Align the child stack in clone(2).
Also let clone(2) set the TLS for x86.
Also ensure we initialize the TLS before we clone(2) for all architectures.
Change-Id: Ie5fa4466e1c9ee116a281dfedef574c5ba60c0b5
diff --git a/libc/arch-x86/bionic/__bionic_clone.S b/libc/arch-x86/bionic/__bionic_clone.S
index cb0a363..af6ef19 100644
--- a/libc/arch-x86/bionic/__bionic_clone.S
+++ b/libc/arch-x86/bionic/__bionic_clone.S
@@ -6,9 +6,12 @@
pushl %esi
pushl %edi
- # Align 'child_stack' to 16 bytes.
- movl 20(%esp), %ecx
- andl $~15, %ecx
+ # Load system call arguments into registers.
+ movl 16(%esp), %ebx # flags
+ movl 20(%esp), %ecx # child_stack
+ movl 24(%esp), %edx # parent_tid
+ movl 28(%esp), %esi # tls
+ movl 32(%esp), %edi # child_tid
# Copy 'fn' and 'arg' onto the child stack
movl 36(%esp), %eax # Read 'fn'.
@@ -19,11 +22,6 @@
# Make the system call.
movl $__NR_clone, %eax
- movl 16(%esp), %ebx # flags
- #movl %ecx, %ecx # child stack (already there)
- movl 24(%esp), %edx # parent_tid
- movl 28(%esp), %esi # tls
- movl 32(%esp), %edi # child_tid
int $0x80
# Check result.
diff --git a/libc/arch-x86/bionic/__set_tls.c b/libc/arch-x86/bionic/__set_tls.c
index 7ed4b01..722ec6f 100644
--- a/libc/arch-x86/bionic/__set_tls.c
+++ b/libc/arch-x86/bionic/__set_tls.c
@@ -25,77 +25,50 @@
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
+
+#include <limits.h>
#include <pthread.h>
+#include <stdbool.h>
+#include <asm/ldt.h>
-struct user_desc {
- unsigned int entry_number;
- unsigned long base_addr;
- unsigned int limit;
- unsigned int seg_32bit:1;
- unsigned int contents:2;
- unsigned int read_exec_only:1;
- unsigned int limit_in_pages:1;
- unsigned int seg_not_present:1;
- unsigned int useable:1;
- unsigned int empty:25;
-};
+extern int __set_thread_area(struct user_desc*);
-extern int __set_thread_area(struct user_desc *u_info);
+__LIBC_HIDDEN__ void __init_user_desc(struct user_desc* result, bool allocate, void* base_addr) {
+ if (allocate) {
+ // Let the kernel choose.
+ result->entry_number = -1;
+ } else {
+ // Get the existing entry number from %gs.
+ uint32_t gs;
+ __asm__ __volatile__("movw %%gs, %w0" : "=q"(gs) /*output*/);
+ result->entry_number = (gs & 0xffff) >> 3;
+ }
-/* the following can't be const, since the first call will
- * update the 'entry_number' field
- */
-static struct user_desc _tls_desc =
-{
- -1,
- 0,
- 0x1000,
- 1,
- 0,
- 0,
- 1,
- 0,
- 1,
- 0
-};
+ result->base_addr = (uintptr_t) base_addr;
-static pthread_mutex_t _tls_desc_lock = PTHREAD_MUTEX_INITIALIZER;
+ result->limit = PAGE_SIZE;
-struct _thread_area_head {
- void *self;
-};
-
-/* we implement thread local storage through the gs: segment descriptor
- * we create a segment descriptor for the tls
- */
-int __set_tls(void *ptr)
-{
- int rc, segment;
-
- pthread_mutex_lock(&_tls_desc_lock);
- _tls_desc.base_addr = (unsigned long)ptr;
-
- /* We also need to write the location of the tls to ptr[0] */
- ((struct _thread_area_head *)ptr)->self = ptr;
-
- rc = __set_thread_area( &_tls_desc );
- if (rc != 0)
- {
- /* could not set thread local area */
- pthread_mutex_unlock(&_tls_desc_lock);
- return -1;
- }
-
- /* this weird computation comes from GLibc */
- segment = _tls_desc.entry_number*8 + 3;
- asm __volatile__ (
- " movw %w0, %%gs" :: "q"(segment)
- );
- pthread_mutex_unlock(&_tls_desc_lock);
-
- return 0;
+ result->seg_32bit = 1;
+ result->contents = MODIFY_LDT_CONTENTS_DATA;
+ result->read_exec_only = 0;
+ result->limit_in_pages = 1;
+ result->seg_not_present = 0;
+ result->useable = 1;
}
+int __set_tls(void* ptr) {
+ struct user_desc tls_descriptor;
+ __init_user_desc(&tls_descriptor, true, ptr);
+ int rc = __set_thread_area(&tls_descriptor);
+ if (rc != -1) {
+ // Change %gs to be new GDT entry.
+ uint16_t table_indicator = 0; // GDT
+ uint16_t rpl = 3; // Requested privilege level
+ uint16_t selector = (tls_descriptor.entry_number << 3) | table_indicator | rpl;
+ __asm__ __volatile__("movw %w0, %%gs" : /*output*/ : "q"(selector) /*input*/ : /*clobber*/);
+ }
+ return rc;
+}