[PATCH v2 0/1] gdb, fortran: Fix local variable lookup in Fortran parser

[PATCH v2 0/1] gdb, fortran: Fix local variable lookup in Fortran parser

[Abdul Basit Ijaz]

This change fixes https://sourceware.org/bugzilla/show_bug.cgi?id=34059.

The Fortran expression parser in GDB ("gdb/f-exp.y") previously performed
symbol lookup in this order when parsing identifiers:

- SEARCH_STRUCT_DOMAIN (types/structs)
- SEARCH_VFT ("C-like" name lookups for variables/types/functions)
- SEARCH_MODULE_DOMAIN (modules)

It searched for "types before variables", causing type names from shared
libraries to shadow local variable names.

This issue is fixed in the Fortran expression parser in GDB ("gdb/f-exp.y")
by prioritizing SEARCH_VFT over other search domains during symbol lookup.

Changes since V1:
- Fix this feedback from Kevin:
 https://sourceware.org/pipermail/gdb-patches/2026-April/227028.html

Thanks & Best Regards,
Abdul Basit

Abdul Basit Ijaz (1):
  gdb, fortran: Fix local variable lookup in Fortran parser

 gdb/f-exp.y                                   |  2 +-
 .../gdb.fortran/var-type-precedence-lib.c     | 30 ++++++++++
 .../gdb.fortran/var-type-precedence.exp       | 60 +++++++++++++++++++
 .../gdb.fortran/var-type-precedence.f90       | 40 +++++++++++++
 4 files changed, 131 insertions(+), 1 deletion(-)
 create mode 100644 gdb/testsuite/gdb.fortran/var-type-precedence-lib.c
 create mode 100644 gdb/testsuite/gdb.fortran/var-type-precedence.exp
 create mode 100644 gdb/testsuite/gdb.fortran/var-type-precedence.f90

-- 
2.34.1

Intel Deutschland GmbH
Registered Address: Dornacher Strasse 1, 85622 Feldkirchen, Germany
Tel: +49 89 991 430, www.intel.de
Managing Directors: Harry Demas, Jeffrey Schneiderman, Yin Chong Sorrell
Chairperson of the Supervisory Board: Nicole Lau
Registered Seat: Munich
Commercial Register: Amtsgericht Muenchen HRB 186928

[PATCH v2 1/1] gdb, fortran: Fix local variable lookup in Fortran parser

[Abdul Basit Ijaz]

This change fixes https://sourceware.org/bugzilla/show_bug.cgi?id=34059.

The Fortran expression parser in GDB ("gdb/f-exp.y") previously performed
symbol lookup in this order when parsing identifiers:

- SEARCH_STRUCT_DOMAIN (types/structs)
- SEARCH_VFT ("C-like" name lookups for variables/types/functions)
- SEARCH_MODULE_DOMAIN (modules)

It searched for "types before variables", causing type names from shared
libraries to shadow local variable names.

For a reproducer like the one given below, the Fortran parser fails to
look up local variable name "array" and treats it as a type value instead
of a variable, because there's a conflicting "array" type from system
libraries.

1 program test
2
3  ! Declare variables used in this test.
4  integer, dimension (-2:2) :: array
5
6  array = 1
7
8  print *, ""           ! Break here
9  print *, array
10
11 end program test

Before the change, GDB shows:

'''
./gdb --data-directory=./data-directory --args /tmp/a.out
GNU gdb (GDB) 18.0.50.20260408-git
Copyright (C) 2026 Free Software Foundation, Inc.
...
Reading symbols from /tmp/a.out...
(gdb) break 8
Breakpoint 1 at 0x11b3: file test.f90, line 8.
(gdb) run
Starting program: /tmp/a.out
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".

Breakpoint 1, test () at test.f90:8
8         print *, ""           ! Break here
(gdb) info locals
array = (1, 1, 1, 1, 1)
(gdb) print array
Attempt to use a type name as an expression
(gdb) ptype array
type = Type array
    Type, C_Union :: :: u
    PTR TO -> ( char :: scratch(0:15 ))
End Type array
'''

This issue is fixed in the Fortran expression parser in GDB ("gdb/f-exp.y")
by prioritizing SEARCH_VFT over other search domains during symbol lookup.
After the change, the 'array' variable is resolved to the correct value.

'''
(gdb) print array
$1 = (1, 1, 1, 1, 1)
(gdb) ptype array
type = integer(kind=4) (-2:2)
'''
---
 gdb/f-exp.y                                   |  2 +-
 .../gdb.fortran/var-type-precedence-lib.c     | 30 ++++++++++
 .../gdb.fortran/var-type-precedence.exp       | 60 +++++++++++++++++++
 .../gdb.fortran/var-type-precedence.f90       | 40 +++++++++++++
 4 files changed, 131 insertions(+), 1 deletion(-)
 create mode 100644 gdb/testsuite/gdb.fortran/var-type-precedence-lib.c
 create mode 100644 gdb/testsuite/gdb.fortran/var-type-precedence.exp
 create mode 100644 gdb/testsuite/gdb.fortran/var-type-precedence.f90

diff --git a/gdb/f-exp.y b/gdb/f-exp.y
index 278e2091403..4216112c10b 100644
--- a/gdb/f-exp.y
+++ b/gdb/f-exp.y
@@ -1651,8 +1651,8 @@ yylex (void)
     struct block_symbol result;
     const domain_search_flags lookup_domains[] =
     {
-      SEARCH_STRUCT_DOMAIN,
       SEARCH_VFT,
+      SEARCH_STRUCT_DOMAIN,
       SEARCH_MODULE_DOMAIN
     };
     int hextype;
diff --git a/gdb/testsuite/gdb.fortran/var-type-precedence-lib.c b/gdb/testsuite/gdb.fortran/var-type-precedence-lib.c
new file mode 100644
index 00000000000..87bd19fad84
--- /dev/null
+++ b/gdb/testsuite/gdb.fortran/var-type-precedence-lib.c
@@ -0,0 +1,30 @@
+/* Copyright 2026 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/>.  */
+
+/* Define a struct type that will conflict with Fortran variable name.  */
+struct type_shadowing_var
+{
+  int value;
+};
+
+/* Global variables to ensure types are in debug info.  */
+static struct type_shadowing_var global_conflicting_var = {42};
+
+/* Function to ensure library is linked and types are used.  */
+void
+fortran_var_type_order_test (void)
+{
+  global_conflicting_var.value = 42;
+}
diff --git a/gdb/testsuite/gdb.fortran/var-type-precedence.exp b/gdb/testsuite/gdb.fortran/var-type-precedence.exp
new file mode 100644
index 00000000000..8c9f80d43d9
--- /dev/null
+++ b/gdb/testsuite/gdb.fortran/var-type-precedence.exp
@@ -0,0 +1,60 @@
+# Copyright 2026 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/>.
+
+# Test variable lookup when local Fortran variable names conflict with
+# type names from a C shared library.
+
+require allow_fortran_tests
+
+standard_testfile var-type-precedence.f90 var-type-precedence-lib.c
+load_lib fortran.exp
+
+set libname "${testfile}-lib"
+set srcfile_lib ${srcdir}/${subdir}/${srcfile2}
+set binfile_lib [standard_output_file ${libname}.so]
+
+# Compile the C shared library.
+if {[gdb_compile_shlib ${srcfile_lib} ${binfile_lib} \
+	{debug}] != ""} {
+  untested "failed to compile C shared library"
+  return
+}
+
+# Compile the Fortran main program with the C shared library.
+if {[prepare_for_testing "failed to prepare" $testfile \
+	${srcfile} [list debug f90 shlib=${binfile_lib}]]} {
+  return
+}
+
+if {![fortran_runto_main]} {
+  return
+}
+
+set bp_loc [gdb_get_line_number "break-here"]
+gdb_breakpoint "$srcfile:$bp_loc"
+gdb_continue_to_breakpoint "stop-at-bp" ".*$srcfile:$bp_loc.*"
+
+set integer4 [fortran_int4]
+
+# Test that local variable 'type_shadowing_var' is resolved correctly.
+gdb_test "print type_shadowing_var" "= \\(1, 1, 1, 1, 1\\)" \
+    "print local type_shadowing_var variable"
+gdb_test "ptype type_shadowing_var" "type = $integer4 \\(-2:2\\)" \
+    "ptype local type_shadowing_var"
+
+# Verify the C types exist in debug info by checking info types.
+gdb_test "info types type_shadowing_var" \
+    ".*File.*var-type-precedence-lib\\.c:.*struct type_shadowing_var.*" \
+    "C type type_shadowing_var exists in debug info"
diff --git a/gdb/testsuite/gdb.fortran/var-type-precedence.f90 b/gdb/testsuite/gdb.fortran/var-type-precedence.f90
new file mode 100644
index 00000000000..d692018faba
--- /dev/null
+++ b/gdb/testsuite/gdb.fortran/var-type-precedence.f90
@@ -0,0 +1,40 @@
+! Copyright 2026 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/> .
+
+! Source code for var-type-precedence test to verify that local Fortran
+! variables take precedence over conflicting C type names from shared
+! libraries.
+
+program test
+  use iso_c_binding
+  implicit none
+
+  interface
+    subroutine fortran_var_type_order_test () bind (C)
+    end subroutine fortran_var_type_order_test
+  end interface
+
+  ! Declare variables with names that conflict with types in C library.
+  integer, dimension (-2:2) :: type_shadowing_var
+
+  ! Call C library function to ensure it's linked.
+  call fortran_var_type_order_test ()
+
+  type_shadowing_var = 1
+
+  print *, "" ! break-here
+  print *, type_shadowing_var
+
+end program test
-- 
2.34.1

Intel Deutschland GmbH
Registered Address: Dornacher Strasse 1, 85622 Feldkirchen, Germany
Tel: +49 89 991 430, www.intel.de
Managing Directors: Harry Demas, Jeffrey Schneiderman, Yin Chong Sorrell
Chairperson of the Supervisory Board: Nicole Lau
Registered Seat: Munich
Commercial Register: Amtsgericht Muenchen HRB 186928

Re: [PATCH v2 1/1] gdb, fortran: Fix local variable lookup in Fortran parser

[Kevin Buettner]

Hi Abdul,

One small nit, but otherwise it's okay...

On Thu, 30 Apr 2026 18:29:55 +0200
Abdul Basit Ijaz <abdul.b.ijaz@intel.com> wrote:

> +! along with this program.  If not, see <http://www.gnu.org/licenses/> .

In the above line, there's a stray space before the period at the
end of the line.

With that fixed...

Approved-by: Kevin Buettner <kevinb@redhat.com>

RE: [PATCH v2 1/1] gdb, fortran: Fix local variable lookup in Fortran parser

[Ijaz, Abdul B]

Thanks Kevin for the feedback.

>> +! along with this program.  If not, see <http://www.gnu.org/licenses/> .

Kevin>In the above line, there's a stray space before the period at the end of the line.

Abdul>I will fix it before merging.

Best Regards
Abdul Basit

-----Original Message-----
From: Kevin Buettner <kevinb@redhat.com> 
Sent: Friday, May 1, 2026 7:48 PM
To: gdb-patches@sourceware.org
Cc: Ijaz, Abdul B <abdul.b.ijaz@intel.com>
Subject: Re: [PATCH v2 1/1] gdb, fortran: Fix local variable lookup in Fortran parser

Hi Abdul,

One small nit, but otherwise it's okay...

On Thu, 30 Apr 2026 18:29:55 +0200
Abdul Basit Ijaz <abdul.b.ijaz@intel.com> wrote:

> +! along with this program.  If not, see <http://www.gnu.org/licenses/> .

In the above line, there's a stray space before the period at the end of the line.

With that fixed...

Approved-by: Kevin Buettner <kevinb@redhat.com>

Intel Deutschland GmbH
Registered Address: Dornacher Strasse 1, 85622 Feldkirchen, Germany
Tel: +49 89 991 430, www.intel.de
Managing Directors: Harry Demas, Jeffrey Schneiderman, Yin Chong Sorrell
Chairperson of the Supervisory Board: Nicole Lau
Registered Seat: Munich
Commercial Register: Amtsgericht Muenchen HRB 186928