[PATCH] gdb/python: smarter symbol lookup for gdb.lookup_static_symbol

Andrew Burgess
2019-09-23T16:46:49Z

When using gdb.lookup_static_symbol I think that GDB should find
static symbols (global symbol with static linkage) from the current
object file ahead of static symbols from other object files.

This means that if we have two source files f1.c and f2.c, and both
files contains 'static int foo;', then when we are stopped in f1.c a
call to 'gdb.lookup_static_symbol ("foo")' will find f1.c::foo, and if
we are stopped in f2.c we would find 'f2.c::foo'.

Given that gdb.lookup_static_symbol always returns a single symbol,
but there can be multiple static symbols with the same name GDB is
always making a choice about which symbols to return. I think that it
makes sense for the choice GDB makes in this case to match what a user
would get on the command line if they asked to 'print foo'.

gdb/testsuite/ChangeLog:

* gdb.python/py-symbol.c: Declare and call function from new
py-symbol-2.c file.
* gdb.python/py-symbol.exp: Compile both source files, and add new
tests for gdb.lookup_static_symbol.
* gdb.python/py-symbol-2.c: New file.

gdb/doc/ChangeLog:

* python.texi (Symbols In Python): Extend documentation for
gdb.lookup_static_symbol.

gdb/ChangeLog:

* python/py-symbol.c (gdbpy_lookup_static_symbol): Lookup in
static block of current object file first.
---
gdb/ChangeLog | 5 +++++
gdb/doc/ChangeLog | 5 +++++
gdb/doc/python.texi | 8 ++++++++
gdb/python/py-symbol.c | 25 +++++++++++++++++++++++-
gdb/testsuite/ChangeLog | 8 ++++++++
gdb/testsuite/gdb.python/py-symbol-2.c | 26 +++++++++++++++++++++++++
gdb/testsuite/gdb.python/py-symbol.c | 9 +++++++++
gdb/testsuite/gdb.python/py-symbol.exp | 35 ++++++++++++++++++++++------------
8 files changed, 108 insertions(+), 13 deletions(-)
create mode 100644 gdb/testsuite/gdb.python/py-symbol-2.c

diff --git a/gdb/doc/python.texi b/gdb/doc/python.texi
index 832283dede8..12f169afa78 100644
--- a/gdb/doc/python.texi
+++ b/gdb/doc/python.texi
@@ -4869,6 +4869,14 @@
up such variables, iterate over the variables of the function's
@code{gdb.Block} and check that @code{block.addr_class} is
@code{gdb.SYMBOL_LOC_STATIC}.
+
+There can be multiple global symbols with static linkage with the same
+name. This function will only return the first matching symbol that
+it finds. Which symbol is found depends on where @value{GDBN} is
+currently stopped, as @value{GDBN} will first search for matching
+symbols in the current object file, and then search all other object
+files. If the application is not yet running then @value{GDBN} will
+search all object files.
@end defun

A @code{gdb.Symbol} object has the following attributes:
diff --git a/gdb/python/py-symbol.c b/gdb/python/py-symbol.c
index 2b10e21d872..ae9aca6c5d0 100644
--- a/gdb/python/py-symbol.c
+++ b/gdb/python/py-symbol.c
@@ -487,9 +487,32 @@ gdbpy_lookup_static_symbol (PyObject *self, PyObject *args, PyObject *kw)
&domain))
return NULL;

+ /* In order to find static symbols associated with the "current" object
+ file ahead of those from other object files, we first need to see if
+ we can acquire a current block. If this fails however, then we still
+ want to search all static symbols, so don't throw an exception just
+ yet. */
+ const struct block *block = NULL;
try
{
- symbol = lookup_static_symbol (name, (domain_enum) domain).symbol;
+ struct frame_info *selected_frame
+ = get_selected_frame (_("No frame selected."));
+ block = get_frame_block (selected_frame, NULL);
+ }
+ catch (const gdb_exception &except)
+ {
+ /* Nothing. */
+ }
+
+ try
+ {
+ if (block != nullptr)
+ symbol
+ = lookup_symbol_in_static_block (name, block,
+ (domain_enum) domain).symbol;
+
+ if (symbol == nullptr)
+ symbol = lookup_static_symbol (name, (domain_enum) domain).symbol;
}
catch (const gdb_exception &except)
{
diff --git a/gdb/testsuite/gdb.python/py-symbol-2.c b/gdb/testsuite/gdb.python/py-symbol-2.c
new file mode 100644
index 00000000000..12872efe4b7
--- /dev/null
+++ b/gdb/testsuite/gdb.python/py-symbol-2.c
@@ -0,0 +1,26 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+ Copyright 2010-2019 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/>. */
+
+static int rr = 99; /* line of other rr */
+
+void
+function_in_other_file (void)
+{
+ /* Nothing. */
+}
+
+
diff --git a/gdb/testsuite/gdb.python/py-symbol.c b/gdb/testsuite/gdb.python/py-symbol.c
index 06a931bf5d9..51325dcd450 100644
--- a/gdb/testsuite/gdb.python/py-symbol.c
+++ b/gdb/testsuite/gdb.python/py-symbol.c
@@ -38,6 +38,10 @@ namespace {
};
#endif

+#ifdef USE_TWO_FILES
+extern void function_in_other_file (void);
+#endif
+
int qq = 72; /* line of qq */
static int rr = 42; /* line of rr */

@@ -70,5 +74,10 @@ int main (int argc, char *argv[])
sclass.seti (42);
sclass.valueofi ();
#endif
+
+#ifdef USE_TWO_FILES
+ function_in_other_file ();
+#endif
+
return 0; /* Break at end. */
}
diff --git a/gdb/testsuite/gdb.python/py-symbol.exp b/gdb/testsuite/gdb.python/py-symbol.exp
index 5617f127e5b..296845783b1 100644
--- a/gdb/testsuite/gdb.python/py-symbol.exp
+++ b/gdb/testsuite/gdb.python/py-symbol.exp
@@ -18,9 +18,11 @@

load_lib gdb-python.exp

-standard_testfile
+standard_testfile py-symbol.c py-symbol-2.c

-if {[prepare_for_testing "failed to prepare" $testfile $srcfile debug]} {
+set opts { debug additional_flags=-DUSE_TWO_FILES }
+if {[prepare_for_testing "failed to prepare" $testfile \
+ [list $srcfile $srcfile2] $opts]} {
return -1
}

@@ -48,6 +50,7 @@ gdb_test "python print (gdb.lookup_global_symbol('qq').needs_frame)" \
"False" \
"print whether qq needs a frame"

+# Similarly, test looking up a static symbol before we runto_main.
set rr_line [gdb_get_line_number "line of rr"]
gdb_test "python print (gdb.lookup_global_symbol ('rr') is None)" "True" \
"lookup_global_symbol for static var"
@@ -100,10 +103,23 @@ gdb_test "python print (func.print_name)" "func" "test func.print_name"
gdb_test "python print (func.linkage_name)" "func" "test func.linkage_name"
gdb_test "python print (func.addr_class == gdb.SYMBOL_LOC_BLOCK)" "True" "test func.addr_class"

-gdb_breakpoint [gdb_get_line_number "Break at end."]
+# Stop in a second file and ensure we find its local static symbol.
+gdb_breakpoint "function_in_other_file"
+gdb_continue_to_breakpoint "function_in_other_file"
+gdb_test "python print (gdb.lookup_static_symbol ('rr').value ())" "99" \
+ "print value of rr from other file"
+
+# Now continue back to the first source file.
+set linenum [gdb_get_line_number "Break at end."]
+gdb_breakpoint "$srcfile:$linenum"
gdb_continue_to_breakpoint "Break at end for variable a" ".*Break at end.*"
gdb_py_test_silent_cmd "python frame = gdb.selected_frame()" "Get Frame" 0

+# Check that we find the static sybol local to this file over the
+# static symbol from the second source file.
+gdb_test "python print (gdb.lookup_static_symbol ('rr').value ())" "42" \
+ "print value of rr from main file"
+
# Test is_variable attribute.
gdb_py_test_silent_cmd "python a = gdb.lookup_symbol(\'a\')" "Get variable a" 0
gdb_test "python print (a\[0\].is_variable)" "True" "test a.is_variable"
@@ -145,17 +161,12 @@ gdb_test "python print (t\[0\].symtab)" "${py_symbol_c}" "get symtab"

# C++ tests
# Recompile binary.
-if { [gdb_compile "${srcdir}/${subdir}/${srcfile}" "${binfile}-cxx" executable "debug c++"] != "" } {
- untested "failed to compile in C++ mode"
+lappend opts { c++ }
+if {[prepare_for_testing "failed to prepare" "${binfile}-cxx" \
+ [list $srcfile $srcfile2] $opts]} {
return -1
}

-# Start with a fresh gdb.
-gdb_exit
-gdb_start
-gdb_reinitialize_dir $srcdir/$subdir
-gdb_load ${binfile}-cxx
-
gdb_test "python print (gdb.lookup_global_symbol ('(anonymous namespace)::anon') is None)" \
"True" "anon is None"
gdb_test "python print (gdb.lookup_static_symbol ('(anonymous namespace)::anon').value ())" \
@@ -189,7 +200,7 @@ gdb_test "python print (cplusfunc.addr_class == gdb.SYMBOL_LOC_BLOCK)" "True" "t
# Test is_valid when the objfile is unloaded. This must be the last
# test as it unloads the object file in GDB.
# Start with a fresh gdb.
-clean_restart ${testfile}
+clean_restart ${binfile}
if ![runto_main] then {
fail "cannot run to main."
return 0
--
2.14.5