user_regset_writeback_fn(9) [suse man page]
USER_REGSET_WRITEBAC(9) Machine State USER_REGSET_WRITEBAC(9) NAME
user_regset_writeback_fn - type of writeback function in struct user_regset SYNOPSIS
typedef int user_regset_writeback_fn(struct task_struct * target, const struct user_regset * regset, int immediate); ARGUMENTS
target thread being examined regset regset being examined immediate zero if writeback at completion of next context switch is OK DESCRIPTION
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. Kernel Hackers Manual 2.6. July 2010 USER_REGSET_WRITEBAC(9)
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STRUCT
USER_REGSET(9) Machine State STRUCT USER_REGSET(9) NAME
struct_user_regset - accessible thread CPU state SYNOPSIS
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; }; MEMBERS
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. 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. DESCRIPTION
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. Kernel Hackers Manual 2.6. July 2010 STRUCT USER_REGSET(9)