[gdb/symtab] Store external var decls in psymtab

Consider a test-case consisting of source file test.c:
...
extern int aaa;
int
main (void)
{
  return 0;
}
...
and test-2.c:
...
int aaa = 33;
...
compiled with debug info only for test.c:
...
$ gcc -c test.c -g; gcc -c test2.c; gcc test.o test2.o -g
...

When trying to print aaa, we get:
...
$ gdb -batch a.out -ex "print aaa"
'aaa' has unknown type; cast it to its declared type
...
but with -readnow we have:
...
$ gdb -readnow -batch a.out -ex "print aaa"
$1 = 33
...

In the -readnow case, the symbol for aaa in the full symtab has
LOC_UNRESOLVED, and the symbol type is combined with the minimal symbol
address, to read the value and print it without cast.

Without the -readnow, we create partial symbols, but the aaa decl is missing
from the partial symtabs, so we find it only in the minimal symbols, resulting
in the cast request.  If the aaa decl would have been in the partial symtabs,
it would have been found, and the full symtab would have been expanded, after
which things would be as with -readnow.

The function add_partial_symbol has a comment on the LOC_UNRESOLVED +
minimal symbol addres construct at DW_TAG_variable handling:
...
      else if (pdi->is_external)
	{
	  /* Global Variable.
	     Don't enter into the minimal symbol tables as there is
	     a minimal symbol table entry from the ELF symbols already.
	     Enter into partial symbol table if it has a location
	     descriptor or a type.
	     If the location descriptor is missing, new_symbol will create
	     a LOC_UNRESOLVED symbol, the address of the variable will then
	     be determined from the minimal symbol table whenever the variable
	     is referenced.
...
but it's not triggered due to this test in scan_partial_symbols:
...
            case DW_TAG_variable:
	    ...
              if (!pdi->is_declaration)
                {
                  add_partial_symbol (pdi, cu);
                }
...

Fix this in scan_partial_symbols by allowing external variable decls to be
added to the partial symtabs.

Build and reg-tested on x86_64-linux.

The patch caused this regression:
...
(gdb) print a_thread_local^M
Cannot find thread-local storage for process 0, executable file tls/tls:^M
Cannot find thread-local variables on this target^M
(gdb) FAIL: gdb.threads/tls.exp: print a_thread_local
...
while without the patch we have:
...
(gdb) print a_thread_local^M
Cannot read `a_thread_local' without registers^M
(gdb) PASS: gdb.threads/tls.exp: print a_thread_local
...

However, without the patch but with -readnow we have the same FAIL as with the
patch (filed as PR25807).  In other words, the patch has the effect that we
get the same result with and without -readnow.

This can be explained as follows.  Without the patch, and without -readnow, we
have two a_thread_locals, the def and the decl:
...
$ gdb -batch outputs/gdb.threads/tls/tls \
    -ex "maint expand-symtabs" \
    -ex "print a_thread_local" \
    -ex "maint print symbols" \
    | grep "a_thread_local;"
Cannot read `a_thread_local' without registers
 int a_thread_local; computed at runtime
 int a_thread_local; unresolved
...
while without the patch and with -readnow, we have the opposite order:
...
$ gdb -readnow -batch outputs/gdb.threads/tls/tls  \
    -ex "maint expand-symtabs" \
    -ex "print a_thread_local" \
    -ex "maint print symbols" \
    | grep "a_thread_local;"
Cannot find thread-local storage for process 0, executable file tls/tls:
Cannot find thread-local variables on this target
 int a_thread_local; unresolved
 int a_thread_local; computed at runtime
...

With the patch we have the same order with and without -readnow, but just a
different one than before without -readnow.

Mark the "Cannot find thread-local variables on this target" variant a PR25807
kfail.

gdb/ChangeLog:

2020-04-22  Tom de Vries  <tdevries@suse.de>

	PR symtab/25764
	* dwarf2/read.c (scan_partial_symbols): Allow external variable decls
	in psymtabs.

gdb/testsuite/ChangeLog:

2020-04-22  Tom de Vries  <tdevries@suse.de>

	PR symtab/25764
	* gdb.base/psym-external-decl-2.c: New test.
	* gdb.base/psym-external-decl.c: New test.
	* gdb.base/psym-external-decl.exp: New file.
	* gdb.threads/tls.exp: Add PR25807 kfail.

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index fdafdb99db4d748b97dd378115016b6ff20e6cbb..c4b92762330e40bed78a45d5d5f9ee108b4e2a1b 100644 (file)
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,9 @@
+2020-04-22  Tom de Vries  <tdevries@suse.de>
+
+       PR symtab/25764
+       * dwarf2/read.c (scan_partial_symbols): Allow external variable decls
+       in psymtabs.
+
 2020-04-22  Tom de Vries  <tdevries@suse.de>
 
        PR symtab/25801

diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index 450c53b519643efdf6d21a6b4595ebf172c95e48..c2a9103510f0ff7c7e108e12922a1b3fd9ec74ba 100644 (file)
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -7951,7 +7951,8 @@ scan_partial_symbols (struct partial_die_info *first_die, CORE_ADDR *lowpc,
            case DW_TAG_variable:
            case DW_TAG_typedef:
            case DW_TAG_union_type:
-             if (!pdi->is_declaration)
+             if (!pdi->is_declaration
+                 || (pdi->tag == DW_TAG_variable && pdi->is_external))
                {
                  add_partial_symbol (pdi, cu);
                }

diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 1331fe5248b29621ca9656996aeea0c05e6d6ede..a81c37fe7800c6a40968a010939d00eb49fc1058 100644 (file)
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,11 @@
+2020-04-22  Tom de Vries  <tdevries@suse.de>
+
+       PR symtab/25764
+       * gdb.base/psym-external-decl-2.c: New test.
+       * gdb.base/psym-external-decl.c: New test.
+       * gdb.base/psym-external-decl.exp: New file.
+       * gdb.threads/tls.exp: Add PR25807 kfail.
+
 2020-04-22  Tom de Vries  <tdevries@suse.de>
 
        PR symtab/25801

diff --git a/gdb/testsuite/gdb.base/psym-external-decl-2.c b/gdb/testsuite/gdb.base/psym-external-decl-2.c
new file mode 100644 (file)
index 0000000..76e0587
--- /dev/null
+++ b/gdb/testsuite/gdb.base/psym-external-decl-2.c
@@ -0,0 +1,18 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2020 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 aaa = 33;

diff --git a/gdb/testsuite/gdb.base/psym-external-decl.c b/gdb/testsuite/gdb.base/psym-external-decl.c
new file mode 100644 (file)
index 0000000..7a4b107
--- /dev/null
+++ b/gdb/testsuite/gdb.base/psym-external-decl.c
@@ -0,0 +1,25 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2020 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/>.  */
+
+extern int aaa;
+
+int
+main (void)
+{
+  return 0;
+}
+

diff --git a/gdb/testsuite/gdb.base/psym-external-decl.exp b/gdb/testsuite/gdb.base/psym-external-decl.exp
new file mode 100644 (file)
index 0000000..bbcc274
--- /dev/null
+++ b/gdb/testsuite/gdb.base/psym-external-decl.exp
@@ -0,0 +1,30 @@
+# Copyright 2020 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 psym-external-decl-2.c
+
+set srcfiles [list $srcfile $srcfile2]
+
+if { [build_executable_from_specs \
+         "failed to prepare" \
+         $testfile [list] \
+         $srcfile [list debug] \
+         $srcfile2 [list]] == -1 } {
+    return -1
+}
+
+clean_restart $testfile
+
+gdb_test "print aaa" " = 33"

diff --git a/gdb/testsuite/gdb.threads/tls.exp b/gdb/testsuite/gdb.threads/tls.exp
index fca5fa6db230422c735ff7b35e0fac755cebf9aa..8147a6c132737cce3c60f666e63a5733194d248c 100644 (file)
--- a/gdb/testsuite/gdb.threads/tls.exp
+++ b/gdb/testsuite/gdb.threads/tls.exp
@@ -153,8 +153,14 @@ proc check_thread_stack {number spin_threads spin_threads_level} {
 
 clean_restart ${binfile}
 
-gdb_test "print a_thread_local" \
-    "Cannot read .a_thread_local. without registers"
+gdb_test_multiple "print a_thread_local" "" {
+    -re -wrap "Cannot find thread-local variables on this target" {
+       kfail "gdb/25807" $gdb_test_name
+    }
+    -re -wrap "Cannot read .a_thread_local. without registers" {
+       pass $gdb_test_name
+    }
+}
 
 if ![runto_main] then {
    fail "can't run to main"