Switch to inline assembler in crtbegin.

Using __builtin_frame_address was clever, but didn't work for arm64 (for
reasons which were never investigated) and the ChromeOS folks claim it
causes trouble for x86 with ARC++ (though without a reproduceable test case).

Naked functions turn out to be quite unevenly supported: some architectures
do the right thing, others don't; some architectures warn, others don't (and
the warnings don't always match the platforms that _actually_ have problems).

Inline assembler also removes the guessing games: everyone knows what the
couple of instructions _ought_ to be, and now we don't have to reason about
what the compiler will actually do (yet still keep the majority of the code
in C).

Bug: N/A
Test: builds, boots
Change-Id: I14207ef50ca46b6eca273c3cb7509c311146a3ca

libc/Android.bp

@@ -1984,14 +1984,6 @@ cc_object {
     srcs: ["arch-common/bionic/crtbegin.c"],
 
     arch: {
-        arm64: {
-            srcs: [
-                "arch-arm64/bionic/crtbegin.c",
-            ],
-            exclude_srcs: [
-                "arch-common/bionic/crtbegin.c",
-            ],
-        },
         mips: {
             srcs: [
                 "arch-mips/bionic/crtbegin.c",
@@ -2029,14 +2021,6 @@ cc_object {
     srcs: ["arch-common/bionic/crtbegin.c"],
 
     arch: {
-        arm64: {
-            srcs: [
-                "arch-arm64/bionic/crtbegin.c",
-            ],
-            exclude_srcs: [
-                "arch-common/bionic/crtbegin.c",
-            ],
-        },
         mips: {
             srcs: [
                 "arch-mips/bionic/crtbegin.c",

libc/arch-arm64/bionic/crtbegin.c

@@ -1,70 +0,0 @@
-/*
- * Copyright (C) 2013 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 "../../bionic/libc_init_common.h"
-#include <stddef.h>
-#include <stdint.h>
-
-__attribute__ ((section (".preinit_array")))
-void (*__PREINIT_ARRAY__)(void) = (void (*)(void)) -1;
-
-__attribute__ ((section (".init_array")))
-void (*__INIT_ARRAY__)(void) = (void (*)(void)) -1;
-
-__attribute__ ((section (".fini_array")))
-void (*__FINI_ARRAY__)(void) = (void (*)(void)) -1;
-
-
-__LIBC_HIDDEN__ void do_arm64_start(void* raw_args) {
-  structors_array_t array;
-  array.preinit_array = &__PREINIT_ARRAY__;
-  array.init_array = &__INIT_ARRAY__;
-  array.fini_array = &__FINI_ARRAY__;
-  __libc_init(raw_args, NULL, &main, &array);
-}
-
-/*
- * Put the value of sp in x0 and call do_arm64_init(). The latter will then
- * then be able to access the stack as prepared by the kernel's execve system
- * call (via the first argument).
- */
-__asm__ (
-"        .text                      \n"
-"        .align  2                  \n"
-"        .global _start             \n"
-"        .hidden _start             \n"
-"        .type   _start, %function  \n"
-"_start:                            \n"
-"        add     x0, sp, xzr        \n"
-"        b       do_arm64_start   \n"
-"        .size   _start, .-_start   \n"
-);
-
-#include "../../arch-common/bionic/__dso_handle.h"
-#include "../../arch-common/bionic/atexit.h"
-#include "../../arch-common/bionic/pthread_atfork.h"

libc/arch-common/bionic/crtbegin.c

@@ -30,33 +30,42 @@
 #include <stddef.h>
 #include <stdint.h>
 
-__attribute__ ((section (".preinit_array")))
+__attribute__((__section__(".preinit_array")))
 void (*__PREINIT_ARRAY__)(void) = (void (*)(void)) -1;
 
-__attribute__ ((section (".init_array")))
+__attribute__((__section__(".init_array")))
 void (*__INIT_ARRAY__)(void) = (void (*)(void)) -1;
 
-__attribute__ ((section (".fini_array")))
+__attribute__((__section__(".fini_array")))
 void (*__FINI_ARRAY__)(void) = (void (*)(void)) -1;
 
-__LIBC_HIDDEN__
+static void _start_main(void* raw_args) {
-#ifdef __i386__
-__attribute__((force_align_arg_pointer))
-#endif
-void _start() {
   structors_array_t array;
   array.preinit_array = &__PREINIT_ARRAY__;
   array.init_array = &__INIT_ARRAY__;
   array.fini_array = &__FINI_ARRAY__;
 
-  void* raw_args = (void*) ((uintptr_t) __builtin_frame_address(0) + sizeof(void*));
-#ifdef __x86_64__
-  // 16-byte stack alignment is required by x86_64 ABI
-  asm("andq  $~15, %rsp");
-#endif
   __libc_init(raw_args, NULL, &main, &array);
 }
 
+#define PRE ".text; .global _start; .type _start,%function; _start:"
+#define POST "; .size _start, .-_start"
+
+#if defined(__aarch64__)
+__asm__(PRE "mov x0,sp; b _start_main" POST);
+#elif defined(__arm__)
+__asm__(PRE "mov r0,sp; b _start_main" POST);
+#elif defined(__i386__)
+__asm__(PRE "movl %esp,%eax; andl $~0xf,%esp; pushl %eax; calll _start_main" POST);
+#elif defined(__x86_64__)
+__asm__(PRE "movq %rsp,%rdi; andq $~0xf,%rsp; callq _start_main" POST);
+#else
+#error unsupported architecture
+#endif
+
+#undef PRE
+#undef POST
+
 #include "__dso_handle.h"
 #include "atexit.h"
 #include "pthread_atfork.h"