[PATCH][gdb/exp] Fix printing of type of optimized out vla

Tom de Vries
2018-07-03T14:18:29Z

Hi,

Consider this snippet from gcc/testsuite/gcc.dg/guality/vla-1.c:
...
int __attribute__((noinline))
f1 (int i)
{
char a[i + 1];
a[0] = 5; /* { dg-final { gdb-test .+1 "i" "5" } } */
return a[0]; /* { dg-final { gdb-test . "sizeof (a)" "6" } } */
}
...

When we compile the test-case with -O1 -g, and query the size of optimized
out vla 'a', we get:
...
$ ./gdb -batch -ex "b f1" -ex "r" -ex "p sizeof (a)" vla-1.exe
Breakpoint 1 at 0x4004a8: file vla-1.c, line 17.

Breakpoint 1, f1 (i=i@entry=5) at vla-1.c:17
17 return a[0];
$1 = 0
...
while we expect a size of '6'.

The problem is that default_read_var_value does not resolve the dynamic type
of a variable if the variable is optimized out.

This patch fixes that, and consequently gdb prints '6', as expected.

Tested on x86_64-linux.

OK for trunk?

Thanks,
- Tom

[gdb/exp] Fix printing of type of optimized out vla

2018-07-03 Tom de Vries <tdevries@suse.de>

* findvar.c (default_read_var_value): Also resolve dynamic type for
LOC_OPTIMIZED_OUT vars.

* gdb.base/vla-optimized-out.c: New test.
* gdb.base/vla-optimized-out.exp: New file.

---
gdb/findvar.c | 2 ++
gdb/testsuite/gdb.base/vla-optimized-out.c | 34 +++++++++++++++++++++++
gdb/testsuite/gdb.base/vla-optimized-out.exp | 40 ++++++++++++++++++++++++++++
3 files changed, 76 insertions(+)

diff --git a/gdb/findvar.c b/gdb/findvar.c
index 8ad5e25cb2..ebaff923a1 100644
--- a/gdb/findvar.c
+++ b/gdb/findvar.c
@@ -789,6 +789,8 @@ default_read_var_value (struct symbol *var, const struct block *var_block,
break;

case LOC_OPTIMIZED_OUT:
+ if (is_dynamic_type (type))
+ type = resolve_dynamic_type (type, NULL, /* Unused address. */ 0);
return allocate_optimized_out_value (type);

default:
diff --git a/gdb/testsuite/gdb.base/vla-optimized-out.c b/gdb/testsuite/gdb.base/vla-optimized-out.c
new file mode 100644
index 0000000000..913e8ea867
--- /dev/null
+++ b/gdb/testsuite/gdb.base/vla-optimized-out.c
@@ -0,0 +1,34 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+ Copyright 2018 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/>. */
+
+int __attribute__((noinline, noclone))
+f1 (int i)
+{
+ char a[i + 1];
+ a[0] = 5;
+ return a[0];
+}
+
+int
+main (void)
+{
+ volatile int j;
+ int i = 5;
+ asm volatile ("" : "=r" (i) : "0" (i));
+ j = f1 (i);
+ return 0;
+}
diff --git a/gdb/testsuite/gdb.base/vla-optimized-out.exp b/gdb/testsuite/gdb.base/vla-optimized-out.exp
new file mode 100644
index 0000000000..39abb795c8
--- /dev/null
+++ b/gdb/testsuite/gdb.base/vla-optimized-out.exp
@@ -0,0 +1,40 @@
+# Copyright 2018 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/>.
+
+# Check whether we can determine the size of an optimized-out vla.
+
+standard_testfile
+
+if { [prepare_for_testing "failed to prepare" $testfile $srcfile \
+ {debug optimize=-O1}] } {
+ return -1
+}
+
+proc vla_optimized_out { } {
+ if ![runto f1] {
+ fail "can't run to f1"
+ return
+ }
+
+ gdb_test "p a" \
+ { = <optimized out>} \
+ "printed optimized out vla"
+
+ gdb_test "p sizeof (a)" \
+ { = 6} \
+ "printed size of optimized out vla"
+}
+
+vla_optimized_out