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, 0 insertions, 6 deletions

diff --git a/sysdeps/i386/nptl/tls.h b/sysdeps/i386/nptl/tls.h
index d010e14920..e5f4e83eb4 100644
--- a/sysdeps/i386/nptl/tls.h
+++ b/sysdeps/i386/nptl/tls.h
@@ -102,15 +102,9 @@ union user_desc_init
    struct pthread even when not linked with -lpthread.  */
 # define TLS_INIT_TCB_SIZE sizeof (struct pthread)
 
-/* Alignment requirements for the initial TCB.  */
-# define TLS_INIT_TCB_ALIGN __alignof__ (struct pthread)
-
 /* This is the size of the TCB.  */
 # define TLS_TCB_SIZE sizeof (struct pthread)
 
-/* Alignment requirements for the TCB.  */
-# define TLS_TCB_ALIGN __alignof__ (struct pthread)
-
 /* The TCB can have any size and the memory following the address the
    thread pointer points to is unspecified.  Allocate the TCB there.  */
 # define TLS_TCB_AT_TP	1