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https://github.com/jart/cosmopolitan.git
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2fc507c98f
* modelines: tw -> sw shiftwidth, not textwidth. * space-surround modelines * fix irregular modelines * Fix modeline in titlegen.c
113 lines
4.2 KiB
ArmAsm
113 lines
4.2 KiB
ArmAsm
/*-*- mode:unix-assembly; indent-tabs-mode:t; tab-width:8; coding:utf-8 -*-│
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│ vi: set noet ft=asm ts=8 sw=8 fenc=utf-8 :vi │
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╞══════════════════════════════════════════════════════════════════════════════╡
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│ Copyright 2022 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/sysv/consts/nr.h"
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#include "libc/macros.internal.h"
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// Relinquishes scheduled quantum.
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//
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// @return 0 on success, or -1 w/ errno
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.ftrace1
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sched_yield:
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.ftrace2
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#ifdef __x86_64__
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push %rbp
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mov %rsp,%rbp
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xor %eax,%eax
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mov __hostos(%rip),%dl
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#if SupportsMetal()
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testb $_HOSTMETAL,%dl
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jnz 9f
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#endif
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#if SupportsWindows()
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// Windows Support
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//
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// A value of zero, together with the bAlertable parameter set to
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// FALSE, causes the thread to relinquish the remainder of its time
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// slice to any other thread that is ready to run, if there are no
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// pending user APCs on the calling thread. If there are no other
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// threads ready to run and no user APCs are queued, the function
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// returns immediately, and the thread continues execution.
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// ──Quoth MSDN
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testb $_HOSTWINDOWS,%dl
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jz 1f
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xor %ecx,%ecx
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xor %edx,%edx
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ntcall __imp_SleepEx
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xor %eax,%eax
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jmp 9f
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1:
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#endif
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#if SupportsSystemv()
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// On XNU we polyfill sched_yield() using sleep() which'll
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// be polyfilled using select() with a zero timeout, which
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// means to wait zero microseconds and then returns a zero
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// and this hopefully will give other threads a chance too
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// XNU has a special version we use called select_nocancel
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//
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// "If the readfds, writefds, and errorfds arguments are
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// all null pointers and the timeout argument is not a
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// null pointer, the pselect() or select() function shall
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// block for the time specified, or until interrupted by
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// a signal." ──Quoth IEEE 1003.1-2017 §functions/select
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//
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// On other platforms, sched_yield() takes no arguments.
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push $0 // timeout.tv_usec
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push $0 // timeout.tv_sec
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xor %edi,%edi // nfds
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xor %esi,%esi // readfds
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xor %edx,%edx // writefds
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xor %r10d,%r10d // exceptfds
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mov %rsp,%r8 // timeout
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mov __NR_sched_yield,%eax // ordinal
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clc // linux
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syscall
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// It should not be possible for this to fail so we don't
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// bother going through the errno ritual. If this somehow
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// fails a positive or negative errno might get returned.
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#endif
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9: leave
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ret
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#elif defined(__aarch64__)
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stp x29,x30,[sp,-32]!
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mov x29,sp
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mov x3,0
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mov x2,0
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add x4,sp,16
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mov x1,0
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mov w0,0
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stp xzr,xzr,[sp,16]
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mov x8,#0x7c // sched_yield() for gnu/systemd
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mov x16,#0x5d // select(0,0,0,0,&blah) for xnu
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svc 0
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ldp x29,x30,[sp],32
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ret
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#else
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#error "arch unsupported"
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#endif
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.endfn sched_yield,globl
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.previous
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