[PATCH] Support for corefiles for arm-none-eabi target.

[Fredrik Hederstierna <fredrik@hederstierna.com>]

From: fredrikhederstierna <fredrik@hederstierna.com>

---
 gdb/Makefile.in     |   6 +
 gdb/arm-none-tdep.c | 161 +++++++++++++++++++++++++++
 gdb/arm-none-tdep.h |  31 ++++++
 gdb/arm-tdep.c      |  11 ++
 gdb/configure.tgt   |   3 +-
 gdb/none-tdep.c     | 264 ++++++++++++++++++++++++++++++++++++++++++++
 gdb/none-tdep.h     |  27 +++++
 sim/arm/wrapper.c   |   4 +
 8 files changed, 506 insertions(+), 1 deletion(-)
 create mode 100644 gdb/arm-none-tdep.c
 create mode 100644 gdb/arm-none-tdep.h
 create mode 100644 gdb/none-tdep.c
 create mode 100644 gdb/none-tdep.h

diff --git a/gdb/Makefile.in b/gdb/Makefile.in
index 8a160896e2..61a13312ce 100644
--- a/gdb/Makefile.in
+++ b/gdb/Makefile.in
@@ -721,6 +721,7 @@ ALL_TARGET_OBS = \
 	arm-fbsd-tdep.o \
 	arm-linux-tdep.o \
 	arm-netbsd-tdep.o \
+	arm-none-tdep.o \
 	arm-obsd-tdep.o \
 	arm-pikeos-tdep.o \
 	arm-symbian-tdep.o \
@@ -788,6 +789,7 @@ ALL_TARGET_OBS = \
 	nds32-tdep.o \
 	nios2-linux-tdep.o \
 	nios2-tdep.o \
+	none-tdep.o \
 	nto-tdep.o \
 	obsd-tdep.o \
 	or1k-linux-tdep.o \
@@ -1225,6 +1227,7 @@ HFILES_NO_SRCDIR = \
 	arch-utils.h \
 	arm-linux-tdep.h \
 	arm-netbsd-tdep.h \
+	arm-none-tdep.h \
 	arm-tdep.h \
 	async-event.h \
 	auto-load.h \
@@ -1350,6 +1353,7 @@ HFILES_NO_SRCDIR = \
 	netbsd-tdep.h \
 	nds32-tdep.h \
 	nios2-tdep.h \
+	none-tdep.h \
 	nto-tdep.h \
 	objc-lang.h \
 	objfiles.h \
@@ -2152,6 +2156,7 @@ ALLDEPFILES = \
 	arm-linux-tdep.c \
 	arm-netbsd-nat.c \
 	arm-netbsd-tdep.c \
+	arm-none-tdep.c \
 	arm-obsd-tdep.c \
 	arm-symbian-tdep.c \
 	arm-tdep.c \
@@ -2238,6 +2243,7 @@ ALLDEPFILES = \
 	nds32-tdep.c \
 	nios2-linux-tdep.c \
 	nios2-tdep.c \
+	none-tdep.c \
 	obsd-nat.c \
 	obsd-tdep.c \
 	posix-hdep.c \
diff --git a/gdb/arm-none-tdep.c b/gdb/arm-none-tdep.c
new file mode 100644
index 0000000000..0288e13175
--- /dev/null
+++ b/gdb/arm-none-tdep.c
@@ -0,0 +1,161 @@
+/* none on ARM target support.
+
+   Copyright (C) 2020 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   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 "defs.h"
+#include "arm-tdep.h"
+#include "arm-none-tdep.h"
+
+/* Core file and register set support.  */
+#define ARM_NONE_SIZEOF_GREGSET (18 * ARM_INT_REGISTER_SIZE)
+
+/* Support VFP register format.  */
+#define ARM_NONE_SIZEOF_VFP (32 * 8 + 4)
+
+/* The index to access CSPR in user_regs as defined in GLIBC.  */
+#define ARM_NONE_CPSR_GREGNUM 16
+
+/* The ARM none register setup is based on the ARM GNU/Linux design.  */
+
+static void
+arm_none_supply_gregset (const struct regset *regset,
+			 struct regcache *regcache,
+			 int regnum, const void *gregs_buf, size_t len)
+{
+  struct gdbarch *gdbarch = regcache->arch ();
+  enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
+  const gdb_byte *gregs = (const gdb_byte *) gregs_buf;
+  int regno;
+  CORE_ADDR reg_pc;
+  gdb_byte pc_buf[ARM_INT_REGISTER_SIZE];
+
+  for (regno = ARM_A1_REGNUM; regno < ARM_PC_REGNUM; regno++)
+    if (regnum == -1 || regnum == regno)
+      regcache->raw_supply (regno, gregs + ARM_INT_REGISTER_SIZE * regno);
+
+  if (regnum == ARM_PS_REGNUM || regnum == -1)
+    {
+      if (arm_apcs_32)
+	regcache->raw_supply (ARM_PS_REGNUM,
+			      gregs + ARM_INT_REGISTER_SIZE * ARM_NONE_CPSR_GREGNUM);
+      else
+	regcache->raw_supply (ARM_PS_REGNUM,
+			     gregs + ARM_INT_REGISTER_SIZE * ARM_PC_REGNUM);
+    }
+
+  if (regnum == ARM_PC_REGNUM || regnum == -1)
+    {
+      reg_pc = extract_unsigned_integer (
+		 gregs + ARM_INT_REGISTER_SIZE * ARM_PC_REGNUM,
+		 ARM_INT_REGISTER_SIZE, byte_order);
+      reg_pc = gdbarch_addr_bits_remove (gdbarch, reg_pc);
+      store_unsigned_integer (pc_buf, ARM_INT_REGISTER_SIZE, byte_order,
+			      reg_pc);
+      regcache->raw_supply (ARM_PC_REGNUM, pc_buf);
+    }
+}
+
+static void
+arm_none_collect_gregset (const struct regset *regset,
+			  const struct regcache *regcache,
+			  int regnum, void *gregs_buf, size_t len)
+{
+  gdb_byte *gregs = (gdb_byte *) gregs_buf;
+  int regno;
+
+  for (regno = ARM_A1_REGNUM; regno < ARM_PC_REGNUM; regno++)
+    if (regnum == -1 || regnum == regno)
+      regcache->raw_collect (regno,
+			    gregs + ARM_INT_REGISTER_SIZE * regno);
+
+  if (regnum == ARM_PS_REGNUM || regnum == -1)
+    {
+      if (arm_apcs_32)
+	regcache->raw_collect (ARM_PS_REGNUM,
+			      gregs + ARM_INT_REGISTER_SIZE * ARM_NONE_CPSR_GREGNUM);
+      else
+	regcache->raw_collect (ARM_PS_REGNUM,
+			      gregs + ARM_INT_REGISTER_SIZE * ARM_PC_REGNUM);
+    }
+
+  if (regnum == ARM_PC_REGNUM || regnum == -1)
+    regcache->raw_collect (ARM_PC_REGNUM,
+			   gregs + ARM_INT_REGISTER_SIZE * ARM_PC_REGNUM);
+}
+
+/* Support VFP register format.  */
+
+static void
+arm_none_supply_vfp (const struct regset *regset,
+		     struct regcache *regcache,
+		     int regnum, const void *regs_buf, size_t len)
+{
+  const gdb_byte *regs = (const gdb_byte *) regs_buf;
+  int regno;
+
+  if (regnum == ARM_FPSCR_REGNUM || regnum == -1)
+    regcache->raw_supply (ARM_FPSCR_REGNUM, regs + 32 * 8);
+
+  for (regno = ARM_D0_REGNUM; regno <= ARM_D31_REGNUM; regno++)
+    if (regnum == -1 || regnum == regno)
+      regcache->raw_supply (regno, regs + (regno - ARM_D0_REGNUM) * 8);
+}
+
+static void
+arm_none_collect_vfp (const struct regset *regset,
+		      const struct regcache *regcache,
+		      int regnum, void *regs_buf, size_t len)
+{
+  gdb_byte *regs = (gdb_byte *) regs_buf;
+  int regno;
+
+  if (regnum == ARM_FPSCR_REGNUM || regnum == -1)
+    regcache->raw_collect (ARM_FPSCR_REGNUM, regs + 32 * 8);
+
+  for (regno = ARM_D0_REGNUM; regno <= ARM_D31_REGNUM; regno++)
+    if (regnum == -1 || regnum == regno)
+      regcache->raw_collect (regno, regs + (regno - ARM_D0_REGNUM) * 8);
+}
+
+static const struct regset arm_none_gregset =
+  {
+    nullptr, arm_none_supply_gregset, arm_none_collect_gregset
+  };
+
+static const struct regset arm_none_vfpregset =
+  {
+    nullptr, arm_none_supply_vfp, arm_none_collect_vfp
+  };
+
+/* Iterate over core file register note sections.  */
+
+void
+arm_none_iterate_over_regset_sections (struct gdbarch *gdbarch,
+				       iterate_over_regset_sections_cb *cb,
+				       void *cb_data,
+				       const struct regcache *regcache)
+{
+  struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);
+
+  cb (".reg", ARM_NONE_SIZEOF_GREGSET, ARM_NONE_SIZEOF_GREGSET,
+	&arm_none_gregset, nullptr, cb_data);
+
+  if (tdep->vfp_register_count > 0)
+    cb (".reg-arm-vfp", ARM_NONE_SIZEOF_VFP, ARM_NONE_SIZEOF_VFP,
+	&arm_none_vfpregset, "VFP floating-point", cb_data);
+}
diff --git a/gdb/arm-none-tdep.h b/gdb/arm-none-tdep.h
new file mode 100644
index 0000000000..7e2784ff93
--- /dev/null
+++ b/gdb/arm-none-tdep.h
@@ -0,0 +1,31 @@
+/* none on ARM target support, prototypes.
+
+   Copyright (C) 2020 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   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/>.  */
+
+#ifndef ARM_NONE_TDEP_H
+#define ARM_NONE_TDEP_H
+
+#include "bfd.h"
+#include "regset.h"
+
+void
+  arm_none_iterate_over_regset_sections (struct gdbarch *gdbarch,
+					 iterate_over_regset_sections_cb *cb,
+					 void *cb_data,
+					 const struct regcache *regcache);
+#endif /* ARM_NONE_TDEP_H */
diff --git a/gdb/arm-tdep.c b/gdb/arm-tdep.c
index a214f22d7a..c361818367 100644
--- a/gdb/arm-tdep.c
+++ b/gdb/arm-tdep.c
@@ -50,6 +50,8 @@
 #include "arch/arm.h"
 #include "arch/arm-get-next-pcs.h"
 #include "arm-tdep.h"
+#include "none-tdep.h"
+#include "arm-none-tdep.h"
 #include "gdb/sim-arm.h"
 
 #include "elf-bfd.h"
@@ -4205,6 +4207,10 @@ arm_register_sim_regno (struct gdbarch *gdbarch, int regnum)
   if (regnum >= ARM_WCGR0_REGNUM && regnum <= ARM_WCGR7_REGNUM)
     return regnum - ARM_WCGR0_REGNUM + SIM_ARM_IWMMXT_COP1R8_REGNUM;
 
+  /* The ARM simulator does not support D0-D31 nor FPSCR.  */
+  if (regnum >= ARM_D0_REGNUM && regnum <= ARM_FPSCR_REGNUM)
+    return -1;
+
   if (reg < NUM_GREGS)
     return SIM_ARM_R0_REGNUM + reg;
   reg -= NUM_GREGS;
@@ -9453,6 +9459,11 @@ arm_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
   /* Virtual tables.  */
   set_gdbarch_vbit_in_delta (gdbarch, 1);
 
+  /* Default none core file support, can be overridden by osabi.  */
+  none_init_corefile (gdbarch);
+  set_gdbarch_iterate_over_regset_sections (gdbarch,
+                                            arm_none_iterate_over_regset_sections);
+
   /* Hook in the ABI-specific overrides, if they have been registered.  */
   gdbarch_init_osabi (info, gdbarch);
 
diff --git a/gdb/configure.tgt b/gdb/configure.tgt
index d865ecdcb6..789541d49f 100644
--- a/gdb/configure.tgt
+++ b/gdb/configure.tgt
@@ -64,7 +64,8 @@ arc*-*-*)
 
 arm*-*-*)
 	cpu_obs="aarch32-tdep.o arch/aarch32.o arch/arm.o \
-		 arch/arm-get-next-pcs.o arm-tdep.o";;
+		 arch/arm-get-next-pcs.o arm-tdep.o \
+		 none-tdep.o arm-none-tdep.o";;
 
 hppa*-*-*)
 	# Target: HP PA-RISC
diff --git a/gdb/none-tdep.c b/gdb/none-tdep.c
new file mode 100644
index 0000000000..b7a49924c6
--- /dev/null
+++ b/gdb/none-tdep.c
@@ -0,0 +1,264 @@
+/* Target-dependent code for none, architecture independent.
+
+   Copyright (C) 2020 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   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 "defs.h"
+#include "none-tdep.h"
+#include "regset.h"
+#include "elf-bfd.h"            /* for elfcore_write_* */
+#include "inferior.h"
+
+using none_collect_thread_registers_ftype
+  = void (const struct regcache *, ptid_t, bfd *,
+	  gdb::unique_xmalloc_ptr<char> &, int *, enum gdb_signal);
+
+/* The ARM none corefile setup is based on the ARM GNU/Linux design.  */
+
+/* Structure for passing information from
+   none_collect_thread_registers via an iterator to
+   none_collect_regset_section_cb.  */
+
+struct none_collect_regset_section_cb_data
+{
+  none_collect_regset_section_cb_data (struct gdbarch *gdbarch,
+				       const struct regcache *regcache,
+				       bfd *obfd,
+				       gdb::unique_xmalloc_ptr<char> &note_data,
+				       int *note_size,
+				       unsigned long lwp,
+				       enum gdb_signal stop_signal)
+    : gdbarch (gdbarch), regcache (regcache), obfd (obfd),
+      note_data (note_data), note_size (note_size),
+      lwp (lwp), stop_signal (stop_signal)
+  {}
+
+  struct gdbarch *gdbarch;
+  const struct regcache *regcache;
+  bfd *obfd;
+  gdb::unique_xmalloc_ptr<char> &note_data;
+  int *note_size;
+  unsigned long lwp;
+  enum gdb_signal stop_signal;
+  bool abort_iteration = false;
+};
+
+/* Callback for iterate_over_regset_sections that records a single
+   regset in the corefile note section.  */
+
+static void
+none_collect_regset_section_cb (const char *sect_name, int supply_size,
+				int collect_size, const struct regset *regset,
+				const char *human_name, void *cb_data)
+{
+  struct none_collect_regset_section_cb_data *data
+    = (struct none_collect_regset_section_cb_data *) cb_data;
+  bool variable_size_section = (regset != nullptr
+				&& regset->flags & REGSET_VARIABLE_SIZE);
+
+  if (!variable_size_section)
+    gdb_assert (supply_size == collect_size);
+
+  if (data->abort_iteration)
+    return;
+
+  gdb_assert (regset && regset->collect_regset);
+
+  /* This is intentionally zero-initialized by using std::vector, so
+     that any padding bytes in the core file will show as 0.  */
+  std::vector<gdb_byte> buf (collect_size);
+
+  regset->collect_regset (regset, data->regcache, -1, buf.data (),
+			  collect_size);
+
+  /* PRSTATUS still needs to be treated specially.  */
+  if (strcmp (sect_name, ".reg") == 0)
+    data->note_data.reset (elfcore_write_prstatus
+			     (data->obfd, data->note_data.release (),
+			      data->note_size, data->lwp,
+			      gdb_signal_to_host (data->stop_signal),
+			      buf.data ()));
+  else
+    data->note_data.reset (elfcore_write_register_note
+			     (data->obfd, data->note_data.release (),
+			      data->note_size, sect_name, buf.data (),
+			      collect_size));
+
+  if (data->note_data == nullptr)
+    data->abort_iteration = 1;
+}
+
+/* Records the thread's register state for the corefile note
+   section.  */
+
+static void
+none_collect_thread_registers (const struct regcache *regcache,
+			       ptid_t ptid, bfd *obfd,
+			       gdb::unique_xmalloc_ptr<char> &note_data,
+			       int *note_size, enum gdb_signal stop_signal)
+{
+  struct gdbarch *gdbarch = regcache->arch ();
+  unsigned long lwp;
+
+  /* For remote targets the LWP may not be available, so use the TID.  */
+  lwp = ptid.lwp ();
+  if (lwp == 0)
+    lwp = ptid.tid ();
+
+  none_collect_regset_section_cb_data data (gdbarch, regcache, obfd, note_data,
+					    note_size, lwp, stop_signal);
+
+  gdbarch_iterate_over_regset_sections (gdbarch,
+					none_collect_regset_section_cb,
+					&data, regcache);
+}
+
+struct none_corefile_thread_data
+{
+  none_corefile_thread_data (struct gdbarch *gdbarch,
+			     bfd *obfd,
+			     gdb::unique_xmalloc_ptr<char> &note_data,
+			     int *note_size,
+			     enum gdb_signal stop_signal)
+    : gdbarch (gdbarch), obfd (obfd), note_data (note_data),
+      note_size (note_size), stop_signal (stop_signal)
+  {}
+
+  struct gdbarch *gdbarch;
+  bfd *obfd;
+  gdb::unique_xmalloc_ptr<char> &note_data;
+  int *note_size;
+  enum gdb_signal stop_signal;
+};
+
+/* Records the thread's register state for the corefile note
+   section.  */
+
+static void
+none_corefile_thread (struct thread_info *info,
+		      struct none_corefile_thread_data *args)
+{
+  struct regcache *regcache;
+
+  regcache = get_thread_arch_regcache (info->inf->process_target (),
+				       info->ptid, args->gdbarch);
+
+  target_fetch_registers (regcache, -1);
+  none_collect_thread_registers
+    (regcache, info->ptid, args->obfd, args->note_data,
+     args->note_size, args->stop_signal);
+}
+
+/* Find the signalled thread.  In case there's more than one signalled
+   thread, prefer the current thread, if it is signalled.  If no
+   thread was signalled, default to the current thread, unless it has
+   exited, in which case return nullptr.  */
+
+static thread_info *
+find_signalled_thread ()
+{
+  thread_info *curr_thr = inferior_thread ();
+  if (curr_thr->state != THREAD_EXITED
+      && curr_thr->suspend.stop_signal != GDB_SIGNAL_0)
+    return curr_thr;
+
+  for (thread_info *thr : current_inferior ()->non_exited_threads ())
+    if (thr->suspend.stop_signal != GDB_SIGNAL_0)
+      return thr;
+
+  /* Default to the current thread, unless it has exited.  */
+  if (curr_thr->state != THREAD_EXITED)
+    return curr_thr;
+
+  return nullptr;
+}
+
+/* Fills the "to_make_corefile_note" target vector.  Builds the note
+   section for a corefile, and returns it in a malloc buffer.  */
+
+static gdb::unique_xmalloc_ptr<char>
+none_make_corefile_notes_1 (struct gdbarch *gdbarch, bfd *obfd, int *note_size,
+			    none_collect_thread_registers_ftype collect)
+{
+  gdb::unique_xmalloc_ptr<char> note_data;
+
+  /* Process information.  */
+  if (get_exec_file (0))
+    {
+      const char *fname = lbasename (get_exec_file (0));
+      std::string psargs = fname;
+      note_data.reset (elfcore_write_prpsinfo (obfd, note_data.release (),
+					       note_size, fname,
+					       psargs.c_str ()));
+    }
+
+  if (!note_data)
+    return nullptr;
+
+  /* Thread register information.  */
+  try
+    {
+      update_thread_list ();
+    }
+  catch (const gdb_exception_error &e)
+    {
+      exception_print (gdb_stderr, e);
+    }
+
+  /* Like the kernel, prefer dumping the signalled thread first.
+     "First thread" is what tools use to infer the signalled
+     thread.  */
+  thread_info *signalled_thr = find_signalled_thread ();
+  gdb_signal stop_signal;
+
+  if (signalled_thr != nullptr)
+    stop_signal = signalled_thr->suspend.stop_signal;
+  else
+    stop_signal = GDB_SIGNAL_0;
+
+  none_corefile_thread_data thread_args (gdbarch, obfd, note_data, note_size,
+					 stop_signal);
+
+  if (signalled_thr != nullptr)
+    none_corefile_thread (signalled_thr, &thread_args);
+  for (thread_info *thr : current_inferior ()->non_exited_threads ())
+    {
+      if (thr == signalled_thr)
+	continue;
+
+      none_corefile_thread (thr, &thread_args);
+    }
+
+  return note_data;
+}
+
+static gdb::unique_xmalloc_ptr<char>
+none_make_corefile_notes (struct gdbarch *gdbarch, bfd *obfd, int *note_size)
+{
+  return none_make_corefile_notes_1 (gdbarch, obfd, note_size,
+                                     none_collect_thread_registers);
+}
+
+/* Setup default core file support for none targets.
+   Can be overridden later by OSABI.  */
+
+void
+none_init_corefile (struct gdbarch *gdbarch)
+{
+  /* Default core file support.  */
+  set_gdbarch_make_corefile_notes (gdbarch, none_make_corefile_notes);
+}
diff --git a/gdb/none-tdep.h b/gdb/none-tdep.h
new file mode 100644
index 0000000000..f25b124019
--- /dev/null
+++ b/gdb/none-tdep.h
@@ -0,0 +1,27 @@
+/* Target-dependent code for none, architecture independent.
+
+   Copyright (C) 2020 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   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/>.  */
+
+#ifndef NONE_TDEP_H
+#define NONE_TDEP_H
+
+#include "gdbarch.h"
+
+void none_init_corefile (struct gdbarch *gdbarch);
+
+#endif /* none-tdep.h */
diff --git a/sim/arm/wrapper.c b/sim/arm/wrapper.c
index 68f8242288..759dac0331 100644
--- a/sim/arm/wrapper.c
+++ b/sim/arm/wrapper.c
@@ -515,6 +515,10 @@ arm_reg_fetch (SIM_CPU *cpu, int rn, unsigned char *memory, int length)
 
   init ();
 
+  /* Check that memory and length are valid before trying read reg.  */
+  if ((memory == NULL) || (length == 0))
+    return 0;
+
   switch ((enum sim_arm_regs) rn)
     {
     case SIM_ARM_R0_REGNUM:
-- 
2.17.1