gdb: Add native support for ARC in GNU/Linux

With this patch in place it is possible to build a GDB that
can run on ARC (GNU/Linux) hosts for debugging ARC targets.

The "arc-linux-nat.c" is a rather small one that mostly deals
with registers and a few thread related hooks.

v2 [1]:
- Remove "void" from the input of "_initialize_arc_linux_nat ()"

[1] Tom's remark after the first patch
https://sourceware.org/pipermail/gdb-patches/2020-November/173223.html

gdb/ChangeLog:

	* Makefile.in (ALLDEPFILES): Add arc-linux-nat.c.
	* configure.host (host to gdb names): Add arc*-*-linux*.
	* configure.nat (gdb_host_cpu): Add arc.
	* arc-linux-nat.c: New.

5 files changed, 335 insertions, 0 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 92bb56d..c961d72 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,10 @@
+2020-12-22  Anton Kolesov  <anton.kolesov@synopsys.com>
+
+	* Makefile.in (ALLDEPFILES): Add arc-linux-nat.c.
+	* configure.host (host to gdb names): Add arc*-*-linux*.
+	* configure.nat (gdb_host_cpu): Add arc.
+	* arc-linux-nat.c: New.
+
 2020-12-22  Shahab Vahedi  <shahab@synopsys.com>
 
 	* arc-linux-tdep.c (supply_register): New.
diff --git a/gdb/Makefile.in b/gdb/Makefile.in
index 997c99c..999b294 100644
--- a/gdb/Makefile.in
+++ b/gdb/Makefile.in
@@ -2152,6 +2152,7 @@ ALLDEPFILES = \
 	amd64-ravenscar-thread.c \
 	amd64-sol2-tdep.c \
 	amd64-tdep.c \
+	arc-linux-nat.c \
 	arc-tdep.c \
 	arm.c \
 	arm-bsd-tdep.c \
diff --git a/gdb/arc-linux-nat.c b/gdb/arc-linux-nat.c
new file mode 100644
index 0000000..41301fd
--- /dev/null
+++ b/gdb/arc-linux-nat.c
@@ -0,0 +1,320 @@
+/* Native-dependent code for GNU/Linux ARC.
+
+   Copyright 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 "frame.h"
+#include "inferior.h"
+#include "gdbcore.h"
+#include "regcache.h"
+#include "gdbsupport/gdb_assert.h"
+#include "target.h"
+#include "linux-nat.h"
+#include "nat/gdb_ptrace.h"
+
+#include <stdint.h>
+#include <sys/types.h>
+#include <sys/param.h>
+#include <signal.h>
+#include <sys/user.h>
+#include <sys/ioctl.h>
+#include "gdbsupport/gdb_wait.h"
+#include <fcntl.h>
+#include <sys/procfs.h>
+#include <linux/elf.h>
+
+#include "gregset.h"
+#include "arc-tdep.h"
+#include "arc-linux-tdep.h"
+#include "arch/arc.h"
+
+/* Defines ps_err_e, struct ps_prochandle.  */
+#include "gdb_proc_service.h"
+
+/* Linux starting with 4.12 supports NT_ARC_V2 note type, which adds R30,
+   R58 and R59 registers, which are specific to ARC HS and aren't
+   available in ARC 700.  */
+#if defined (NT_ARC_V2) && defined (__ARCHS__)
+#define ARC_HAS_V2_REGSET
+#endif
+
+class arc_linux_nat_target final : public linux_nat_target
+{
+public:
+  /* Add ARC register access methods.  */
+  void fetch_registers (struct regcache *, int) override;
+  void store_registers (struct regcache *, int) override;
+
+  const struct target_desc *read_description () override;
+
+  /* Handle threads  */
+  void low_prepare_to_resume (struct lwp_info *lp) override;
+};
+
+static arc_linux_nat_target the_arc_linux_nat_target;
+
+/* Read general registers from target process/thread (via ptrace)
+   into REGCACHE.  */
+
+static void
+fetch_gregs (struct regcache *regcache, int regnum)
+{
+  const int tid = get_ptrace_pid (regcache->ptid ());
+  struct iovec iov;
+  gdb_gregset_t regs;
+
+  iov.iov_base = &regs;
+  iov.iov_len = sizeof (gdb_gregset_t);
+
+  if (ptrace (PTRACE_GETREGSET, tid, NT_PRSTATUS, (void *) &iov) < 0)
+    perror_with_name (_("Couldn't get general registers"));
+  else
+    arc_linux_supply_gregset (NULL, regcache, regnum, &regs, 0);
+}
+
+#ifdef ARC_HAS_V2_REGSET
+/* Read ARC v2 registers from target process/thread (via ptrace)
+   into REGCACHE.  */
+
+static void
+fetch_v2_regs (struct regcache *regcache, int regnum)
+{
+  const int tid = get_ptrace_pid (regcache->ptid ());
+  struct iovec iov;
+  bfd_byte v2_buffer[ARC_LINUX_SIZEOF_V2_REGSET];
+
+  iov.iov_base = &v2_buffer;
+  iov.iov_len = ARC_LINUX_SIZEOF_V2_REGSET;
+
+  if (ptrace (PTRACE_GETREGSET, tid, NT_ARC_V2, (void *) &iov) < 0)
+    perror_with_name (_("Couldn't get ARC HS registers"));
+  else
+    arc_linux_supply_v2_regset (NULL, regcache, regnum, v2_buffer, 0);
+}
+#endif
+
+/* Store general registers from REGCACHE into the target process/thread.  */
+
+static void
+store_gregs (const struct regcache *regcache, int regnum)
+{
+  const int tid = get_ptrace_pid (regcache->ptid ());
+  struct iovec iov;
+  gdb_gregset_t regs;
+
+  iov.iov_base = &regs;
+  iov.iov_len = sizeof (gdb_gregset_t);
+
+  if (ptrace (PTRACE_GETREGSET, tid, NT_PRSTATUS, (void *) &iov) < 0)
+    perror_with_name (_("Couldn't get general registers"));
+  else
+    {
+      arc_linux_collect_gregset (NULL, regcache, regnum, regs, 0);
+
+      if (ptrace (PTRACE_SETREGSET, tid, NT_PRSTATUS, (void *) &iov) < 0)
+	perror_with_name (_("Couldn't write general registers"));
+    }
+}
+
+#ifdef ARC_HAS_V2_REGSET
+/* Store ARC v2 registers from REGCACHE into the target process/thread.  */
+
+static void
+store_v2_regs (const struct regcache *regcache, int regnum)
+{
+  const int tid = get_ptrace_pid (regcache->ptid ());
+  struct iovec iov;
+  bfd_byte v2_buffer[ARC_LINUX_SIZEOF_V2_REGSET];
+
+  iov.iov_base = &v2_buffer;
+  iov.iov_len = ARC_LINUX_SIZEOF_V2_REGSET;
+
+  if (ptrace (PTRACE_GETREGSET, tid, NT_ARC_V2, (void *) &iov) < 0)
+    perror_with_name (_("Couldn't get ARC HS registers"));
+  else
+    {
+      arc_linux_collect_v2_regset (NULL, regcache, regnum, v2_buffer, 0);
+
+      if (ptrace (PTRACE_SETREGSET, tid, NT_ARC_V2, (void *) &iov) < 0)
+	perror_with_name (_("Couldn't write ARC HS registers"));
+    }
+}
+#endif
+
+/* Target operation: Read REGNUM register (all registers if REGNUM == -1)
+   from target process into REGCACHE.  */
+
+void
+arc_linux_nat_target::fetch_registers (struct regcache *regcache, int regnum)
+{
+
+  if (regnum == -1 || regnum <= ARC_LAST_REGNUM)
+    fetch_gregs (regcache, regnum);
+
+#ifdef ARC_HAS_V2_REGSET
+  if (regnum == -1
+      || regnum == ARC_R30_REGNUM
+      || regnum == ARC_R58_REGNUM
+      || regnum == ARC_R59_REGNUM)
+      fetch_v2_regs (regcache, regnum);
+#endif
+}
+
+/* Target operation: Store REGNUM register (all registers if REGNUM == -1)
+   to the target process from REGCACHE.  */
+
+void
+arc_linux_nat_target::store_registers (struct regcache *regcache, int regnum)
+{
+  if (regnum == -1 || regnum <= ARC_LAST_REGNUM)
+    store_gregs (regcache, regnum);
+
+#ifdef ARC_HAS_V2_REGSET
+  if (regnum == -1
+      || regnum == ARC_R30_REGNUM
+      || regnum == ARC_R58_REGNUM
+      || regnum == ARC_R59_REGNUM)
+    store_v2_regs (regcache, regnum);
+#endif
+}
+
+/* Copy general purpose register(s) from REGCACHE into regset GREGS.
+   This function is exported to proc-service.c  */
+
+void
+fill_gregset (const struct regcache *regcache,
+	      gdb_gregset_t *gregs, int regnum)
+{
+  arc_linux_collect_gregset (NULL, regcache, regnum, gregs, 0);
+}
+
+/* Copy all the general purpose registers from regset GREGS into REGCACHE.
+   This function is exported to proc-service.c.  */
+
+void
+supply_gregset (struct regcache *regcache, const gdb_gregset_t *gregs)
+{
+  arc_linux_supply_gregset (NULL, regcache, -1, gregs, 0);
+}
+
+/* ARC doesn't have separate FP registers.  This function is exported
+   to proc-service.c.  */
+
+void
+fill_fpregset (const struct regcache *regcache,
+	       gdb_fpregset_t *fpregsetp, int regnum)
+{
+  if (arc_debug)
+    debug_printf ("arc-linux-nat: fill_fpregset called.");
+  return;
+}
+
+/* ARC doesn't have separate FP registers.  This function is exported
+   to proc-service.c.  */
+
+void
+supply_fpregset (struct regcache *regcache, const gdb_fpregset_t *fpregsetp)
+{
+  if (arc_debug)
+    debug_printf ("arc-linux-nat: supply_fpregset called.");
+  return;
+}
+
+/* Implement the "read_description" method of linux_nat_target.  */
+
+const struct target_desc *
+arc_linux_nat_target::read_description ()
+{
+  /* This is a native target, hence description is hardcoded.  */
+#ifdef __ARCHS__
+  arc_arch_features features (4, ARC_ISA_ARCV2);
+#else
+  arc_arch_features features (4, ARC_ISA_ARCV1);
+#endif
+  return arc_lookup_target_description (features);
+}
+
+/* As described in arc_linux_collect_gregset(), we need to write resume-PC
+   to ERET.  However by default GDB for native targets doesn't write
+   registers if they haven't been changed.  This is a callback called by
+   generic GDB, and in this callback we have to rewrite PC value so it
+   would force rewrite of register on target.  It seems that the only
+   other arch that utilizes this hook is x86/x86-64 for HW breakpoint
+   support.  But then, AFAIK no other arch has this stop_pc/eret
+   complexity.
+
+   No better way was found, other than this fake write of register value,
+   to force GDB into writing register to target.  Is there any?  */
+
+void
+arc_linux_nat_target::low_prepare_to_resume (struct lwp_info *lwp)
+{
+  /* When new processes and threads are created we do not have the address
+     space for them and calling get_thread_regcache will cause an internal
+     error in GDB.  It looks like that checking for last_resume_kind is the
+     sensible way to determine processes for which we cannot get regcache.
+     Ultimately, a better way would be removing the need for
+     low_prepare_to_resume in the first place.  */
+  if (lwp->last_resume_kind == resume_stop)
+    return;
+
+  struct regcache *regcache = get_thread_regcache (this, lwp->ptid);
+  struct gdbarch *gdbarch = regcache->arch ();
+
+  /* Read current PC value, then write it back.  It is required to call
+     invalidate(), otherwise GDB will note that new value is equal to old
+     value and will skip write.  */
+  ULONGEST new_pc;
+  regcache_cooked_read_unsigned (regcache, gdbarch_pc_regnum (gdbarch),
+				 &new_pc);
+  regcache->invalidate (gdbarch_pc_regnum (gdbarch));
+  regcache_cooked_write_unsigned (regcache, gdbarch_pc_regnum (gdbarch),
+				  new_pc);
+}
+
+/* Fetch the thread-local storage pointer for libthread_db.  Note that
+   this function is not called from GDB, but is called from libthread_db.
+   This is required to debug multithreaded applications with NPTL.  */
+
+ps_err_e
+ps_get_thread_area (struct ps_prochandle *ph, lwpid_t lwpid, int idx,
+		    void **base)
+{
+  if (arc_debug >= 2)
+    debug_printf ("arc-linux-nat: ps_get_thread_area called");
+
+  if (ptrace (PTRACE_GET_THREAD_AREA, lwpid, NULL, base) != 0)
+    return PS_ERR;
+
+  /* IDX is the bias from the thread pointer to the beginning of the
+     thread descriptor.  It has to be subtracted due to implementation
+     quirks in libthread_db.  */
+  *base = (void *) ((char *) *base - idx);
+
+  return PS_OK;
+}
+
+/* Suppress warning from -Wmissing-prototypes.  */
+void _initialize_arc_linux_nat ();
+void
+_initialize_arc_linux_nat ()
+{
+  /* Register the target.  */
+  linux_target = &the_arc_linux_nat_target;
+  add_inf_child_target (&the_arc_linux_nat_target);
+}
diff --git a/gdb/configure.host b/gdb/configure.host
index ce52823..e94a19b 100644
--- a/gdb/configure.host
+++ b/gdb/configure.host
@@ -60,6 +60,7 @@ case "${host_cpu}" in
 
 aarch64*)		gdb_host_cpu=aarch64 ;;
 alpha*)			gdb_host_cpu=alpha ;;
+arc*)			gdb_host_cpu=arc ;;
 arm*)			gdb_host_cpu=arm ;;
 hppa*)			gdb_host_cpu=pa ;;
 i[34567]86*)		gdb_host_cpu=i386 ;;
@@ -91,6 +92,8 @@ alpha*-*-netbsd* | alpha*-*-knetbsd*-gnu)
 			gdb_host=nbsd ;;
 alpha*-*-openbsd*)	gdb_host=nbsd ;;
 
+arc*-*-linux*)		gdb_host=linux ;;
+
 arm*-*-freebsd*)	gdb_host=fbsd ;;
 arm*-*-linux*)		gdb_host=linux ;;
 arm*-*-netbsdelf* | arm*-*-knetbsd*-gnu)
diff --git a/gdb/configure.nat b/gdb/configure.nat
index ef2218f..0e36e09 100644
--- a/gdb/configure.nat
+++ b/gdb/configure.nat
@@ -238,6 +238,10 @@ case ${gdb_host} in
 		nat/aarch64-linux.o \
 		nat/aarch64-sve-linux-ptrace.o"
 		;;
+	    arc)
+		# Host: ARC based machine running GNU/Linux
+		NATDEPFILES="${NATDEPFILES} arc-linux-nat.o"
+		;;
 	    arm)
 		# Host: ARM based machine running GNU/Linux
 		NATDEPFILES="${NATDEPFILES} arm-linux-nat.o \