Merge "Improve the _FILE_OFFSET_BITS docs and link to them."
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Treehugger Robot
Gerrit Code Review
commit
8b9037a05e
7 changed files with 41 additions and 35 deletions
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@ -1,8 +1,6 @@
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32-bit ABI bugs
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===============
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# 32-bit ABI bugs
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`off_t` is 32-bit
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-----------------
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## 32-bit `off_t` and `_FILE_OFFSET_BITS=64`
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On 32-bit Android, `off_t` is a signed 32-bit integer. This limits functions
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that use `off_t` to working on files no larger than 2GiB.
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@ -34,13 +32,19 @@ all functions that take an `off_t` become unavailable. You've asked for their
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increase your target API level, you'll have more and more of the functions
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available. API 12 adds some of the `<unistd.h>` functions, API 21 adds `mmap`,
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and by API 24 you have everything including `<stdio.h>`. See the
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[linker map](libc/libc.map.txt) for full details.
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[linker map](libc/libc.map.txt) for full details. Note also that in NDK r16 and
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later, we inline an mmap64 implementation in the headers when you target an API
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before 21 because it's an easy special case that's often needed. This means
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that code using `_FILE_OFFSET_BITS=64` and `mmap` will always compile.
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If your code stops compiling when you move to NDK r15 or later, removing any
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definition of `_FILE_OFFSET_BITS=64` will restore the behavior you used to have:
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you'll have a 32-bit `off_t` and use the 32-bit functions.
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In the 64-bit ABI, `off_t` is always 64-bit.
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`sigset_t` is too small for real-time signals
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---------------------------------------------
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## `sigset_t` is too small for real-time signals
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On 32-bit Android, `sigset_t` is too small for ARM and x86 (but correct for
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MIPS). This means that there is no support for real-time signals in 32-bit
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@ -49,8 +53,7 @@ code.
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In the 64-bit ABI, `sigset_t` is the correct size for every architecture.
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`time_t` is 32-bit
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------------------
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## `time_t` is 32-bit
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On 32-bit Android, `time_t` is 32-bit. The header `<time64.h>` and type
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`time64_t` exist as a workaround, but the kernel interfaces exposed on 32-bit
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@ -58,8 +61,7 @@ Android all use the 32-bit `time_t`.
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In the 64-bit ABI, `time_t` is 64-bit.
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`pthread_mutex_t` is too small for large pids
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---------------------------------------------
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## `pthread_mutex_t` is too small for large pids
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This doesn't generally affect Android devices, because on devices
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`/proc/sys/kernel/pid_max` is usually too small to hit the 16-bit limit,
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@ -173,6 +173,7 @@ int renameat(int __old_dir_fd, const char* __old_path, int __new_dir_fd, const c
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int fseek(FILE* __fp, long __offset, int __whence);
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long ftell(FILE* __fp);
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/* See https://android.googlesource.com/platform/bionic/+/master/docs/32-bit-abi.md */
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#if defined(__USE_FILE_OFFSET64)
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int fgetpos(FILE* __fp, fpos_t* __pos) __RENAME(fgetpos64) __INTRODUCED_IN(24);
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int fsetpos(FILE* __fp, const fpos_t* __pos) __RENAME(fsetpos64) __INTRODUCED_IN(24);
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@ -205,25 +205,28 @@
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* In our header files we test against __USE_BSD and __USE_GNU.
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*/
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#if defined(_GNU_SOURCE)
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# define __USE_BSD 1
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# define __USE_GNU 1
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# define __USE_BSD 1
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# define __USE_GNU 1
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#endif
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#if defined(_BSD_SOURCE)
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# define __USE_BSD 1
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# define __USE_BSD 1
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#endif
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/* _FILE_OFFSET_BITS 64 support. */
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/*
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* _FILE_OFFSET_BITS 64 support.
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* See https://android.googlesource.com/platform/bionic/+/master/docs/32-bit-abi.md
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*/
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#if !defined(__LP64__) && defined(_FILE_OFFSET_BITS) && _FILE_OFFSET_BITS == 64
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#define __USE_FILE_OFFSET64 1
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# define __USE_FILE_OFFSET64 1
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/*
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* Note that __RENAME_IF_FILE_OFFSET64 is only valid if the off_t and off64_t
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* functions were both added at the same API level because if you use this,
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* you only have one declaration to attach __INTRODUCED_IN to.
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*/
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#define __RENAME_IF_FILE_OFFSET64(func) __RENAME(func)
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# define __RENAME_IF_FILE_OFFSET64(func) __RENAME(func)
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#else
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#define __RENAME_IF_FILE_OFFSET64(func)
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# define __RENAME_IF_FILE_OFFSET64(func)
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#endif
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/*
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@ -44,8 +44,9 @@ __BEGIN_DECLS
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#define MREMAP_MAYMOVE 1
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#define MREMAP_FIXED 2
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#if defined(__USE_FILE_OFFSET64)
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/*
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* See https://android.googlesource.com/platform/bionic/+/master/docs/32-bit-abi.md
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*
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* mmap64 wasn't really around until L, but we added an inline for it since it
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* allows a lot more code to compile with _FILE_OFFSET_BITS=64.
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*
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@ -54,17 +55,18 @@ __BEGIN_DECLS
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* mmap64 to every translation unit that includes this header. Instead, just
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* preserve the old behavior for GCC and emit a useful diagnostic.
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*/
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#if defined(__USE_FILE_OFFSET64)
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void* mmap(void* __addr, size_t __size, int __prot, int __flags, int __fd, off_t __offset)
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#if !defined(__clang__) && __ANDROID_API__ < __ANDROID_API_L__
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__attribute__((error("mmap is not available with _FILE_OFFSET_BITS=64 when using GCC until "
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"android-21. Either raise your minSdkVersion, disable "
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"_FILE_OFFSET_BITS=64, or switch to Clang.")));
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#else
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# if !defined(__clang__) && __ANDROID_API__ < __ANDROID_API_L__
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__attribute__((error("mmap is not available with _FILE_OFFSET_BITS=64 when using GCC until "
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"android-21. Either raise your minSdkVersion, disable "
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"_FILE_OFFSET_BITS=64, or switch to Clang.")));
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# else
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__RENAME(mmap64);
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#endif /* defined(__clang__) */
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# endif
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#else
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void* mmap(void* __addr, size_t __size, int __prot, int __flags, int __fd, off_t __offset);
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#endif /* defined(__USE_FILE_OFFSET64) */
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#endif
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#if __ANDROID_API__ >= __ANDROID_API_L__
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void* mmap64(void* __addr, size_t __size, int __prot, int __flags, int __fd, off64_t __offset) __INTRODUCED_IN(21);
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@ -34,6 +34,7 @@
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__BEGIN_DECLS
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/* See https://android.googlesource.com/platform/bionic/+/master/docs/32-bit-abi.md */
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#if defined(__USE_FILE_OFFSET64)
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ssize_t sendfile(int __out_fd, int __in_fd, off_t* __offset, size_t __count) __RENAME(sendfile64) __INTRODUCED_IN(21);
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#else
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@ -95,12 +95,13 @@ typedef uint64_t dev_t;
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typedef __kernel_time_t __time_t;
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typedef __time_t time_t;
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/* This historical accident means that we had a 32-bit off_t on 32-bit architectures. */
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/* See https://android.googlesource.com/platform/bionic/+/master/docs/32-bit-abi.md */
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#if defined(__USE_FILE_OFFSET64) || defined(__LP64__)
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typedef int64_t off_t;
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typedef off_t loff_t;
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typedef loff_t off64_t;
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#else
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/* This historical accident means that we had a 32-bit off_t on 32-bit architectures. */
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typedef __kernel_off_t off_t;
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typedef __kernel_loff_t loff_t;
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typedef loff_t off64_t;
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@ -168,16 +168,10 @@ int dup3(int __old_fd, int __new_fd, int __flags) __INTRODUCED_IN(21);
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int fsync(int __fd);
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int fdatasync(int __fd) __INTRODUCED_IN(9);
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#if defined(__USE_FILE_OFFSET64)
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off_t lseek(int __fd, off_t __offset, int __whence) __RENAME(lseek64);
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#else
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off_t lseek(int __fd, off_t __offset, int __whence);
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#endif
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off64_t lseek64(int __fd, off64_t __offset, int __whence);
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/* See https://android.googlesource.com/platform/bionic/+/master/docs/32-bit-abi.md */
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#if defined(__USE_FILE_OFFSET64)
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int truncate(const char* __path, off_t __length) __RENAME(truncate64) __INTRODUCED_IN(21);
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off_t lseek(int __fd, off_t __offset, int __whence) __RENAME(lseek64);
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ssize_t pread(int __fd, void* __buf, size_t __count, off_t __offset)
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__overloadable __RENAME(pread64) __INTRODUCED_IN(12);
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ssize_t pwrite(int __fd, const void* __buf, size_t __count, off_t __offset)
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@ -185,6 +179,7 @@ ssize_t pwrite(int __fd, const void* __buf, size_t __count, off_t __offset)
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int ftruncate(int __fd, off_t __length) __RENAME(ftruncate64) __INTRODUCED_IN(12);
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#else
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int truncate(const char* __path, off_t __length);
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off_t lseek(int __fd, off_t __offset, int __whence);
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ssize_t pread(int __fd, void* __buf, size_t __count, off_t __offset)
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__overloadable __RENAME_CLANG(pread);
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ssize_t pwrite(int __fd, const void* __buf, size_t __count, off_t __offset)
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@ -193,6 +188,7 @@ int ftruncate(int __fd, off_t __length);
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#endif
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int truncate64(const char* __path, off64_t __length) __INTRODUCED_IN(21);
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off64_t lseek64(int __fd, off64_t __offset, int __whence);
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ssize_t pread64(int __fd, void* __buf, size_t __count, off64_t __offset)
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__INTRODUCED_IN(12) __overloadable __RENAME_CLANG(pread64);
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ssize_t pwrite64(int __fd, const void* __buf, size_t __count, off64_t __offset)
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