USB Gadget: documentation update

[linux-2.6] / include / linux / regset.h

/*
 * User-mode machine state access
 *
 * Copyright (C) 2007 Red Hat, Inc.  All rights reserved.
 *
 * This copyrighted material is made available to anyone wishing to use,
 * modify, copy, or redistribute it subject to the terms and conditions
 * of the GNU General Public License v.2.
 *
 * Red Hat Author: Roland McGrath.
 */

#ifndef _LINUX_REGSET_H
#define _LINUX_REGSET_H 1

#include <linux/compiler.h>
#include <linux/types.h>
#include <linux/uaccess.h>
struct task_struct;
struct user_regset;


/**
 * user_regset_active_fn - type of @active function in &struct user_regset
 * @target:     thread being examined
 * @regset:     regset being examined
 *
 * Return -%ENODEV if not available on the hardware found.
 * Return %0 if no interesting state in this thread.
 * Return >%0 number of @size units of interesting state.
 * Any get call fetching state beyond that number will
 * see the default initialization state for this data,
 * so a caller that knows what the default state is need
 * not copy it all out.
 * This call is optional; the pointer is %NULL if there
 * is no inexpensive check to yield a value < @n.
 */
typedef int user_regset_active_fn(struct task_struct *target,
                                  const struct user_regset *regset);

/**
 * user_regset_get_fn - type of @get function in &struct user_regset
 * @target:     thread being examined
 * @regset:     regset being examined
 * @pos:        offset into the regset data to access, in bytes
 * @count:      amount of data to copy, in bytes
 * @kbuf:       if not %NULL, a kernel-space pointer to copy into
 * @ubuf:       if @kbuf is %NULL, a user-space pointer to copy into
 *
 * Fetch register values.  Return %0 on success; -%EIO or -%ENODEV
 * are usual failure returns.  The @pos and @count values are in
 * bytes, but must be properly aligned.  If @kbuf is non-null, that
 * buffer is used and @ubuf is ignored.  If @kbuf is %NULL, then
 * ubuf gives a userland pointer to access directly, and an -%EFAULT
 * return value is possible.
 */
typedef int user_regset_get_fn(struct task_struct *target,
                               const struct user_regset *regset,
                               unsigned int pos, unsigned int count,
                               void *kbuf, void __user *ubuf);

/**
 * user_regset_set_fn - type of @set function in &struct user_regset
 * @target:     thread being examined
 * @regset:     regset being examined
 * @pos:        offset into the regset data to access, in bytes
 * @count:      amount of data to copy, in bytes
 * @kbuf:       if not %NULL, a kernel-space pointer to copy from
 * @ubuf:       if @kbuf is %NULL, a user-space pointer to copy from
 *
 * Store register values.  Return %0 on success; -%EIO or -%ENODEV
 * are usual failure returns.  The @pos and @count values are in
 * bytes, but must be properly aligned.  If @kbuf is non-null, that
 * buffer is used and @ubuf is ignored.  If @kbuf is %NULL, then
 * ubuf gives a userland pointer to access directly, and an -%EFAULT
 * return value is possible.
 */
typedef int user_regset_set_fn(struct task_struct *target,
                               const struct user_regset *regset,
                               unsigned int pos, unsigned int count,
                               const void *kbuf, const void __user *ubuf);

/**
 * user_regset_writeback_fn - type of @writeback function in &struct user_regset
 * @target:     thread being examined
 * @regset:     regset being examined
 * @immediate:  zero if writeback at completion of next context switch is OK
 *
 * This call is optional; usually the pointer is %NULL.  When
 * provided, there is some user memory associated with this regset's
 * hardware, such as memory backing cached register data on register
 * window machines; the regset's data controls what user memory is
 * used (e.g. via the stack pointer value).
 *
 * Write register data back to user memory.  If the @immediate flag
 * is nonzero, it must be written to the user memory so uaccess or
 * access_process_vm() can see it when this call returns; if zero,
 * then it must be written back by the time the task completes a
 * context switch (as synchronized with wait_task_inactive()).
 * Return %0 on success or if there was nothing to do, -%EFAULT for
 * a memory problem (bad stack pointer or whatever), or -%EIO for a
 * hardware problem.
 */
typedef int user_regset_writeback_fn(struct task_struct *target,
                                     const struct user_regset *regset,
                                     int immediate);

/**
 * struct user_regset - accessible thread CPU state
 * @n:                  Number of slots (registers).
 * @size:               Size in bytes of a slot (register).
 * @align:              Required alignment, in bytes.
 * @bias:               Bias from natural indexing.
 * @core_note_type:     ELF note @n_type value used in core dumps.
 * @get:                Function to fetch values.
 * @set:                Function to store values.
 * @active:             Function to report if regset is active, or %NULL.
 * @writeback:          Function to write data back to user memory, or %NULL.
 *
 * This data structure describes a machine resource we call a register set.
 * This is part of the state of an individual thread, not necessarily
 * actual CPU registers per se.  A register set consists of a number of
 * similar slots, given by @n.  Each slot is @size bytes, and aligned to
 * @align bytes (which is at least @size).
 *
 * These functions must be called only on the current thread or on a
 * thread that is in %TASK_STOPPED or %TASK_TRACED state, that we are
 * guaranteed will not be woken up and return to user mode, and that we
 * have called wait_task_inactive() on.  (The target thread always might
 * wake up for SIGKILL while these functions are working, in which case
 * that thread's user_regset state might be scrambled.)
 *
 * The @pos argument must be aligned according to @align; the @count
 * argument must be a multiple of @size.  These functions are not
 * responsible for checking for invalid arguments.
 *
 * When there is a natural value to use as an index, @bias gives the
 * difference between the natural index and the slot index for the
 * register set.  For example, x86 GDT segment descriptors form a regset;
 * the segment selector produces a natural index, but only a subset of
 * that index space is available as a regset (the TLS slots); subtracting
 * @bias from a segment selector index value computes the regset slot.
 *
 * If nonzero, @core_note_type gives the n_type field (NT_* value)
 * of the core file note in which this regset's data appears.
 * NT_PRSTATUS is a special case in that the regset data starts at
 * offsetof(struct elf_prstatus, pr_reg) into the note data; that is
 * part of the per-machine ELF formats userland knows about.  In
 * other cases, the core file note contains exactly the whole regset
 * (@n * @size) and nothing else.  The core file note is normally
 * omitted when there is an @active function and it returns zero.
 */
struct user_regset {
        user_regset_get_fn              *get;
        user_regset_set_fn              *set;
        user_regset_active_fn           *active;
        user_regset_writeback_fn        *writeback;
        unsigned int                    n;
        unsigned int                    size;
        unsigned int                    align;
        unsigned int                    bias;
        unsigned int                    core_note_type;
};

/**
 * struct user_regset_view - available regsets
 * @name:       Identifier, e.g. UTS_MACHINE string.
 * @regsets:    Array of @n regsets available in this view.
 * @n:          Number of elements in @regsets.
 * @e_machine:  ELF header @e_machine %EM_* value written in core dumps.
 * @e_flags:    ELF header @e_flags value written in core dumps.
 * @ei_osabi:   ELF header @e_ident[%EI_OSABI] value written in core dumps.
 *
 * A regset view is a collection of regsets (&struct user_regset,
 * above).  This describes all the state of a thread that can be seen
 * from a given architecture/ABI environment.  More than one view might
 * refer to the same &struct user_regset, or more than one regset
 * might refer to the same machine-specific state in the thread.  For
 * example, a 32-bit thread's state could be examined from the 32-bit
 * view or from the 64-bit view.  Either method reaches the same thread
 * register state, doing appropriate widening or truncation.
 */
struct user_regset_view {
        const char *name;
        const struct user_regset *regsets;
        unsigned int n;
        u32 e_flags;
        u16 e_machine;
        u8 ei_osabi;
};

/*
 * This is documented here rather than at the definition sites because its
 * implementation is machine-dependent but its interface is universal.
 */
/**
 * task_user_regset_view - Return the process's native regset view.
 * @tsk: a thread of the process in question
 *
 * Return the &struct user_regset_view that is native for the given process.
 * For example, what it would access when it called ptrace().
 * Throughout the life of the process, this only changes at exec.
 */
const struct user_regset_view *task_user_regset_view(struct task_struct *tsk);


/*
 * These are helpers for writing regset get/set functions in arch code.
 * Because @start_pos and @end_pos are always compile-time constants,
 * these are inlined into very little code though they look large.
 *
 * Use one or more calls sequentially for each chunk of regset data stored
 * contiguously in memory.  Call with constants for @start_pos and @end_pos,
 * giving the range of byte positions in the regset that data corresponds
 * to; @end_pos can be -1 if this chunk is at the end of the regset layout.
 * Each call updates the arguments to point past its chunk.
 */

static inline int user_regset_copyout(unsigned int *pos, unsigned int *count,
                                      void **kbuf,
                                      void __user **ubuf, const void *data,
                                      const int start_pos, const int end_pos)
{
        if (*count == 0)
                return 0;
        BUG_ON(*pos < start_pos);
        if (end_pos < 0 || *pos < end_pos) {
                unsigned int copy = (end_pos < 0 ? *count
                                     : min(*count, end_pos - *pos));
                data += *pos - start_pos;
                if (*kbuf) {
                        memcpy(*kbuf, data, copy);
                        *kbuf += copy;
                } else if (__copy_to_user(*ubuf, data, copy))
                        return -EFAULT;
                else
                        *ubuf += copy;
                *pos += copy;
                *count -= copy;
        }
        return 0;
}

static inline int user_regset_copyin(unsigned int *pos, unsigned int *count,
                                     const void **kbuf,
                                     const void __user **ubuf, void *data,
                                     const int start_pos, const int end_pos)
{
        if (*count == 0)
                return 0;
        BUG_ON(*pos < start_pos);
        if (end_pos < 0 || *pos < end_pos) {
                unsigned int copy = (end_pos < 0 ? *count
                                     : min(*count, end_pos - *pos));
                data += *pos - start_pos;
                if (*kbuf) {
                        memcpy(data, *kbuf, copy);
                        *kbuf += copy;
                } else if (__copy_from_user(data, *ubuf, copy))
                        return -EFAULT;
                else
                        *ubuf += copy;
                *pos += copy;
                *count -= copy;
        }
        return 0;
}

/*
 * These two parallel the two above, but for portions of a regset layout
 * that always read as all-zero or for which writes are ignored.
 */
static inline int user_regset_copyout_zero(unsigned int *pos,
                                           unsigned int *count,
                                           void **kbuf, void __user **ubuf,
                                           const int start_pos,
                                           const int end_pos)
{
        if (*count == 0)
                return 0;
        BUG_ON(*pos < start_pos);
        if (end_pos < 0 || *pos < end_pos) {
                unsigned int copy = (end_pos < 0 ? *count
                                     : min(*count, end_pos - *pos));
                if (*kbuf) {
                        memset(*kbuf, 0, copy);
                        *kbuf += copy;
                } else if (__clear_user(*ubuf, copy))
                        return -EFAULT;
                else
                        *ubuf += copy;
                *pos += copy;
                *count -= copy;
        }
        return 0;
}

static inline int user_regset_copyin_ignore(unsigned int *pos,
                                            unsigned int *count,
                                            const void **kbuf,
                                            const void __user **ubuf,
                                            const int start_pos,
                                            const int end_pos)
{
        if (*count == 0)
                return 0;
        BUG_ON(*pos < start_pos);
        if (end_pos < 0 || *pos < end_pos) {
                unsigned int copy = (end_pos < 0 ? *count
                                     : min(*count, end_pos - *pos));
                if (*kbuf)
                        *kbuf += copy;
                else
                        *ubuf += copy;
                *pos += copy;
                *count -= copy;
        }
        return 0;
}

/**
 * copy_regset_to_user - fetch a thread's user_regset data into user memory
 * @target:     thread to be examined
 * @view:       &struct user_regset_view describing user thread machine state
 * @setno:      index in @view->regsets
 * @offset:     offset into the regset data, in bytes
 * @size:       amount of data to copy, in bytes
 * @data:       user-mode pointer to copy into
 */
static inline int copy_regset_to_user(struct task_struct *target,
                                      const struct user_regset_view *view,
                                      unsigned int setno,
                                      unsigned int offset, unsigned int size,
                                      void __user *data)
{
        const struct user_regset *regset = &view->regsets[setno];

        if (!access_ok(VERIFY_WRITE, data, size))
                return -EIO;

        return regset->get(target, regset, offset, size, NULL, data);
}

/**
 * copy_regset_from_user - store into thread's user_regset data from user memory
 * @target:     thread to be examined
 * @view:       &struct user_regset_view describing user thread machine state
 * @setno:      index in @view->regsets
 * @offset:     offset into the regset data, in bytes
 * @size:       amount of data to copy, in bytes
 * @data:       user-mode pointer to copy from
 */
static inline int copy_regset_from_user(struct task_struct *target,
                                        const struct user_regset_view *view,
                                        unsigned int setno,
                                        unsigned int offset, unsigned int size,
                                        const void __user *data)
{
        const struct user_regset *regset = &view->regsets[setno];

        if (!access_ok(VERIFY_READ, data, size))
                return -EIO;

        return regset->set(target, regset, offset, size, NULL, data);
}


#endif  /* <linux/regset.h> */