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# zx_thread_read_state

## Summary

Read one aspect of thread state.

## Declaration

```c
#include <zircon/syscalls.h>

zx_status_t zx_thread_read_state(zx_handle_t handle,
                                 uint32_t kind,
                                 void* buffer,
                                 size_t buffer_size);
```

## Description

`zx_thread_read_state()` reads one aspect of state of the thread. The thread
state may only be read when the thread is halted for an exception or the thread
is suspended.

The thread state is highly processor specific. See the structures in
zircon/syscalls/debug.h for the contents of the structures on each platform.

## STATES

### ZX_THREAD_STATE_GENERAL_REGS

The buffer must point to a `zx_thread_state_general_regs_t` structure that
contains the general registers for the current architecture.

### ZX_THREAD_STATE_FP_REGS

The buffer must point to a `zx_thread_state_fp_regs_t` structure. On 64-bit
ARM platforms, float point state is in the vector registers and this structure
is empty.

### ZX_THREAD_STATE_VECTOR_REGS

The buffer must point to a `zx_thread_state_vector_regs_t` structure.

### ZX_THREAD_STATE_DEBUG_REGS

The buffer must point to a `zx_thread_state_debug_regs_t` structure. All input
fields will be ignored and overwritten with the actual values for the thread.

### ZX_THREAD_STATE_SINGLE_STEP

The buffer must point to a `zx_thread_state_single_step_t` value, which
may contain either 0 (normal running), or 1 (single stepping enabled).

## Rights

*handle* must be of type **ZX_OBJ_TYPE_THREAD** and have **ZX_RIGHT_READ**.

## Return value

`zx_thread_read_state()` returns **ZX_OK** on success.
In the event of failure, a negative error value is returned.

## Errors

**ZX_ERR_BAD_HANDLE**  *handle* is not a valid handle.

**ZX_ERR_WRONG_TYPE**  *handle* is not that of a thread.

**ZX_ERR_ACCESS_DENIED**  *handle* lacks **ZX_RIGHT_READ**.

**ZX_ERR_INVALID_ARGS**  *kind* is not valid or *buffer* is an invalid pointer.

**ZX_ERR_NO_MEMORY**  Failure due to lack of memory.
There is no good way for userspace to handle this (unlikely) error.
In a future build this error will no longer occur.

**ZX_ERR_BUFFER_TOO_SMALL**  The buffer length *buffer_size* is too small to
hold the data required by *kind*.

**ZX_ERR_BAD_STATE**  The thread is not stopped at a point where state
is available. The thread state may only be read when the thread is stopped due
to an exception.

**ZX_ERR_NOT_SUPPORTED**  *kind* is not supported.
This can happen, for example, when trying to read a register set that
is not supported by the hardware the program is currently running on.

## See also

[thread_write_state](thread_write_state.md).