETVAL". gdb/testsuite/ChangeLog: * gdb.ada/fin_fun_out: New testcase.
next reply other threads:[~2015-11-09 18:08 UTC|newest] Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top 2015-11-09 18:08 sergiodj+buildbot [this message] 2015-11-09 18:12 ` Failures on RHEL-s390x-m64, branch master sergiodj+buildbot 2015-11-09 18:13 ` Failures on Fedora-x86_64-m32, " sergiodj+buildbot 2015-11-09 18:20 ` Failures on Fedora-x86_64-native-extended-gdbserver-m32, " sergiodj+buildbot 2015-11-09 18:24 ` Failures on Debian-i686, " sergiodj+buildbot 2015-11-09 18:26 ` Failures on AIX-POWER7-plain, " sergiodj+buildbot 2015-11-09 18:26 ` Failures on Debian-s390x-native-extended-gdbserver-m64, " sergiodj+buildbot 2015-11-09 18:28 ` Failures on Fedora-x86_64-native-gdbserver-m64, " sergiodj+buildbot 2015-11-09 18:31 ` Failures on Fedora-x86_64-native-extended-gdbserver-m64, " sergiodj+buildbot 2015-11-09 18:32 ` Failures on Fedora-x86_64-native-gdbserver-m32, " sergiodj+buildbot 2015-11-09 19:03 ` Failures on Debian-i686-native-gdbserver, " sergiodj+buildbot 2015-11-09 19:05 ` Failures on Debian-i686-native-extended-gdbserver, " sergiodj+buildbot 2015-11-09 19:44 ` Failures on Fedora-ppc64be-native-gdbserver-m64, " sergiodj+buildbot 2015-11-09 20:06 ` Failures on Fedora-ppc64be-native-extended-gdbserver-m64, " sergiodj+buildbot 2015-11-09 20:39 ` Failures on Fedora-ppc64le-native-extended-gdbserver-m64, " sergiodj+buildbot 2015-11-10 5:19 ` Failures on Fedora-ppc64le-native-gdbserver-m64, " sergiodj+buildbot
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