/* Subroutines used for code generation for eBPF.
   Copyright (C) 2019-2020 Free Software Foundation, Inc.

This file is part of GCC.

GCC 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, or (at your option)
any later version.

GCC 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 GCC; see the file COPYING3.  If not see
<http://www.gnu.org/licenses/>.  */

#define IN_TARGET_CODE 1

#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "tm.h"
#include "rtl.h"
#include "regs.h"
#include "insn-config.h"
#include "insn-attr.h"
#include "recog.h"
#include "output.h"
#include "alias.h"
#include "tree.h"
#include "stringpool.h"
#include "attribs.h"
#include "varasm.h"
#include "stor-layout.h"
#include "calls.h"
#include "function.h"
#include "explow.h"
#include "memmodel.h"
#include "emit-rtl.h"
#include "reload.h"
#include "tm_p.h"
#include "target.h"
#include "target-def.h"
#include "basic-block.h"
#include "expr.h"
#include "optabs.h"
#include "bitmap.h"
#include "df.h"
#include "c-family/c-common.h"
#include "diagnostic.h"
#include "builtins.h"
#include "predict.h"
#include "langhooks.h"

/* Per-function machine data.  */
struct GTY(()) machine_function
{
  /* Number of bytes saved on the stack for local variables.  */
  int local_vars_size;

  /* Number of bytes saved on the stack for callee-saved
     registers.  */
  int callee_saved_reg_size;
};

/* Data structures for the eBPF specific built-ins.  */

/* Maximum number of arguments taken by a builtin function, plus
   one.  */
#define BPF_BUILTIN_MAX_ARGS 5

enum bpf_builtins
{
  BPF_BUILTIN_UNUSED = 0,
  /* Built-ins for kernel helpers.  */
#define DEF_HELPER(V,D,N,T) BPF_BUILTIN_HELPER_##D,
#  include "bpf-helpers.def"
#undef DEF_HELPER
  BPF_BUILTIN_HELPER_MAX,
  /* Built-ins for non-generic loads and stores.  */
  BPF_BUILTIN_LOAD_BYTE = BPF_BUILTIN_HELPER_MAX,
  BPF_BUILTIN_LOAD_HALF,
  BPF_BUILTIN_LOAD_WORD,
  BPF_BUILTIN_MAX,
};

/* This table is indexed by an enum bpf_builtin.  */
static const char *bpf_helper_names[] =
{
  NULL,
#define DEF_HELPER(V,D,N,T) #N,
#  include "bpf-helpers.def"
#undef DEF_HELPER
  NULL,
  NULL,
  NULL,
  NULL
};

/* Return the builtin code corresponding to the kernel helper builtin
   __builtin_NAME, or 0 if the name doesn't correspond to a kernel
   helper builtin.  */

static inline int
bpf_helper_code (const char *name)
{
  int i;

  for (i = 1; i < BPF_BUILTIN_HELPER_MAX; ++i)
    if (strcmp (name, bpf_helper_names[i]) == 0)
      return i;

  return 0;
}

static GTY (()) tree bpf_builtins[(int) BPF_BUILTIN_MAX];

/* Initialize the per-function machine status.  */

static struct machine_function *
bpf_init_machine_status (void)
{
  /* Note this initializes all fields to 0, which is just OK for
     us.  */
  return ggc_cleared_alloc<machine_function> ();
}

/* Override options and do some other initialization.  */

static void
bpf_option_override (void)
{
  /* Set the initializer for the per-function status structure.  */
  init_machine_status = bpf_init_machine_status;
}

#undef TARGET_OPTION_OVERRIDE
#define TARGET_OPTION_OVERRIDE bpf_option_override

/* Define target-specific CPP macros.  This function in used in the
   definition of TARGET_CPU_CPP_BUILTINS in bpf.h */

#define builtin_define(TXT) cpp_define (pfile, TXT)

void
bpf_target_macros (cpp_reader *pfile)
{
  builtin_define ("__BPF__");
  
  if (TARGET_BIG_ENDIAN)
    builtin_define ("__BPF_BIG_ENDIAN__");
  else
    builtin_define ("__BPF_LITTLE_ENDIAN__");

  /* Define BPF_KERNEL_VERSION_CODE */
  {
    const char *version_code;
    char *kernel_version_code;

    switch (bpf_kernel)
      {
      case LINUX_V4_0: version_code = "0x40000"; break;
      case LINUX_V4_1: version_code = "0x40100"; break;
      case LINUX_V4_2: version_code = "0x40200"; break;
      case LINUX_V4_3: version_code = "0x40300"; break;
      case LINUX_V4_4: version_code = "0x40400"; break;
      case LINUX_V4_5: version_code = "0x40500"; break;
      case LINUX_V4_6: version_code = "0x40600"; break;
      case LINUX_V4_7: version_code = "0x40700"; break;
      case LINUX_V4_8: version_code = "0x40800"; break;
      case LINUX_V4_9: version_code = "0x40900"; break;
      case LINUX_V4_10: version_code = "0x40a00"; break;
      case LINUX_V4_11: version_code = "0x40b00"; break;
      case LINUX_V4_12: version_code = "0x40c00"; break;
      case LINUX_V4_13: version_code = "0x40d00"; break;
      case LINUX_V4_14: version_code = "0x40e00"; break;
      case LINUX_V4_15: version_code = "0x40f00"; break;
      case LINUX_V4_16: version_code = "0x41000"; break;
      case LINUX_V4_17: version_code = "0x42000"; break;
      case LINUX_V4_18: version_code = "0x43000"; break;
      case LINUX_V4_19: version_code = "0x44000"; break;
      case LINUX_V4_20: version_code = "0x45000"; break;
      case LINUX_V5_0: version_code = "0x50000"; break;
      case LINUX_V5_1: version_code = "0x50100"; break;
      case LINUX_V5_2: version_code = "0x50200"; break;
      default:
	gcc_unreachable ();      
      }

    kernel_version_code = ACONCAT (("__BPF_KERNEL_VERSION_CODE__=",
				    version_code, NULL));
    builtin_define (kernel_version_code);
  }
}

/* Output assembly directives to switch to section NAME.  The section
   should have attributes as specified by FLAGS, which is a bit mask
   of the 'SECTION_*' flags defined in 'output.h'.  If DECL is
   non-NULL, it is the 'VAR_DECL' or 'FUNCTION_DECL' with which this
   section is associated.  */

static void
bpf_asm_named_section (const char *name,
		       unsigned int flags ATTRIBUTE_UNUSED,
		       tree decl ATTRIBUTE_UNUSED)
{
  fprintf (asm_out_file, "\t.section\t%s\n", name);
}

#undef TARGET_ASM_NAMED_SECTION
#define TARGET_ASM_NAMED_SECTION bpf_asm_named_section

/* Return an RTX representing the place where a function returns or
   receives a value of data type RET_TYPE, a tree node representing a
   data type.  */

static rtx
bpf_function_value (const_tree ret_type,
		    const_tree fntype_or_decl,
		    bool outgoing ATTRIBUTE_UNUSED)
{
  enum machine_mode mode;
  int unsignedp;

  mode = TYPE_MODE (ret_type);
  if (INTEGRAL_TYPE_P (ret_type))
    mode = promote_function_mode (ret_type, mode, &unsignedp,
				  fntype_or_decl, 1);

  return gen_rtx_REG (mode, BPF_R0);
}

#undef TARGET_FUNCTION_VALUE
#define TARGET_FUNCTION_VALUE bpf_function_value

/* Return true if REGNO is the number of a hard register in which the
   values of called function may come back.  */

static bool
bpf_function_value_regno_p (const unsigned int regno)
{
  return (regno == BPF_R0);
}

#undef TARGET_FUNCTION_VALUE_REGNO_P
#define TARGET_FUNCTION_VALUE_REGNO_P bpf_function_value_regno_p

/* Compute the size of the function's stack frame, including the local
   area and the register-save area.  */

static void
bpf_compute_frame_layout (void)
{
  int stack_alignment = STACK_BOUNDARY / BITS_PER_UNIT;
  int padding_locals, regno;

  /* Set the space used in the stack by local variables.  This is
     rounded up to respect the minimum stack alignment.  */
  cfun->machine->local_vars_size = get_frame_size ();

  padding_locals = cfun->machine->local_vars_size % stack_alignment;
  if (padding_locals)
    padding_locals = stack_alignment - padding_locals;

  cfun->machine->local_vars_size += padding_locals;

  /* Set the space used in the stack by callee-saved used registers in
     the current function.  There is no need to round up, since the
     registers are all 8 bytes wide.  */
  for (regno = 0; regno < FIRST_PSEUDO_REGISTER; regno++)
    if ((df_regs_ever_live_p (regno)
	 && !call_used_or_fixed_reg_p (regno))
	|| (cfun->calls_alloca
	    && regno == STACK_POINTER_REGNUM))
      cfun->machine->callee_saved_reg_size += 8;

  /* Check that the total size of the frame doesn't exceed the limit
     imposed by eBPF.  */
  if ((cfun->machine->local_vars_size
       + cfun->machine->callee_saved_reg_size) > bpf_frame_limit)
    {
      static int stack_limit_exceeded = 0;

      if (!stack_limit_exceeded)
	error ("eBPF stack limit exceeded");
      stack_limit_exceeded = 1;
    }
}

#undef TARGET_COMPUTE_FRAME_LAYOUT
#define TARGET_COMPUTE_FRAME_LAYOUT bpf_compute_frame_layout

/* Expand to the instructions in a function prologue.  This function
   is called when expanding the 'prologue' pattern in bpf.md.  */

void
bpf_expand_prologue (void)
{
  int regno, fp_offset;
  rtx insn;
  HOST_WIDE_INT size;

  size = (cfun->machine->local_vars_size
	  + cfun->machine->callee_saved_reg_size);
  fp_offset = -cfun->machine->local_vars_size;

  /* Save callee-saved hard registes.  The register-save-area starts
     right after the local variables.  */
  for (regno = 0; regno < FIRST_PSEUDO_REGISTER; regno++)
    {
      if ((df_regs_ever_live_p (regno)
	   && !call_used_or_fixed_reg_p (regno))
	  || (cfun->calls_alloca
	      && regno == STACK_POINTER_REGNUM))
	{
	  rtx mem;

	  if (!IN_RANGE (fp_offset, -1 - 0x7fff, 0x7fff))
	    /* This has been already reported as an error in
	       bpf_compute_frame_layout. */
	    break;
	  else
	    {
	      mem = gen_frame_mem (DImode,
				   plus_constant (DImode,
						  hard_frame_pointer_rtx,
						  fp_offset - 8));
	      insn = emit_move_insn (mem, gen_rtx_REG (DImode, regno));
	      RTX_FRAME_RELATED_P (insn) = 1;
	      fp_offset -= 8;
	    }
	}
    }

  /* Set the stack pointer, if the function allocates space
     dynamically.  Note that the value of %sp should be directly
     derived from %fp, for the kernel verifier to track it as a stack
     accessor.  */
  if (cfun->calls_alloca)
    {
      insn = emit_move_insn (stack_pointer_rtx,
			     hard_frame_pointer_rtx);
      RTX_FRAME_RELATED_P (insn) = 1;
      
      if (size > 0)
	{
	  insn = emit_insn (gen_rtx_SET (stack_pointer_rtx,
					 gen_rtx_PLUS (Pmode,
						       stack_pointer_rtx,
						       GEN_INT (-size))));
	  RTX_FRAME_RELATED_P (insn) = 1;
	}
    }
}

/* Expand to the instructions in a function epilogue.  This function
   is called when expanding the 'epilogue' pattern in bpf.md.  */

void
bpf_expand_epilogue (void)
{
  int regno, fp_offset;
  rtx insn;

  fp_offset = -cfun->machine->local_vars_size;

  /* Restore callee-saved hard registes from the stack.  */
  for (regno = 0; regno < FIRST_PSEUDO_REGISTER; regno++)
    {
      if ((df_regs_ever_live_p (regno)
	   && !call_used_or_fixed_reg_p (regno))
	  || (cfun->calls_alloca
	      && regno == STACK_POINTER_REGNUM))
	{
	  rtx mem;

	  if (!IN_RANGE (fp_offset, -1 - 0x7fff, 0x7fff))
	    /* This has been already reported as an error in
	       bpf_compute_frame_layout. */
	    break;
	  else
	    {
	      mem = gen_frame_mem (DImode,
				   plus_constant (DImode,
						  hard_frame_pointer_rtx,
						  fp_offset - 8));
	      insn = emit_move_insn (gen_rtx_REG (DImode, regno), mem);
	      RTX_FRAME_RELATED_P (insn) = 1;
	      fp_offset -= 8;
	    }
	}
    }

  emit_jump_insn (gen_exit ());
}

/* Return the initial difference between the specified pair of
   registers.  The registers that can figure in FROM, and TO, are
   specified by ELIMINABLE_REGS in bpf.h.

   This function is used in the definition of
   INITIAL_ELIMINATION_OFFSET in bpf.h  */

HOST_WIDE_INT
bpf_initial_elimination_offset (int from, int to)
{
  HOST_WIDE_INT ret;

  if (from == ARG_POINTER_REGNUM && to == STACK_POINTER_REGNUM)
    ret = (cfun->machine->local_vars_size
	   + cfun->machine->callee_saved_reg_size);
  else if (from == ARG_POINTER_REGNUM && to == FRAME_POINTER_REGNUM)
    ret = 0;
  else
    gcc_unreachable ();

  return ret;
}

/* Return the number of consecutive hard registers, starting at
   register number REGNO, required to hold a value of mode MODE.  */

static unsigned int
bpf_hard_regno_nregs (unsigned int regno ATTRIBUTE_UNUSED,
		      enum machine_mode mode)
{
  return CEIL (GET_MODE_SIZE (mode), UNITS_PER_WORD);
}

#undef TARGET_HARD_REGNO_NREGS
#define TARGET_HARD_REGNO_NREGS bpf_hard_regno_nregs

/* Return true if it is permissible to store a value of mode MODE in
   hard register number REGNO, or in several registers starting with
   that one.  */

static bool
bpf_hard_regno_mode_ok (unsigned int regno ATTRIBUTE_UNUSED,
			enum machine_mode mode)
{
  switch (mode)
    {
    case E_SImode:
    case E_DImode:
    case E_HImode:
    case E_QImode:
    case E_TImode:
    case E_SFmode:
    case E_DFmode:
      return true;
    default:
      return false;
    }
}

#undef TARGET_HARD_REGNO_MODE_OK
#define TARGET_HARD_REGNO_MODE_OK bpf_hard_regno_mode_ok

/* Return true if a function must have and use a frame pointer.  */

static bool
bpf_frame_pointer_required (void)
{
  /* We do not have a stack pointer, so we absolutely depend on the
     frame-pointer in order to access the stack... and fishes walk and
     pigs fly glglgl */
  return true;
}

#undef TARGET_FRAME_POINTER_REQUIRED
#define TARGET_FRAME_POINTER_REQUIRED bpf_frame_pointer_required

/* Return `true' if the given RTX X is a valid base for an indirect
   memory access.  STRICT has the same meaning than in
   bpf_legitimate_address_p.  */

static inline bool
bpf_address_base_p (rtx x, bool strict)
{
  return (GET_CODE (x) == REG
	  && (REGNO (x) < 11
	      || (!strict && REGNO (x) >= FIRST_PSEUDO_REGISTER)));
}

/* Return true if X (a RTX) is a legitimate memory address on the
   target machine for a memory operand of mode MODE.  */

static bool
bpf_legitimate_address_p (machine_mode mode ATTRIBUTE_UNUSED,
			  rtx x,
			  bool strict)
{
  switch (GET_CODE (x))
    {
    case REG:
      return bpf_address_base_p (x, strict);

    case PLUS:
      {
	/* Accept (PLUS ADDR_BASE CONST_INT), provided CONST_INT fits
	   in a signed 16-bit.

	   Note that LABEL_REF and SYMBOL_REF are not allowed in
	   REG+IMM addresses, because it is almost certain they will
	   overload the offset field.  */

	rtx x0 = XEXP (x, 0);
	rtx x1 = XEXP (x, 1);
	
	if (bpf_address_base_p (x0, strict) && GET_CODE (x1) == CONST_INT)
	  return IN_RANGE (INTVAL (x1), -1 - 0x7fff, 0x7fff);

	break;
      }
    default:
      break;
    }

  return false;
}

#undef TARGET_LEGITIMATE_ADDRESS_P
#define TARGET_LEGITIMATE_ADDRESS_P bpf_legitimate_address_p

/* Describe the relative costs of RTL expressions.  Return true when
   all subexpressions of X have been processed, and false when
   `rtx_cost' should recurse.  */

static bool
bpf_rtx_costs (rtx x ATTRIBUTE_UNUSED,
	       enum machine_mode mode ATTRIBUTE_UNUSED,
	       int outer_code ATTRIBUTE_UNUSED,
	       int opno ATTRIBUTE_UNUSED,
               int *total ATTRIBUTE_UNUSED,
	       bool speed ATTRIBUTE_UNUSED)
{
  /* To be written.  */
  return false;
}

#undef TARGET_RTX_COSTS
#define TARGET_RTX_COSTS bpf_rtx_costs

/* Return true if an argument at the position indicated by CUM should
   be passed by reference.  If the hook returns true, a copy of that
   argument is made in memory and a pointer to the argument is passed
   instead of the argument itself.  */

static bool
bpf_pass_by_reference (cumulative_args_t cum ATTRIBUTE_UNUSED,
		       const function_arg_info &arg)
{
  unsigned num_bytes = arg.type_size_in_bytes ();

  /* Pass aggregates and values bigger than 5 words by reference.
     Everything else is passed by copy.  */
  return (arg.aggregate_type_p () || (num_bytes > 8*5));
}

#undef TARGET_PASS_BY_REFERENCE
#define TARGET_PASS_BY_REFERENCE bpf_pass_by_reference

/* Return a RTX indicating whether a function argument is passed in a
   register and if so, which register.  */

static rtx
bpf_function_arg (cumulative_args_t ca, const function_arg_info &arg)
{
  CUMULATIVE_ARGS *cum = get_cumulative_args (ca);

  if (*cum < 5)
    return gen_rtx_REG (arg.mode, *cum + 1);
  else
    /* An error will be emitted for this in
       bpf_function_arg_advance.  */
    return NULL_RTX;
}

#undef TARGET_FUNCTION_ARG
#define TARGET_FUNCTION_ARG bpf_function_arg

/* Update the summarizer variable pointed by CA to advance past an
   argument in the argument list.  */

static void
bpf_function_arg_advance (cumulative_args_t ca,
			  const function_arg_info &arg)
{
  CUMULATIVE_ARGS *cum = get_cumulative_args (ca);
  unsigned num_bytes = arg.type_size_in_bytes ();
  unsigned num_words = CEIL (num_bytes, UNITS_PER_WORD);

  if (*cum <= 5 && *cum + num_words > 5)
    error ("too many function arguments for eBPF");

  *cum += num_words;
}

#undef TARGET_FUNCTION_ARG_ADVANCE
#define TARGET_FUNCTION_ARG_ADVANCE bpf_function_arg_advance

/* Output the assembly code for a constructor.  Since eBPF doesn't
   support indirect calls, constructors are not supported.  */

static void
bpf_output_constructor (rtx symbol, int priority ATTRIBUTE_UNUSED)
{
  tree decl = SYMBOL_REF_DECL (symbol);

  if (decl)
    sorry_at (DECL_SOURCE_LOCATION (decl),
	      "no constructors");
  else
    sorry ("no constructors");
}

#undef TARGET_ASM_CONSTRUCTOR
#define TARGET_ASM_CONSTRUCTOR bpf_output_constructor

/* Output the assembly code for a destructor.  Since eBPF doesn't
   support indirect calls, destructors are not supported.  */

static void
bpf_output_destructor (rtx symbol, int priority ATTRIBUTE_UNUSED)
{
  tree decl = SYMBOL_REF_DECL (symbol);

  if (decl)
    sorry_at (DECL_SOURCE_LOCATION (decl),
	      "no destructors");
  else
    sorry ("no destructors");
}

#undef TARGET_ASM_DESTRUCTOR
#define TARGET_ASM_DESTRUCTOR bpf_output_destructor

/* Return the appropriate instruction to CALL to a function.  TARGET
   is an RTX denoting the address of the called function.

   The main purposes of this function are:
   - To reject indirect CALL instructions, which are not supported by
     eBPF.
   - To recognize calls to kernel helper functions and emit the
     corresponding CALL N instruction.

   This function is called from the expansion of the 'call' pattern in
   bpf.md.  */

const char *
bpf_output_call (rtx target)
{
  rtx xops[1];

  switch (GET_CODE (target))
    {
    case CONST_INT:
      output_asm_insn ("call\t%0", &target);
      break;
    case SYMBOL_REF:
      {
	const char *function_name = XSTR (target, 0);
	int code;
      
	if (strncmp (function_name, "__builtin_bpf_helper_", 21) == 0
	    && ((code = bpf_helper_code (function_name + 21)) != 0))
	  {
	    xops[0] = GEN_INT (code);
	    output_asm_insn ("call\t%0", xops);
	  }
	else
	  output_asm_insn ("call\t%0", &target);

	break;
      }
    default:
      error ("indirect call in function, which are not supported by eBPF");
      output_asm_insn ("call 0", NULL);
      break;
    }

  return "";
}

/* Print an instruction operand.  This function is called in the macro
   PRINT_OPERAND defined in bpf.h */

void
bpf_print_operand (FILE *file, rtx op, int code ATTRIBUTE_UNUSED)
{
  switch (GET_CODE (op))
    {
    case REG:
      fprintf (file, "%s", reg_names[REGNO (op)]);
      break;
    case MEM:
      output_address (GET_MODE (op), XEXP (op, 0));
      break;
    case CONST_DOUBLE:
      if (CONST_DOUBLE_HIGH (op))
	fprintf (file, HOST_WIDE_INT_PRINT_DOUBLE_HEX,
		 CONST_DOUBLE_HIGH (op), CONST_DOUBLE_LOW (op));
      else if (CONST_DOUBLE_LOW (op) < 0)
	fprintf (file, HOST_WIDE_INT_PRINT_HEX, CONST_DOUBLE_LOW (op));
      else
	fprintf (file, HOST_WIDE_INT_PRINT_DEC, CONST_DOUBLE_LOW (op));
      break;
    default:
      output_addr_const (file, op);
    }
}

/* Print an operand which is an address.  This function should handle
   any legit address, as accepted by bpf_legitimate_address_p, and
   also addresses that are valid in CALL instructions.

   This function is called in the PRINT_OPERAND_ADDRESS macro defined
   in bpf.h */

void
bpf_print_operand_address (FILE *file, rtx addr)
{
  switch (GET_CODE (addr))
    {
    case REG:
      fprintf (file, "[%s+0]", reg_names[REGNO (addr)]);
      break;
    case PLUS:
      {
	rtx op0 = XEXP (addr, 0);
	rtx op1 = XEXP (addr, 1);

	if (GET_CODE (op0) == REG && GET_CODE (op1) == CONST_INT)
	  {
	    fprintf (file, "[%s+", reg_names[REGNO (op0)]);
	    output_addr_const (file, op1);
	    fputs ("]", file);
	  }
	else
	  fatal_insn ("invalid address in operand", addr);
	break;
      }
    case MEM:
      /* Fallthrough.  */
    case LABEL_REF:
      /* Fallthrough.  */
      fatal_insn ("unsupported operand", addr);
      break;
    default:
      output_addr_const (file, addr);
      break;
    }
}

/* Add a BPF builtin function with NAME, CODE and TYPE.  Return
   the function decl or NULL_TREE if the builtin was not added.  */

static tree
def_builtin (const char *name, enum bpf_builtins code, tree type)
{
  tree t
    = add_builtin_function (name, type, code, BUILT_IN_MD, NULL, NULL_TREE);

  bpf_builtins[code] = t;
  return t;
}

/* Define machine-specific built-in functions.  */

static void
bpf_init_builtins (void)
{
  /* Built-ins for calling kernel helpers.  */

  tree pt = build_pointer_type (void_type_node);
  tree const_void_type
    = build_qualified_type (void_type_node, TYPE_QUAL_CONST);
  tree cpt = build_pointer_type (const_void_type);
  tree st = short_integer_type_node;
  tree ust = uint16_type_node;
  tree it = integer_type_node;
  tree ut = unsigned_type_node;
  tree const_char_type
    = build_qualified_type (char_type_node, TYPE_QUAL_CONST);
  tree cst = build_pointer_type (const_char_type);
  tree vt = void_type_node;
  tree ult = long_unsigned_type_node;
  tree u32t = uint32_type_node;
  tree u64t = uint64_type_node;
  tree llt = long_long_integer_type_node;
  tree ullt = long_long_unsigned_type_node;
  
#define TYPES build_function_type_list
#define VTYPES build_varargs_function_type_list
#define DEF_HELPER(V,D,N,T)				\
  do							\
    {							\
      if (bpf_kernel >= (V))				\
	def_builtin ("__builtin_bpf_helper_" #N,	\
		     BPF_BUILTIN_HELPER_##D,		\
		     T);				\
    } while (0);
#  include "bpf-helpers.def"
#undef TYPES
#undef VTYPES
#undef DEF_HELPER

  /* Built-ins for BPF_LD_ABS and BPF_LD_IND instructions.  */

  def_builtin ("__builtin_bpf_load_byte", BPF_BUILTIN_LOAD_BYTE,
	       build_function_type_list (ullt, ullt, 0));
  def_builtin ("__builtin_bpf_load_half", BPF_BUILTIN_LOAD_HALF,
	       build_function_type_list (ullt, ullt, 0));
  def_builtin ("__builtin_bpf_load_word", BPF_BUILTIN_LOAD_WORD,
	       build_function_type_list (ullt, ullt, 0));
}

#undef TARGET_INIT_BUILTINS
#define TARGET_INIT_BUILTINS bpf_init_builtins

/* Expand a call to a BPF-specific built-in function that was set up
   with bpf_init_builtins.  */

static rtx
bpf_expand_builtin (tree exp, rtx target,
		    rtx subtarget ATTRIBUTE_UNUSED,
		    machine_mode mode ATTRIBUTE_UNUSED,
		    int ignore)
{
  tree fndecl = TREE_OPERAND (CALL_EXPR_FN (exp), 0);
  int code = DECL_MD_FUNCTION_CODE (fndecl);

  if (code >= 1 && code < BPF_BUILTIN_HELPER_MAX)
    {
      /* This is a builtin to call a kernel helper function.

	 For these builtins, we just expand the function call normally
	 with expand_call like we would do for a libcall. The function
	 bpf_output_call below will then do The Right Thing (TM),
	 recognizing the name of the called __builtin_helper_* symbol
	 and emitting the corresponding CALL N instruction whenever
	 necessary.  */

      return expand_call (exp, target, ignore);
    }
  else if (code == BPF_BUILTIN_LOAD_BYTE
	   || code == BPF_BUILTIN_LOAD_HALF
	   || code == BPF_BUILTIN_LOAD_WORD)
    {
      /* Expand an indirect load from the sk_buff in the context.
	 There is just one argument to the builtin, which is the
	 offset.

	 We try first to expand a ldabs* instruction.  In case this
	 fails, we try a ldind* instruction.  */

      enum insn_code abs_icode
	= (code == BPF_BUILTIN_LOAD_BYTE ? CODE_FOR_ldabsb
	   : code == BPF_BUILTIN_LOAD_HALF ? CODE_FOR_ldabsh
	   : CODE_FOR_ldabsw);

      enum insn_code ind_icode
	= (code == BPF_BUILTIN_LOAD_BYTE ? CODE_FOR_ldindb
	   : code == BPF_BUILTIN_LOAD_HALF ? CODE_FOR_ldindh
	   : CODE_FOR_ldindw);

      tree offset_arg = CALL_EXPR_ARG (exp, 0);
      struct expand_operand ops[2];

      create_input_operand (&ops[0], expand_normal (offset_arg),
			    TYPE_MODE (TREE_TYPE (offset_arg)));
      create_input_operand (&ops[1], const0_rtx, SImode);

      if (!maybe_expand_insn (abs_icode, 2, ops)
	  && !maybe_expand_insn (ind_icode, 2, ops))
	{
	  error ("invalid argument to built-in function");
	  return gen_rtx_REG (ops[0].mode, BPF_R0);
	}

      /* The result of the load is in R0.  */
      return gen_rtx_REG (ops[0].mode, BPF_R0);
    }

  gcc_unreachable ();
}

#undef TARGET_EXPAND_BUILTIN
#define TARGET_EXPAND_BUILTIN bpf_expand_builtin

/* Initialize target-specific function library calls.  This is mainly
   used to call library-provided soft-fp operations, since eBPF
   doesn't support floating-point in "hardware".  */

static void
bpf_init_libfuncs (void)
{
  set_conv_libfunc (sext_optab, DFmode, SFmode,
		    "__bpf_extendsfdf2");
  set_conv_libfunc (trunc_optab, SFmode, DFmode,
		    "__bpf_truncdfsf2");
  set_conv_libfunc (sfix_optab, SImode, DFmode,
		    "__bpf_fix_truncdfsi");
  set_conv_libfunc (sfloat_optab, DFmode, SImode,
		    "__bpf_floatsidf");
  set_conv_libfunc (ufloat_optab, DFmode, SImode,
		    "__bpf_floatunsidf");
}

#undef TARGET_INIT_LIBFUNCS
#define TARGET_INIT_LIBFUNCS bpf_init_libfuncs

/* Define the mechanism that will be used for describing frame unwind
   information to the debugger.  In eBPF it is not possible to unwind
   frames.  */

static enum unwind_info_type
bpf_debug_unwind_info ()
{
  return UI_NONE;
}

#undef TARGET_DEBUG_UNWIND_INFO
#define TARGET_DEBUG_UNWIND_INFO bpf_debug_unwind_info

/* Output assembly directives to assemble data of various sized and
   alignments.  */

#undef TARGET_ASM_BYTE_OP
#define TARGET_ASM_BYTE_OP "\t.byte\t"
#undef TARGET_ASM_ALIGNED_HI_OP
#define TARGET_ASM_ALIGNED_HI_OP "\t.half\t"
#undef TARGET_ASM_ALIGNED_SI_OP
#define TARGET_ASM_ALIGNED_SI_OP "\t.word\t"
#undef TARGET_ASM_ALIGNED_DI_OP
#define TARGET_ASM_ALIGNED_DI_OP "\t.dword\t"

/* Finally, build the GCC target.  */

struct gcc_target targetm = TARGET_INITIALIZER;

#include "gt-bpf.h"