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commit 10bba58b7eece4eac0db07c100217b709efd4727
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Wed Jan 24 15:27:49 2018 -0800

    nptl: Update struct pthread_unwind_buf [BZ #22743]
    
    In glibc 2.27, the size of cancel_jmp_buf in struct pthread_unwind_buf
    has been increased to match the size of __jmp_buf_tag on Linux/x86 in
    order to save and restore shadow stack.  Struct pthread_unwind_buf is
    used in <pthread.h>, whose address is passed from applications to
    libpthread.  To access the private data in struct pthread_unwind_buf,
    which is placed after cancel_jmp_buf, in libpthread, we must know which
    struct pthread_unwind_buf, before glibc 27 and after glibc 2.27, is used
    in caller.  If the size of caller's struct pthread_unwind_buf is smaller
    than what libpthread expects, libpthread will override caller's stack
    since struct pthread_unwind_buf is placed on caller's stack.
    
    We enable shadow stack at run-time only if program and all used shared
    objects, including dlopened ones, are shadow stack enabled, which means
    that they must be compiled with GCC 8 or above and glibc 2.27 or above.
    Since we need to save and restore shadow stack only if shadow stack is
    enabled, we can safely assume that caller is compiled with smaller
    struct pthread_unwind_buf on stack if shadow stack isn't enabled at
    run-time.  For callers with larger struct pthread_unwind_buf, but
    shadow stack isn't enabled, we just have some unused space on caller's
    stack.
    
    struct pthread_unwind_buf is changed to union of
    
    1. struct cancel_jmp_buf[1], which contains the common fields of struct
    updated_pthread_unwind_buf and struct compat_pthread_unwind_buf.
    2. struct updated_pthread_unwind_buf, which is the updated layout of
    the cleanup buffer.
    3. struct compat_pthread_unwind_buf, which is the compatible layout of
    the cleanup buffer.
    
    A macro, UNWIND_BUF_PRIV, is added to get the pointer to the priv field.
    By default, it uses the priv field of struct compat_pthread_unwind_buf.
    If a target defines NEED_SAVED_MASK_IN_CANCEL_JMP_BUF, it must provide
    its own version of UNEIND_BUF_PRIV to get the pointer to the priv field.
    On Linux/x86, it uses the priv field of struct compat_pthread_unwind_buf
    if shadow stack is disabled and struct updated_pthread_unwind_buf if
    shadow stack is enabled.
    
    	[BZ #22743]
    	* csu/libc-start.c (LIBC_START_MAIN): Use the updated version
    	of the cleanup buffer.
    	* nptl/cleanup.c (__pthread_register_cancel): Use UNWIND_BUF_PRIV
    	to access the priv field in the cleanup buffer.
    	(__pthread_unregister_cancel): Likewise.
    	* nptl/cleanup_defer.c (__pthread_register_cancel_defer):
    	Likewise.
    	(__pthread_unregister_cancel_restore): Likewise.
    	* nptl/unwind.c (unwind_stop): Likewise.
    	(__pthread_unwind_next): Likewise.
    	* nptl/descr.h (pthread_unwind_buf_data): New.
    	(updated_pthread_unwind_buf): Likewise.
    	(compat_pthread_unwind_buf): Likewise.
    	(pthread_unwind_buf): Updated to use updated_pthread_unwind_buf
    	and compat_pthread_unwind_buf.
    	(UNWIND_BUF_PRIV): New.  Macro to get pointer to the priv field
    	in the cleanup buffer.
    	* nptl/pthread_create.c (START_THREAD_DEFN): Use the updated
    	version of the cleanup buffer.
    	(__pthread_create_2_1): Use THREAD_COPY_ADDITONAL_INFO to copy
    	additonal info if defined.
    	* sysdeps/unix/sysv/linux/x86/nptl/pthreadP.h: Use the updated
    	version of the cleanup buffer to check cancel_jmp_buf size.
    	* sysdeps/unix/sysv/linux/x86/pthreaddef.h
    	(THREAD_COPY_ADDITONAL_INFO): New.
    	(UNWIND_BUF_PRIV): Likewise.

diff --git a/csu/libc-start.c b/csu/libc-start.c
index 605222f..4433344 100644
--- a/csu/libc-start.c
+++ b/csu/libc-start.c
@@ -298,8 +298,10 @@ LIBC_START_MAIN (int (*main) (int, char **, char ** MAIN_AUXVEC_DECL),
       struct pthread *self = THREAD_SELF;
 
       /* Store old info.  */
-      unwind_buf.priv.data.prev = THREAD_GETMEM (self, cleanup_jmp_buf);
-      unwind_buf.priv.data.cleanup = THREAD_GETMEM (self, cleanup);
+      unwind_buf.updated.priv.data.prev
+	= THREAD_GETMEM (self, cleanup_jmp_buf);
+      unwind_buf.updated.priv.data.cleanup
+	= THREAD_GETMEM (self, cleanup);
 
       /* Store the new cleanup handler info.  */
       THREAD_SETMEM (self, cleanup_jmp_buf, &unwind_buf);
diff --git a/nptl/cleanup.c b/nptl/cleanup.c
index d21b86e..403ffc9 100644
--- a/nptl/cleanup.c
+++ b/nptl/cleanup.c
@@ -28,8 +28,10 @@ __pthread_register_cancel (__pthread_unwind_buf_t *buf)
   struct pthread *self = THREAD_SELF;
 
   /* Store old info.  */
-  ibuf->priv.data.prev = THREAD_GETMEM (self, cleanup_jmp_buf);
-  ibuf->priv.data.cleanup = THREAD_GETMEM (self, cleanup);
+  UNWIND_BUF_PRIV (self, ibuf)->data.prev
+    = THREAD_GETMEM (self, cleanup_jmp_buf);
+  UNWIND_BUF_PRIV (self, ibuf)->data.cleanup
+    = THREAD_GETMEM (self, cleanup);
 
   /* Store the new cleanup handler info.  */
   THREAD_SETMEM (self, cleanup_jmp_buf, (struct pthread_unwind_buf *) buf);
@@ -42,7 +44,9 @@ __cleanup_fct_attribute
 __pthread_unregister_cancel (__pthread_unwind_buf_t *buf)
 {
   struct pthread_unwind_buf *ibuf = (struct pthread_unwind_buf *) buf;
+  struct pthread *self = THREAD_SELF;
 
-  THREAD_SETMEM (THREAD_SELF, cleanup_jmp_buf, ibuf->priv.data.prev);
+  THREAD_SETMEM (self, cleanup_jmp_buf,
+		 UNWIND_BUF_PRIV (self, ibuf)->data.prev);
 }
 hidden_def (__pthread_unregister_cancel)
diff --git a/nptl/cleanup_defer.c b/nptl/cleanup_defer.c
index 5701ce4..20ace32 100644
--- a/nptl/cleanup_defer.c
+++ b/nptl/cleanup_defer.c
@@ -28,8 +28,10 @@ __pthread_register_cancel_defer (__pthread_unwind_buf_t *buf)
   struct pthread *self = THREAD_SELF;
 
   /* Store old info.  */
-  ibuf->priv.data.prev = THREAD_GETMEM (self, cleanup_jmp_buf);
-  ibuf->priv.data.cleanup = THREAD_GETMEM (self, cleanup);
+  UNWIND_BUF_PRIV (self, ibuf)->data.prev
+    = THREAD_GETMEM (self, cleanup_jmp_buf);
+  UNWIND_BUF_PRIV (self, ibuf)->data.cleanup
+    = THREAD_GETMEM (self, cleanup);
 
   int cancelhandling = THREAD_GETMEM (self, cancelhandling);
 
@@ -49,9 +51,9 @@ __pthread_register_cancel_defer (__pthread_unwind_buf_t *buf)
 	cancelhandling = curval;
       }
 
-  ibuf->priv.data.canceltype = (cancelhandling & CANCELTYPE_BITMASK
-				? PTHREAD_CANCEL_ASYNCHRONOUS
-				: PTHREAD_CANCEL_DEFERRED);
+  UNWIND_BUF_PRIV (self, ibuf)->data.canceltype
+    = (cancelhandling & CANCELTYPE_BITMASK
+       ? PTHREAD_CANCEL_ASYNCHRONOUS : PTHREAD_CANCEL_DEFERRED);
 
   /* Store the new cleanup handler info.  */
   THREAD_SETMEM (self, cleanup_jmp_buf, (struct pthread_unwind_buf *) buf);
@@ -65,10 +67,12 @@ __pthread_unregister_cancel_restore (__pthread_unwind_buf_t *buf)
   struct pthread *self = THREAD_SELF;
   struct pthread_unwind_buf *ibuf = (struct pthread_unwind_buf *) buf;
 
-  THREAD_SETMEM (self, cleanup_jmp_buf, ibuf->priv.data.prev);
+  THREAD_SETMEM (self, cleanup_jmp_buf,
+		 UNWIND_BUF_PRIV (self, ibuf)->data.prev);
 
   int cancelhandling;
-  if (ibuf->priv.data.canceltype != PTHREAD_CANCEL_DEFERRED
+  if ((UNWIND_BUF_PRIV (self, ibuf)->data.canceltype
+       != PTHREAD_CANCEL_DEFERRED)
       && ((cancelhandling = THREAD_GETMEM (self, cancelhandling))
 	  & CANCELTYPE_BITMASK) == 0)
     {
diff --git a/nptl/descr.h b/nptl/descr.h
index 1cc6b09..a30d4fe 100644
--- a/nptl/descr.h
+++ b/nptl/descr.h
@@ -55,11 +55,30 @@
    / PTHREAD_KEY_2NDLEVEL_SIZE)
 
 
+/* Private data in the cleanup buffer.  */
+union pthread_unwind_buf_data
+{
+  /* This is the placeholder of the public version.  */
+  void *pad[4];
+
+ struct
+  {
+    /* Pointer to the previous cleanup buffer.  */
+    struct pthread_unwind_buf *prev;
 
+    /* Backward compatibility: state of the old-style cleanup
+       handler at the time of the previous new-style cleanup handler
+       installment.  */
+    struct _pthread_cleanup_buffer *cleanup;
 
-/* Internal version of the buffer to store cancellation handler
+    /* Cancellation type before the push call.  */
+    int canceltype;
+  } data;
+};
+
+/* Internal updated version of the buffer to store cancellation handler
    information.  */
-struct pthread_unwind_buf
+struct updated_pthread_unwind_buf
 {
   struct
   {
@@ -70,27 +89,49 @@ struct pthread_unwind_buf
 #endif
   } cancel_jmp_buf[1];
 
-  union
+  union pthread_unwind_buf_data priv;
+};
+
+/* Internal compatible version of the buffer to store cancellation
+   handler information.  */
+struct compat_pthread_unwind_buf
+{
+  struct
   {
-    /* This is the placeholder of the public version.  */
-    void *pad[4];
+    __jmp_buf jmp_buf;
+    int mask_was_saved;
+  } cancel_jmp_buf[1];
+
+  union pthread_unwind_buf_data priv;
+};
 
+/* Internal version of the buffer to store cancellation handler
+   information.  */
+struct pthread_unwind_buf
+{
+  union
+  {
+    /* The common fields of updated and compatible versions.  */
     struct
     {
-      /* Pointer to the previous cleanup buffer.  */
-      struct pthread_unwind_buf *prev;
-
-      /* Backward compatibility: state of the old-style cleanup
-	 handler at the time of the previous new-style cleanup handler
-	 installment.  */
-      struct _pthread_cleanup_buffer *cleanup;
-
-      /* Cancellation type before the push call.  */
-      int canceltype;
-    } data;
-  } priv;
+      __jmp_buf jmp_buf;
+      int mask_was_saved;
+    } cancel_jmp_buf[1];
+    struct updated_pthread_unwind_buf updated;
+    struct compat_pthread_unwind_buf compat;
+  };
 };
 
+/* Get pointer to the priv field from THREAD_SELF, "self", and pointer
+   to the cleanup buffer, "p".  By default, the compatible version is
+   used.  If a target defines NEED_SAVED_MASK_IN_CANCEL_JMP_BUF, it
+   must provide its own version of UNEIND_BUF_PRIV.  */
+#ifndef UNWIND_BUF_PRIV
+# ifdef NEED_SAVED_MASK_IN_CANCEL_JMP_BUF
+#  error "UNWIND_BUF_PRIV is undefined!"
+# endif
+# define UNWIND_BUF_PRIV(self,p) (&((p)->compat.priv))
+#endif
 
 /* Opcodes and data types for communication with the signal handler to
    change user/group IDs.  */
diff --git a/nptl/pthread_create.c b/nptl/pthread_create.c
index caaf07c..77647dc 100644
--- a/nptl/pthread_create.c
+++ b/nptl/pthread_create.c
@@ -428,8 +428,8 @@ START_THREAD_DEFN
   struct pthread_unwind_buf unwind_buf;
 
   /* No previous handlers.  */
-  unwind_buf.priv.data.prev = NULL;
-  unwind_buf.priv.data.cleanup = NULL;
+  unwind_buf.updated.priv.data.prev = NULL;
+  unwind_buf.updated.priv.data.cleanup = NULL;
 
   int not_first_call;
   not_first_call = setjmp ((struct __jmp_buf_tag *) unwind_buf.cancel_jmp_buf);
@@ -701,6 +701,11 @@ __pthread_create_2_1 (pthread_t *newthread, const pthread_attr_t *attr,
   THREAD_COPY_POINTER_GUARD (pd);
 #endif
 
+  /* Copy additonal info.  */
+#ifdef THREAD_COPY_ADDITONAL_INFO
+  THREAD_COPY_ADDITONAL_INFO (pd);
+#endif
+
   /* Verify the sysinfo bits were copied in allocate_stack if needed.  */
 #ifdef NEED_DL_SYSINFO
   CHECK_THREAD_SYSINFO (pd);
diff --git a/nptl/unwind.c b/nptl/unwind.c
index b37a063..f58be0e 100644
--- a/nptl/unwind.c
+++ b/nptl/unwind.c
@@ -66,7 +66,8 @@ unwind_stop (int version, _Unwind_Action actions,
       /* Handle the compatibility stuff.  Execute all handlers
 	 registered with the old method which would be unwound by this
 	 step.  */
-      struct _pthread_cleanup_buffer *oldp = buf->priv.data.cleanup;
+      struct _pthread_cleanup_buffer *oldp
+	= UNWIND_BUF_PRIV (self, buf)->data.cleanup;
       void *cfa = (void *) (_Unwind_Ptr) _Unwind_GetCFA (context);
 
       if (curp != oldp && (do_longjump || FRAME_LEFT (cfa, curp, adj)))
@@ -133,6 +134,7 @@ __pthread_unwind_next (__pthread_unwind_buf_t *buf)
 {
   struct pthread_unwind_buf *ibuf = (struct pthread_unwind_buf *) buf;
 
-  __pthread_unwind ((__pthread_unwind_buf_t *) ibuf->priv.data.prev);
+  __pthread_unwind ((__pthread_unwind_buf_t *)
+		    UNWIND_BUF_PRIV (THREAD_SELF, ibuf)->data.prev);
 }
 hidden_def (__pthread_unwind_next)
diff --git a/sysdeps/unix/sysv/linux/x86/nptl/pthreadP.h b/sysdeps/unix/sysv/linux/x86/nptl/pthreadP.h
index 247a62e..a3076bf 100644
--- a/sysdeps/unix/sysv/linux/x86/nptl/pthreadP.h
+++ b/sysdeps/unix/sysv/linux/x86/nptl/pthreadP.h
@@ -23,7 +23,7 @@
 
 extern struct pthread_unwind_buf ____pthread_unwind_buf_private;
 
-_Static_assert (sizeof (____pthread_unwind_buf_private.cancel_jmp_buf)
+_Static_assert (sizeof (____pthread_unwind_buf_private.updated.cancel_jmp_buf)
 		>= sizeof (struct __jmp_buf_tag),
 		"size of cancel_jmp_buf < sizeof __jmp_buf_tag");
 
diff --git a/sysdeps/unix/sysv/linux/x86/pthreaddef.h b/sysdeps/unix/sysv/linux/x86/pthreaddef.h
index a405a65..899fcd6 100644
--- a/sysdeps/unix/sysv/linux/x86/pthreaddef.h
+++ b/sysdeps/unix/sysv/linux/x86/pthreaddef.h
@@ -20,3 +20,17 @@
 
 /* Need saved_mask in cancel_jmp_buf.  */
 #define NEED_SAVED_MASK_IN_CANCEL_JMP_BUF 1
+
+/* Wee need to copy feature_1 in pthread_create.  */
+#define THREAD_COPY_ADDITONAL_INFO(descr)				\
+  ((descr)->header.feature_1						\
+   = THREAD_GETMEM (THREAD_SELF, header.feature_1))
+
+/* Use the compatible struct __cancel_jmp_buf_tag if shadow stack is
+   disabled.  */
+#undef UNWIND_BUF_PRIV
+#define UNWIND_BUF_PRIV(self,p) \
+  (__extension__ ({							\
+     unsigned int feature_1 = THREAD_GETMEM (self, header.feature_1);	\
+     (((feature_1 & (1 << 1)) == 0)					\
+      ? &((p)->compat.priv) : &((p)->updated.priv));}))

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