xtensa: libgcc: fix PR target/95571

Rewrite uw_install_context without function calls to avoid register
spilling in _Unwind_RaiseException during return context installation.

2020-06-08  Max Filippov  <jcmvbkbc@gmail.com>
gcc/testsuite/
	* g++.target/xtensa/pr95571.C: New test.
	* g++.target/xtensa/xtensa.exp: New testsuite.

libgcc/
	* config/xtensa/unwind-dw2-xtensa.c (uw_install_context): Merge
	with uw_install_context_1.

gcc/testsuite/g++.target/xtensa/pr95571.C

@@ -0,0 +1,43 @@
+/* { dg-do run } */
+
+extern "C" void abort(void);
+extern "C" void __xtensa_libgcc_window_spill(void);
+
+static int call;
+static int cnt;
+
+extern "C" void *memcpy(void *dst, const void *src, unsigned int sz)
+{
+  char *a = (char *)dst;
+  const char *b = (const char *)src;
+
+  if (call++ == cnt)
+    __xtensa_libgcc_window_spill();
+
+  while (sz--)
+    *a++ = *b++;
+
+  return dst;
+}
+
+int main()
+{
+  int i;
+
+  for (i = 0; i < 100; ++i)
+    {
+      call = 0;
+      cnt = i;
+
+      try
+	{
+	  throw 1;
+	}
+      catch (int v)
+	{
+	  if (v != 1)
+	    abort ();
+	}
+    }
+  return 0;
+}

gcc/testsuite/g++.target/xtensa/xtensa.exp

@@ -0,0 +1,43 @@
+#  Specific regression driver for Xtensa.
+#  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.
+#
+#  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/>.  */
+
+# GCC testsuite that uses the `dg.exp' driver.
+
+# Exit immediately if this isn't an Xtensa target.
+if {![istarget xtensa*-*-*] } then {
+  return
+}
+
+# Load support procs.
+load_lib g++-dg.exp
+
+global DEFAULT_CXXFLAGS
+if ![info exists DEFAULT_CXXFLAGS] then {
+    set DEFAULT_CXXFLAGS " -pedantic-errors"
+}
+
+# Initialize `dg'.
+dg-init
+
+# Main loop.
+dg-runtest [lsort [glob -nocomplain $srcdir/$subdir/*.C]] \
+        "" $DEFAULT_CXXFLAGS
+
+# All done.
+dg-finish

libgcc/config/xtensa/unwind-dw2-xtensa.c

@@ -481,37 +481,35 @@ uw_init_context_1 (struct _Unwind_Context *context, void *outer_cfa,
 
 /* Install TARGET into CURRENT so that we can return to it.  This is a
    macro because __builtin_eh_return must be invoked in the context of
-   our caller.  */
+   our caller, and also because spilling registers of the caller before
+   the context installation may result in reload of wrong register values
+   after the context installation due to the change of the stack pointer
+   in the base save area.  This spilling may be caused by an interrupt
+   handler on baremetal host.  */
 
 #define uw_install_context(CURRENT, TARGET, FRAMES)			 \
   do									 \
     {									 \
-      long offset = uw_install_context_1 ((CURRENT), (TARGET));		 \
       void *handler = __builtin_frob_return_addr ((TARGET)->ra);	 \
-      __builtin_eh_return (offset, handler);				 \
+      long i;								 \
+									 \
+      /* The eh_return insn assumes a window size of 8, so don't bother	 \
+	 copying the save areas for registers a8-a15 since they won't be \
+	 reloaded.  */							 \
+      for (i = 0; i < 2; ++i)						 \
+	{								 \
+	  _Unwind_Word *c = (CURRENT)->reg[i];				 \
+	  _Unwind_Word *t = (TARGET)->reg[i];				 \
+	  int j;							 \
+									 \
+	  if (t && c && t != c)						 \
+	    for (j = 0; j < 4; ++j)					 \
+	      *c++ = *t++;						 \
+	}								 \
+      __builtin_eh_return (0, handler);					 \
     }									 \
   while (0)
 
-static long
-uw_install_context_1 (struct _Unwind_Context *current,
-		      struct _Unwind_Context *target)
-{
-  long i;
-
-  /* The eh_return insn assumes a window size of 8, so don't bother copying
-     the save areas for registers a8-a15 since they won't be reloaded.  */
-  for (i = 0; i < 2; ++i)
-    {
-      void *c = current->reg[i];
-      void *t = target->reg[i];
-
-      if (t && c && t != c)
-	memcpy (c, t, 4 * sizeof (_Unwind_Word));
-    }
-
-  return 0;
-}
-
 static inline _Unwind_Ptr
 uw_identify_context (struct _Unwind_Context *context)
 {