[v2] backends: Add set_initial_registers_tid callback for LoongArch

diff --git a/backends/ChangeLog b/backends/ChangeLog
index c60d6cdb..ddb4e0af 100644
--- a/backends/ChangeLog
+++ b/backends/ChangeLog
@@ -1,3 +1,9 @@ 
+2023-05-09  Youling Tang  <tangyouling@loongson.cn>
+
+	* Makefile.am (loongarch_SRCS): Add loongarch_initreg.c.
+	* loongarch_initreg.c: New file.
+	* loongarch_init.c (loongarch_init): Hook set_initial_registers_tid.
+
 2023-04-07  Youling Tang  <tangyouling@loongson.cn>
 
 	* Makefile.am (loongarch_SRCS): Add loongarch_corenote.c.
diff --git a/backends/Makefile.am b/backends/Makefile.am
index c7a953a1..bbb2aac7 100644
--- a/backends/Makefile.am
+++ b/backends/Makefile.am
@@ -97,7 +97,7 @@  csky_SRCS = csky_attrs.c csky_init.c csky_symbol.c csky_cfi.c \
 	    csky_regs.c csky_initreg.c csky_corenote.c
 
 loongarch_SRCS = loongarch_init.c loongarch_symbol.c loongarch_cfi.c \
-	    loongarch_regs.c loongarch_retval.c \
+	    loongarch_regs.c loongarch_retval.c loongarch_initreg.c \
 	    loongarch_unwind.c loongarch_corenote.c
 
 arc_SRCS = arc_init.c arc_symbol.c
diff --git a/backends/loongarch_init.c b/backends/loongarch_init.c
index 0b99d113..2f0d46c9 100644
--- a/backends/loongarch_init.c
+++ b/backends/loongarch_init.c
@@ -54,6 +54,7 @@  loongarch_init (Elf *elf __attribute__ ((unused)),
   /* gcc/config/ #define DWARF_FRAME_REGISTERS.  */
   eh->frame_nregs = 74;
   HOOK (eh, check_special_symbol);
+  HOOK (eh, set_initial_registers_tid);
   HOOK (eh, return_value_location);
   HOOK (eh, unwind);
 
diff --git a/backends/loongarch_initreg.c b/backends/loongarch_initreg.c
new file mode 100644
index 00000000..74cb62f5
--- /dev/null
+++ b/backends/loongarch_initreg.c
@@ -0,0 +1,88 @@ 
+/* Fetch live process registers from TID.
+   Copyright (C) 2023 OpenAnolis community LoongArch SIG.
+   Copyright (C) 2023 Loongson Technology Corporation Limted.
+   This file is part of elfutils.
+
+   This file is free software; you can redistribute it and/or modify
+   it under the terms of either
+
+     * the GNU Lesser General Public License as published by the Free
+       Software Foundation; either version 3 of the License, or (at
+       your option) any later version
+
+   or
+
+     * the GNU General Public License as published by the Free
+       Software Foundation; either version 2 of the License, or (at
+       your option) any later version
+
+   or both in parallel, as here.
+
+   elfutils 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 copies of the GNU General Public License and
+   the GNU Lesser General Public License along with this program.  If
+   not, see <http://www.gnu.org/licenses/>.  */
+
+#ifdef HAVE_CONFIG_H
+# include <config.h>
+#endif
+
+#include "system.h"
+#include <assert.h>
+#if defined __loongarch__ && defined __linux__
+# include <sys/uio.h>
+# include <sys/procfs.h>
+# include <sys/ptrace.h>
+#endif
+
+#define BACKEND loongarch_
+#include "libebl_CPU.h"
+
+bool
+loongarch_set_initial_registers_tid (pid_t tid __attribute__ ((unused)),
+				 ebl_tid_registers_t *setfunc __attribute__ ((unused)),
+				 void *arg __attribute__ ((unused)))
+{
+#if !defined __loongarch__ || !defined __linux__
+  return false;
+#else /* __loongarch__ */
+
+  /* General registers.  */
+  struct user_regs_struct gregs;
+  struct iovec iovec;
+  iovec.iov_base = &gregs;
+  iovec.iov_len = sizeof (gregs);
+  if (ptrace (PTRACE_GETREGSET, tid, NT_PRSTATUS, &iovec) != 0)
+    return false;
+
+  /* $r0 is constant 0.  */
+  Dwarf_Word zero = 0;
+  if (! setfunc (0, 1, &zero, arg))
+    return false;
+
+  /* $r1-$r31.  */
+  if (! setfunc (1, 32, (Dwarf_Word *) &gregs.regs[1], arg))
+    return false;
+
+  /* PC.  */
+  if (! setfunc (-1, 1, (Dwarf_Word *) &gregs.csr_era, arg))
+    return false;
+
+  /* Floating-point registers (only 64bits are used).  */
+  struct user_fp_struct fregs;
+  iovec.iov_base = &fregs;
+  iovec.iov_len = sizeof (fregs);
+  if (ptrace (PTRACE_GETREGSET, tid, NT_FPREGSET, &iovec) != 0)
+    return false;
+
+  /* $f0-$f31 */
+  if (! setfunc (32, 32, (Dwarf_Word *) &fregs.fpr[0], arg))
+    return false;
+
+  return true;
+#endif /* __loongarch__ */
+}