Add runtime support needed for C++ exceptions

Implements __gnu_Unwind_Find_got(), which is called from libgcc while
unwinding.

	* libc/sysdeps/linux/arm/Makefile.arch (CSRC): Add find._got.c.
	* libc/sysdeps/linux/arm/find_got.c: New file.

Signed-off-by: Mickaël Guêné <mickael.guene@st.com>
Signed-off-by: Christophe Lyon <christophe.lyon@st.com>

libc/sysdeps/linux/arm/Makefile.arch

@@ -23,7 +23,7 @@ $(eval $(call cache-output-var,IS_EABI,$(CC_IS_EABI_CHECK) -x c - -E -dM </dev/n
 
 CSRC-$(IS_EABI) += aeabi_assert.c aeabi_atexit.c aeabi_errno_addr.c \
 	aeabi_localeconv.c aeabi_memclr.c aeabi_memcpy.c \
-	aeabi_memmove.c aeabi_memset.c find_exidx.c
+	aeabi_memmove.c aeabi_memset.c find_exidx.c find_got.c
 SSRC-$(IS_EABI) += syscall-eabi.S
 CSRC-$(if $(IS_EABI),,y)) += syscall.c
 ARCH_OBJ_FILTEROUT-$(IS_EABI) := syscall.c

libc/sysdeps/linux/arm/find_got.c

@@ -0,0 +1,72 @@
+/* Copyright (C) 2018 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <link.h>
+#include <unwind.h>
+
+#if __FDPIC__
+#include <bits/elf-fdpic.h>
+
+struct got_callback_data
+{
+  _Unwind_Ptr pc;
+  _Unwind_Ptr got;
+};
+
+static __always_inline int
+__dl_addr_in_loadaddr(void *p, struct elf32_fdpic_loadaddr loadaddr)
+{
+	struct elf32_fdpic_loadmap *map = loadaddr.map;
+	int c;
+
+	for (c = 0; c < map->nsegs; c++)
+		if ((void *)map->segs[c].addr <= p &&
+		    (char *)p < (char *)map->segs[c].addr + map->segs[c].p_memsz)
+			return 1;
+
+	return 0;
+}
+
+/* Callback to return the GOT value if the module contains PC.  */
+static int
+find_got_callback (struct dl_phdr_info * info, size_t size, void * ptr)
+{
+    int match = 0;
+    struct got_callback_data *data = (struct got_callback_data *) ptr;
+
+    if (__dl_addr_in_loadaddr((void *) data->pc, info->dlpi_addr)) {
+        match = 1;
+        data->got = (_Unwind_Ptr) info->dlpi_addr.got_value;
+    }
+
+    return match;
+}
+
+/* Find the GOT that corresponds to the module containing PC.  */
+_Unwind_Ptr __gnu_Unwind_Find_got (_Unwind_Ptr pc);
+_Unwind_Ptr __gnu_Unwind_Find_got (_Unwind_Ptr pc)
+{
+  struct got_callback_data data;
+
+  data.pc = pc;
+  if (dl_iterate_phdr (find_got_callback, &data) <= 0)
+    return 0;
+
+  return data.got;
+}
+#endif
+