[PATCH] libgcc: Add a weak stub for __sync_synchronize

[Bernd Edlinger <bernd.edlinger@hotmail.de>]

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Hi,

this fixes a problem with a missing symbol __sync_synchronize
which happens when newlib is used together with libstdc++ for
the non-threaded simulator target arm-none-eabi.

There are several questions on stackoverflow about this issue.

I would like to add a weak symbol for this target, since this
is only a default implementation and not meant to override a
possibly more sophisticated synchronization function from the
c-runtime.


Regression tested successfully on arm-none-eabi with newlib-3.3.0.

Is it OK for trunk?


Thanks
Bernd.

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From f8a3df552f4b98308096659c66b4c8ea68580f25 Mon Sep 17 00:00:00 2001
From: Bernd Edlinger <bernd.edlinger@hotmail.de>
Date: Mon, 2 Nov 2020 11:43:44 +0100
Subject: [PATCH] libgcc: Add a weak stub for __sync_synchronize

This patch adds a default implementation for __sync_synchronize,
which prevents many unresolved symbol errors on arm-none-eabi.
This happens often in C++ programs even without any threading.

libgcc:
2020-11-02  Bernd Edlinger  <bernd.edlinger@hotmail.de>

	* config.host: Use t-eabi for arm-none-eabi.
	* config/arm/t-eabi: New.
	* config/arm/eabi-sync.c: New.
---
 libgcc/config.host            |  2 +-
 libgcc/config/arm/eabi-sync.c | 39 +++++++++++++++++++++++++++++++++++++++
 libgcc/config/arm/t-eabi      |  1 +
 3 files changed, 41 insertions(+), 1 deletion(-)
 create mode 100644 libgcc/config/arm/eabi-sync.c
 create mode 100644 libgcc/config/arm/t-eabi

diff --git a/libgcc/config.host b/libgcc/config.host
index fd8e55e..e25abf4 100644
--- a/libgcc/config.host
+++ b/libgcc/config.host
@@ -495,7 +495,7 @@ arm*-*-eabi* | arm*-*-symbianelf* | arm*-*-rtems*)
 	tm_file="$tm_file arm/bpabi-lib.h"
 	case ${host} in
 	arm*-*-eabi* | arm*-*-rtems*)
-	  tmake_file="${tmake_file} arm/t-bpabi t-crtfm"
+	  tmake_file="${tmake_file} arm/t-bpabi t-crtfm arm/t-eabi"
 	  extra_parts="crtbegin.o crtend.o crti.o crtn.o"
 	  ;;
 	arm*-*-symbianelf*)
diff --git a/libgcc/config/arm/eabi-sync.c b/libgcc/config/arm/eabi-sync.c
new file mode 100644
index 0000000..bffdd4a
--- /dev/null
+++ b/libgcc/config/arm/eabi-sync.c
@@ -0,0 +1,39 @@
+/* Copyright (C) 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.
+
+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/>.  */
+
+void __attribute__ ((weak))
+__sync_synchronize (void)
+{
+#if defined (__ARM_ARCH_6__) || defined (__ARM_ARCH_6J__)       \
+    || defined (__ARM_ARCH_6K__) || defined (__ARM_ARCH_6T2__)  \
+    || defined (__ARM_ARCH_6Z__) || defined (__ARM_ARCH_6ZK__)  \
+    || defined (__ARM_ARCH_7__) || defined (__ARM_ARCH_7A__)
+#if defined (__ARM_ARCH_7__) || defined (__ARM_ARCH_7A__)
+    __asm __volatile ("dmb" : : : "memory");
+#else
+    __asm __volatile ("mcr p15, 0, r0, c7, c10, 5" : : : "memory");
+#endif
+#else
+    __asm __volatile ("nop" : : : "memory");
+#endif
+}
diff --git a/libgcc/config/arm/t-eabi b/libgcc/config/arm/t-eabi
new file mode 100644
index 0000000..556032f
--- /dev/null
+++ b/libgcc/config/arm/t-eabi
@@ -0,0 +1 @@
+LIB2ADD_ST += $(srcdir)/config/arm/eabi-sync.c
-- 
1.9.1