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https://github.com/jart/cosmopolitan.git
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eeb20775d2
This will help C++ code that uses exceptions to be tinier. For example, this change shaves away 1000 lines of assembly code from LLVM's libcxx, which is 0.7% of all assembly instructions in the entire library.
97 lines
4.8 KiB
C
97 lines
4.8 KiB
C
/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
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│ vi: set et ft=c ts=2 sts=2 sw=2 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/calls/calls.h"
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#include "libc/calls/internal.h"
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#include "libc/calls/syscall-nt.internal.h"
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#include "libc/calls/syscall-sysv.internal.h"
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#include "libc/dce.h"
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#include "libc/intrin/describeflags.internal.h"
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#include "libc/intrin/strace.internal.h"
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#include "libc/intrin/weaken.h"
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#include "libc/log/backtrace.internal.h"
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#include "libc/runtime/zipos.internal.h"
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#include "libc/sysv/errfuns.h"
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/**
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* Changes current position of file descriptor, e.g.
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*
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* int fd = open("hello.bin", O_RDONLY);
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* lseek(fd, 100, SEEK_SET); // set position to 100th byte
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* read(fd, buf, 8); // read bytes 100 through 107
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*
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* This function may be used to inspect the current position:
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*
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* int64_t pos = lseek(fd, 0, SEEK_CUR);
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*
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* You may seek past the end of file. If a write happens afterwards
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* then the gap leading up to it will be filled with zeroes. Please
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* note that lseek() by itself will not extend the physical medium.
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*
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* If dup() is used then the current position will be shared across
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* multiple file descriptors. If you seek in one it will implicitly
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* seek the other too.
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*
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* The current position of a file descriptor is shared between both
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* processes and threads. For example, if an fd is inherited across
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* fork(), and both the child and parent want to read from it, then
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* changes made by one are observable to the other.
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*
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* The pread() and pwrite() functions obfuscate the need for having
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* global shared file position state. Consider using them, since it
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* helps avoid the gotchas of this interface described above.
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*
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* This function is supported by all OSes within our support vector
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* and our unit tests demonstrate the behaviors described above are
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* consistent across platforms.
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*
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* @param fd is a number returned by open()
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* @param offset is 0-indexed byte count w.r.t. `whence`
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* @param whence can be one of:
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* - `SEEK_SET`: Sets the file position to `offset` [default]
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* - `SEEK_CUR`: Sets the file position to `position + offset`
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* - `SEEK_END`: Sets the file position to `filesize + offset`
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* @return new position relative to beginning, or -1 w/ errno
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* @raise ESPIPE if `fd` is a pipe, socket, or fifo
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* @raise EBADF if `fd` isn't an open file descriptor
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* @raise EINVAL if resulting offset would be negative
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* @raise EINVAL if `whence` isn't valid
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* @asyncsignalsafe
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* @vforksafe
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*/
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int64_t lseek(int fd, int64_t offset, int whence) {
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int64_t rc;
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if (fd < g_fds.n && g_fds.p[fd].kind == kFdZip) {
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rc = _weaken(__zipos_seek)(
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(struct ZiposHandle *)(intptr_t)g_fds.p[fd].handle, offset, whence);
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} else if (IsLinux() || IsXnu() || IsFreebsd() || IsOpenbsd()) {
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rc = sys_lseek(fd, offset, whence, 0);
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} else if (IsNetbsd()) {
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rc = sys_lseek(fd, offset, offset, whence);
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} else if (IsWindows()) {
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rc = sys_lseek_nt(fd, offset, whence);
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} else {
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rc = enosys();
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}
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STRACE("lseek(%d, %'ld, %s) → %'ld% m", fd, offset, DescribeWhence(whence),
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rc);
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return rc;
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}
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__weak_reference(lseek, lseek64);
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