Fix regression introduced in "break *<EXPR>" by explicit location patches.

A relatively recent patch support for explicit locations, and part
of that patch cleaned up the way we parse breakpoint locations.
Unfortunatly, a small regression crept in for "*<EXPR>" breakpoint
locations. In particular, on PIE programs, one can see the issue by
doing the following, with any program:

    (gdb) b *main
    Breakpoint 1 at 0x51a: file hello.c, line 3.
    (gdb) run
    Starting program: /[...]/hello
    Error in re-setting breakpoint 1: Warning:
    Cannot insert breakpoint 1.
    Cannot access memory at address 0x51a

    Warning:
    Cannot insert breakpoint 1.
    Cannot access memory at address 0x51a

Just for the record, this regression was introduced by:

    commit a06efdd6effd149a1d392df8d62824e44872003a
    Date:   Tue Aug 11 17:09:35 2015 -0700
    Subject: Explicit locations: introduce address locations

What happens is that the patch makes the implicit assumption that
the address computed the first time is static, as if it was designed
to only support litteral expressions (Eg. "*0x1234"). This allows
the shortcut of not re-computing the breakpoint location's address
when re-setting breakpoints.

However, this does not work in general, as demonstrated in the example
above.

This patch plugs that hole simply by saving the original expression
used to compute the address as part of the address location, so as
to then re-evaluate that expression during breakpoint re-set.

gdb/ChangeLog:

        * location.h (new_address_location): Add new parameters
        "addr_string" and "addr_string_len".
        (get_address_string_location): Add declaration.
        * location.c (new_address_location): Add new parameters
        "addr_string" and "addr_string_len".  If not NULL, store
        a copy of the addr_string in the new location as well.
        (get_address_string_location): New function.
        (string_to_event_location): Update call to new_address_location.
        * linespec.c (event_location_to_sals) <ADDRESS_LOCATION>:
        Save the event location in the parser's state before
        passing it to convert_address_location_to_sals.
        * breakpoint.c (create_thread_event_breakpoint): Update call
        to new_address_location.
        (init_breakpoint_sal): Get the event location's string, if any,
        and use it to update call to new_address_location.
        * python/py-finishbreakpoint.c (bpfinishpy_init):
        Update call to new_address_location.
        * spu-tdep.c (spu_catch_start): Likewise.

        * config/djgpp/fnchange.lst: Add entries for
        gdb/testsuite/gdb.base/break-fun-addr1.c and
        gdb/testsuite/gdb.base/break-fun-addr2.c.

gdb/testsuite/ChangeLog:

        * gdb.base/break-fun-addr.exp: New file.
        * gdb.base/break-fun-addr1.c: New file.
        * gdb.base/break-fun-addr2.c: New file.

3 files changed, 134 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.base/break-fun-addr.exp b/gdb/testsuite/gdb.base/break-fun-addr.exp
new file mode 100644
index 0000000..e8bed3f
--- /dev/null
+++ b/gdb/testsuite/gdb.base/break-fun-addr.exp
@@ -0,0 +1,84 @@
+# Copyright 2016 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/>.
+
+# The purpose of this testcase is to verify that, when using a breakpoint
+# location of the form "*<EXPR>" (Eg: "*main"), GDB is able to start
+# the program and stop at the correct location.  With programs built
+# as PIE, this means that GDB needs to re-evaluate the location once
+# the program as started, since PIE ensures that the address of all
+# symbols have changed after load.
+#
+# PIE is not always supported by the target system, so instead of
+# creating a testcase building executables with PIE, this testcase
+# takes a slightly different approach.  It builds a first program,
+# breaks on *main, and then runs to that breakpoint. It then builds
+# a second program, different from the first one, and loads that
+# executable within the same GDB session.  Similarly to the PIE case,
+# the address of main should be different, and therefore GDB should
+# recalculate it.  We verify that by checking that running to that
+# breakpoint still works, and that we land at the first instruction
+# of that function in both cases.
+
+set testfile1 "break-fun-addr1"
+set srcfile1 ${testfile1}.c
+set binfile1 [standard_output_file ${testfile1}]
+
+if  { [gdb_compile "${srcdir}/${subdir}/${srcfile1}" "${binfile1}" executable {debug}] != "" } {
+    untested "Couldn't compile ${srcfile1}"
+    return -1
+}
+
+# Start the debugger with the first executable, put a breakpoint
+# on the first instruction of function "main" ("*main"), then
+# run to that breakpoint.
+
+clean_restart ${binfile1}
+
+with_test_prefix "${binfile1}" {
+
+    gdb_test "break *main" \
+        "Breakpoint.*at.* file .*$srcfile1, line .*" \
+
+    gdb_run_cmd
+    gdb_test "" \
+             "Breakpoint.* main \\(\\) at .*$srcfile1:.*" \
+             "run to breakpoint at *main"
+
+    # Verify also that we stopped at the start of the function...
+    gdb_test "p \$pc == main" " = 1"
+}
+
+set testfile2 "break-fun-addr2"
+set srcfile2 ${testfile2}.c
+set binfile2 [standard_output_file ${testfile2}]
+
+if  { [gdb_compile "${srcdir}/${subdir}/${srcfile2}" "${binfile2}" executable {debug}] != "" } {
+    untested "Couldn't compile ${srcfile2}"
+    return -1
+}
+
+# Now, keeping the same GDB process (so as to keep the same breakpoint),
+# start a new debugging session with a different executable.
+gdb_load ${binfile2}
+
+with_test_prefix "${binfile2}" {
+
+    gdb_run_cmd
+    gdb_test "" \
+             "Breakpoint.* main \\(\\) at .*$srcfile2:.*" \
+             "run to breakpoint at *main"
+
+    gdb_test "p \$pc == main" " = 1"
+}
diff --git a/gdb/testsuite/gdb.base/break-fun-addr1.c b/gdb/testsuite/gdb.base/break-fun-addr1.c
new file mode 100644
index 0000000..1545b21
--- /dev/null
+++ b/gdb/testsuite/gdb.base/break-fun-addr1.c
@@ -0,0 +1,22 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2016 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
+main (void)
+{
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.base/break-fun-addr2.c b/gdb/testsuite/gdb.base/break-fun-addr2.c
new file mode 100644
index 0000000..13eec05
--- /dev/null
+++ b/gdb/testsuite/gdb.base/break-fun-addr2.c
@@ -0,0 +1,28 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2016 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
+compute_something (int i)
+{
+  return i - 1;
+}
+
+int
+main (void)
+{
+  return compute_something (1);
+}