[v5] aarch64: Add split-stack initial support

Message ID 1501096098-2433-1-git-send-email-adhemerval.zanella@linaro.org
State New
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Commit Message

Adhemerval Zanella July 26, 2017, 7:08 p.m.
This is an update patch based on my previous submission [1].  The changes
from previous version are:

  - Update aarch64_supports_split_stack to return true an let the loader
    to actually emit an error if it does not provide the required TCB
    field.  The TCB field support is planed for GLIBC 2.27.

  - Some cleanup on morestack-c.c to avoid code duplication (ss_pointer
    function).

I am still some sporadic failures, but it due missing linker support
for split calls due not enough stack size (on pprof and other go tests
that call backtrace on signal handling).  This could be mitigate by
increasing the BACKOFF to a higher value, but to not deviate from other
ports with split-stack support this patch is using the default values
(initial stack size of 16k and backoff of 4k).  This should be correctly
handled with proper gold suppor (as for other ports).

--

This patch adds the split-stack support on aarch64 (PR #67877).  As for
other ports this patch should be used along with glibc and gold support.

The support is done similar to other architectures: a split-stack field
is allocated before TCB by glibc, a target-specific __morestack implementation
and helper functions are added in libgcc and compiler supported in adjusted
(split-stack prologue, va_start for argument handling).  I also plan to
send the gold support to adjust stack allocation acrosss split-stack
and default code calls.

Current approach is to set the final stack adjustments using a 2 instructions
at most (mov/movk) which limits stack allocation to upper limit of 4GB.
The morestack call is non standard with x10 hollding the requested stack
pointer, x11 the argument pointer (if required), and x12 to return
continuation address.  Unwinding is handled by a personality routine that
knows how to find stack segments.

Split-stack prologue on function entry is as follow (this goes before the
usual function prologue):

function:
	mrs    x9, tpidr_el0
	mov    x10, <required stack allocation>
	movk   x10, #0x0, lsl #16
	sub    x10, sp, x10
	mov    x11, sp   	# if function has stacked arguments
	adrp   x12, main_fn_entry
	add    x12, x12, :lo12:.L2
	cmp    x9, x10
	b.lt   <main_fn_entry>
	b      __morestack
main_fn_entry:
	[function prologue]

Notes:

1. Even if a function does not allocate a stack frame, a split-stack prologue
   is created.  It is to avoid issues with tail call for external symbols
   which might require linker adjustment (libgo/runtime/go-varargs.c).

2. Basic-block reordering (enabled with -O2) will move split-stack TCB ldr
   to after the required stack calculation.

3. Similar to powerpc, When the linker detects a call from split-stack to
   non-split-stack code, it adds 16k (or more) to the value found in "allocate"
   instructions (so non-split-stack code gets a larger stack).  The amount is
   tunable by a linker option.  The edit means aarch64 does not need to
   implement __morestack_non_split, necessary on x86 because insufficient
   space is available there to edit the stack comparison code.  This feature
   is only implemented in the GNU gold linker.

4. AArch64 does not handle >4G stack initially and although it is possible
   to implement it, limiting to 4G allows to materize the allocation with
   only 2 instructions (mov + movk) and thus simplifying the linker
   adjustments required.  Supporting multiple threads each requiring more
   than 4G of stack is probably not that important, and likely to OOM at
   run time.

5. The TCB support on GLIBC is meant to be included in version 2.26.

6. The continuation address materialized on x12 is done using 'adrp'
   plus add and a static relocation.  Current code uses the
   aarch64_expand_mov_immediate function and since a better alternative
   would be 'adp', it could be a future optimization (not implemented
   in this patch).

libgcc/ChangeLog:

	* libgcc/config.host: Use t-stack and t-statck-aarch64 for
	aarch64*-*-linux.
	* libgcc/config/aarch64/morestack-c.c: New file.
	* libgcc/config/aarch64/morestack.S: Likewise.
	* libgcc/config/aarch64/t-stack-aarch64: Likewise.
	* libgcc/generic-morestack.c (__splitstack_find): Add aarch64-specific
	code.

gcc/ChangeLog:

	* common/config/aarch64/aarch64-common.c
	(aarch64_supports_split_stack): New function.
	(TARGET_SUPPORTS_SPLIT_STACK): New macro.
	* gcc/config/aarch64/aarch64-linux.h (TARGET_ASM_FILE_END): Remove
	macro.
	* gcc/config/aarch64/aarch64-protos.h: Add
	aarch64_expand_split_stack_prologue and
	aarch64_split_stack_space_check.
	* gcc/config/aarch64/aarch64.c (aarch64_gen_far_branch): Add suport
	to emit 'b' instruction to rtx different than LABEL_REF.
	(aarch64_expand_builtin_va_start): Use internal argument pointer
	instead of virtual_incoming_args_rtx.
	(morestack_ref): New symbol.
	(aarch64_load_split_stack_value): New function.
	(aarch64_expand_split_stack_prologue): Likewise.
	(aarch64_internal_arg_pointer): Likewise.
	(aarch64_split_stack_space_check): Likewise.
	(aarch64_file_end): Emit the split-stack note sections.
	(TARGET_ASM_FILE_END): New macro.
	(TARGET_INTERNAL_ARG_POINTER): Likewise.
	* gcc/config/aarch64/aarch64.h (aarch64_frame): Add
	split_stack_arg_pointer to setup the argument pointer when using
	split-stack.
	* gcc/config/aarch64/aarch64.md
	(UNSPECV_SPLIT_STACK_RETURN): Likewise.
	(split_stack_prologue): New expand.
	(split_stack_space_check): Likewise.
	(split_stack_cond_call): Likewise.
---
 gcc/common/config/aarch64/aarch64-common.c |  16 +-
 gcc/config/aarch64/aarch64-linux.h         |   2 -
 gcc/config/aarch64/aarch64-protos.h        |   2 +
 gcc/config/aarch64/aarch64.c               | 174 +++++++++++++++++++-
 gcc/config/aarch64/aarch64.h               |   3 +
 gcc/config/aarch64/aarch64.md              |  56 +++++++
 libgcc/config.host                         |   1 +
 libgcc/config/aarch64/morestack-c.c        |  87 ++++++++++
 libgcc/config/aarch64/morestack.S          | 248 +++++++++++++++++++++++++++++
 libgcc/config/aarch64/t-stack-aarch64      |   3 +
 libgcc/generic-morestack.c                 |   1 +
 11 files changed, 588 insertions(+), 5 deletions(-)
 create mode 100644 libgcc/config/aarch64/morestack-c.c
 create mode 100644 libgcc/config/aarch64/morestack.S
 create mode 100644 libgcc/config/aarch64/t-stack-aarch64

-- 
2.7.4

Patch hide | download patch | download mbox

diff --git a/gcc/common/config/aarch64/aarch64-common.c b/gcc/common/config/aarch64/aarch64-common.c
index a0b7f48..474dfa1 100644
--- a/gcc/common/config/aarch64/aarch64-common.c
+++ b/gcc/common/config/aarch64/aarch64-common.c
@@ -107,6 +107,21 @@  aarch64_handle_option (struct gcc_options *opts,
     }
 }
 
+/* -fsplit-stack uses a TCB field available on glibc-2.27.  GLIBC also
+   exports symbol, __tcb_private_ss, to signal it has the field available
+   on TCB bloc.  This aims to prevent binaries linked against newer
+   GLIBC to run on non-supported ones.  */
+
+static bool
+aarch64_supports_split_stack (bool report ATTRIBUTE_UNUSED,
+			      struct gcc_options *opts ATTRIBUTE_UNUSED)
+{
+  return true;
+}
+
+#undef TARGET_SUPPORTS_SPLIT_STACK
+#define TARGET_SUPPORTS_SPLIT_STACK aarch64_supports_split_stack
+
 struct gcc_targetm_common targetm_common = TARGETM_COMMON_INITIALIZER;
 
 /* An ISA extension in the co-processor and main instruction set space.  */
@@ -340,4 +355,3 @@  aarch64_rewrite_mcpu (int argc, const char **argv)
 }
 
 #undef AARCH64_CPU_NAME_LENGTH
-
diff --git a/gcc/config/aarch64/aarch64-linux.h b/gcc/config/aarch64/aarch64-linux.h
index c45fc1d..b8daba4 100644
--- a/gcc/config/aarch64/aarch64-linux.h
+++ b/gcc/config/aarch64/aarch64-linux.h
@@ -80,8 +80,6 @@ 
     }						\
   while (0)
 
-#define TARGET_ASM_FILE_END file_end_indicate_exec_stack
-
 /* Uninitialized common symbols in non-PIE executables, even with
    strong definitions in dependent shared libraries, will resolve
    to COPY relocated symbol in the executable.  See PR65780.  */
diff --git a/gcc/config/aarch64/aarch64-protos.h b/gcc/config/aarch64/aarch64-protos.h
index e397ff4..5bb6411 100644
--- a/gcc/config/aarch64/aarch64-protos.h
+++ b/gcc/config/aarch64/aarch64-protos.h
@@ -396,6 +396,8 @@  void aarch64_err_no_fpadvsimd (machine_mode, const char *);
 void aarch64_expand_epilogue (bool);
 void aarch64_expand_mov_immediate (rtx, rtx);
 void aarch64_expand_prologue (void);
+void aarch64_expand_split_stack_prologue (void);
+void aarch64_split_stack_space_check (rtx, rtx);
 void aarch64_expand_vector_init (rtx, rtx);
 void aarch64_init_cumulative_args (CUMULATIVE_ARGS *, const_tree, rtx,
 				   const_tree, unsigned);
diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
index 9aa59e7..ae014909 100644
--- a/gcc/config/aarch64/aarch64.c
+++ b/gcc/config/aarch64/aarch64.c
@@ -951,7 +951,12 @@  aarch64_gen_far_branch (rtx * operands, int pos_label, const char * dest,
     snprintf (buffer, sizeof (buffer), "%s%s", branch_format, label_ptr);
     output_asm_insn (buffer, operands);
 
-    snprintf (buffer, sizeof (buffer), "b\t%%l%d\n%s:", pos_label, label_ptr);
+    if (GET_CODE (operands[pos_label]) == LABEL_REF)
+      snprintf (buffer, sizeof (buffer), "b\t%%l%d\n%s:", pos_label,
+		label_ptr);
+    else
+      snprintf (buffer, sizeof (buffer), "b\t%%%d\n%s:", pos_label,
+		label_ptr);
     operands[pos_label] = dest_label;
     output_asm_insn (buffer, operands);
     return "";
@@ -10365,7 +10370,7 @@  aarch64_expand_builtin_va_start (tree valist, rtx nextarg ATTRIBUTE_UNUSED)
   /* Emit code to initialize STACK, which points to the next varargs stack
      argument.  CUM->AAPCS_STACK_SIZE gives the number of stack words used
      by named arguments.  STACK is 8-byte aligned.  */
-  t = make_tree (TREE_TYPE (stack), virtual_incoming_args_rtx);
+  t = make_tree (TREE_TYPE (stack), crtl->args.internal_arg_pointer);
   if (cum->aapcs_stack_size > 0)
     t = fold_build_pointer_plus_hwi (t, cum->aapcs_stack_size * UNITS_PER_WORD);
   t = build2 (MODIFY_EXPR, TREE_TYPE (stack), stack, t);
@@ -15070,6 +15075,165 @@  aarch64_sched_can_speculate_insn (rtx_insn *insn)
     }
 }
 
+/* -fsplit-stack support.  */
+
+/* A SYMBOL_REF for __morestack.  */
+static GTY(()) rtx morestack_ref;
+
+/* Load split-stack area from thread pointer position.  The split-stack is
+   allocate just before thread pointer.  */
+
+static rtx
+aarch64_load_split_stack_value (bool use_hard_reg)
+{
+  /* Offset from thread pointer to split-stack area.  */
+  const int psso = -8;
+
+  rtx ssvalue = use_hard_reg
+		? gen_rtx_REG (Pmode, R9_REGNUM) : gen_reg_rtx (Pmode);
+  ssvalue = aarch64_load_tp (ssvalue);
+  rtx mem = gen_rtx_MEM (Pmode, plus_constant (Pmode, ssvalue, psso));
+  emit_move_insn (ssvalue, mem);
+  return ssvalue;
+}
+
+/* Emit -fsplit-stack prologue, which goes before the regular function
+   prologue.  */
+
+void
+aarch64_expand_split_stack_prologue (void)
+{
+  rtx ssvalue, reg10, reg11, reg12, cc, cmp, jump;
+  HOST_WIDE_INT allocate;
+  rtx_code_label *ok_label = NULL;
+
+  gcc_assert (flag_split_stack && reload_completed);
+
+  /* It limits total maximum stack allocation on 4G so its value can be
+     materialized using two instructions at most (movn/movk).  It might be
+     used by the linker to add some extra space for split calling non split
+     stack functions.  */
+  allocate = cfun->machine->frame.frame_size;
+  if (allocate > ((int64_t)1 << 32))
+    {
+      sorry ("Stack frame larger than 4G is not supported for -fsplit-stack");
+      return;
+    }
+
+  if (morestack_ref == NULL_RTX)
+    {
+      morestack_ref = gen_rtx_SYMBOL_REF (Pmode, "__morestack");
+      SYMBOL_REF_FLAGS (morestack_ref) |= (SYMBOL_FLAG_LOCAL
+					   | SYMBOL_FLAG_FUNCTION);
+    }
+
+  ssvalue = aarch64_load_split_stack_value (true);
+
+  /* Always emit two insns to calculate the requested stack, so the linker
+     can edit them when adjusting size for calling non-split-stack code.  */
+  reg10 = gen_rtx_REG (Pmode, R10_REGNUM);
+  emit_insn (gen_rtx_SET (reg10, GEN_INT (allocate & 0xffff)));
+  emit_insn (gen_insv_immdi (reg10, GEN_INT (16),
+			     GEN_INT ((allocate & 0xffff0000) >> 16)));
+  emit_insn (gen_sub3_insn (reg10, stack_pointer_rtx, reg10));
+
+  ok_label = gen_label_rtx ();
+
+  /* If function uses stacked arguments save the old stack value so morestack
+     can return it.  */
+  reg11 = gen_rtx_REG (Pmode, R11_REGNUM);
+  if (crtl->args.size
+      || cfun->machine->frame.saved_varargs_size)
+    emit_move_insn (reg11, stack_pointer_rtx);
+
+  /* x12 holds the continuation address used to return to function.  */
+  reg12 = gen_rtx_REG (Pmode, R12_REGNUM);
+  aarch64_expand_mov_immediate (reg12, gen_rtx_LABEL_REF (VOIDmode, ok_label));
+
+  /* Jump to __morestack call if current ss guard is not suffice.  */
+  cc = aarch64_gen_compare_reg (GE, ssvalue, reg10);
+  cmp = gen_rtx_fmt_ee (GE, VOIDmode, cc, const0_rtx);
+  jump = gen_split_stack_cond_call (morestack_ref, cmp, ok_label, reg12);
+
+  aarch64_emit_unlikely_jump (jump);
+  JUMP_LABEL (jump) = ok_label;
+  LABEL_NUSES (ok_label)++;
+
+  /* __morestack will call us here.  */
+  emit_label (ok_label);
+}
+
+/* Implement TARGET_ASM_FILE_END.  */
+
+static void
+aarch64_file_end (void)
+{
+  file_end_indicate_exec_stack ();
+
+  if (flag_split_stack)
+    {
+      file_end_indicate_split_stack ();
+
+      switch_to_section (data_section);
+      fprintf (asm_out_file, "\t.align 3\n");
+      fprintf (asm_out_file, "\t.quad __libc_tcb_private_ss\n");
+    }
+}
+
+/* Return the internal arg pointer used for function incoming arguments.  */
+
+static rtx
+aarch64_internal_arg_pointer (void)
+{
+  if (flag_split_stack
+     && (lookup_attribute ("no_split_stack", DECL_ATTRIBUTES (cfun->decl))
+         == NULL))
+    {
+      if (cfun->machine->frame.split_stack_arg_pointer == NULL_RTX)
+	{
+	  rtx pat;
+
+	  cfun->machine->frame.split_stack_arg_pointer = gen_reg_rtx (Pmode);
+	  REG_POINTER (cfun->machine->frame.split_stack_arg_pointer) = 1;
+
+	  /* Put the pseudo initialization right after the note at the
+	     beginning of the function.  */
+	  pat = gen_rtx_SET (cfun->machine->frame.split_stack_arg_pointer,
+			     gen_rtx_REG (Pmode, R11_REGNUM));
+	  push_topmost_sequence ();
+	  emit_insn_after (pat, get_insns ());
+	  pop_topmost_sequence ();
+	}
+      return plus_constant (Pmode, cfun->machine->frame.split_stack_arg_pointer,
+			    FIRST_PARM_OFFSET (current_function_decl));
+    }
+  return virtual_incoming_args_rtx;
+}
+
+/* Emit -fsplit-stack dynamic stack allocation space check.  */
+
+void
+aarch64_split_stack_space_check (rtx size, rtx label)
+{
+  rtx ssvalue, cc, cmp, jump, temp;
+  rtx requested = gen_reg_rtx (Pmode);
+
+  /* Load __private_ss from TCB.  */
+  ssvalue = aarch64_load_split_stack_value (false);
+
+  temp = gen_reg_rtx (Pmode);
+
+  /* And compare it with frame pointer plus required stack.  */
+  size = force_reg (Pmode, size);
+  emit_move_insn (requested, gen_rtx_MINUS (Pmode, stack_pointer_rtx, size));
+
+  /* Jump to label call if current ss guard is not suffice.  */
+  cc = aarch64_gen_compare_reg (GE, temp, ssvalue);
+  cmp = gen_rtx_fmt_ee (GEU, VOIDmode, cc, const0_rtx);
+  jump = emit_jump_insn (gen_condjump (cmp, cc, label));
+  JUMP_LABEL (jump) = label;
+}
+
 /* Target-specific selftests.  */
 
 #if CHECKING_P
@@ -15142,6 +15306,9 @@  aarch64_run_selftests (void)
 #undef TARGET_ASM_FILE_START
 #define TARGET_ASM_FILE_START aarch64_start_file
 
+#undef TARGET_ASM_FILE_END
+#define TARGET_ASM_FILE_END aarch64_file_end
+
 #undef TARGET_ASM_OUTPUT_MI_THUNK
 #define TARGET_ASM_OUTPUT_MI_THUNK aarch64_output_mi_thunk
 
@@ -15227,6 +15394,9 @@  aarch64_run_selftests (void)
 #undef TARGET_FRAME_POINTER_REQUIRED
 #define TARGET_FRAME_POINTER_REQUIRED aarch64_frame_pointer_required
 
+#undef TARGET_INTERNAL_ARG_POINTER
+#define TARGET_INTERNAL_ARG_POINTER aarch64_internal_arg_pointer
+
 #undef TARGET_GIMPLE_FOLD_BUILTIN
 #define TARGET_GIMPLE_FOLD_BUILTIN aarch64_gimple_fold_builtin
 
diff --git a/gcc/config/aarch64/aarch64.h b/gcc/config/aarch64/aarch64.h
index 7f91edb..1406bec 100644
--- a/gcc/config/aarch64/aarch64.h
+++ b/gcc/config/aarch64/aarch64.h
@@ -607,6 +607,9 @@  struct GTY (()) aarch64_frame
   unsigned wb_candidate2;
 
   bool laid_out;
+
+  /* Alternative internal arg pointer for -fsplit-stack.  */
+  rtx split_stack_arg_pointer;
 };
 
 typedef struct GTY (()) machine_function
diff --git a/gcc/config/aarch64/aarch64.md b/gcc/config/aarch64/aarch64.md
index f876a2b..4c914de 100644
--- a/gcc/config/aarch64/aarch64.md
+++ b/gcc/config/aarch64/aarch64.md
@@ -150,6 +150,7 @@ 
     UNSPECV_SET_FPSR		; Represent assign of FPSR content.
     UNSPECV_BLOCKAGE		; Represent a blockage
     UNSPECV_PROBE_STACK_RANGE	; Represent stack range probing.
+    UNSPECV_SPLIT_STACK_CALL    ; Represent a morestack call
   ]
 )
 
@@ -5631,3 +5632,58 @@ 
 
 ;; ldp/stp peephole patterns
 (include "aarch64-ldpstp.md")
+
+;; Handle -fsplit-stack
+(define_expand "split_stack_prologue"
+  [(const_int 0)]
+  ""
+{
+  aarch64_expand_split_stack_prologue ();
+  DONE;
+})
+
+;; If there are operand 0 bytes available on the stack, jump to
+;; operand 1.
+(define_expand "split_stack_space_check"
+  [(set (match_dup 2) (compare:CC (match_dup 3) (match_dup 2)))
+   (set (pc) (if_then_else
+	      (geu (match_dup 4) (const_int 0))
+	      (label_ref (match_operand 1))
+	      (pc)))]
+  ""
+{
+  aarch64_split_stack_space_check (operands[0], operands[1]);
+  DONE;
+})
+
+;; A __morestack call using branch
+
+(define_expand "split_stack_cond_call"
+  [(match_operand 0 "aarch64_call_insn_operand" "")
+   (match_operand 1 "" "")
+   (match_operand 2 "" "")
+   (match_operand 3 "" "")]
+  ""
+{
+  emit_jump_insn (gen_split_stack_cond_call_di (operands[0], operands[1],
+						operands[2], operands[3]));
+  DONE;
+})
+
+
+(define_insn "split_stack_cond_call_<mode>"
+  [(set (pc)
+        (if_then_else
+          (match_operand 1 "aarch64_comparison_operator" "")
+          (label_ref (match_operand 2 "" ""))
+          (pc)))
+   (set (reg:P 1) (unspec_volatile:P [(match_operand:P 0 "aarch64_call_insn_operand" "")
+                                    (reg:P 1)]
+                                   UNSPECV_SPLIT_STACK_CALL))
+   (use (match_operand:P 3 "register_operand" ""))]
+  ""
+  {
+    return aarch64_gen_far_branch (operands, 0, "Lbcond", "b%M1\\t");
+  }
+  [(set_attr "type" "branch")]
+)
diff --git a/libgcc/config.host b/libgcc/config.host
index ae8836e..10157ac 100644
--- a/libgcc/config.host
+++ b/libgcc/config.host
@@ -352,6 +352,7 @@  aarch64*-*-linux*)
 	md_unwind_header=aarch64/linux-unwind.h
 	tmake_file="${tmake_file} ${cpu_type}/t-aarch64"
 	tmake_file="${tmake_file} ${cpu_type}/t-softfp t-softfp t-crtfm"
+	tmake_file="${tmake_file} t-stack aarch64/t-stack-aarch64"
 	;;
 alpha*-*-linux*)
 	tmake_file="${tmake_file} alpha/t-alpha alpha/t-ieee t-crtfm alpha/t-linux"
diff --git a/libgcc/config/aarch64/morestack-c.c b/libgcc/config/aarch64/morestack-c.c
new file mode 100644
index 0000000..d065d33
--- /dev/null
+++ b/libgcc/config/aarch64/morestack-c.c
@@ -0,0 +1,87 @@ 
+/* AArch64 support for -fsplit-stack.
+ * Copyright (C) 2016 Free Software Foundation, Inc.
+ *
+ * This file 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.
+ *
+ * This file 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.
+ *
+ * Under Section 7 of GPL version 3, you are granted additional
+ * permissions described in the GCC Runtime Library Exception, version
+ * 3.1, as published by the Free Software Foundation.
+ *
+ * You should have received a copy of the GNU General Public License and
+ * a copy of the GCC Runtime Library Exception along with this program;
+ * see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
+ * <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef inhibit_libc
+
+#include <stdint.h>
+#include <stdlib.h>
+#include <stddef.h>
+#include "generic-morestack.h"
+
+#define INITIAL_STACK_SIZE  0x4000
+#define BACKOFF             0x1000
+
+void __generic_morestack_set_initial_sp (void *sp, size_t len);
+void *__morestack_get_guard (void);
+void __morestack_set_guard (void *);
+void *__morestack_make_guard (void *stack, size_t size);
+void __morestack_load_mmap (void);
+
+/* split-stack area position from thread pointer.  */
+static inline void *
+ss_pointer (void)
+{
+#define SS_OFFSET	(-8)
+  return (void*) ((uintptr_t) __builtin_thread_pointer() + SS_OFFSET);
+}
+
+/* Initialize the stack guard when the program starts or when a new
+   thread.  This is called from a constructor using ctors section.  */
+void
+__stack_split_initialize (void)
+{
+  register uintptr_t* sp __asm__ ("sp");
+  uintptr_t *ss = ss_pointer ();
+  *ss = (uintptr_t)sp - INITIAL_STACK_SIZE;
+  __generic_morestack_set_initial_sp (sp, INITIAL_STACK_SIZE);
+}
+
+/* Return current __private_ss.  */
+void *
+__morestack_get_guard (void)
+{
+  void **ss = ss_pointer ();
+  return *ss;
+}
+
+/* Set __private_ss to ptr.  */
+void
+__morestack_set_guard (void *ptr)
+{
+  void **ss = ss_pointer ();
+  *ss = ptr;
+}
+
+/* Return the stack guard value for given stack.  */
+void *
+__morestack_make_guard (void *stack, size_t size)
+{
+  return (void*)((uintptr_t) stack - size + BACKOFF);
+}
+
+/* Make __stack_split_initialize a high priority constructor.  */
+static void (*const ctors []) 
+  __attribute__ ((used, section (".ctors.65535"), aligned (sizeof (void *))))
+  = { __stack_split_initialize, __morestack_load_mmap };
+
+#endif /* !defined (inhibit_libc) */
diff --git a/libgcc/config/aarch64/morestack.S b/libgcc/config/aarch64/morestack.S
new file mode 100644
index 0000000..6dc9ba7
--- /dev/null
+++ b/libgcc/config/aarch64/morestack.S
@@ -0,0 +1,248 @@ 
+# AArch64 support for -fsplit-stack.
+# Copyright (C) 2016 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.
+
+# Under Section 7 of GPL version 3, you are granted additional
+# permissions described in the GCC Runtime Library Exception, version
+# 3.1, as published by the Free Software Foundation.
+
+# You should have received a copy of the GNU General Public License and
+# a copy of the GCC Runtime Library Exception along with this program;
+# see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
+# <http://www.gnu.org/licenses/>.
+
+/* Define an entry point visible from C.  */
+#define ENTRY(name)						\
+  .globl name;							\
+  .type name,%function;						\
+  .align 4;							\
+  name##:
+
+#define END(name)						\
+  .size name,.-name
+
+/* __morestack frame size.  */
+#define MORESTACK_FRAMESIZE	112
+/* Offset from __morestack frame where the new stack size is saved and
+   passed to __generic_morestack.  */
+#define NEWSTACK_SAVE		96
+
+# Excess space needed to call ld.so resolver for lazy plt resolution.
+# Go uses sigaltstack so this doesn't need to also cover signal frame size.
+#define BACKOFF			0x1000
+# Large excess allocated when calling non-split-stack code.
+#define NON_SPLIT_STACK		0x100000
+
+/* split-stack area position from thread pointer.  */
+#define SPLITSTACK_PTR_TP	-8
+
+	.text
+ENTRY(__morestack_non_split)
+	.cfi_startproc
+# We use a cleanup to restore the tcbhead_t.__private_ss if
+# an exception is thrown through this code.
+	add	x10, x10, NON_SPLIT_STACK
+	.cfi_endproc
+END(__morestack_non_split)
+# Fall through into __morestack
+
+# This function is called with non-standard calling conventions, on entry
+# x10 is the requested stack pointer.  The split-stack prologue is in the
+# form:
+#
+# function:
+#	mrs    x9, tpidr_el0
+#	mov    x10, <required stack allocation>
+#	movk   x10, #0x0, lsl #16
+#	sub    x10, sp, x10
+#	mov    x11, sp   	# if function has stacked arguments
+#	adrp   x12, main_fn_entry
+#	add    x12, x12, :lo12:.L2
+#	cmp    x9, x10
+#	b.lt   <main_fn_entry>
+#	b      __morestack
+# main_fn_entry:
+#	[function prologue]
+#
+# The N bit is also restored to indicate that the function is called
+# (so the prologue addition can set up the argument pointer correctly).
+
+ENTRY(__morestack)
+.LFB1:
+	.cfi_startproc
+
+#ifdef __PIC__
+	.cfi_personality 0x9b,DW.ref.__gcc_personality_v0
+	.cfi_lsda 0x1b,.LLSDA1
+#else
+	.cfi_personality 0x3,__gcc_personality_v0
+	.cfi_lsda 0x3,.LLSDA1
+#endif
+
+	# Calculate requested stack size.
+	sub	x10, sp, x10
+	# Save parameters
+	stp	x29, x30, [sp, -MORESTACK_FRAMESIZE]!
+	.cfi_def_cfa_offset MORESTACK_FRAMESIZE
+	.cfi_offset 29, -MORESTACK_FRAMESIZE
+	.cfi_offset 30, -MORESTACK_FRAMESIZE+8
+	add	x29, sp, 0
+	.cfi_def_cfa_register 29
+	# Adjust the requested stack size for the frame pointer save.
+	stp	x0, x1, [sp, 16]
+	stp	x2, x3, [sp, 32]
+	add	x10, x10, BACKOFF
+	stp	x4, x5, [sp, 48]
+	stp	x6, x7, [sp, 64]
+	stp 	x8, x12, [sp, 80]
+	str	x10, [sp, 96]
+
+	# void __morestack_block_signals (void)
+	bl	__morestack_block_signals
+
+	# void *__generic_morestack (size_t *pframe_size,
+	#			     void *old_stack,
+	#			     size_t param_size)
+	# pframe_size: is the size of the required stack frame (the function
+	#	       amount of space remaining on the allocated stack).
+	# old_stack: points at the parameters the old stack
+	# param_size: size in bytes of parameters to copy to the new stack.
+	add	x0, x29, NEWSTACK_SAVE
+	add	x1, x29, MORESTACK_FRAMESIZE
+	mov	x2, 0
+	bl	__generic_morestack
+
+	# Start using new stack
+	mov	sp, x0
+
+	# Set __private_ss stack guard for the new stack.
+	ldr	x9, [x29, NEWSTACK_SAVE]
+	add	x0, x0, BACKOFF
+	sub	x0, x0, x9
+.LEHB0:
+	mrs	x1, tpidr_el0
+	str	x0, [x1, SPLITSTACK_PTR_TP]
+
+	# void __morestack_unblock_signals (void)
+	bl	__morestack_unblock_signals
+
+	# Set up for a call to the target function.
+	ldp	x0, x1, [x29, 16]
+	ldp	x2, x3, [x29, 32]
+	ldp	x4, x5, [x29, 48]
+	ldp	x6, x7, [x29, 64]
+	ldp	x8, x12, [x29, 80]
+	add	x11, x29, MORESTACK_FRAMESIZE
+	# Indicate __morestack was called.
+	cmp	x12, 0
+	blr	x12
+
+	stp	x0, x1, [x29, 16]
+	stp	x2, x3, [x29, 32]
+	stp	x4, x5, [x29, 48]
+	stp	x6, x7, [x29, 64]
+
+	bl	__morestack_block_signals
+
+	# void *__generic_releasestack (size_t *pavailable)
+	add	x0, x29, NEWSTACK_SAVE
+	bl	__generic_releasestack
+
+	# Reset __private_ss stack guard to value for old stack
+	ldr	x9, [x29, NEWSTACK_SAVE]
+	add	x0, x0, BACKOFF
+	sub	x0, x0, x9
+
+	# Update TCB split stack field
+.LEHE0:
+	mrs	x1, tpidr_el0
+	str	x0, [x1, SPLITSTACK_PTR_TP]
+
+	bl __morestack_unblock_signals
+
+	# Use old stack again.
+	add	sp, x29, MORESTACK_FRAMESIZE
+
+	ldp	x0, x1, [x29, 16]
+	ldp	x2, x3, [x29, 32]
+	ldp	x4, x5, [x29, 48]
+	ldp	x6, x7, [x29, 64]
+	ldp	x29, x30, [x29]
+
+	.cfi_remember_state
+	.cfi_restore 30
+	.cfi_restore 29
+	.cfi_def_cfa 31, 0
+
+	ret
+
+# This is the cleanup code called by the stack unwinder when
+# unwinding through code between .LEHB0 and .LEHE0 above.
+cleanup:
+	.cfi_restore_state
+	# Reuse the new stack allocation to save/restore the
+	# exception header
+	str	x0, [x29, NEWSTACK_SAVE]
+	# size_t __generic_findstack (void *stack)
+	add	x0, x29, MORESTACK_FRAMESIZE
+	bl	__generic_findstack
+	sub	x0, x29, x0
+	add	x0, x0, BACKOFF
+	# Restore split-stack guard value
+	mrs	x1, tpidr_el0
+	str	x0, [x1, SPLITSTACK_PTR_TP]
+	ldr	x0, [x29, NEWSTACK_SAVE]
+	b	_Unwind_Resume
+        .cfi_endproc
+END(__morestack)
+
+	.section .gcc_except_table,"a",@progbits
+	.align 4
+.LLSDA1:
+	# @LPStart format (omit)
+        .byte   0xff
+	# @TType format (omit)
+        .byte   0xff
+	# Call-site format (uleb128)
+        .byte   0x1
+	# Call-site table length
+        .uleb128 .LLSDACSE1-.LLSDACSB1
+.LLSDACSB1:
+	# region 0 start
+        .uleb128 .LEHB0-.LFB1
+	# length
+        .uleb128 .LEHE0-.LEHB0
+	# landing pad
+        .uleb128 cleanup-.LFB1
+	# no action (ie a cleanup)
+        .uleb128 0
+.LLSDACSE1:
+
+
+	.global __gcc_personality_v0
+#ifdef __PIC__
+	# Build a position independent reference to the personality function.
+	.hidden DW.ref.__gcc_personality_v0
+	.weak   DW.ref.__gcc_personality_v0
+	.section .data.DW.ref.__gcc_personality_v0,"awG",@progbits,DW.ref.__gcc_personality_v0,comdat
+	.type   DW.ref.__gcc_personality_v0, @object
+	.align 3
+DW.ref.__gcc_personality_v0:
+	.size   DW.ref.__gcc_personality_v0, 8
+	.quad   __gcc_personality_v0
+#endif
+
+	.section .note.GNU-stack,"",@progbits
+	.section .note.GNU-split-stack,"",@progbits
+	.section .note.GNU-no-split-stack,"",@progbits
diff --git a/libgcc/config/aarch64/t-stack-aarch64 b/libgcc/config/aarch64/t-stack-aarch64
new file mode 100644
index 0000000..4babb4e
--- /dev/null
+++ b/libgcc/config/aarch64/t-stack-aarch64
@@ -0,0 +1,3 @@ 
+# Makefile fragment to support -fsplit-stack for aarch64.
+LIB2ADD_ST += $(srcdir)/config/aarch64/morestack.S \
+	      $(srcdir)/config/aarch64/morestack-c.c
diff --git a/libgcc/generic-morestack.c b/libgcc/generic-morestack.c
index adbe436..e91ceb4 100644
--- a/libgcc/generic-morestack.c
+++ b/libgcc/generic-morestack.c
@@ -943,6 +943,7 @@  __splitstack_find (void *segment_arg, void *sp, size_t *len,
       nsp -= 2 * 160;
 #elif defined __s390__
       nsp -= 2 * 96;
+#elif defined __aarch64__
 #else
 #error "unrecognized target"
 #endif