Fix __get_tls() in static C library to use kernel helpers.

This is needed to fix gdbserver's handling of threaded programs,
among other things.

Change-Id: I823387c602cef9891532da946a01db14be780ab0

3 files changed, 74 insertions, 15 deletions

diff --git a/libc/Android.mk b/libc/Android.mk
index 510864f17..f700ca074 100644
--- a/libc/Android.mk
+++ b/libc/Android.mk
@@ -64,7 +64,6 @@ libc_common_src_files := \
 	unistd/sleep.c \
 	unistd/statfs.c \
 	unistd/strsignal.c \
-	unistd/sysconf.c \
 	unistd/syslog.c \
 	unistd/system.c \
 	unistd/tcgetpgrp.c \
@@ -245,7 +244,6 @@ libc_common_src_files := \
 	tzcode/localtime.c \
 	tzcode/strftime.c \
 	tzcode/strptime.c \
-	bionic/__errno.c \
 	bionic/__set_errno.c \
 	bionic/_rand48.c \
 	bionic/cpuacct.c \
@@ -314,6 +312,23 @@ libc_common_src_files := \
 	regex/regexec.c \
 	regex/regfree.c \
 
+# The following files are common, but must be compiled
+# with different C flags when building a static C library.
+#
+# The reason for this is the implementation of __get_tls()
+# that will differ between the shared and static versions
+# of the library.
+#
+# See comments in private/bionic_tls.h for more details.
+#
+# NOTE: bionic/pthread.c is added later to this list
+#       because it needs special handling on ARM, see
+#       below.
+#
+libc_static_common_src_files := \
+        unistd/sysconf.c \
+        bionic/__errno.c \
+
 # Architecture specific source files go here
 # =========================================================
 ifeq ($(TARGET_ARCH),arm)
@@ -348,11 +363,13 @@ libc_common_src_files += \
 # can set breakpoints in them without messing
 # up any thumb code.
 libc_common_src_files += \
-	bionic/pthread.c.arm \
 	bionic/pthread-rwlocks.c.arm \
 	bionic/pthread-timers.c.arm \
 	bionic/ptrace.c.arm
 
+libc_static_common_src_files += \
+        bionic/pthread.c.arm \
+
 # these are used by the static and dynamic versions of the libc
 # respectively
 libc_arch_static_src_files := \
@@ -383,11 +400,13 @@ libc_common_src_files += \
 	arch-x86/string/strcmp_wrapper.S \
 	arch-x86/string/strncmp_wrapper.S \
 	arch-x86/string/strlen.S \
-	bionic/pthread.c \
 	bionic/pthread-rwlocks.c \
 	bionic/pthread-timers.c \
 	bionic/ptrace.c
 
+libc_static_common_src_files += \
+        bionic/pthread.c \
+
 # this is needed for static versions of libc
 libc_arch_static_src_files := \
 	arch-x86/bionic/dl_iterate_phdr_static.c
@@ -420,11 +439,14 @@ libc_common_src_files += \
 	string/strncmp.c \
 	string/memcmp.c \
 	string/strlen.c \
-	bionic/pthread.c \
 	bionic/pthread-rwlocks.c \
 	bionic/pthread-timers.c \
 	bionic/ptrace.c \
 	unistd/socketcalls.c
+
+libc_static_common_src_files += \
+        bionic/pthread.c \
+
 endif # sh
 
 endif # !x86
@@ -584,10 +606,12 @@ include $(CLEAR_VARS)
 
 LOCAL_SRC_FILES := \
 	$(libc_arch_static_src_files) \
+	$(libc_static_common_src_files) \
 	bionic/libc_init_static.c
 
 LOCAL_C_INCLUDES := $(libc_common_c_includes)
-LOCAL_CFLAGS := $(libc_common_cflags)
+LOCAL_CFLAGS := $(libc_common_cflags) \
+                -DLIBC_STATIC
 
 LOCAL_MODULE := libc_nomalloc
 LOCAL_WHOLE_STATIC_LIBRARIES := libc_common
@@ -603,6 +627,7 @@ include $(CLEAR_VARS)
 
 LOCAL_SRC_FILES := \
 	$(libc_arch_static_src_files) \
+	$(libc_static_common_src_files) \
 	bionic/dlmalloc.c \
 	bionic/malloc_debug_common.c \
 	bionic/libc_init_static.c
@@ -627,6 +652,7 @@ LOCAL_C_INCLUDES := $(libc_common_c_includes)
 
 LOCAL_SRC_FILES := \
 	$(libc_arch_dynamic_src_files) \
+	$(libc_static_common_src_files) \
 	bionic/dlmalloc.c \
 	bionic/malloc_debug_common.c \
 	bionic/libc_init_dynamic.c
diff --git a/libc/docs/CHANGES.TXT b/libc/docs/CHANGES.TXT
index d1d82de49..4d094d02e 100644
--- a/libc/docs/CHANGES.TXT
+++ b/libc/docs/CHANGES.TXT
@@ -73,6 +73,13 @@ Differences between current and Android 2.2:
 - <dlfcn.h>: fixed dlopen() implementation to support dlopen(NULL, ...).
   This allows one to look at the dynamic symbols exported by an executable.
 
+- <private/bionic_tls.h>: use kernel helper functions for static versions
+  of the C library. This is necessary because we don't know where the corresponding
+  machine code is going to run, and the optimization for __get_tls() might
+  not match the features of the target device where we run a static executable
+  linked to the C library. This fixes one of the bug that explains why gdbserver
+  didn't work well with threads.
+
 -------------------------------------------------------------------------------
 Differences between Android 2.2. and Android 2.1:
 
diff --git a/libc/private/bionic_tls.h b/libc/private/bionic_tls.h
index 241257768..008fd2ff7 100644
--- a/libc/private/bionic_tls.h
+++ b/libc/private/bionic_tls.h
@@ -88,22 +88,48 @@ extern int __set_tls(void *ptr);
 
 /* get the TLS */
 #ifdef __arm__
-/* Linux kernel helpers for its TLS implementation */
-/* For performance reasons, avoid calling the kernel helper
+/* The standard way to get the TLS is to call a kernel helper
+ * function (i.e. a function provided at a fixed address in a
+ * "magic page" mapped in all user-space address spaces ), which
+ * contains the most appropriate code path for the target device.
+ *
+ * However, for performance reasons, we're going to use our own
+ * machine code for the system's C shared library.
+ *
+ * We cannot use this optimization in the static version of the
+ * C library, because we don't know where the corresponding code
+ * is going to run.
+ */
+#  ifdef LIBC_STATIC
+
+/* Use the kernel helper in static C library. */
+  typedef volatile void* (__kernel_get_tls_t)(void);
+#    define __get_tls() (*(__kernel_get_tls_t *)0xffff0fe0)()
+
+#  else /* !LIBC_STATIC */
+/* Use optimized code path.
  * Note that HAVE_ARM_TLS_REGISTER is build-specific
  * (it must match your kernel configuration)
  */
-#  ifdef HAVE_ARM_TLS_REGISTER
-#    define __get_tls() \
+#    ifdef HAVE_ARM_TLS_REGISTER
+ /* We can read the address directly from a coprocessor
+  * register, which avoids touching the data cache
+  * completely.
+  */
+#      define __get_tls() \
     ({ register unsigned int __val asm("r0"); \
        asm ("mrc p15, 0, r0, c13, c0, 3" : "=r"(__val) ); \
        (volatile void*)__val; })
-#  else /* !HAVE_ARM_TLS_REGISTER */
-#    define __get_tls() ( *((volatile void **) 0xffff0ff0) )
-#  endif
-#else
+#    else /* !HAVE_ARM_TLS_REGISTER */
+ /* The kernel provides the address of the TLS at a fixed
+  * address of the magic page too.
+  */
+#      define __get_tls() ( *((volatile void **) 0xffff0ff0) )
+#    endif
+#  endif /* !LIBC_STATIC */
+#else /* !ARM */
 extern void*  __get_tls( void );
-#endif
+#endif /* !ARM */
 
 /* return the stack base and size, used by our malloc debugger */
 extern void*  __get_stack_base(int  *p_stack_size);