Re: [PATCH] Use GCC5/DWARF5 DW_AT_noreturn to mark functions that don't return normally.

Mark Wielaard
2015-01-23T16:33:45Z

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On Wed, 2015-01-21 at 17:07 +0000, Pedro Alves wrote:
>
> On 01/15/2015 11:56 PM, Mark Wielaard wrote:
>
> > create mode 100644 gdb/testsuite/gdb.base/noreturn.c
> > create mode 100644 gdb/testsuite/gdb.base/noreturn.exp
>
> How about "noreturn-return.{c|exp}", to go with noreturn_finish ?
>
> > create mode 100644 gdb/testsuite/gdb.base/noreturn_finish.c
> > create mode 100644 gdb/testsuite/gdb.base/noreturn_finish.exp
>
> But please use '-' instead of '_':
>
> gdb/testsuite/gdb.base/noreturn-finish.c
> gdb/testsuite/gdb.base/noreturn-finish.exp

OK, changed all file and test names.

> > diff --git a/gdb/testsuite/gdb.base/noreturn.c b/gdb/testsuite/gdb.base/noreturn.c
> > new file mode 100644
> > index 0000000..e39cf15
> > --- /dev/null
> > +++ b/gdb/testsuite/gdb.base/noreturn.c
> > @@ -0,0 +1,13 @@
>
> Please add a copyright header. Even though some of our old
> files don't have it, all new files should, even if the file
> is small (so that we don't have to recall adding it back
> if the file grows in future).

Added.
Note that most .c files in gdb.base don't have such a header.

> > +void __attribute__((noreturn))
> > +noreturn_func ()
>
> noreturn_func (void)

Added the void.
Note most existing .c tests in gdb.base don't declare functions with
void arguments.

> > +{
> > + while (1)
> > + ;
>
> Please don't make the test loop forever if GDB crashes.
> Does e.g., "abort()" like the other test work here too?

Changed.
It isn't semantically the same, but it does work.

> > +}
> > +
> > +int
> > +main ()
>
> likewise (void)

Added.

> > +{
> > + noreturn_func ();
> > + return 0;
> > +}
> > diff --git a/gdb/testsuite/gdb.base/noreturn.exp b/gdb/testsuite/gdb.base/noreturn.exp
> > new file mode 100644
> > index 0000000..885642f
> > --- /dev/null
> > +++ b/gdb/testsuite/gdb.base/noreturn.exp
> > @@ -0,0 +1,54 @@
> > +# Copyright 2015 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 .c
>
> You can drop the ".c", as it's the default.

Dropped. It is used in other .exp files though.

> > +
> > +if { [gdb_compile "${srcdir}/${subdir}/${srcfile}" "${binfile}" executable {debug}] != "" } {
> > + untested noreturn.exp
> > + return -1
> > +}
>
> Use prepare_for_testing, like:
>
> if [prepare_for_testing "failed to prepare" ${testfile} ${srcfile} {debug}] {
> return -1
> }

Changed. This idiom comes from existing .exp files though.

> > +
> > +proc noreturn_test { } {
> > + global gdb_prompt
> > +
> > + if { ! [ runto_main ] } then {
> > + untested noreturn.exp
>
> Use $testfile, like "untested ${testfile}.exp".

Changed.

> > + return -1
> > + }
> > +
> > + gdb_test "break noreturn_func" "Breakpoint \[0123456789\].*" \
> > + "set break on noreturn_func"
> > + gdb_test "continue" "Breakpoint.* noreturn_func.*" \
> > + "continue to noreturn_func"
>
> gdb_breakpoint "noreturn_func"
> gdb_continue_to_breakpoint "noreturn_func"

Changed. Note that the above comes from existing .exp testcases.

> > +
> > + gdb_test_multiple "return" "return from noreturn_func" {
> > + -re "warning: Function does not return normally to caller" {
> > + verbose -log "saw warning"
> > + exp_continue
> > + }
> > + -re "Make noreturn_func return now.*y or n. $" {
> > + send_gdb "n\n"
> > + exp_continue
> > + }
> > + -re "Not confirmed.*$gdb_prompt $" {
> > + pass "noreturn_func return cancelled"
> > + }
>
> Make the test message be the same in all paths, like:
>
> set test "return from noreturn_func"
> gdb_test_multiple "return" $test {
> -re "warning: Function does not return normally to caller" {
> verbose -log "saw warning"
> exp_continue
> }
> -re "Make noreturn_func return now.*y or n. $" {
> send_gdb "n\n"
> exp_continue
> }
> -re "Not confirmed.*$gdb_prompt $" {
> pass $test
> }

Changed

> > + }
> > +}
> > +
> > +clean_restart ${binfile}
>
> prepare_for_testing does this for you.

Dropped.

> > +
> > +set timeout 30
>
> I don't see why this is necessary.

Dropped.

> I think this is just a copy/paste?

Yes, I just took the testcases you recommended and changed them to test
the new warning messages added.

> > +noreturn_test
> > diff --git a/gdb/testsuite/gdb.base/noreturn_finish.c b/gdb/testsuite/gdb.base/noreturn_finish.c
> > new file mode 100644
> > index 0000000..cd52769
> > --- /dev/null
> > +++ b/gdb/testsuite/gdb.base/noreturn_finish.c
> > @@ -0,0 +1,14 @@
> > +#include <stdlib.h>
> > +
> > +void __attribute__((noreturn))
> > +noreturn_func ()
> > +{
> > + abort ();
> > +}
> > +
> > +int
> > +main ()
> > +{
> > + noreturn_func ();
> > + return 0;
> > +}
>
> Same comments apply to noreturn_finish.c|exp.

Same changes made.

> Otherwise OK.

Pushed as attached after retesting under GCC 5 and 4.8.2.

Thanks,

Mark

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From 743649fd80776de922475362bf3ac8b44511bb24 Mon Sep 17 00:00:00 2001
From: Mark Wielaard <mjw@redhat.com>
Date: Tue, 9 Dec 2014 11:45:41 +0100
Subject: [PATCH] Use GCC5/DWARF5 DW_AT_noreturn to mark functions that don't
return normally.

Add a flag field is_noreturn to struct func_type. Make calling_convention
a small bit field to not increase the size of the struct. Set is_noreturn
if the new GCC5/DWARF5 DW_AT_noreturn is set on a DW_TAG_subprogram.
Use this information to warn the user before doing a finish or return from
a function that does not return normally to its caller.

(gdb) finish
warning: Function endless does not return normally.
Try to finish anyway? (y or n)

(gdb) return
warning: Function does not return normally to caller.
Make endless return now? (y or n)

gdb/ChangeLog

* dwarf2read.c (read_subroutine_type): Set TYPE_NO_RETURN from
DW_AT_noreturn.
* gdbtypes.h (struct func_type): Add is_noreturn field flag. Make
calling_convention an 8 bit bit field.
(TYPE_NO_RETURN): New macro.
* infcmd.c (finish_command): Query if function does not return
normally.
* stack.c (return_command): Likewise.

gdb/testsuite/ChangeLog

* gdb.base/noreturn-return.c: New file.
* gdb.base/noreturn-return.exp: New file.
* gdb.base/noreturn-finish.c: New file.
* gdb.base/noreturn-finish.exp: New file.

include/ChangeLog

* dwarf2.def (DW_AT_noreturn): New DWARF5 attribute.

The dwarf2.h addition and the code to emit the new attribute is already in
the gcc tree.
---
gdb/ChangeLog | 11 +++++++
gdb/dwarf2read.c | 6 ++++
gdb/gdbtypes.h | 12 +++++--
gdb/infcmd.c | 9 +++++-
gdb/stack.c | 8 +++--
gdb/testsuite/ChangeLog | 7 ++++
gdb/testsuite/gdb.base/noreturn-finish.c | 31 ++++++++++++++++++
gdb/testsuite/gdb.base/noreturn-finish.exp | 51 ++++++++++++++++++++++++++++++
gdb/testsuite/gdb.base/noreturn-return.c | 31 ++++++++++++++++++
gdb/testsuite/gdb.base/noreturn-return.exp | 51 ++++++++++++++++++++++++++++++
include/ChangeLog | 4 +++
include/dwarf2.def | 2 ++
12 files changed, 218 insertions(+), 5 deletions(-)
create mode 100644 gdb/testsuite/gdb.base/noreturn-finish.c
create mode 100644 gdb/testsuite/gdb.base/noreturn-finish.exp
create mode 100644 gdb/testsuite/gdb.base/noreturn-return.c
create mode 100644 gdb/testsuite/gdb.base/noreturn-return.exp

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 818eb7c..c195f5d 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,14 @@
+2015-01-15 Mark Wielaard <mjw@redhat.com>
+
+ * dwarf2read.c (read_subroutine_type): Set TYPE_NO_RETURN from
+ DW_AT_noreturn.
+ * gdbtypes.h (struct func_type): Add is_noreturn field flag. Make
+ calling_convention an 8 bit bit field.
+ (TYPE_NO_RETURN): New macro.
+ * infcmd.c (finish_command): Query if function does not return
+ normally.
+ * stack.c (return_command): Likewise.
+
2015-01-23 Pedro Alves <palves@redhat.com>

* linux-nat.c (linux_is_async_p): New macro.
diff --git a/gdb/dwarf2read.c b/gdb/dwarf2read.c
index 96b2537..9d765c5 100644
--- a/gdb/dwarf2read.c
+++ b/gdb/dwarf2read.c
@@ -14343,6 +14343,12 @@ read_subroutine_type (struct die_info *die, struct dwarf2_cu *cu)
else
TYPE_CALLING_CONVENTION (ftype) = DW_CC_normal;

+ /* Record whether the function returns normally to its caller or not
+ if the DWARF producer set that information. */
+ attr = dwarf2_attr (die, DW_AT_noreturn, cu);
+ if (attr && (DW_UNSND (attr) != 0))
+ TYPE_NO_RETURN (ftype) = 1;
+
/* We need to add the subroutine type to the die immediately so
we don't infinitely recurse when dealing with parameters
declared as the same subroutine type. */
diff --git a/gdb/gdbtypes.h b/gdb/gdbtypes.h
index 7c06a4f..ba5c857 100644
--- a/gdb/gdbtypes.h
+++ b/gdb/gdbtypes.h
@@ -1019,9 +1019,16 @@ struct func_type
{
/* * The calling convention for targets supporting multiple ABIs.
Right now this is only fetched from the Dwarf-2
- DW_AT_calling_convention attribute. */
+ DW_AT_calling_convention attribute. The value is one of the
+ DW_CC enum dwarf_calling_convention constants. */

- unsigned calling_convention;
+ unsigned calling_convention : 8;
+
+ /* * Whether this function normally returns to its caller. It is
+ set from the DW_AT_noreturn attribute if set on the
+ DW_TAG_subprogram. */
+
+ unsigned int is_noreturn : 1;

/* * Only those DW_TAG_GNU_call_site's in this function that have
DW_AT_GNU_tail_call set are linked in this list. Function
@@ -1245,6 +1252,7 @@ extern void allocate_gnat_aux_type (struct type *);
#define TYPE_GNAT_SPECIFIC(thistype) TYPE_MAIN_TYPE(thistype)->type_specific.gnat_stuff
#define TYPE_DESCRIPTIVE_TYPE(thistype) TYPE_GNAT_SPECIFIC(thistype)->descriptive_type
#define TYPE_CALLING_CONVENTION(thistype) TYPE_MAIN_TYPE(thistype)->type_specific.func_stuff->calling_convention
+#define TYPE_NO_RETURN(thistype) TYPE_MAIN_TYPE(thistype)->type_specific.func_stuff->is_noreturn
#define TYPE_TAIL_CALL_LIST(thistype) TYPE_MAIN_TYPE(thistype)->type_specific.func_stuff->tail_call_list
#define TYPE_BASECLASS(thistype,index) TYPE_FIELD_TYPE(thistype, index)
#define TYPE_N_BASECLASSES(thistype) TYPE_CPLUS_SPECIFIC(thistype)->n_baseclasses
diff --git a/gdb/infcmd.c b/gdb/infcmd.c
index 7b26663..9a1fb8d 100644
--- a/gdb/infcmd.c
+++ b/gdb/infcmd.c
@@ -1872,7 +1872,14 @@ finish_command (char *arg, int from_tty)
if (execution_direction == EXEC_REVERSE)
printf_filtered (_("Run back to call of "));
else
- printf_filtered (_("Run till exit from "));
+ {
+ if (function != NULL && TYPE_NO_RETURN (function->type)
+ && !query (_("warning: Function %s does not return normally.\n"
+ "Try to finish anyway? "),
+ SYMBOL_PRINT_NAME (function)))
+ error (_("Not confirmed."));
+ printf_filtered (_("Run till exit from "));
+ }

print_stack_frame (get_selected_frame (NULL), 1, LOCATION, 0);
}
diff --git a/gdb/stack.c b/gdb/stack.c
index 0201d0a..5f2a3dc 100644
--- a/gdb/stack.c
+++ b/gdb/stack.c
@@ -2462,8 +2462,12 @@ return_command (char *retval_exp, int from_tty)
confirmed = query (_("%sMake selected stack frame return now? "),
query_prefix);
else
- confirmed = query (_("%sMake %s return now? "), query_prefix,
- SYMBOL_PRINT_NAME (thisfun));
+ {
+ if (TYPE_NO_RETURN (thisfun->type))
+ warning ("Function does not return normally to caller.");
+ confirmed = query (_("%sMake %s return now? "), query_prefix,
+ SYMBOL_PRINT_NAME (thisfun));
+ }
if (!confirmed)
error (_("Not confirmed"));
}
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 1a17ba4..5b53cdd 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,10 @@
+2015-01-15 Mark Wielaard <mjw@redhat.com>
+
+ * gdb.base/noreturn-return.c: New file.
+ * gdb.base/noreturn-return.exp: New file.
+ * gdb.base/noreturn-finish.c: New file.
+ * gdb.base/noreturn-finish.exp: New file.
+
2015-01-23 Pedro Alves <palves@redhat.com>

* gdb.threads/continue-pending-after-query.c: New file.
diff --git a/gdb/testsuite/gdb.base/noreturn-finish.c b/gdb/testsuite/gdb.base/noreturn-finish.c
new file mode 100644
index 0000000..3ec48cd
--- /dev/null
+++ b/gdb/testsuite/gdb.base/noreturn-finish.c
@@ -0,0 +1,31 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+ Copyright 2015 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/>. */
+
+#include <stdlib.h>
+
+void __attribute__((noreturn))
+noreturn_func (void)
+{
+ abort ();
+}
+
+int
+main (void)
+{
+ noreturn_func ();
+ return 0;
+}
diff --git a/gdb/testsuite/gdb.base/noreturn-finish.exp b/gdb/testsuite/gdb.base/noreturn-finish.exp
new file mode 100644
index 0000000..a2ae0db
--- /dev/null
+++ b/gdb/testsuite/gdb.base/noreturn-finish.exp
@@ -0,0 +1,51 @@
+# Copyright 2015 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
+
+if [prepare_for_testing "failed to prepare" ${testfile} ${srcfile} {debug}] {
+ return -1
+}
+
+proc noreturn_finish_test { } {
+ global gdb_prompt
+
+ if { ! [ runto_main ] } then {
+ untested ${testfile}.exp
+ return -1
+ }
+
+ gdb_breakpoint "noreturn_func"
+ gdb_continue_to_breakpoint "noreturn_func"
+
+ set test "cancel finish from noreturn_func"
+ gdb_test_multiple "finish" $test {
+ -re "warning: Function noreturn_func does not return normally" {
+ verbose -log "saw warning"
+ exp_continue
+ }
+ -re "Try to finish anyway.*y or n.* $" {
+ send_gdb "n\n"
+ exp_continue
+ }
+ -re ".*$gdb_prompt $" {
+ pass $test
+ }
+ }
+}
+
+clean_restart ${binfile}
+
+noreturn_finish_test
diff --git a/gdb/testsuite/gdb.base/noreturn-return.c b/gdb/testsuite/gdb.base/noreturn-return.c
new file mode 100644
index 0000000..3ec48cd
--- /dev/null
+++ b/gdb/testsuite/gdb.base/noreturn-return.c
@@ -0,0 +1,31 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+ Copyright 2015 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/>. */
+
+#include <stdlib.h>
+
+void __attribute__((noreturn))
+noreturn_func (void)
+{
+ abort ();
+}
+
+int
+main (void)
+{
+ noreturn_func ();
+ return 0;
+}
diff --git a/gdb/testsuite/gdb.base/noreturn-return.exp b/gdb/testsuite/gdb.base/noreturn-return.exp
new file mode 100644
index 0000000..8a64a3e
--- /dev/null
+++ b/gdb/testsuite/gdb.base/noreturn-return.exp
@@ -0,0 +1,51 @@
+# Copyright 2015 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
+
+if [prepare_for_testing "failed to prepare" ${testfile} ${srcfile} {debug}] {
+ return -1
+}
+
+proc noreturn_test { } {
+ global gdb_prompt
+
+ if { ! [ runto_main ] } then {
+ untested ${testfile}.exp
+ return -1
+ }
+
+ gdb_breakpoint "noreturn_func"
+ gdb_continue_to_breakpoint "noreturn_func"
+
+ set test "cancel return from noreturn_func"
+ gdb_test_multiple "return" $test {
+ -re "warning: Function does not return normally to caller" {
+ verbose -log "saw warning"
+ exp_continue
+ }
+ -re "Make noreturn_func return now.*y or n. $" {
+ send_gdb "n\n"
+ exp_continue
+ }
+ -re "Not confirmed.*$gdb_prompt $" {
+ pass $test
+ }
+ }
+}
+
+clean_restart ${binfile}
+
+noreturn_test
diff --git a/include/ChangeLog b/include/ChangeLog
index 31f1e18..21b6ae6 100644
--- a/include/ChangeLog
+++ b/include/ChangeLog
@@ -1,3 +1,7 @@
+2015-01-15 Mark Wielaard <mjw@redhat.com>
+
+ * dwarf2.def (DW_AT_noreturn): New DWARF5 attribute.
+
2015-01-14 Jan-Benedict Glaw <jbglaw@lug-owl.de>

* libiberty.h: Merge from GCC.
diff --git a/include/dwarf2.def b/include/dwarf2.def
index 5da3ae0..3aecdfc 100644
--- a/include/dwarf2.def
+++ b/include/dwarf2.def
@@ -306,6 +306,8 @@ DW_AT (DW_AT_data_bit_offset, 0x6b)
DW_AT (DW_AT_const_expr, 0x6c)
DW_AT (DW_AT_enum_class, 0x6d)
DW_AT (DW_AT_linkage_name, 0x6e)
+/* DWARF 5. */
+DW_AT (DW_AT_noreturn, 0x87)

DW_AT_DUP (DW_AT_lo_user, 0x2000) /* Implementation-defined range start. */
DW_AT_DUP (DW_AT_hi_user, 0x3fff) /* Implementation-defined range end. */
--
1.8.3.1