[ARM/FDPIC,v5,04/21,ARM] FDPIC: Add support for FDPIC for arm architecture

Message ID 20190515124006.25840-5-christophe.lyon@st.com
State New
Headers show
Series
  • FDPIC ABI for ARM
Related show

Commit Message

Christophe Lyon May 15, 2019, 12:39 p.m.
The FDPIC register is hard-coded to r9, as defined in the ABI.

We have to disable tailcall optimizations if we don't know if the
target function is in the same module. If not, we have to set r9 to
the value associated with the target module.

When generating a symbol address, we have to take into account whether
it is a pointer to data or to a function, because different
relocations are needed.

2019-XX-XX  Christophe Lyon  <christophe.lyon@st.com>
	Mickaël Guêné <mickael.guene@st.com>

	* config/arm/arm-c.c (__FDPIC__): Define new pre-processor macro
	in FDPIC mode.
	* config/arm/arm-protos.h (arm_load_function_descriptor): Declare
	new function.
	* config/arm/arm.c (arm_option_override): Define pic register to
	FDPIC_REGNUM.
	(arm_function_ok_for_sibcall): Disable sibcall optimization if we
	have no decl or go through PLT.
	(arm_load_pic_register): Handle TARGET_FDPIC.
	(arm_is_segment_info_known): New function.
	(arm_pic_static_addr): Add support for FDPIC.
	(arm_load_function_descriptor): New function.
	(arm_assemble_integer): Add support for FDPIC.
	* config/arm/arm.h (PIC_OFFSET_TABLE_REG_CALL_CLOBBERED):
	Define. (FDPIC_REGNUM): New define.
	* config/arm/arm.md (call): Add support for FDPIC.
	(call_value): Likewise.
	(*restore_pic_register_after_call): New pattern.
	(untyped_call): Disable if FDPIC.
	(untyped_return): Likewise.
	* config/arm/unspecs.md (UNSPEC_PIC_RESTORE): New.

Change-Id: I8fb1a6b85ace672184013568c5d28fbda2f7fda4

-- 
2.6.3

Patch

diff --git a/gcc/config/arm/arm-c.c b/gcc/config/arm/arm-c.c
index 6e256ee..34695fa 100644
--- a/gcc/config/arm/arm-c.c
+++ b/gcc/config/arm/arm-c.c
@@ -203,6 +203,8 @@  arm_cpu_builtins (struct cpp_reader* pfile)
       builtin_define ("__ARM_EABI__");
     }
 
+  def_or_undef_macro (pfile, "__FDPIC__", TARGET_FDPIC);
+
   def_or_undef_macro (pfile, "__ARM_ARCH_EXT_IDIV__", TARGET_IDIV);
   def_or_undef_macro (pfile, "__ARM_FEATURE_IDIV", TARGET_IDIV);
 
diff --git a/gcc/config/arm/arm-protos.h b/gcc/config/arm/arm-protos.h
index 485bc68..272968a 100644
--- a/gcc/config/arm/arm-protos.h
+++ b/gcc/config/arm/arm-protos.h
@@ -139,6 +139,7 @@  extern int arm_max_const_double_inline_cost (void);
 extern int arm_const_double_inline_cost (rtx);
 extern bool arm_const_double_by_parts (rtx);
 extern bool arm_const_double_by_immediates (rtx);
+extern rtx arm_load_function_descriptor (rtx funcdesc);
 extern void arm_emit_call_insn (rtx, rtx, bool);
 bool detect_cmse_nonsecure_call (tree);
 extern const char *output_call (rtx *);
diff --git a/gcc/config/arm/arm.c b/gcc/config/arm/arm.c
index 45abcd8..d9397b5 100644
--- a/gcc/config/arm/arm.c
+++ b/gcc/config/arm/arm.c
@@ -3485,6 +3485,15 @@  arm_option_override (void)
   if (flag_pic && TARGET_VXWORKS_RTP)
     arm_pic_register = 9;
 
+  /* If in FDPIC mode then force arm_pic_register to be r9.  */
+  if (TARGET_FDPIC)
+    {
+      arm_pic_register = FDPIC_REGNUM;
+      if (! TARGET_ARM && ! TARGET_THUMB2)
+	sorry ("FDPIC mode is supported on architecture versions that "
+	       "support ARM or Thumb-2 only.");
+    }
+
   if (arm_pic_register_string != NULL)
     {
       int pic_register = decode_reg_name (arm_pic_register_string);
@@ -7295,6 +7304,21 @@  arm_function_ok_for_sibcall (tree decl, tree exp)
   if (cfun->machine->sibcall_blocked)
     return false;
 
+  if (TARGET_FDPIC)
+    {
+      /* In FDPIC, never tailcall something for which we have no decl:
+	 the target function could be in a different module, requiring
+	 a different FDPIC register value.  */
+      if (decl == NULL)
+	return false;
+
+      /* Don't tailcall if we go through the PLT since the FDPIC
+	 register is then corrupted and we don't restore it after
+	 static function calls.  */
+      if (!targetm.binds_local_p (decl))
+	return false;
+    }
+
   /* Never tailcall something if we are generating code for Thumb-1.  */
   if (TARGET_THUMB1)
     return false;
@@ -7711,7 +7735,9 @@  arm_load_pic_register (unsigned long saved_regs ATTRIBUTE_UNUSED, rtx pic_reg)
 {
   rtx l1, labelno, pic_tmp, pic_rtx;
 
-  if (crtl->uses_pic_offset_table == 0 || TARGET_SINGLE_PIC_BASE)
+  if (crtl->uses_pic_offset_table == 0
+      || TARGET_SINGLE_PIC_BASE
+      || TARGET_FDPIC)
     return;
 
   gcc_assert (flag_pic);
@@ -7780,28 +7806,142 @@  arm_load_pic_register (unsigned long saved_regs ATTRIBUTE_UNUSED, rtx pic_reg)
   emit_use (pic_reg);
 }
 
+/* Try to determine whether an object, referenced via ORIG, will be
+   placed in the text or data segment.  This is used in FDPIC mode, to
+   decide which relocations to use when accessing ORIG.  IS_READONLY
+   is set to true if ORIG is a read-only location, false otherwise.
+   Return true if we could determine the location of ORIG, false
+   otherwise.  IS_READONLY is valid only when we return true.  */
+static bool
+arm_is_segment_info_known (rtx orig, bool *is_readonly)
+{
+  bool res = false;
+
+  *is_readonly = false;
+
+  if (GET_CODE (orig) == LABEL_REF)
+    {
+      res = true;
+      *is_readonly = true;
+    }
+  else if (SYMBOL_REF_P (orig))
+    {
+      if (CONSTANT_POOL_ADDRESS_P (orig))
+	{
+	  res = true;
+	  *is_readonly = true;
+	}
+      else if (SYMBOL_REF_LOCAL_P (orig)
+	       && !SYMBOL_REF_EXTERNAL_P (orig)
+	       && SYMBOL_REF_DECL (orig)
+	       && (!DECL_P (SYMBOL_REF_DECL (orig))
+		   || !DECL_COMMON (SYMBOL_REF_DECL (orig))))
+	{
+	  tree decl = SYMBOL_REF_DECL (orig);
+	  tree init = (TREE_CODE (decl) == VAR_DECL)
+	    ? DECL_INITIAL (decl) : (TREE_CODE (decl) == CONSTRUCTOR)
+	    ? decl : 0;
+	  int reloc = 0;
+	  bool named_section, readonly;
+
+	  if (init && init != error_mark_node)
+	    reloc = compute_reloc_for_constant (init);
+
+	  named_section = TREE_CODE (decl) == VAR_DECL
+	    && lookup_attribute ("section", DECL_ATTRIBUTES (decl));
+	  readonly = decl_readonly_section (decl, reloc);
+
+	  /* We don't know where the link script will put a named
+	     section, so return false in such a case.  */
+	  res = !named_section;
+
+	  if (!named_section)
+	    *is_readonly = readonly;
+	}
+      else
+	{
+	  /* We don't know.  */
+	  res = false;
+	}
+    }
+  else
+    gcc_unreachable ();
+
+  return res;
+}
+
 /* Generate code to load the address of a static var when flag_pic is set.  */
 static rtx_insn *
 arm_pic_static_addr (rtx orig, rtx reg)
 {
   rtx l1, labelno, offset_rtx;
+  rtx_insn *insn;
 
   gcc_assert (flag_pic);
 
-  /* We use an UNSPEC rather than a LABEL_REF because this label
-     never appears in the code stream.  */
-  labelno = GEN_INT (pic_labelno++);
-  l1 = gen_rtx_UNSPEC (Pmode, gen_rtvec (1, labelno), UNSPEC_PIC_LABEL);
-  l1 = gen_rtx_CONST (VOIDmode, l1);
+  bool is_readonly = false;
+  bool info_known = false;
 
-  /* On the ARM the PC register contains 'dot + 8' at the time of the
-     addition, on the Thumb it is 'dot + 4'.  */
-  offset_rtx = plus_constant (Pmode, l1, TARGET_ARM ? 8 : 4);
-  offset_rtx = gen_rtx_UNSPEC (Pmode, gen_rtvec (2, orig, offset_rtx),
-                               UNSPEC_SYMBOL_OFFSET);
-  offset_rtx = gen_rtx_CONST (Pmode, offset_rtx);
+  if (TARGET_FDPIC
+      && SYMBOL_REF_P (orig)
+      && !SYMBOL_REF_FUNCTION_P (orig))
+      info_known = arm_is_segment_info_known (orig, &is_readonly);
 
-  return emit_insn (gen_pic_load_addr_unified (reg, offset_rtx, labelno));
+  if (TARGET_FDPIC
+      && SYMBOL_REF_P (orig)
+      && !SYMBOL_REF_FUNCTION_P (orig)
+      && !info_known)
+    {
+      /* We don't know where orig is stored, so we have be
+	 pessimistic and use a GOT relocation.  */
+      rtx pat;
+      rtx mem;
+      rtx pic_reg = gen_rtx_REG (Pmode, FDPIC_REGNUM);
+
+      pat = gen_calculate_pic_address (reg, pic_reg, orig);
+
+      /* Make the MEM as close to a constant as possible.  */
+      mem = SET_SRC (pat);
+      gcc_assert (MEM_P (mem) && !MEM_VOLATILE_P (mem));
+      MEM_READONLY_P (mem) = 1;
+      MEM_NOTRAP_P (mem) = 1;
+
+      insn = emit_insn (pat);
+    }
+  else if (TARGET_FDPIC
+	   && SYMBOL_REF_P (orig)
+	   && (SYMBOL_REF_FUNCTION_P (orig)
+	       || (info_known && !is_readonly)))
+    {
+      /* We use the GOTOFF relocation.  */
+      rtx pic_reg = gen_rtx_REG (Pmode, FDPIC_REGNUM);
+
+      rtx l1 = gen_rtx_UNSPEC (Pmode, gen_rtvec (1, orig), UNSPEC_PIC_SYM);
+      emit_insn (gen_movsi (reg, l1));
+      insn = emit_insn (gen_addsi3 (reg, reg, pic_reg));
+    }
+  else
+    {
+      /* Not FDPIC, not SYMBOL_REF_P or readonly: we can use
+	 PC-relative access.  */
+      /* We use an UNSPEC rather than a LABEL_REF because this label
+	 never appears in the code stream.  */
+      labelno = GEN_INT (pic_labelno++);
+      l1 = gen_rtx_UNSPEC (Pmode, gen_rtvec (1, labelno), UNSPEC_PIC_LABEL);
+      l1 = gen_rtx_CONST (VOIDmode, l1);
+
+      /* On the ARM the PC register contains 'dot + 8' at the time of the
+	 addition, on the Thumb it is 'dot + 4'.  */
+      offset_rtx = plus_constant (Pmode, l1, TARGET_ARM ? 8 : 4);
+      offset_rtx = gen_rtx_UNSPEC (Pmode, gen_rtvec (2, orig, offset_rtx),
+				   UNSPEC_SYMBOL_OFFSET);
+      offset_rtx = gen_rtx_CONST (Pmode, offset_rtx);
+
+      insn = emit_insn (gen_pic_load_addr_unified (reg, offset_rtx,
+						   labelno));
+    }
+
+  return insn;
 }
 
 /* Return nonzero if X is valid as an ARM state addressing register.  */
@@ -16112,9 +16252,36 @@  get_jump_table_size (rtx_jump_table_data *insn)
   return 0;
 }
 
+/* Emit insns to load the function address from FUNCDESC (an FDPIC
+   function descriptor) into a register and the GOT address into the
+   FDPIC register, returning an rtx for the register holding the
+   function address.  */
+
+rtx
+arm_load_function_descriptor (rtx funcdesc)
+{
+  rtx fnaddr_reg = gen_reg_rtx (Pmode);
+  rtx pic_reg = gen_rtx_REG (Pmode, FDPIC_REGNUM);
+  rtx fnaddr = gen_rtx_MEM (Pmode, funcdesc);
+  rtx gotaddr = gen_rtx_MEM (Pmode, plus_constant (Pmode, funcdesc, 4));
+  rtx par = gen_rtx_PARALLEL (VOIDmode, rtvec_alloc (3));
+
+  emit_move_insn (fnaddr_reg, fnaddr);
+  /* The ABI requires the entry point address to be loaded first, so
+     prevent the load from being moved after that of the GOT
+     address.  */
+  XVECEXP (par, 0, 0) = gen_rtx_UNSPEC (VOIDmode,
+					gen_rtvec (2, pic_reg, gotaddr),
+					UNSPEC_PIC_RESTORE);
+  XVECEXP (par, 0, 1) = gen_rtx_USE (VOIDmode, gotaddr);
+  XVECEXP (par, 0, 2) = gen_rtx_CLOBBER (VOIDmode, pic_reg);
+  emit_insn (par);
+
+  return fnaddr_reg;
+}
+
 /* Return the maximum amount of padding that will be inserted before
    label LABEL.  */
-
 static HOST_WIDE_INT
 get_label_padding (rtx label)
 {
@@ -23069,9 +23236,37 @@  arm_assemble_integer (rtx x, unsigned int size, int aligned_p)
 		  && (!SYMBOL_REF_LOCAL_P (x)
 		      || (SYMBOL_REF_DECL (x)
 			  ? DECL_WEAK (SYMBOL_REF_DECL (x)) : 0))))
-	    fputs ("(GOT)", asm_out_file);
+	    {
+	      if (TARGET_FDPIC && SYMBOL_REF_FUNCTION_P (x))
+		fputs ("(GOTFUNCDESC)", asm_out_file);
+	      else
+		fputs ("(GOT)", asm_out_file);
+	    }
 	  else
-	    fputs ("(GOTOFF)", asm_out_file);
+	    {
+	      if (TARGET_FDPIC && SYMBOL_REF_FUNCTION_P (x))
+		fputs ("(GOTOFFFUNCDESC)", asm_out_file);
+	      else
+		{
+		  bool is_readonly;
+
+		  if (arm_is_segment_info_known (x, &is_readonly))
+		    fputs ("(GOTOFF)", asm_out_file);
+		  else
+		    fputs ("(GOT)", asm_out_file);
+		}
+	    }
+	}
+
+      /* For FDPIC we also have to mark symbol for .data section.  */
+      if (TARGET_FDPIC
+	  && NEED_GOT_RELOC
+	  && flag_pic
+	  && !making_const_table
+	  && SYMBOL_REF_P (x))
+	{
+	  if (SYMBOL_REF_FUNCTION_P (x))
+	    fputs ("(FUNCDESC)", asm_out_file);
 	}
       fputc ('\n', asm_out_file);
       return true;
diff --git a/gcc/config/arm/arm.h b/gcc/config/arm/arm.h
index 4866e1e..7b50ef5 100644
--- a/gcc/config/arm/arm.h
+++ b/gcc/config/arm/arm.h
@@ -892,6 +892,9 @@  extern int arm_arch_cmse;
    Pascal), so the following is not true.  */
 #define STATIC_CHAIN_REGNUM	12
 
+/* r9 is the FDPIC register (base register for GOT and FUNCDESC accesses).  */
+#define FDPIC_REGNUM		9
+
 /* Define this to be where the real frame pointer is if it is not possible to
    work out the offset between the frame pointer and the automatic variables
    until after register allocation has taken place.  FRAME_POINTER_REGNUM
@@ -1948,6 +1951,10 @@  extern unsigned arm_pic_register;
    data addresses in memory.  */
 #define PIC_OFFSET_TABLE_REGNUM arm_pic_register
 
+/* For FDPIC, the FDPIC register is call-clobbered (otherwise PLT
+   entries would need to handle saving and restoring it).  */
+#define PIC_OFFSET_TABLE_REG_CALL_CLOBBERED TARGET_FDPIC
+
 /* We can't directly access anything that contains a symbol,
    nor can we indirect via the constant pool.  One exception is
    UNSPEC_TLS, which is always PIC.  */
diff --git a/gcc/config/arm/arm.md b/gcc/config/arm/arm.md
index 0aecd03..9036255 100644
--- a/gcc/config/arm/arm.md
+++ b/gcc/config/arm/arm.md
@@ -8127,6 +8127,23 @@ 
     rtx callee, pat;
     tree addr = MEM_EXPR (operands[0]);
     
+    /* Force FDPIC register (r9) before call.  */
+    if (TARGET_FDPIC)
+      {
+	/* No need to update r9 if calling a static function.
+	   In other words: set r9 for indirect or non-local calls.  */
+	callee = XEXP (operands[0], 0);
+	if (!SYMBOL_REF_P (callee)
+	    || !SYMBOL_REF_LOCAL_P (callee)
+	    || arm_is_long_call_p (SYMBOL_REF_DECL (callee)))
+	  {
+	    emit_insn (gen_blockage ());
+	    rtx pic_reg = gen_rtx_REG (Pmode, FDPIC_REGNUM);
+	    emit_move_insn (pic_reg, get_hard_reg_initial_val (Pmode, FDPIC_REGNUM));
+	    emit_insn (gen_rtx_USE (VOIDmode, pic_reg));
+	 }
+      }
+
     /* In an untyped call, we can get NULL for operand 2.  */
     if (operands[2] == NULL_RTX)
       operands[2] = const0_rtx;
@@ -8140,6 +8157,13 @@ 
 	: !REG_P (callee))
       XEXP (operands[0], 0) = force_reg (Pmode, callee);
 
+    if (TARGET_FDPIC && !SYMBOL_REF_P (XEXP (operands[0], 0)))
+      {
+	/* Indirect call: set r9 with FDPIC value of callee.  */
+	XEXP (operands[0], 0)
+	  = arm_load_function_descriptor (XEXP (operands[0], 0));
+      }
+
     if (detect_cmse_nonsecure_call (addr))
       {
 	pat = gen_nonsecure_call_internal (operands[0], operands[1],
@@ -8151,10 +8175,38 @@ 
 	pat = gen_call_internal (operands[0], operands[1], operands[2]);
 	arm_emit_call_insn (pat, XEXP (operands[0], 0), false);
       }
+
+    /* Restore FDPIC register (r9) after call.  */
+    if (TARGET_FDPIC)
+      {
+	/* No need to update r9 if calling a static function.  */
+	if (!SYMBOL_REF_P (callee)
+	    || !SYMBOL_REF_LOCAL_P (callee)
+	    || arm_is_long_call_p (SYMBOL_REF_DECL (callee)))
+	  {
+	    rtx pic_reg = gen_rtx_REG (Pmode, FDPIC_REGNUM);
+	    emit_move_insn (pic_reg, get_hard_reg_initial_val (Pmode, FDPIC_REGNUM));
+	    emit_insn (gen_rtx_USE (VOIDmode, pic_reg));
+	    emit_insn (gen_blockage ());
+	  }
+      }
     DONE;
   }"
 )
 
+(define_insn "*restore_pic_register_after_call"
+  [(parallel [(unspec [(match_operand:SI 0 "s_register_operand" "=r,r")
+		       (match_operand:SI 1 "nonimmediate_operand" "r,m")]
+	       UNSPEC_PIC_RESTORE)
+	      (use (match_dup 1))
+	      (clobber (match_dup 0))])
+  ]
+  ""
+  "@
+  mov\t%0, %1
+  ldr\t%0, %1"
+)
+
 (define_expand "call_internal"
   [(parallel [(call (match_operand 0 "memory_operand" "")
 	            (match_operand 1 "general_operand" ""))
@@ -8215,6 +8267,30 @@ 
     rtx pat, callee;
     tree addr = MEM_EXPR (operands[1]);
     
+    /* Force FDPIC register (r9) before call.  */
+    if (TARGET_FDPIC)
+      {
+	/* No need to update the FDPIC register (r9) if calling a static function.
+	   In other words: set r9 for indirect or non-local calls.  */
+	callee = XEXP (operands[1], 0);
+	if (!SYMBOL_REF_P (callee)
+	    || !SYMBOL_REF_LOCAL_P (callee)
+	    || arm_is_long_call_p (SYMBOL_REF_DECL (callee)))
+	  {
+	    rtx par = gen_rtx_PARALLEL (VOIDmode, rtvec_alloc (3));
+	    rtx fdpic_reg = gen_rtx_REG (Pmode, FDPIC_REGNUM);
+	    rtx initial_fdpic_reg =
+		get_hard_reg_initial_val (Pmode, FDPIC_REGNUM);
+
+	    XVECEXP (par, 0, 0) = gen_rtx_UNSPEC (VOIDmode,
+		gen_rtvec (2, fdpic_reg, initial_fdpic_reg),
+		UNSPEC_PIC_RESTORE);
+	    XVECEXP (par, 0, 1) = gen_rtx_USE (VOIDmode, initial_fdpic_reg);
+	    XVECEXP (par, 0, 2) = gen_rtx_CLOBBER (VOIDmode, fdpic_reg);
+	    emit_insn (par);
+	  }
+      }
+
     /* In an untyped call, we can get NULL for operand 2.  */
     if (operands[3] == 0)
       operands[3] = const0_rtx;
@@ -8228,6 +8304,14 @@ 
 	: !REG_P (callee))
       XEXP (operands[1], 0) = force_reg (Pmode, callee);
 
+    if (TARGET_FDPIC
+	&& !SYMBOL_REF_P (XEXP (operands[1], 0)))
+      {
+	/* Indirect call: set r9 with FDPIC value of callee.  */
+	XEXP (operands[1], 0)
+	  = arm_load_function_descriptor (XEXP (operands[1], 0));
+      }
+
     if (detect_cmse_nonsecure_call (addr))
       {
 	pat = gen_nonsecure_call_value_internal (operands[0], operands[1],
@@ -8240,6 +8324,28 @@ 
 				       operands[2], operands[3]);
 	arm_emit_call_insn (pat, XEXP (operands[1], 0), false);
       }
+    /* Restore FDPIC register (r9) after call.  */
+    if (TARGET_FDPIC)
+      {
+	/* No need to update r9 if calling a static function.  */
+	if (!SYMBOL_REF_P (callee)
+	    || !SYMBOL_REF_LOCAL_P (callee)
+	    || arm_is_long_call_p (SYMBOL_REF_DECL (callee)))
+	  {
+	    rtx par = gen_rtx_PARALLEL (VOIDmode, rtvec_alloc (3));
+	    rtx fdpic_reg = gen_rtx_REG (Pmode, FDPIC_REGNUM);
+	    rtx initial_fdpic_reg =
+		get_hard_reg_initial_val (Pmode, FDPIC_REGNUM);
+
+	    XVECEXP (par, 0, 0) = gen_rtx_UNSPEC (VOIDmode,
+		gen_rtvec (2, fdpic_reg, initial_fdpic_reg),
+		UNSPEC_PIC_RESTORE);
+	    XVECEXP (par, 0, 1) = gen_rtx_USE (VOIDmode, initial_fdpic_reg);
+	    XVECEXP (par, 0, 2) = gen_rtx_CLOBBER (VOIDmode, fdpic_reg);
+	    emit_insn (par);
+	  }
+      }
+
     DONE;
   }"
 )
@@ -8582,7 +8688,7 @@ 
 		    (const_int 0))
 	      (match_operand 1 "" "")
 	      (match_operand 2 "" "")])]
-  "TARGET_EITHER"
+  "TARGET_EITHER && !TARGET_FDPIC"
   "
   {
     int i;
@@ -8649,7 +8755,7 @@ 
 (define_expand "untyped_return"
   [(match_operand:BLK 0 "memory_operand" "")
    (match_operand 1 "" "")]
-  "TARGET_EITHER"
+  "TARGET_EITHER && !TARGET_FDPIC"
   "
   {
     int i;
diff --git a/gcc/config/arm/unspecs.md b/gcc/config/arm/unspecs.md
index 174bcc5..bda35d5 100644
--- a/gcc/config/arm/unspecs.md
+++ b/gcc/config/arm/unspecs.md
@@ -89,6 +89,7 @@ 
   UNSPEC_SP_SET		; Represent the setting of stack protector's canary
   UNSPEC_SP_TEST	; Represent the testing of stack protector's canary
 			; against the guard.
+  UNSPEC_PIC_RESTORE	; Use to restore fdpic register
 ])
 
 (define_c_enum "unspec" [