Remove TLS_TCB_ALIGN and TLS_INIT_TCB_ALIGN

TLS_INIT_TCB_ALIGN is not actually used.  TLS_TCB_ALIGN was likely
introduced to support a configuration where the thread pointer
has not the same alignment as THREAD_SELF.  Only ia64 seems to use
that, but for the stack/pointer guard, not for storing tcbhead_t.
Some ports use TLS_TCB_OFFSET and TLS_PRE_TCB_SIZE to shift
the thread pointer, potentially landing in a different residue class
modulo the alignment, but the changes should not impact that.

In general, given that TLS variables have their own alignment
requirements, having different alignment for the (unshifted) thread
pointer and struct pthread would potentially result in dynamic
offsets, leading to more complexity.

hppa had different values before: __alignof__ (tcbhead_t), which
seems to be 4, and __alignof__ (struct pthread), which was 8
(old default) and is now 32.  However, it defines THREAD_SELF as:

/* Return the thread descriptor for the current thread.  */
# define THREAD_SELF \
  ({ struct pthread *__self;			\
	__self = __get_cr27();			\
	__self - 1;				\
   })

So the thread pointer points after struct pthread (hence __self - 1),
and they have to have the same alignment on hppa as well.

Similarly, on ia64, the definitions were different.  We have:

# define TLS_PRE_TCB_SIZE \
  (sizeof (struct pthread)						\
   + (PTHREAD_STRUCT_END_PADDING < 2 * sizeof (uintptr_t)		\
      ? ((2 * sizeof (uintptr_t) + __alignof__ (struct pthread) - 1)	\
	 & ~(__alignof__ (struct pthread) - 1))				\
      : 0))
# define THREAD_SELF \
  ((struct pthread *) ((char *) __thread_self - TLS_PRE_TCB_SIZE))

And TLS_PRE_TCB_SIZE is a multiple of the struct pthread alignment
(confirmed by the new _Static_assert in sysdeps/ia64/libc-tls.c).

On m68k, we have a larger gap between tcbhead_t and struct pthread.
But as far as I can tell, the port is fine with that.  The definition
of TCB_OFFSET is sufficient to handle the shifted TCB scenario.

This fixes commit 23c77f60181eb549f11ec2f913b4270af29eee38
("nptl: Increase default TCB alignment to 32").

Reviewed-by: H.J. Lu <hjl.tools@gmail.com>

1 files changed, 5 insertions, 9 deletions

diff --git a/sysdeps/generic/tls.h b/sysdeps/generic/tls.h
index f581c9a992..b7aafce251 100644
--- a/sysdeps/generic/tls.h
+++ b/sysdeps/generic/tls.h
@@ -19,6 +19,11 @@
 /* An architecture-specific version of this file has to defined a
    number of symbols:
 
+     TCB_ALIGNMENT
+
+     Alignment of THREAD_SELF (struct pthread *) and the thread
+     pointer.
+
      TLS_TCB_AT_TP  or  TLS_DTV_AT_TP
 
      The presence of one of these symbols signals which variant of
@@ -43,15 +48,6 @@
      dynamic linker itself.  There are no threads in use at that time.
 
 
-     TLS_TCB_ALIGN
-
-     Alignment requirements for the TCB structure.
-
-     TLS_INIT_TCB_ALIGN
-
-     Similarly, but for the structure used at startup time.
-
-
      INSTALL_DTV(tcb, init_dtv)
 
      This macro must install the given initial DTV into the thread control