Re: PATCH: NPTL support for MIPS

[Daniel Jacobowitz <drow at false dot org>]

On Wed, Mar 16, 2005 at 03:25:20PM -0800, Roland McGrath wrote:
> > This is entirely within LinuxThreads.  Both libc.so and libpthread.so
> > will try to access p_errno, which has to be at a common offset in this
> > structure.  This "padding" is unused in libc.so, but used in
> > libpthread.so, and it lives before p_errno - so when it isn't included,
> > libc clobbers the wrong location in the descriptor when it tries to set
> > errno.
> 
> Why is it located there?

#if !defined USE_TLS || !TLS_DTV_AT_TP
  /* This overlaps tcbhead_t (see tls.h), as used for TLS without threads.  */
  union
  {
    struct
    {
      void *tcb;                /* Pointer to the TCB.  This is not always
                                   the address of this thread descriptor.  */
      union dtv *dtvp;
      pthread_descr self;       /* Pointer to this structure */
      int multiple_threads;
# ifdef NEED_DL_SYSINFO
      uintptr_t sysinfo;
# endif
    } data;
    void *__padding[16];
  } p_header;

Because if !TLS_DTV_AT_TP, this is the TCB, so it has to be first.  But
MIPS does use TLS_DTV_AT_TP when using TLS, so it is unnecessary.

BTW, could you remove this now-empty file from CVS?
  sysdeps/unix/sysv/linux/mips/mips32/kern64/sysdep.h

-- 
Daniel Jacobowitz
CodeSourcery, LLC