[PATCH] RISC-V: Add initial return value location support.

[Jim Wilson <jimw at sifive dot com>]

Started with the aarch64 support and modified it for RISC-V.  The flattened
structure support hasn't been written yet, but the rest of it should be
correct for the LP64D ABI.  We have potentially 6 different ABIs to support,
so this requires checking elf header flags in riscv_init when setting the hook.

Signed-off-by: Jim Wilson <jimw@sifive.com>
---
 backends/ChangeLog      |   8 ++
 backends/Makefile.am    |   2 +-
 backends/riscv_init.c   |  10 +-
 backends/riscv_retval.c | 251 ++++++++++++++++++++++++++++++++++++++++
 4 files changed, 269 insertions(+), 2 deletions(-)
 create mode 100644 backends/riscv_retval.c

diff --git a/backends/ChangeLog b/backends/ChangeLog
index c8234072..637aa8c2 100644
--- a/backends/ChangeLog
+++ b/backends/ChangeLog
@@ -1,5 +1,13 @@
 2018-12-27  Jim Wilson  <jimw@sifive.com>
 
+	* Makefile.am (riscv_SRCS): Add riscv_retval.c.
+	* riscv_init.c: Include libelfP.h.
+	(riscv_return_value_location_lp64d): Declare.
+	(riscv_init): Delete unused attribute from elf parameter.  Register
+	riscv_return_value_location_lp64d hook if 64-bit ELF and 64-bit FP
+	registers.
+	* riscv_retval.c: New file.
+
 	* riscv_corenote.c (prstatus_regs): Change offset from 1 to 8.
 	(PRSTATUS_REGSET_ITEMS): New.
 
diff --git a/backends/Makefile.am b/backends/Makefile.am
index 9d340425..fedeb93a 100644
--- a/backends/Makefile.am
+++ b/backends/Makefile.am
@@ -132,7 +132,7 @@ libebl_bpf_pic_a_SOURCES = $(bpf_SRCS)
 am_libebl_bpf_pic_a_OBJECTS = $(bpf_SRCS:.c=.os)
 
 riscv_SRCS = riscv_init.c riscv_symbol.c riscv_cfi.c riscv_regs.c \
-	     riscv_initreg.c riscv_corenote.c
+	     riscv_initreg.c riscv_corenote.c riscv_retval.c
 libebl_riscv_pic_a_SOURCES = $(riscv_SRCS)
 am_libebl_riscv_pic_a_OBJECTS = $(riscv_SRCS:.c=.os)
 
diff --git a/backends/riscv_init.c b/backends/riscv_init.c
index 8b7ce8b5..ecee2910 100644
--- a/backends/riscv_init.c
+++ b/backends/riscv_init.c
@@ -33,12 +33,16 @@
 #define RELOC_PREFIX	R_RISCV_
 #include "libebl_CPU.h"
 
+#include "libelfP.h"
+
 /* This defines the common reloc hooks based on riscv_reloc.def.  */
 #include "common-reloc.c"
 
+extern __typeof (EBLHOOK (return_value_location))
+  riscv_return_value_location_lp64d attribute_hidden;
 
 const char *
-riscv_init (Elf *elf __attribute__ ((unused)),
+riscv_init (Elf *elf,
 	    GElf_Half machine __attribute__ ((unused)),
 	    Ebl *eh,
 	    size_t ehlen)
@@ -59,6 +63,10 @@ riscv_init (Elf *elf __attribute__ ((unused)),
   HOOK (eh, machine_flag_check);
   HOOK (eh, set_initial_registers_tid);
   HOOK (eh, core_note);
+  if (eh->class == ELFCLASS64
+      && ((elf->state.elf64.ehdr->e_flags & EF_RISCV_FLOAT_ABI)
+	  == EF_RISCV_FLOAT_ABI_DOUBLE))
+    eh->return_value_location = riscv_return_value_location_lp64d;
 
   return MODVERSION;
 }
diff --git a/backends/riscv_retval.c b/backends/riscv_retval.c
new file mode 100644
index 00000000..35b6010b
--- /dev/null
+++ b/backends/riscv_retval.c
@@ -0,0 +1,251 @@
+/* Function return value location for Linux/RISC-V ABI.
+   Copyright (C) 2018 Sifive, Inc.
+   Copyright (C) 2013 Red Hat, Inc.
+   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 riscv_
+#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_lp64 (const Dwarf_Op **locp, Dwarf_Word size)
+{
+  static const Dwarf_Op loc[] =
+    {
+      { .atom = DW_OP_reg10 }, { .atom = DW_OP_piece, .number = 8 },
+      { .atom = DW_OP_reg11 }, { .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_breg10 } };
+
+  *locp = loc;
+  return 1;
+}
+
+static int
+pass_in_fpr_lp64f (const Dwarf_Op **locp, Dwarf_Word size)
+{
+  static const Dwarf_Op loc[] =
+    {
+      { .atom = DW_OP_regx, .number = 42 },
+      { .atom = DW_OP_piece, .number = 4 },
+      { .atom = DW_OP_regx, .number = 43 },
+      { .atom = DW_OP_piece, .number = 4 }
+    };
+
+  *locp = loc;
+  return size <= 4 ? 1 : 4;
+}
+
+static int
+pass_in_fpr_lp64d (const Dwarf_Op **locp, Dwarf_Word size)
+{
+  static const Dwarf_Op loc[] =
+    {
+      { .atom = DW_OP_regx, .number = 42 },
+      { .atom = DW_OP_piece, .number = 8 },
+      { .atom = DW_OP_regx, .number = 43 },
+      { .atom = DW_OP_piece, .number = 8 }
+    };
+
+  *locp = loc;
+  return size <= 8 ? 1 : 4;
+}
+
+static int
+flatten_aggregate_arg (Dwarf_Die *typedie __attribute__ ((unused)),
+		       Dwarf_Die *arg0 __attribute__ ((unused)),
+		       Dwarf_Die *arg1 __attribute__ ((unused)))
+{
+  /* ??? */
+  return 1;
+}
+
+static int
+pass_by_flattened_arg (const Dwarf_Op **locp __attribute__ ((unused)),
+		       Dwarf_Word size __attribute__ ((unused)),
+		       Dwarf_Die *arg0 __attribute__ ((unused)),
+		       Dwarf_Die *arg1 __attribute__ ((unused)))
+{
+  /* ??? */
+  return -2;
+}
+
+int
+riscv_return_value_location_lp64d (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)
+    {
+      Dwarf_Die arg0, arg1;
+
+      if (dwarf_aggregate_size (&typedie, &size) < 0)
+	return -1;
+      /* A struct containing just one floating-point real is passed as though
+	 it were a standalone floating-point real.  A struct containing two
+	 floating-point reals is passed in two floating-point registers, if
+	 neither is more than FLEN bits wide.  A struct containing just one
+	 complex floating-point number is passed as though it were a struct
+	 containing two floating-point reals.  A struct containing one
+	 floating-point real and one integer (or bitfield), in either order,
+	 is passed in a floating-point register and an integer register,
+	 provided the floating-point real is no more than FLEN bits wide and
+	 the integer is no more than XLEN bits wide.  */
+      if (tag == DW_TAG_structure_type
+	  && flatten_aggregate_arg (&typedie, &arg0, &arg1))
+	return pass_by_flattened_arg (locp, size, &arg0, &arg1);
+      /* Aggregates larger than 2*XLEN bits are passed by reference.  */
+      else if (size > 16)
+	return pass_by_ref (locp);
+      /* Aggregates whose total size is no more than XLEN bits are passed in
+	 a register.  Aggregates whose total size is no more than 2*XLEN bits
+	 are passed in a pair of registers.  */
+      else
+	return pass_in_gpr_lp64 (locp, size);
+    }
+
+  if (tag == DW_TAG_base_type
+      || tag == DW_TAG_pointer_type || tag == DW_TAG_ptr_to_member_type)
+    {
+      if (dwarf_bytesize_aux (&typedie, &size) < 0)
+	{
+	  if (tag == DW_TAG_pointer_type || tag == DW_TAG_ptr_to_member_type)
+	    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 XLEN bits wide are passed in a single
+		 argument register.  Scalars that are 2*XLEN bits wide are
+		 passed in a pair of argument registers.  Scalars wider than
+		 2*XLEN are passed by reference; there are none for LP64D.  */
+	      return pass_in_gpr_lp64 (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_lp64d (locp, size);
+
+		case 16: /* quad */
+		  return pass_in_gpr_lp64 (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 */
+		  return pass_in_fpr_lp64f (locp, size);
+
+		case 16: /* double _Complex */
+		  return pass_in_fpr_lp64d (locp, size);
+
+		case 32: /* long double _Complex */
+		  return pass_by_ref (locp);
+
+		default:
+		  return -2;
+		}
+	    }
+
+	  return -2;
+	}
+      else
+	return pass_in_gpr_lp64 (locp, size);
+    }
+
+  *locp = NULL;
+  return 0;
+}
-- 
2.19.2