* [PATCH v2 1/1] gdb, fortran: Fix local variable lookup in Fortran parser
2026-04-30 16:29 [PATCH v2 0/1] gdb, fortran: Fix local variable lookup in Fortran parser Abdul Basit Ijaz
@ 2026-04-30 16:29 ` Abdul Basit Ijaz
2026-05-01 17:47 ` Kevin Buettner
0 siblings, 1 reply; 4+ messages in thread
From: Abdul Basit Ijaz @ 2026-04-30 16:29 UTC (permalink / raw)
To: gdb-patches; +Cc: abdul.b.ijaz, tom, kevinb
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
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