[PATCH] gdbserver: Add LoongArch/Linux port support

[PATCH] gdbserver: Add LoongArch/Linux port support

[Youling Tang]

Implement LoongArch/Linux port support, including XML target description
handling based on features determined and GPR regset support including
dynamic sizing of the latter, and software breakpoint handling.

FPR regset and hardware breakpoint/watchpoint functions are not supported
yet (because the gdb part is not supported).

Some test results of gdbserver are as follows:
$ make check-gdb RUNTESTFLAGS='gdb.server/server-connect.exp'
  # of expected passes		18

2022-05-31  Youling Tang <tangyouling@loongson.cn>

	gdb/
	* NEWS: Mention LoongArch GNU/Linux GDBserver support.
	* arch/loongarch.h: Declare the loongarch_create_target_description
	function when GDBSERVER is defined.

	gdbserver/
	* linux-loongarch-low.cc: New file.
	* Makefile.in (SFILES): Add linux-loongarch-low.cc and
	arch/loongarch.c.
	* configure.srv <loongarch*-*-linux*> (srv_tgtobj)
	srv_linux_regsets, srv_linux_usrregs, srv_linux_thread_db):
	Define.

Signed-off-by: Youling Tang <tangyouling@loongson.cn>
---
 gdb/NEWS                         |   3 +
 gdb/arch/loongarch.c             |  12 +-
 gdb/arch/loongarch.h             |  13 ++
 gdbserver/Makefile.in            |   2 +
 gdbserver/configure.srv          |   6 +
 gdbserver/linux-loongarch-low.cc | 245 +++++++++++++++++++++++++++++++
 6 files changed, 280 insertions(+), 1 deletion(-)
 create mode 100644 gdbserver/linux-loongarch-low.cc

diff --git a/gdb/NEWS b/gdb/NEWS
index dac6dabfa42..62b592e2d2d 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -687,6 +687,8 @@ QMemTags
 
   ** GDBserver is now supported on RISC-V GNU/Linux.
 
+  ** GDBserver is now supported on LoongArch GNU/Linux.
+
   ** GDBserver no longer supports these host triplets:
 
     i[34567]86-*-lynxos*
@@ -778,6 +780,7 @@ alias [-a] [--] ALIAS = COMMAND [DEFAULT-ARGS...]
 * New targets
 
 GNU/Linux/RISC-V (gdbserver)	riscv*-*-linux*
+GNU/Linux/LoongArch (gdbserver)	loongarch*-*-linux*
 BPF				bpf-unknown-none
 Z80				z80-unknown-*
 
diff --git a/gdb/arch/loongarch.c b/gdb/arch/loongarch.c
index 934f6e489c5..11310c1dd93 100644
--- a/gdb/arch/loongarch.c
+++ b/gdb/arch/loongarch.c
@@ -25,7 +25,13 @@
 #include "../features/loongarch/base32.c"
 #include "../features/loongarch/base64.c"
 
-static target_desc_up
+#ifndef GDBSERVER
+#define STATIC_IN_GDB static
+#else
+#define STATIC_IN_GDB
+#endif
+
+STATIC_IN_GDB target_desc_up
 loongarch_create_target_description (const struct loongarch_gdbarch_features features)
 {
   /* Now we should create a new target description.  */
@@ -51,6 +57,8 @@ loongarch_create_target_description (const struct loongarch_gdbarch_features fea
   return tdesc;
 }
 
+#ifndef GDBSERVER
+
 /* Wrapper used by std::unordered_map to generate hash for feature set.  */
 struct loongarch_gdbarch_features_hasher
 {
@@ -86,3 +94,5 @@ loongarch_lookup_target_description (const struct loongarch_gdbarch_features fea
   loongarch_tdesc_cache.emplace (features, std::move (tdesc));
   return ptr;
 }
+
+#endif /* !GDBSERVER */
diff --git a/gdb/arch/loongarch.h b/gdb/arch/loongarch.h
index 9e10df967d1..8194ea66c0a 100644
--- a/gdb/arch/loongarch.h
+++ b/gdb/arch/loongarch.h
@@ -60,6 +60,17 @@ struct loongarch_gdbarch_features
   }
 };
 
+#ifdef GDBSERVER
+
+/* Create and return a target description that is compatible with FEATURES.
+   This is only used directly from the gdbserver where the created target
+   description is modified after it is return.  */
+
+target_desc_up loongarch_create_target_description
+	(const struct loongarch_gdbarch_features features);
+
+#else
+
 /* Lookup an already existing target description matching FEATURES, or
    create a new target description if this is the first time we have seen
    FEATURES.  For the same FEATURES the same target_desc is always
@@ -70,4 +81,6 @@ struct loongarch_gdbarch_features
 const target_desc *loongarch_lookup_target_description
 	(const struct loongarch_gdbarch_features features);
 
+#endif /* GDBSERVER */
+
 #endif /* ARCH_LOONGARCH_H  */
diff --git a/gdbserver/Makefile.in b/gdbserver/Makefile.in
index 6e14278cd4b..75e497753e8 100644
--- a/gdbserver/Makefile.in
+++ b/gdbserver/Makefile.in
@@ -176,6 +176,7 @@ SFILES = \
 	$(srcdir)/linux-arc-low.cc \
 	$(srcdir)/linux-arm-low.cc \
 	$(srcdir)/linux-ia64-low.cc \
+	$(srcdir)/linux-loongarch-low.cc \
 	$(srcdir)/linux-low.cc \
 	$(srcdir)/linux-m68k-low.cc \
 	$(srcdir)/linux-mips-low.cc \
@@ -211,6 +212,7 @@ SFILES = \
 	$(srcdir)/../gdb/arch/arm.c \
 	$(srcdir)/../gdb/arch/arm-get-next-pcs.c \
 	$(srcdir)/../gdb/arch/arm-linux.c \
+	$(srcdir)/../gdb/arch/loongarch.c \
 	$(srcdir)/../gdb/arch/ppc-linux-common.c \
 	$(srcdir)/../gdb/arch/riscv.c \
 	$(srcdir)/../gdb/nat/aarch64-mte-linux-ptrace.c \
diff --git a/gdbserver/configure.srv b/gdbserver/configure.srv
index d37053628fc..ebb6b32a6c4 100644
--- a/gdbserver/configure.srv
+++ b/gdbserver/configure.srv
@@ -126,6 +126,12 @@ case "${gdbserver_host}" in
 			srv_tgtobj="$srv_linux_obj linux-ia64-low.o"
 			srv_linux_usrregs=yes
 			;;
+  loongarch*-*-linux*)	srv_tgtobj="arch/loongarch.o linux-loongarch-low.o"
+			srv_tgtobj="${srv_tgtobj} ${srv_linux_obj}"
+			srv_linux_regsets=yes
+			srv_linux_usrregs=yes
+			srv_linux_thread_db=yes
+			;;
   m68*-*-linux*)	if test "$gdb_cv_m68k_is_coldfire" = yes; then
                           srv_regobj=reg-cf.o
                         else
diff --git a/gdbserver/linux-loongarch-low.cc b/gdbserver/linux-loongarch-low.cc
new file mode 100644
index 00000000000..da38eafb3c5
--- /dev/null
+++ b/gdbserver/linux-loongarch-low.cc
@@ -0,0 +1,245 @@
+/* GNU/Linux/LoongArch specific low level interface, for the remote server
+   for GDB.
+   Copyright (C) 2022 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 "server.h"
+#include "linux-low.h"
+#include "tdesc.h"
+#include "elf/common.h"
+#include "arch/loongarch.h"
+
+/* Linux target op definitions for the LoongArch architecture.  */
+
+class loongarch_target : public linux_process_target
+{
+public:
+
+  const regs_info *get_regs_info () override;
+
+  int breakpoint_kind_from_pc (CORE_ADDR *pcptr) override;
+
+  const gdb_byte *sw_breakpoint_from_kind (int kind, int *size) override;
+
+protected:
+
+  void low_arch_setup () override;
+
+  bool low_cannot_fetch_register (int regno) override;
+
+  bool low_cannot_store_register (int regno) override;
+
+  bool low_fetch_register (regcache *regcache, int regno) override;
+
+  bool low_supports_breakpoints () override;
+
+  CORE_ADDR low_get_pc (regcache *regcache) override;
+
+  void low_set_pc (regcache *regcache, CORE_ADDR newpc) override;
+
+  bool low_breakpoint_at (CORE_ADDR pc) override;
+};
+
+/* The singleton target ops object.  */
+
+static loongarch_target the_loongarch_target;
+
+bool
+loongarch_target::low_cannot_fetch_register (int regno)
+{
+  gdb_assert_not_reached ("linux target op low_cannot_fetch_register "
+			  "is not implemented by the target");
+}
+
+bool
+loongarch_target::low_cannot_store_register (int regno)
+{
+  gdb_assert_not_reached ("linux target op low_cannot_store_register "
+			  "is not implemented by the target");
+}
+
+/* Implementation of linux target ops method "low_arch_setup".  */
+
+void
+loongarch_target::low_arch_setup ()
+{
+  static const char *expedite_regs[] = { "r3", "pc", NULL };
+  loongarch_gdbarch_features features;
+  target_desc_up tdesc;
+
+  features.xlen = sizeof (elf_greg_t);
+  tdesc = loongarch_create_target_description (features);
+
+  if (!tdesc->expedite_regs)
+    init_target_desc (tdesc.get (), expedite_regs);
+  current_process ()->tdesc = tdesc.release ();
+}
+
+/* Collect GPRs from REGCACHE into BUF.  */
+
+static void
+loongarch_fill_gregset (struct regcache *regcache, void *buf)
+{
+  const struct target_desc *tdesc = regcache->tdesc;
+  elf_gregset_t *regset = (elf_gregset_t *) buf;
+  int regno = find_regno (tdesc, "r0");
+  int i;
+
+  for (i = 1; i < 32; i++)
+    collect_register (regcache, regno + i, *regset + i);
+  collect_register_by_name (regcache, "pc", *regset + 32);
+  collect_register_by_name (regcache, "badv", *regset + 33);
+}
+
+/* Supply GPRs from BUF into REGCACHE.  */
+
+static void
+loongarch_store_gregset (struct regcache *regcache, const void *buf)
+{
+  const struct target_desc *tdesc = regcache->tdesc;
+  const elf_gregset_t *regset = (const elf_gregset_t *) buf;
+  int regno = find_regno (tdesc, "r0");
+  int i;
+
+  supply_register_zeroed (regcache, regno);
+  for (i = 1; i < 32; i++)
+    supply_register (regcache, regno + i, *regset + i);
+  supply_register_by_name (regcache, "pc", *regset + 32);
+  supply_register_by_name (regcache, "badv", *regset + 33);
+}
+
+/* LoongArch/Linux regsets.  */
+static struct regset_info loongarch_regsets[] = {
+  { PTRACE_GETREGSET, PTRACE_SETREGSET, NT_PRSTATUS, sizeof (elf_gregset_t),
+    GENERAL_REGS, loongarch_fill_gregset, loongarch_store_gregset },
+  NULL_REGSET
+};
+
+/* LoongArch/Linux regset information.  */
+static struct regsets_info loongarch_regsets_info =
+  {
+    loongarch_regsets, /* regsets */
+    0, /* num_regsets */
+    NULL, /* disabled_regsets */
+  };
+
+/* Definition of linux_target_ops data member "regs_info".  */
+static struct regs_info loongarch_regs =
+  {
+    NULL, /* regset_bitmap */
+    NULL, /* usrregs */
+    &loongarch_regsets_info,
+  };
+
+/* Implementation of linux target ops method "get_regs_info".  */
+
+const regs_info *
+loongarch_target::get_regs_info ()
+{
+  return &loongarch_regs;
+}
+
+/* Implementation of linux target ops method "low_fetch_register".  */
+
+bool
+loongarch_target::low_fetch_register (regcache *regcache, int regno)
+{
+  const struct target_desc *tdesc = regcache->tdesc;
+
+  if (regno != find_regno (tdesc, "r0"))
+    return false;
+  supply_register_zeroed (regcache, regno);
+  return true;
+}
+
+bool
+loongarch_target::low_supports_breakpoints ()
+{
+  return true;
+}
+
+/* Implementation of linux target ops method "low_get_pc".  */
+
+CORE_ADDR
+loongarch_target::low_get_pc (regcache *regcache)
+{
+  if (register_size (regcache->tdesc, 0) == 8)
+    return linux_get_pc_64bit (regcache);
+  else
+    return linux_get_pc_32bit (regcache);
+}
+
+/* Implementation of linux target ops method "low_set_pc".  */
+
+void
+loongarch_target::low_set_pc (regcache *regcache, CORE_ADDR newpc)
+{
+  if (register_size (regcache->tdesc, 0) == 8)
+    linux_set_pc_64bit (regcache, newpc);
+  else
+    linux_set_pc_32bit (regcache, newpc);
+}
+
+#define loongarch_breakpoint_len 4
+
+/* LoongArch BRK software debug mode instruction.
+   This instruction needs to match gdb/loongarch-tdep.c
+   (loongarch_default_breakpoint).  */
+static const gdb_byte loongarch_breakpoint[] = {0x05, 0x00, 0x2a, 0x00};
+
+/* Implementation of target ops method "breakpoint_kind_from_pc".  */
+
+int
+loongarch_target::breakpoint_kind_from_pc (CORE_ADDR *pcptr)
+{
+  return loongarch_breakpoint_len;
+}
+
+/* Implementation of target ops method "sw_breakpoint_from_kind".  */
+
+const gdb_byte *
+loongarch_target::sw_breakpoint_from_kind (int kind, int *size)
+{
+  *size = loongarch_breakpoint_len;
+  return (const gdb_byte *) &loongarch_breakpoint;
+}
+
+/* Implementation of linux target ops method "low_breakpoint_at".  */
+
+bool
+loongarch_target::low_breakpoint_at (CORE_ADDR pc)
+{
+  gdb_byte insn[loongarch_breakpoint_len];
+
+  read_memory (pc, (unsigned char *) &insn, loongarch_breakpoint_len);
+  if (memcmp (insn, loongarch_breakpoint, loongarch_breakpoint_len) == 0)
+    return true;
+
+  return false;
+}
+
+/* The linux target ops object.  */
+
+linux_process_target *the_linux_target = &the_loongarch_target;
+
+/* Initialize the LoongArch/Linux target.  */
+
+void
+initialize_low_arch ()
+{
+  initialize_regsets_info (&loongarch_regsets_info);
+}
-- 
2.20.1

Re: [PATCH] gdbserver: Add LoongArch/Linux port support

[Eli Zaretskii]

> From: Youling Tang <tangyouling@loongson.cn>
> Date: Tue, 31 May 2022 10:45:42 +0800
> Cc: "Maciej W. Rozycki" <macro@orcam.me.uk>
> 
> 2022-05-31  Youling Tang <tangyouling@loongson.cn>
> 
> 	gdb/
> 	* NEWS: Mention LoongArch GNU/Linux GDBserver support.
> 	* arch/loongarch.h: Declare the loongarch_create_target_description
> 	function when GDBSERVER is defined.
> 
> 	gdbserver/
> 	* linux-loongarch-low.cc: New file.
> 	* Makefile.in (SFILES): Add linux-loongarch-low.cc and
> 	arch/loongarch.c.
> 	* configure.srv <loongarch*-*-linux*> (srv_tgtobj)
> 	srv_linux_regsets, srv_linux_usrregs, srv_linux_thread_db):
> 	Define.

OK for the NEWS part.

Thanks.