[RFA] read_frame_register_value and big endian arches

[Joel Brobecker <brobecker@adacore.com>]

Hello,

I am afraid I introduced a regression on big-endian architectures
(Eg. sparc-solaris, erc32-elf) after my latest patch:
    [RFA/RFC] Restore old handling of multi-register variables
    http://www.sourceware.org/ml/gdb-patches/2011-10/msg00709.html

It's just an oversight: The problem appears when trying to get the value
of an entity stored inside a register, and when the size of the entity
is smaller than the size of the register.

    For instance, the testcase shows a parameter whose type is
    a 2-byte integer.  This parameter is passed by register, in
    a 4-byte register.

In that case, the new function read_frame_register_value was always
reading from the first bytes of the register, which is wrong for
big-endian architectures.

gdb/ChangeLog:

        * findvar.c (read_frame_register_value): Read the correct bytes
        from registers on big-endian architectures.

gdb/testsuite/ChangeLog:

        * gdb.ada/small_reg_param: New testcase.

Tested on x86_64-linux. Also tested on erc32-elf and sparc-solaris,
but with AdaCore's testsuite (I am still forbidden from running
the testsuite on any of our Solaris machine because it crashes
the system really bad). I also checked the patch against AVR,
and make sure that it does not create any regression there.

Also included is a new testcase which, when run manually, reproduces
the problem on erc32-elf, and probably on sparc-solaris too.

---
 gdb/findvar.c                                 |   14 ++++++--
 gdb/testsuite/gdb.ada/small_reg_param.exp     |   46 +++++++++++++++++++++++++
 gdb/testsuite/gdb.ada/small_reg_param/foo.adb |   21 +++++++++++
 gdb/testsuite/gdb.ada/small_reg_param/pck.adb |   22 ++++++++++++
 gdb/testsuite/gdb.ada/small_reg_param/pck.ads |   22 ++++++++++++
 5 files changed, 122 insertions(+), 3 deletions(-)
 create mode 100644 gdb/testsuite/gdb.ada/small_reg_param.exp
 create mode 100644 gdb/testsuite/gdb.ada/small_reg_param/foo.adb
 create mode 100644 gdb/testsuite/gdb.ada/small_reg_param/pck.adb
 create mode 100644 gdb/testsuite/gdb.ada/small_reg_param/pck.ads

diff --git a/gdb/findvar.c b/gdb/findvar.c
index 54e7b4a..426b488 100644
--- a/gdb/findvar.c
+++ b/gdb/findvar.c
@@ -641,11 +641,19 @@ read_frame_register_value (struct value *value, struct frame_info *frame)
     {
       struct value *regval = get_frame_register_value (frame, regnum);
       int reg_len = TYPE_LENGTH (value_type (regval));
+      int reg_offset = 0;
 
+      /* If the register length is larger than the number of bytes
+         remaining to copy, then only copy the appropriate bytes.  */
       if (offset + reg_len > len)
-        reg_len = len - offset;
-      value_contents_copy (value, offset, regval, value_offset (regval),
-			   reg_len);
+	{
+	  reg_len = len - offset;
+	  if (gdbarch_byte_order (get_frame_arch (frame)) == BFD_ENDIAN_BIG)
+	    reg_offset = TYPE_LENGTH (value_type (regval)) - reg_len;
+	}
+
+      value_contents_copy (value, offset, regval,
+                           value_offset (regval) + reg_offset, reg_len);
 
       offset += reg_len;
       regnum++;
diff --git a/gdb/testsuite/gdb.ada/small_reg_param.exp b/gdb/testsuite/gdb.ada/small_reg_param.exp
new file mode 100644
index 0000000..00b066b
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/small_reg_param.exp
@@ -0,0 +1,46 @@
+# Copyright 2011 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/>.
+
+load_lib "ada.exp"
+
+set testdir "small_reg_param"
+set testfile "${testdir}/foo"
+set srcfile ${srcdir}/${subdir}/${testfile}.adb
+set binfile ${objdir}/${subdir}/${testfile}
+
+file mkdir ${objdir}/${subdir}/${testdir}
+if {[gdb_compile_ada "${srcfile}" "${binfile}" executable [list debug optimize=-O1]] != "" } {
+  return -1
+}
+
+clean_restart ${testfile}
+
+if ![runto main] then {
+  perror "Couldn't run ${testfile}"
+  return
+} 
+
+gdb_breakpoint "call_me"
+
+# Continue until we hit the breakpoint inside `Call_Me'.  We verify
+# that the parameter value is correct.
+gdb_test "continue" \
+    "Breakpoint .*, pck\\.call_me \\(w=50\\) at .*/pck.adb:.*" \
+    "continue to call_me"
+
+# And just to make sure, we also verify that the parameter value
+# is correct when we print it manually.
+gdb_test "print w" " = 50"
+
diff --git a/gdb/testsuite/gdb.ada/small_reg_param/foo.adb b/gdb/testsuite/gdb.ada/small_reg_param/foo.adb
new file mode 100644
index 0000000..e6b1f53
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/small_reg_param/foo.adb
@@ -0,0 +1,21 @@
+--  Copyright 2011 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/>.
+
+with Pck; use Pck;
+
+procedure Foo is
+begin
+   Call_Me (50);
+end Foo;
diff --git a/gdb/testsuite/gdb.ada/small_reg_param/pck.adb b/gdb/testsuite/gdb.ada/small_reg_param/pck.adb
new file mode 100644
index 0000000..55455c7
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/small_reg_param/pck.adb
@@ -0,0 +1,22 @@
+--  Copyright 2011 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/>.
+
+package body Pck is
+   Last_Word : Word := 0;
+   procedure Call_Me (W : Word) is
+   begin
+      Last_Word := W;
+   end Call_Me;
+end Pck;
diff --git a/gdb/testsuite/gdb.ada/small_reg_param/pck.ads b/gdb/testsuite/gdb.ada/small_reg_param/pck.ads
new file mode 100644
index 0000000..7ae299a
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/small_reg_param/pck.ads
@@ -0,0 +1,22 @@
+--  Copyright 2011 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/>.
+
+package Pck is
+
+   type Word is range 0 .. 16#FFFF#;
+   for Word'size use 16;
+
+   procedure Call_Me (W : Word);
+end Pck;
-- 
1.7.1