[V3] symlookup: improves symbol lookup when a file is specified.

Message ID 1508313474-19916-1-git-send-email-walfred.tedeschi@intel.com
State New, archived
Headers

Commit Message

Walfred Tedeschi Oct. 18, 2017, 7:57 a.m. UTC
  The provided patch adds a scope lookup with higher priority in the case a
a file is provided for the evaluation.

Usual symbol lookup from GDB follows linker logic.  This is what is
desired most of the time.  In the usage case presented a full qualified
scope is provided, so the lookup has to follow this priority.  Failing in
finding the symbol at this scope usual path is followed.

As use and test case it is presented two shared objects having a global
variable with the same name but comming from different source files.
Without the patch evaluating those variables providing the file scope
returns the wrong value;  It returns the value seen in the first loaded
shared object. Using the patch the value defined in the file scope is
the one returned.

One of the already existing test cases in print-file-var.exp starts to
fail after aplying this patch.  In fact the value that the linker
sees is different then the one debugger can read from the shared object.
In this sense it looks like to me that the test has to be changed.
The fail is in the call:
  print 'print-file-var-lib2.c'::this_version_id == v2

During load of the libraries linker resolves the symbol as the first one
loaded and independent of the scope the symbol will have the same value,
as defined in the first library loaded.
However, when defining the scope the value should represent the value
in that context. Diferent evaluations of the same symbols might also better
spot the issue in users code.

- I haven't changed the test because I wanted to hear the community
thought on the subject.



2017-10-18  Walfred Tedeschi  <walfred.tedeschi@intel.com>

gdb/ChangeLog:

	* symtab.c (lookup_global_symbol): Add new lookup to ensure
	priority on given block.

gdb/testsuite/ChangeLog:

	* gdb.base/print-file-var-dlopen-main.c: New file.
	* gdb.base/print-file-var-dlopen.exp: New test based on
	print-file-var.exp.
	* gdb.base/print-file-var-dlopen-lib1.c: New file.
	* gdb.base/print-file-var-dlopen-lib2.c: New file.


---
 gdb/symtab.c                                       |  4 +
 .../gdb.base/print-file-var-dlopen-lib1.c          | 25 ++++++
 .../gdb.base/print-file-var-dlopen-lib2.c          | 25 ++++++
 .../gdb.base/print-file-var-dlopen-main.c          | 61 +++++++++++++++
 gdb/testsuite/gdb.base/print-file-var-dlopen.exp   | 90 ++++++++++++++++++++++
 5 files changed, 205 insertions(+)
 create mode 100644 gdb/testsuite/gdb.base/print-file-var-dlopen-lib1.c
 create mode 100644 gdb/testsuite/gdb.base/print-file-var-dlopen-lib2.c
 create mode 100644 gdb/testsuite/gdb.base/print-file-var-dlopen-main.c
 create mode 100644 gdb/testsuite/gdb.base/print-file-var-dlopen.exp
  

Patch

diff --git a/gdb/symtab.c b/gdb/symtab.c
index 16a6b2e..a2c307f 100644
--- a/gdb/symtab.c
+++ b/gdb/symtab.c
@@ -2589,6 +2589,10 @@  lookup_global_symbol (const char *name,
   if (objfile != NULL)
     result = solib_global_lookup (objfile, name, domain);
 
+  /* We still need to look on the global scope of current object file.  */
+  if (result.symbol == NULL && objfile != NULL)
+    result = lookup_symbol_in_objfile (objfile, GLOBAL_BLOCK, name, domain);
+
   /* If that didn't work go a global search (of global blocks, heh).  */
   if (result.symbol == NULL)
     {
diff --git a/gdb/testsuite/gdb.base/print-file-var-dlopen-lib1.c b/gdb/testsuite/gdb.base/print-file-var-dlopen-lib1.c
new file mode 100644
index 0000000..09ec947
--- /dev/null
+++ b/gdb/testsuite/gdb.base/print-file-var-dlopen-lib1.c
@@ -0,0 +1,25 @@ 
+/* This testcase is part of GDB, the GNU debugger.
+   Copyright 2012-2017 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 this_version_id = 104;
+
+int
+get_version (void)
+{
+  static int test;
+  test = this_version_id;
+  return test;
+}
diff --git a/gdb/testsuite/gdb.base/print-file-var-dlopen-lib2.c b/gdb/testsuite/gdb.base/print-file-var-dlopen-lib2.c
new file mode 100644
index 0000000..b097cd2
--- /dev/null
+++ b/gdb/testsuite/gdb.base/print-file-var-dlopen-lib2.c
@@ -0,0 +1,25 @@ 
+/* This testcase is part of GDB, the GNU debugger.
+   Copyright 2012-2017 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 this_version_id = 203;
+
+int
+get_version (void)
+{
+  static int test;
+  test = this_version_id;
+  return test;
+}
diff --git a/gdb/testsuite/gdb.base/print-file-var-dlopen-main.c b/gdb/testsuite/gdb.base/print-file-var-dlopen-main.c
new file mode 100644
index 0000000..954a64e
--- /dev/null
+++ b/gdb/testsuite/gdb.base/print-file-var-dlopen-main.c
@@ -0,0 +1,61 @@ 
+/* This testcase is part of GDB, the GNU debugger.
+   Copyright 2017 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 <dlfcn.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+int
+dummy (void)
+{
+  return 1;
+}
+
+int
+main (void)
+{
+  int (*get_version1) (void);
+  int (*get_version2) (void);
+  int v1, v2;
+
+  void *lib1 = dlopen ("print-file-var-dlopen-lib1.so", RTLD_LAZY);
+  void *lib2 = dlopen ("print-file-var-dlopen-lib2.so", RTLD_LAZY);
+
+  if (lib1 == NULL || lib2 == NULL)
+    return 1;
+
+  *(int **) (&get_version1) = dlsym (lib1, "get_version");
+  *(int **) (&get_version2) = dlsym (lib2, "get_version");
+
+  if (get_version1 != NULL
+      && get_version2 != NULL)
+    {
+      v1 = get_version1();
+      v2 = get_version2();
+    }
+
+
+  if (v1 != 104 || v2 != 203)
+    return 1;
+
+  dummy (); /* STOP  */
+
+  dlclose (lib1);
+  dlclose (lib2);
+
+  return 0;
+}
+
diff --git a/gdb/testsuite/gdb.base/print-file-var-dlopen.exp b/gdb/testsuite/gdb.base/print-file-var-dlopen.exp
new file mode 100644
index 0000000..9c3c0e6
--- /dev/null
+++ b/gdb/testsuite/gdb.base/print-file-var-dlopen.exp
@@ -0,0 +1,90 @@ 
+# Copyright 2017 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/>.  */
+
+if {[skip_shlib_tests]} {
+    return 0
+}
+
+set executable print-file-var-dlopen-main
+
+set lib1 "print-file-var-dlopen-lib1"
+set lib2 "print-file-var-dlopen-lib2"
+set libsrc1 $srcdir/$subdir/${lib1}.c
+set libsrc2 $srcdir/$subdir/${lib2}.c
+set libobj1 [standard_output_file ${lib1}.so]
+set libobj2 [standard_output_file ${lib2}.so]
+set lib_dlopen1 [shlib_target_file ${libobj1}]
+set lib_dlopen2 [shlib_target_file ${libobj2}]
+
+set srcfile $srcdir/$subdir/$executable.c
+set binfile [standard_output_file $executable]
+set shlibdir [standard_output_file {}]
+
+set lib_opts debug
+set exec_opts [list debug shlib_load additional_flags=-DSHLIB_NAME=\"${lib_dlopen1}\" \
+additional_flags=-DSHLIB_NAME2=\"${lib_dlopen2}\"]
+
+if { [gdb_compile_shlib $libsrc1 $libobj1 $lib_opts] != ""
+     || [gdb_compile_shlib $libsrc2 $libobj2 $lib_opts] != ""
+     || [gdb_compile $srcfile $binfile executable $exec_opts] != ""} {
+    untested "failed to compile"
+    return -1
+}
+
+clean_restart $executable
+
+if ![runto_main] {
+    untested "could not run to main"
+    return -1
+}
+
+# Create to shared libraries having the symbol "this_version_id" defined in both
+# libraries global scope.  Main program will dllopen one by one and evaluate the
+# symbol "this_version_id" via a function provided by the library assigning the value of
+# "this_version_id" to V1 and V2.
+# Using the scope to perform the evaluations should return the value
+# defined in the c file.
+
+# To avoid adding target-specific code in this testcase, the program
+# sets two local variable named 'v1' and 'v2' with the value of
+# our global variables.  This allows us to compare the value that
+# GDB returns for each query against the actual value seen by
+# the program itself.
+
+# Get past the initialization of variables 'v1' and 'v2'.
+
+set bp_location \
+    [gdb_get_line_number "STOP" "${executable}.c"]
+gdb_test "break $executable.c:$bp_location" \
+         "Breakpoint \[0-9\]+ at 0x\[0-9a-fA-F\]+: .*" \
+         "breapoint past v1 & v2 initialization"
+
+gdb_continue_to_breakpoint "continue to the STOP"
+
+# Now check the value of this_version_id in both print-file-var-lib1.c
+# and print-file-var-lib2.c.
+
+gdb_test "print 'print-file-var-dlopen-lib1.c'::this_version_id == v1" \
+         " = 1"
+
+gdb_test "print 'print-file-var-dlopen-lib2.c'::this_version_id == v2" \
+         " = 1"
+
+gdb_test "print 'print-file-var-dlopen-lib2.c'::get_version::test == v2" \
+         " = 1"
+
+gdb_test "print 'print-file-var-dlopen-lib1.c'::get_version::test == v1" \
+         " = 1"
+