backends: Add initial return value location support for LoongArch

LoongArch ELF ABI specification - Return values:
https://loongson.github.io/LoongArch-Documentation/LoongArch-ELF-ABI-EN.html#_return_values

Signed-off-by: Liwei Ge <geliwei@openanolis.org>
Signed-off-by: Youling Tang <tangyouling@loongson.cn>

4 files changed, 212 insertions, 1 deletions

diff --git a/backends/ChangeLog b/backends/ChangeLog
index 926c76ed..df762073 100644
--- a/backends/ChangeLog
+++ b/backends/ChangeLog
@@ -1,5 +1,11 @@
 2023-04-07  Youling Tang  <tangyouling@loongson.cn>
 
+	* Makefile.am (loongarch_SRCS): Add loongarch_retval.c.
+	* loongarch_init.c (loongarch_init): Hook return_value_location.
+	* loongarch_retval.c: New file.
+
+2023-04-07  Youling Tang  <tangyouling@loongson.cn>
+
 	* Makefile.am (loongarch_SRCS): Add loongarch_cfi.c and loongarch_regs.c.
 	* loongarch_cfi.c: New file.
 	* loongarch_regs.c: Likewise.
diff --git a/backends/Makefile.am b/backends/Makefile.am
index 2b6f08ce..50e78ea5 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_regs.c loongarch_retval.c
 
 arc_SRCS = arc_init.c arc_symbol.c
 
diff --git a/backends/loongarch_init.c b/backends/loongarch_init.c
index 7bfaaa7f..fd63f373 100644
--- a/backends/loongarch_init.c
+++ b/backends/loongarch_init.c
@@ -1,5 +1,7 @@
 /* Initialization of LoongArch specific backend library.
    Copyright (C) 2022 Hengqi Chen
+   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
@@ -51,6 +53,7 @@ loongarch_init (Elf *elf __attribute__ ((unused)),
   /* gcc/config/ #define DWARF_FRAME_REGISTERS.  */
   eh->frame_nregs = 74;
   HOOK (eh, check_special_symbol);
+  HOOK (eh, return_value_location);
 
   return eh;
 }
diff --git a/backends/loongarch_retval.c b/backends/loongarch_retval.c
new file mode 100644
index 00000000..23b33ed5
--- /dev/null
+++ b/backends/loongarch_retval.c
@@ -0,0 +1,202 @@
+/* Function return value location for Linux/LoongArch ABI.
+   Copyright (C) 2013 Red Hat, Inc.
+   Copyright (C) 2023 OpenAnolis community LoongArch SIG.
+   Copyright (C) 2023 Loongson Technology Corporation Limited.
+
+   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 <stdio.h>
+#include <inttypes.h>
+
+#include <assert.h>
+#include <dwarf.h>
+
+#define BACKEND loongarch_
+#include "libebl_CPU.h"
+
+static int
+dwarf_bytesize_aux (Dwarf_Die *die, Dwarf_Word *sizep)
+{
+  int bits;
+  if (((bits = 8 * dwarf_bytesize (die)) < 0
+       && (bits = dwarf_bitsize (die)) < 0)
+      || bits % 8 != 0)
+    return -1;
+
+  *sizep = bits / 8;
+  return 0;
+}
+
+static int
+pass_in_gpr (const Dwarf_Op **locp, Dwarf_Word size)
+{
+  static const Dwarf_Op loc[] =
+    {
+      { .atom = DW_OP_reg4 }, { .atom = DW_OP_piece, .number = 8 },
+      { .atom = DW_OP_reg5 }, { .atom = DW_OP_piece, .number = 8 }
+    };
+
+  *locp = loc;
+  return size <= 8 ? 1 : 4;
+}
+
+static int
+pass_by_ref (const Dwarf_Op **locp)
+{
+  static const Dwarf_Op loc[] = { { .atom = DW_OP_breg4 } };
+
+  *locp = loc;
+  return 1;
+}
+
+static int
+pass_in_fpr (const Dwarf_Op **locp, Dwarf_Word size)
+{
+  static const Dwarf_Op loc[] =
+    {
+      { .atom = DW_OP_regx, .number = 32 },
+      { .atom = DW_OP_piece, .number = 8 },
+      { .atom = DW_OP_regx, .number = 33 },
+      { .atom = DW_OP_piece, .number = 8 }
+    };
+
+  *locp = loc;
+  return size <= 8 ? 1 : 4;
+}
+
+int
+loongarch_return_value_location(Dwarf_Die *functypedie,
+                                const Dwarf_Op **locp)
+{
+  /* Start with the function's type, and get the DW_AT_type attribute,
+     which is the type of the return value.  */
+  Dwarf_Die typedie;
+  int tag = dwarf_peeled_die_type (functypedie, &typedie);
+  if (tag <= 0)
+    return tag;
+
+  Dwarf_Word size = (Dwarf_Word)-1;
+
+  /* If the argument type is a Composite Type that is larger than 16
+     bytes, then the argument is copied to memory allocated by the
+     caller and the argument is replaced by a pointer to the copy.  */
+  if (tag == DW_TAG_structure_type || tag == DW_TAG_union_type
+      || tag == DW_TAG_class_type || tag == DW_TAG_array_type)
+    {
+      if (dwarf_aggregate_size (&typedie, &size) < 0)
+	return -1;
+
+      /* Aggregates larger than 2*GRLEN bits are passed by reference.  */
+      if (size > 16)
+	return pass_by_ref (locp);
+      /* Aggregates whose total size is no more than GRLEN bits are passed in
+	 a register.  Aggregates whose total size is no more than 2*GRLEN bits
+	 are passed in a pair of registers.  */
+      else
+	return pass_in_gpr (locp, size);
+    }
+
+  if (tag == DW_TAG_base_type || dwarf_is_pointer (tag))
+    {
+      if (dwarf_bytesize_aux (&typedie, &size) < 0)
+	{
+	  if (dwarf_is_pointer (tag))
+	    size = 8;
+	  else
+	    return -1;
+	}
+
+      Dwarf_Attribute attr_mem;
+      if (tag == DW_TAG_base_type)
+	{
+	  Dwarf_Word encoding;
+	  if (dwarf_formudata (dwarf_attr_integrate (&typedie, DW_AT_encoding,
+						     &attr_mem),
+			       &encoding) != 0)
+	    return -1;
+
+	  switch (encoding)
+	    {
+	    case DW_ATE_boolean:
+	    case DW_ATE_signed:
+	    case DW_ATE_unsigned:
+	    case DW_ATE_unsigned_char:
+	    case DW_ATE_signed_char:
+	      /* Scalars that are at most GRLEN bits wide are passed in a single
+		 argument register.  Scalars that are 2*GRLEN bits wide are
+		 passed in a pair of argument registers.  Scalars wider than
+		 2*GRLEN are passed by reference.  */
+	      return pass_in_gpr (locp, size);
+
+	    case DW_ATE_float:
+	      /* A real floating-point argument is passed in a floating-point
+		 argument register if it is no more than FLEN bits wide,
+		 otherwise it is passed according to the integer calling
+		 convention.  */
+	      switch (size)
+		{
+		case 4: /* single */
+                case 8: /* double */
+                  return pass_in_fpr (locp, size);
+
+                case 16: /* quad */
+	          return pass_in_gpr (locp, size);
+
+		default:
+		  return -2;
+		}
+
+	    case DW_ATE_complex_float:
+	      /* A complex floating-point number is passed as though it were a
+		 struct containing two floating-point reals.  */
+	      switch (size)
+		{
+		case 8: /* float _Complex */
+                case 16: /* double _Complex */
+                  return pass_in_fpr (locp, size);
+
+                case 32: /* long double _Complex */
+		  return pass_by_ref (locp);
+
+		default:
+		  return -2;
+		}
+	    }
+
+	  return -2;
+	}
+      else
+	return pass_in_gpr (locp, size);
+    }
+
+  *locp = NULL;
+  return 0;
+}