mirror of
https://github.com/jart/cosmopolitan.git
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77 lines
3.2 KiB
ArmAsm
77 lines
3.2 KiB
ArmAsm
/*-*- mode:unix-assembly; indent-tabs-mode:t; tab-width:8; coding:utf-8 -*-│
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│vi: set et ft=asm ts=8 tw=8 fenc=utf-8 :vi│
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╞══════════════════════════════════════════════════════════════════════════════╡
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│ Copyright 2020 Justine Alexandra Roberts Tunney │
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│ │
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│ Permission to use, copy, modify, and/or distribute this software for │
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│ any purpose with or without fee is hereby granted, provided that the │
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│ above copyright notice and this permission notice appear in all copies. │
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│ │
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│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL │
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│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED │
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│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE │
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│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL │
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│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR │
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│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER │
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│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR │
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│ PERFORMANCE OF THIS SOFTWARE. │
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╚─────────────────────────────────────────────────────────────────────────────*/
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#include "libc/dce.h"
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#include "libc/macros.h"
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.privileged
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// Forks process without copying page tables.
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//
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// This is the same as fork() except it's optimized for the case
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// where the caller invokes execve() immediately afterwards. You
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// can also call functions like close(), dup2(), etc. You cannot
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// call read() safely but you can call pread(). Call _exit() but
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// don't call exit(). Look for the vforksafe function annotation
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//
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// Do not make the assumption that the parent is suspended until
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// the child terminates since this impl calls fork() on Windows.
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//
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// @return pid of child process or 0 if forked process
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// @returnstwice
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// @vforksafe
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vfork:
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#if SupportsWindows()
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testb IsWindows()
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jnz sys_fork_nt
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#endif
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mov __NR_vfork(%rip),%eax
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pop %rsi # saves return address in a register
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#if SupportsBsd()
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testb IsBsd()
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jnz vfork.bsd
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#endif
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syscall
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push %rsi # note it happens twice in same page
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#if SupportsLinux()
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cmp $-4095,%eax
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jae systemfive_error
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#endif
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0: ezlea __vforked,di
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test %eax,%eax
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jz 1f
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decl (%rdi)
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jns 2f # openbsd doesn't actually share mem
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1: incl (%rdi)
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2: ret
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.endfn vfork,globl
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#if SupportsBsd()
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vfork.bsd:
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syscall
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push %rsi
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jc systemfive_errno
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#if SupportsXnu()
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testb IsXnu()
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jz 0b
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neg %edx # edx is 0 for parent and 1 for child
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not %edx # eax always returned with childs pid
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and %edx,%eax
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#endif /* XNU */
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jmp 0b
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.endfn vfork.bsd
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#endif /* BSD */
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