[roland/exit-thread] Clean up __exit_thread.

  This cleans things up in a few ways: 
* It removes a Linuxism from the pthreaddef.h files.
* It removes duplication across all the pthreaddef.h
  files except i386 and x86_64.
* It avoids the useless errno setting code on non-x86.
* It removes the undocumented and unsupported __exit_thread entry point
  from libc.a.

I verified on i386 and x86_64 builds that the code generated for
start_thread in pthread_create.c is at least about as good as before.  

On x86_64, it perturbed the code generation substantially because the
compiler knowing that the syscall sequence can never return changes how
it organizes the blocks; probably the new code is better.

On i386, the old code used 'int $0x80' and now it uses the vDSO entry point
like regular syscall stubs do.  This should perform marginally better.  It
also means that in a situation where wild memory clobberation has corrupted
the TCB, an exitting thread might do more unpredictable things and possibly
never actually exit, whereas before it was more likely to do the syscall.
I don't think that's worth caring about.  But if it is, we can easily add
an i386-specific exit-thread.h to do what the old code did.

I didn't test any other machines, but it's hard to see how they could go
wrong.  I'd appreciate people testing the branch on other machines.

If nobody objects, I'll probably commit this on Monday.


Thanks,
Roland


2014-05-09  Roland McGrath  <roland@hack.frob.com>

	* sysdeps/generic/exit-thread.h: New file.
	* sysdeps/unix/sysv/linux/exit-thread.h: New file.
	* include/unistd.h (__exit_thread): Remove declaration.
	* sysdeps/unix/sysv/linux/Makefile (sysdep_routines): Drop exit-thread.
	* sysdeps/unix/sysv/linux/exit-thread.S: File removed.
	* csu/libc-start.c: Include <exit-thread.h>.
	(LIBC_START_MAIN): Pass no argument to __exit_thread.
	* nptl/pthread_create.c: Include <exit-thread.h>.
	(start_thread): Call __exit_thread in place of __exit_thread_inline.
	* nptl/sysdeps/i386/pthreaddef.h (__exit_thread_inline): Macro removed.
	* nptl/sysdeps/powerpc/pthreaddef.h: Likewise.
	* nptl/sysdeps/s390/pthreaddef.h: Likewise.
	* nptl/sysdeps/sh/pthreaddef.h: Likewise.
	* nptl/sysdeps/sparc/sparc32/pthreaddef.h: Likewise.
	* nptl/sysdeps/sparc/sparc64/pthreaddef.h: Likewise.
	* nptl/sysdeps/x86_64/pthreaddef.h: Likewise.
	* sysdeps/aarch64/nptl/pthreaddef.h: Likewise.
	* sysdeps/alpha/nptl/pthreaddef.h: Likewise.
	* sysdeps/arm/nptl/pthreaddef.h: Likewise.
	* sysdeps/hppa/nptl/pthreaddef.h: Likewise.
	* sysdeps/ia64/nptl/pthreaddef.h: Likewise.
	* sysdeps/m68k/nptl/pthreaddef.h: Likewise.
	* sysdeps/microblaze/nptl/pthreaddef.h: Likewise.
	* sysdeps/mips/nptl/pthreaddef.h: Likewise.
	* sysdeps/tile/nptl/pthreaddef.h: Likewise.
  

On 9 May 2014 21:00, Roland McGrath <roland@hack.frob.com> wrote:
> This cleans things up in a few ways:
> * It removes a Linuxism from the pthreaddef.h files.
> * It removes duplication across all the pthreaddef.h
>   files except i386 and x86_64.
> * It avoids the useless errno setting code on non-x86.
> * It removes the undocumented and unsupported __exit_thread entry point
>   from libc.a.
>
> I verified on i386 and x86_64 builds that the code generated for
> start_thread in pthread_create.c is at least about as good as before.
>
> On x86_64, it perturbed the code generation substantially because the
> compiler knowing that the syscall sequence can never return changes how
> it organizes the blocks; probably the new code is better.
>
> On i386, the old code used 'int $0x80' and now it uses the vDSO entry point
> like regular syscall stubs do.  This should perform marginally better.  It
> also means that in a situation where wild memory clobberation has corrupted
> the TCB, an exitting thread might do more unpredictable things and possibly
> never actually exit, whereas before it was more likely to do the syscall.
> I don't think that's worth caring about.  But if it is, we can easily add
> an i386-specific exit-thread.h to do what the old code did.
>
> I didn't test any other machines, but it's hard to see how they could go
> wrong.  I'd appreciate people testing the branch on other machines.

This looks ok to me and doesn't introduce any test failures on ARM.

> If nobody objects, I'll probably commit this on Monday.
>
>
> Thanks,
> Roland
>
>
> 2014-05-09  Roland McGrath  <roland@hack.frob.com>
>
>         * sysdeps/generic/exit-thread.h: New file.
>         * sysdeps/unix/sysv/linux/exit-thread.h: New file.
>         * include/unistd.h (__exit_thread): Remove declaration.
>         * sysdeps/unix/sysv/linux/Makefile (sysdep_routines): Drop exit-thread.
>         * sysdeps/unix/sysv/linux/exit-thread.S: File removed.
>         * csu/libc-start.c: Include <exit-thread.h>.
>         (LIBC_START_MAIN): Pass no argument to __exit_thread.
>         * nptl/pthread_create.c: Include <exit-thread.h>.
>         (start_thread): Call __exit_thread in place of __exit_thread_inline.
>         * nptl/sysdeps/i386/pthreaddef.h (__exit_thread_inline): Macro removed.
>         * nptl/sysdeps/powerpc/pthreaddef.h: Likewise.
>         * nptl/sysdeps/s390/pthreaddef.h: Likewise.
>         * nptl/sysdeps/sh/pthreaddef.h: Likewise.
>         * nptl/sysdeps/sparc/sparc32/pthreaddef.h: Likewise.
>         * nptl/sysdeps/sparc/sparc64/pthreaddef.h: Likewise.
>         * nptl/sysdeps/x86_64/pthreaddef.h: Likewise.
>         * sysdeps/aarch64/nptl/pthreaddef.h: Likewise.
>         * sysdeps/alpha/nptl/pthreaddef.h: Likewise.
>         * sysdeps/arm/nptl/pthreaddef.h: Likewise.
>         * sysdeps/hppa/nptl/pthreaddef.h: Likewise.
>         * sysdeps/ia64/nptl/pthreaddef.h: Likewise.
>         * sysdeps/m68k/nptl/pthreaddef.h: Likewise.
>         * sysdeps/microblaze/nptl/pthreaddef.h: Likewise.
>         * sysdeps/mips/nptl/pthreaddef.h: Likewise.
>         * sysdeps/tile/nptl/pthreaddef.h: Likewise.
>
> --- a/csu/libc-start.c
> +++ b/csu/libc-start.c
> @@ -20,6 +20,7 @@
>  #include <stdio.h>
>  #include <unistd.h>
>  #include <ldsodefs.h>
> +#include <exit-thread.h>
>
>  extern void __libc_init_first (int argc, char **argv, char **envp);
>  #ifndef SHARED
> @@ -312,7 +313,7 @@ LIBC_START_MAIN (int (*main) (int, char **, char ** MAIN_AUXVEC_DECL),
>
>        if (! atomic_decrement_and_test (ptr))
>         /* Not much left to do but to exit the thread, not the process.  */
> -       __exit_thread (0);
> +       __exit_thread ();
>      }
>  #else
>    /* Nothing fancy, just call the function.  */
> --- a/include/unistd.h
> +++ b/include/unistd.h
> @@ -161,9 +161,6 @@ extern int __libc_enable_secure_internal attribute_relro attribute_hidden;
>  extern void __libc_check_standard_fds (void);
>
>
> -/* Special exit function which only terminates the current thread.  */
> -extern void __exit_thread (int val) __attribute__ ((noreturn));
> -
>  /* Internal name for fork function.  */
>  extern __pid_t __libc_fork (void);
>
> --- a/nptl/pthread_create.c
> +++ b/nptl/pthread_create.c
> @@ -29,6 +29,7 @@
>  #include <libc-internal.h>
>  #include <resolv.h>
>  #include <kernel-features.h>
> +#include <exit-thread.h>
>
>  #include <shlib-compat.h>
>
> @@ -432,7 +433,7 @@ start_thread (void *arg)
>
>       The exit code is zero since in case all threads exit by calling
>       'pthread_exit' the exit status must be 0 (zero).  */
> -  __exit_thread_inline (0);
> +  __exit_thread ();
>
>    /* NOTREACHED */
>    return 0;
> --- a/nptl/sysdeps/i386/pthreaddef.h
> +++ b/nptl/sysdeps/i386/pthreaddef.h
> @@ -38,16 +38,3 @@
>
>  /* Location of current stack frame.  */
>  #define CURRENT_STACK_FRAME    __builtin_frame_address (0)
> -
> -
> -/* XXX Until we have a better place keep the definitions here.  */
> -
> -/* While there is no such syscall.  */
> -#define __exit_thread_inline(val) \
> -  while (1) {                                                                \
> -    if (__builtin_constant_p (val) && (val) == 0)                            \
> -      asm volatile ("xorl %%ebx, %%ebx; int $0x80" :: "a" (__NR_exit));              \
> -    else                                                                     \
> -      asm volatile ("movl %1, %%ebx; int $0x80"                                      \
> -                   :: "a" (__NR_exit), "r" (val));                           \
> -  }
> --- a/nptl/sysdeps/powerpc/pthreaddef.h
> +++ b/nptl/sysdeps/powerpc/pthreaddef.h
> @@ -31,10 +31,3 @@
>
>  /* Location of current stack frame.  */
>  #define CURRENT_STACK_FRAME    __builtin_frame_address (0)
> -
> -
> -/* XXX Until we have a better place keep the definitions here.  */
> -
> -/* While there is no such syscall.  */
> -#define __exit_thread_inline(val) \
> -  INLINE_SYSCALL (exit, 1, (val))
> --- a/nptl/sysdeps/s390/pthreaddef.h
> +++ b/nptl/sysdeps/s390/pthreaddef.h
> @@ -31,10 +31,3 @@
>
>  /* Location of current stack frame.  */
>  #define CURRENT_STACK_FRAME    __builtin_frame_address (0)
> -
> -
> -/* XXX Until we have a better place keep the definitions here.  */
> -
> -/* While there is no such syscall.  */
> -#define __exit_thread_inline(val) \
> -  INLINE_SYSCALL (exit, 1, (val))
> --- a/nptl/sysdeps/sh/pthreaddef.h
> +++ b/nptl/sysdeps/sh/pthreaddef.h
> @@ -32,17 +32,3 @@
>
>  /* Location of current stack frame.  */
>  #define CURRENT_STACK_FRAME    __builtin_frame_address (0)
> -
> -
> -/* XXX Until we have a better place keep the definitions here.  */
> -
> -/* While there is no such syscall.  */
> -#define __exit_thread_inline(val) \
> -  while (1) {                                                                \
> -    if (__builtin_constant_p (val) && (val) == 0)                            \
> -      asm volatile ("mov #0,r4; mov %0,r3; trapa #0x11\n\t" SYSCALL_INST_PAD  \
> -                  :: "i" (__NR_exit));  \
> -    else                                                                     \
> -      asm volatile ("mov %1,r4; mov %0,r3; trapa #0x11\n\t" SYSCALL_INST_PAD  \
> -                   :: "i" (__NR_exit), "r" (val));                           \
> -  }
> --- a/nptl/sysdeps/sparc/sparc32/pthreaddef.h
> +++ b/nptl/sysdeps/sparc/sparc32/pthreaddef.h
> @@ -31,9 +31,3 @@
>  /* Location of current stack frame.  */
>  #define CURRENT_STACK_FRAME  (stack_pointer + (2 * 64))
>  register char *stack_pointer __asm__("%sp");
> -
> -/* XXX Until we have a better place keep the definitions here.  */
> -
> -/* While there is no such syscall.  */
> -#define __exit_thread_inline(val) \
> -  INLINE_SYSCALL (exit, 1, (val))
> --- a/nptl/sysdeps/sparc/sparc64/pthreaddef.h
> +++ b/nptl/sysdeps/sparc/sparc64/pthreaddef.h
> @@ -31,9 +31,3 @@
>  /* Location of current stack frame.  */
>  #define CURRENT_STACK_FRAME  (stack_pointer + (2 * 128))
>  register char *stack_pointer __asm__("%sp");
> -
> -/* XXX Until we have a better place keep the definitions here.  */
> -
> -/* While there is no such syscall.  */
> -#define __exit_thread_inline(val) \
> -  INLINE_SYSCALL (exit, 1, (val))
> --- a/nptl/sysdeps/x86_64/pthreaddef.h
> +++ b/nptl/sysdeps/x86_64/pthreaddef.h
> @@ -42,10 +42,3 @@
>  /* Location of current stack frame.  The frame pointer is not usable.  */
>  #define CURRENT_STACK_FRAME \
>    ({ register char *frame __asm__("rsp"); frame; })
> -
> -
> -/* XXX Until we have a better place keep the definitions here.  */
> -
> -/* While there is no such syscall.  */
> -#define __exit_thread_inline(val) \
> -  asm volatile ("syscall" :: "a" (__NR_exit), "D" (val))
> --- a/sysdeps/aarch64/nptl/pthreaddef.h
> +++ b/sysdeps/aarch64/nptl/pthreaddef.h
> @@ -30,8 +30,3 @@
>
>  /* Location of current stack frame.  */
>  #define CURRENT_STACK_FRAME    __builtin_frame_address (0)
> -
> -
> -/* XXX Until we have a better place keep the definitions here.  */
> -#define __exit_thread_inline(val) \
> -  INLINE_SYSCALL (exit, 1, (val))
> --- a/sysdeps/alpha/nptl/pthreaddef.h
> +++ b/sysdeps/alpha/nptl/pthreaddef.h
> @@ -29,9 +29,3 @@
>
>  /* Location of current stack frame.  */
>  #define CURRENT_STACK_FRAME    __builtin_frame_address (0)
> -
> -/* XXX Until we have a better place keep the definitions here.  */
> -
> -/* While there is no such syscall.  */
> -#define __exit_thread_inline(val) \
> -  INLINE_SYSCALL (exit, 1, (val))
> --- a/sysdeps/arm/nptl/pthreaddef.h
> +++ b/sysdeps/arm/nptl/pthreaddef.h
> @@ -39,8 +39,3 @@
>     return the hard FP minus 12.  Of course, this makes no sense
>     without the obsolete APCS stack layout...  */
>  #define CURRENT_STACK_FRAME    (__builtin_frame_address (0) - 12)
> -
> -
> -/* XXX Until we have a better place keep the definitions here.  */
> -#define __exit_thread_inline(val) \
> -  INLINE_SYSCALL (exit, 1, (val))
> --- a/sysdeps/unix/sysv/linux/exit-thread.S
> +++ b/sysdeps/generic/exit-thread.h
> @@ -1,4 +1,5 @@
> -/* Copyright (C) 1991-2014 Free Software Foundation, Inc.
> +/* Call to terminate the current thread.  Stub version.
> +   Copyright (C) 2014 Free Software Foundation, Inc.
>     This file is part of the GNU C Library.
>
>     The GNU C Library is free software; you can redistribute it and/or
> @@ -15,8 +16,13 @@
>     License along with the GNU C Library; if not, see
>     <http://www.gnu.org/licenses/>.  */
>
> -#include <sysdep.h>
> +/* This causes the current thread to exit, without affecting other
> +   threads in the process if there are any.  If there are no other
> +   threads left, then this has the effect of _exit (0).  */
>
> -PSEUDO (__exit_thread, exit, 1)
> -       /* Shouldn't get here.  */
> -PSEUDO_END(__exit_thread)
> +static inline void __attribute__ ((noreturn, always_inline, unused))
> +__exit_thread (void)
> +{
> +  while (1)
> +    asm ("write me!");
> +}
> --- a/sysdeps/hppa/nptl/pthreaddef.h
> +++ b/sysdeps/hppa/nptl/pthreaddef.h
> @@ -31,9 +31,3 @@
>  /* Location of current stack frame.  */
>  #define CURRENT_STACK_FRAME  stack_pointer
>  register char * stack_pointer __asm__ ("%r30");
> -
> -
> -/* XXX Until we have a better place keep the definitions here.  */
> -
> -#define __exit_thread_inline(val) \
> -  INLINE_SYSCALL (exit, 1, (val))
> --- a/sysdeps/ia64/nptl/pthreaddef.h
> +++ b/sysdeps/ia64/nptl/pthreaddef.h
> @@ -34,9 +34,3 @@
>  /* Location of current stack frame.  */
>  #define CURRENT_STACK_FRAME    __stack_pointer
>  register char *__stack_pointer __asm__ ("sp");
> -
> -/* XXX Until we have a better place keep the definitions here.  */
> -
> -/* While there is no such syscall.  */
> -#define __exit_thread_inline(val) \
> -  INLINE_SYSCALL (exit, 1, (val))
> --- a/sysdeps/m68k/nptl/pthreaddef.h
> +++ b/sysdeps/m68k/nptl/pthreaddef.h
> @@ -31,8 +31,3 @@
>
>  /* Location of current stack frame.  */
>  #define CURRENT_STACK_FRAME    __builtin_frame_address (0)
> -
> -
> -/* XXX Until we have a better place keep the definitions here.  */
> -#define __exit_thread_inline(val) \
> -  INLINE_SYSCALL (exit, 1, (val))
> --- a/sysdeps/microblaze/nptl/pthreaddef.h
> +++ b/sysdeps/microblaze/nptl/pthreaddef.h
> @@ -33,8 +33,3 @@
>
>  /* Location of current stack frame.  */
>  #define CURRENT_STACK_FRAME __builtin_frame_address (0)
> -
> -/* XXX Until we have a better place keep the definitions here.  */
> -
> -#define __exit_thread_inline(val) \
> -  INLINE_SYSCALL (exit, 1, (val))
> --- a/sysdeps/mips/nptl/pthreaddef.h
> +++ b/sysdeps/mips/nptl/pthreaddef.h
> @@ -30,9 +30,3 @@
>
>  /* Location of current stack frame.  */
>  #define CURRENT_STACK_FRAME    __builtin_frame_address (0)
> -
> -
> -/* XXX Until we have a better place keep the definitions here.  */
> -
> -#define __exit_thread_inline(val) \
> -  INLINE_SYSCALL (exit, 1, (val))
> --- a/sysdeps/tile/nptl/pthreaddef.h
> +++ b/sysdeps/tile/nptl/pthreaddef.h
> @@ -34,8 +34,3 @@
>
>  /* Location of current stack frame.  */
>  #define CURRENT_STACK_FRAME    __builtin_frame_address (0)
> -
> -/* XXX Until we have a better place keep the definitions here.  */
> -
> -#define __exit_thread_inline(val) \
> -  INLINE_SYSCALL (exit, 1, (val))
> --- a/sysdeps/unix/sysv/linux/Makefile
> +++ b/sysdeps/unix/sysv/linux/Makefile
> @@ -141,7 +141,7 @@ endif
>  ifeq ($(subdir),posix)
>  sysdep_headers += bits/initspin.h
>
> -sysdep_routines += exit-thread sched_getcpu
> +sysdep_routines += sched_getcpu
>
>  tests += tst-getcpu
>  endif
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/exit-thread.h
> @@ -0,0 +1,38 @@
> +/* Call to terminate the current thread.  Linux version.
> +   Copyright (C) 2014 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <http://www.gnu.org/licenses/>.  */
> +
> +#include <sysdep.h>
> +
> +/* This causes the current thread to exit, without affecting other
> +   threads in the process if there are any.  If there are no other
> +   threads left, then this has the effect of _exit (0).  */
> +
> +static inline void __attribute__ ((noreturn, always_inline, unused))
> +__exit_thread (void)
> +{
> +  /* Doing this in a loop is mostly just to satisfy the compiler that the
> +     function really qualifies as noreturn.  It also means that in some
> +     pathological situation where the system call does not get made or does
> +     not work, the thread will simply spin rather than running off the end
> +     of the caller and doing unexpectedly strange things.  */
> +  while (1)
> +    {
> +      INTERNAL_SYSCALL_DECL (err);
> +      INTERNAL_SYSCALL (exit, err, 1, 0);
> +    }
> +}
  

Committed.

Thanks,
Roland