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This patch implements a new posix_spawn{p} implementation for Linux. The main
difference is it uses the clone syscall directly with CLONE_VM and CLONE_VFORK
flags and a direct allocated stack. The new stack and start function solves
most the vfork limitation (possible parent clobber due stack spilling). The
remaning issue are related to signal handling:
1. That no signal handlers must run in child context, to avoid corrupt
parent's state.
2. Child must synchronize with parent to enforce stack deallocation and
to possible return execv issues.
The first one is solved by blocking all signals in child, even NPTL-internal
ones (SIGCANCEL and SIGSETXID). The second issue is done by a stack allocation
in parent and a synchronization with using a pipe or waitpid (in case or error).
The pipe has the advantage of allowing the child signal an exec error (checked
with new tst-spawn2 test).
There is an inherent race condition in pipe2 usage for architectures that do not
support the syscall directly. In such cases the a pipe plus fctnl is used
instead and it may lead to file descriptor leak in parent (as decribed by fcntl
documentation).
The child process stack is allocate with a mmap with MAP_STACK flag using
default architecture stack size. Although it is slower than use a stack buffer
from parent, it allows some slack for the compatibility code to run scripts
with no shebang (which may use a buffer with size depending of argument list
count).
Performance should be similar to the vfork default posix implementation and
way faster than fork path (vfork on mostly linux ports are basically
clone with CLONE_VM plus CLONE_VFORK). The only difference is the syscalls
required for the stack allocation/deallocation.
It fixes BZ#10354, BZ#14750, and BZ#18433.
Tested on i386, x86_64, powerpc64le, and aarch64.
[BZ #14750]
[BZ #10354]
[BZ #18433]
* include/sched.h (__clone): Add hidden prototype.
(__clone2): Likewise.
* include/unistd.h (__dup): Likewise.
* posix/Makefile (tests): Add tst-spawn2.
* posix/tst-spawn2.c: New file.
* sysdeps/posix/dup.c (__dup): Add hidden definition.
* sysdeps/unix/sysv/linux/aarch64/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/alpha/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/arm/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/hppa/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/i386/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/ia64/clone2.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/m68k/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/microblaze/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/mips/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/nios2/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/powerpc/powerpc32/clone.S (__clone):
Likewise.
* sysdeps/unix/sysv/linux/powerpc/powerpc64/clone.S (__clone):
Likewise.
* sysdeps/unix/sysv/linux/s390/s390-32/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/s390/s390-64/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/sh/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/sparc/sparc32/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/sparc/sparc64/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/tile/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/x86_64/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/nptl-signals.h
(____nptl_is_internal_signal): New function.
* sysdeps/unix/sysv/linux/spawni.c: New file.
109 lines
2.9 KiB
ArmAsm
109 lines
2.9 KiB
ArmAsm
/* clone() implementation for Nios II.
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Copyright (C) 2008-2016 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Andrew Jenner <andrew@codesourcery.com>, 2008.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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/* clone() is even more special than fork() as it mucks with stacks
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and invokes a function in the right context after its all over. */
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#include <sysdep.h>
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#define _ERRNO_H 1
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#include <bits/errno.h>
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#include <tcb-offsets.h>
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#define CLONE_VM 0x00000100
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#define CLONE_THREAD 0x00010000
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/* int clone(int (*fn)(void *arg), void *child_stack, int flags, void *arg,
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void *parent_tidptr, void *tls, void *child_tidptr) */
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.text
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ENTRY(__clone)
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/* Sanity check arguments. */
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movi r2, EINVAL
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/* No NULL function pointers. */
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beq r4, zero, SYSCALL_ERROR_LABEL
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/* No NULL stack pointers. */
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beq r5, zero, SYSCALL_ERROR_LABEL
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subi r5, r5, 8 /* Reserve argument save space. */
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stw r4, 4(r5) /* Save function pointer. */
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stw r7, 0(r5) /* Save argument pointer. */
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/* Load arguments. */
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mov r4, r6
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ldw r6, 0(sp)
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ldw r7, 8(sp)
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ldw r8, 4(sp)
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/* Do the system call. */
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movi r2, SYS_ify (clone)
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/* End FDE now, because in the child the unwind info will be
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wrong. */
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cfi_endproc
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trap
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/* Check for errors. */
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bne r7, zero, SYSCALL_ERROR_LABEL
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/* See if we're on the newly created thread. */
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beq r2, zero, thread_start
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/* Successful return from the parent */
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ret
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thread_start:
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cfi_startproc
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cfi_undefined (ra)
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/* We expect the argument registers to be preserved across system
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calls and across task cloning, so flags should be in r4 here. */
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andhi r2, r4, %hi(CLONE_THREAD)
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bne r2, zero, 2f
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andi r3, r4, CLONE_VM
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movi r2, -1
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bne r3, zero, 3f
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DO_CALL (getpid, 0)
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3:
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stw r2, PID_OFFSET(r23)
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stw r2, TID_OFFSET(r23)
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2:
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ldw r5, 4(sp) /* Function pointer. */
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ldw r4, 0(sp) /* Argument pointer. */
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addi sp, sp, 8
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/* Call the user's function. */
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callr r5
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/* _exit with the result. */
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mov r4, r2
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#ifdef PIC
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nextpc r22
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1: movhi r8, %hiadj(_gp_got - 1b)
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addi r8, r8, %lo(_gp_got - 1b)
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add r22, r22, r8
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ldw r8, %call(HIDDEN_JUMPTARGET(_exit))(r22)
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jmp r8
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#else
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jmpi _exit
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#endif
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cfi_endproc
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cfi_startproc
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PSEUDO_END (__clone)
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libc_hidden_def (__clone)
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weak_alias (__clone, clone)
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