commit 5a66490e3b9738cc70162257788bcc00583032fa
author Ryan Prichard <rprichard@google.com> Thu Nov 22 02:14:14 2018 -0800
committer Ryan Prichard <rprichard@google.com> Tue Dec 04 13:51:46 2018 -0800
tree 3c284f55d4ce2f2af5745627bf271812082d3223
parent 9cfca866ce36458bb942b7eebc4997f7bb94d3ad

Use shared globals so getauxval works earlier

Make getauxval() work in .preinit_array. It still won't be usable for
ifuncs unless we can guarantee that the __loader_shared_globals relocation
is resolved before the ifunc calls [__bionic_]getauxval.

Define __bionic_getauxval for use in replacing calls to
KernelArgumentBlock::getauxval, which doesn't (and sometimes isn't allowed
to) access TLS variables like errno.

Bug: http://b/25751302
Test: bionic unit tests
Change-Id: I461feeaed7f43cfa2a2b6c34147194f0df82b516
Merged-In: I461feeaed7f43cfa2a2b6c34147194f0df82b516
(cherry picked from commit bdab4a2b97c53af0205788875342ec08e6901376)

libc/bionic/__libc_init_main_thread.cpp

diff --git a/libc/bionic/__libc_init_main_thread.cpp b/libc/bionic/__libc_init_main_thread.cpp
index cef3d7d..e6e0c56 100644
--- a/libc/bionic/__libc_init_main_thread.cpp
+++ b/libc/bionic/__libc_init_main_thread.cpp
@@ -30,7 +30,6 @@
 
 #include "private/KernelArgumentBlock.h"
 #include "private/bionic_arc4random.h"
-#include "private/bionic_auxv.h"
 #include "private/bionic_defs.h"
 #include "private/bionic_globals.h"
 #include "private/bionic_ssp.h"
@@ -71,7 +70,7 @@
 // are hazardous, such as accessing non-hidden global variables.
 __BIONIC_WEAK_FOR_NATIVE_BRIDGE
 void __libc_init_main_thread_early(KernelArgumentBlock& args) {
-  __libc_auxv = args.auxv;
+  __libc_shared_globals()->auxv = args.auxv;
 #if defined(__i386__)
   __libc_init_sysinfo(args);
 #endif

libc/bionic/getauxval.cpp

diff --git a/libc/bionic/getauxval.cpp b/libc/bionic/getauxval.cpp
index 607e89c..c8f867b 100644
--- a/libc/bionic/getauxval.cpp
+++ b/libc/bionic/getauxval.cpp
@@ -30,17 +30,27 @@
 #include <sys/cdefs.h>
 #include <sys/auxv.h>
 #include <private/bionic_auxv.h>
+#include <private/bionic_globals.h>
 #include <elf.h>
 #include <errno.h>
 
-__LIBC_HIDDEN__ ElfW(auxv_t)* __libc_auxv = nullptr;
-
-extern "C" unsigned long int getauxval(unsigned long int type) {
-  for (ElfW(auxv_t)* v = __libc_auxv; v->a_type != AT_NULL; ++v) {
+// This function needs to be safe to call before TLS is set up, so it can't
+// access errno or the stack protector.
+__attribute__((no_stack_protector))
+__LIBC_HIDDEN__ unsigned long __bionic_getauxval(unsigned long type, bool& exists) {
+  for (ElfW(auxv_t)* v = __libc_shared_globals()->auxv; v->a_type != AT_NULL; ++v) {
     if (v->a_type == type) {
+      exists = true;
       return v->a_un.a_val;
     }
   }
-  errno = ENOENT;
+  exists = false;
   return 0;
 }
+
+extern "C" unsigned long getauxval(unsigned long type) {
+  bool exists;
+  unsigned long result = __bionic_getauxval(type, exists);
+  if (!exists) errno = ENOENT;
+  return result;
+}

libc/bionic/libc_init_common.cpp

diff --git a/libc/bionic/libc_init_common.cpp b/libc/bionic/libc_init_common.cpp
index 4702e1c..fca628b 100644
--- a/libc/bionic/libc_init_common.cpp
+++ b/libc/bionic/libc_init_common.cpp
@@ -45,7 +45,6 @@
 
 #include "private/KernelArgumentBlock.h"
 #include "private/WriteProtected.h"
-#include "private/bionic_auxv.h"
 #include "private/bionic_defs.h"
 #include "private/bionic_globals.h"
 #include "private/bionic_tls.h"

libc/bionic/libc_init_dynamic.cpp

diff --git a/libc/bionic/libc_init_dynamic.cpp b/libc/bionic/libc_init_dynamic.cpp
index 25d462f..2ec1556 100644
--- a/libc/bionic/libc_init_dynamic.cpp
+++ b/libc/bionic/libc_init_dynamic.cpp
@@ -51,7 +51,6 @@
 #include <elf.h>
 #include "libc_init_common.h"
 
-#include "private/bionic_auxv.h"
 #include "private/bionic_globals.h"
 #include "private/bionic_macros.h"
 #include "private/bionic_ssp.h"
@@ -79,7 +78,6 @@
 // protector.
 __attribute__((noinline))
 static void __libc_preinit_impl(KernelArgumentBlock& args) {
-  __libc_auxv = args.auxv;
 #if defined(__i386__)
   __libc_init_sysinfo(args);
 #endif