7f4d006959
The errno "variable" is required to be thread-specific. It gets defined to a macro which dereferences a pointer returned by a kernel function. In user mode, we cannot simply read/write the thread struct. We do not have thread-local storage mechanism, so for now use the lowest address of the thread stack to store this value, since this is guaranteed to be read/writable by a user thread. The downside of this approach is potential stack corruption if the stack pointer goes down this far but does not exceed the location, since a fault won't be generated in this case. Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>
43 lines
846 B
C
43 lines
846 B
C
/*
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* Copyright (c) 2015 Wind River Systems, Inc.
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*
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* SPDX-License-Identifier: Apache-2.0
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*/
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/** @file
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*
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* @brief Per-thread errno accessor function
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*
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* Allow accessing the errno for the current thread without involving the
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* context switching.
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*/
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#include <kernel_structs.h>
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#include <syscall_handler.h>
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/*
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* Define _k_neg_eagain for use in assembly files as errno.h is
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* not assembly language safe.
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* FIXME: wastes 4 bytes
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*/
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const int _k_neg_eagain = -EAGAIN;
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#ifdef CONFIG_ERRNO
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#ifdef CONFIG_USERSPACE
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int *_impl_z_errno(void)
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{
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/* Initialized to the lowest address in the stack so the thread can
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* directly read/write it
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*/
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return _current->errno_location;
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}
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Z_SYSCALL_HANDLER0_SIMPLE(z_errno);
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#else
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int *_impl_z_errno(void)
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{
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return &_current->errno_var;
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}
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#endif /* CONFIG_USERSPACE */
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#endif /* CONFIG_ERRNO */
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