Implement the "abort" stub in assembly for ARM.

So that we can always get the full stack trace regardless of gcc's handling
of the "noreturn" attribute associated with abort().

(Cherry pick of Id264a5167e7cabbf11515fbc48f5469c527e34d4.)

Bug: 6455193

Conflicts:

	libc/Android.mk

Change-Id: I568fc5303fd1d747075ca933355f914122f94dac

libc/Android.mk

@@ -346,6 +346,7 @@ libc_common_src_files += \
 	arch-arm/bionic/__get_sp.S \
 	arch-arm/bionic/_exit_with_stack_teardown.S \
 	arch-arm/bionic/_setjmp.S \
+	arch-arm/bionic/abort_arm.S \
 	arch-arm/bionic/atomics_arm.S \
 	arch-arm/bionic/clone.S \
 	arch-arm/bionic/eabi.c \

libc/arch-arm/bionic/abort_arm.S

@@ -0,0 +1,42 @@
+/*
+ * Copyright (C) 2012 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <machine/asm.h>
+
+/*
+ * Coding the abort function in assembly so that registers are guaranteed to
+ * be preserved properly regardless of GCC's assumption on the "noreturn"
+ * attribute. When the registers are not properly preserved we won't be able
+ * to unwind the stack all the way to the bottom to fully reveal the call
+ * sequence when the crash happens.
+ */
+ENTRY(abort)
+    .save   {r3, r14}
+    stmfd   sp!, {r3, r14}
+    blx     PIC_SYM(_C_LABEL(__libc_android_abort), PLT)
+END(abort)

libc/unistd/abort.c

@@ -102,29 +102,3 @@ abort(void)
 	(void)kill(getpid(), SIGABRT);
 	_exit(1);
 }
-
-#ifdef __arm__
-/*
- * abort() does not return, which gcc interprets to mean that it doesn't
- * need to preserve any of the callee-save registers.  Unfortunately this
- * includes the link register, so if LR is used there is no way to determine
- * which function called abort().
- *
- * We work around this by inserting a trivial stub that doesn't alter
- * any of the "interesting" registers and thus doesn't need to save them.
- * We can't just call __libc_android_abort from C because gcc uses "bl"
- * without first saving LR, so we use an asm statement.  This also has
- * the side-effect of replacing abort() with __libc_android_abort() in
- * the stack trace.
- *
- * Ideally __libc_android_abort would be static, but I haven't figured out
- * how to tell gcc to call a static function from an asm statement.
- */
-void
-abort(void)
-{
-    asm ("b __libc_android_abort");
-    _exit(1);       /* suppress gcc noreturn warnings */
-}
-#endif
-