[PATCH roland/exit-thread] Clean up __exit_thread.
Will Newton
will.newton@linaro.org
Mon May 12 11:27:00 GMT 2014
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);
> + }
> +}
--
Will Newton
Toolchain Working Group, Linaro
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