Summary
Ask for various properties of various kernel objects.
Declaration
#include <zircon/syscalls.h>
zx_status_t zx_object_get_property(zx_handle_t handle,
uint32_t property,
void* value,
size_t value_size);
Description
zx_object_get_property() requests the value of a kernel object's property.
Getting a property requires ZX_RIGHT_GET_PROPERTY rights on the handle.
The handle parameter indicates the target kernel object. Different properties only work on certain types of kernel objects, as described below.
The property parameter indicates which property to get/set. Property values
have the prefix ZX_PROP_, and are described below.
The value parameter holds the property value, and must be a pointer to a buffer of value_size bytes. Different properties expect different value types/sizes as described below.
PROPERTIES
Property values have the prefix ZX_PROP_, and are defined in
#include <zircon/syscalls/object.h>
ZX_PROP_NAME
handle type: Any of the following:
- Job
- Process
- Thread
- Resource
- Virtual Memory Object (VMO)
- Bus Transaction Initiator (BTI)
value type: char[ZX_MAX_NAME_LEN]
Allowed operations: get, set
The name of the object, as a NUL-terminated string.
Attempting to get or set the name of a thread that has exited will fail with ZX_ERR_BAD_STATE.
ZX_PROP_REGISTER_FS and ZX_PROP_REGISTER_GS
handle type: Thread
value type: uintptr_t
Allowed operations: get, set
The value of the x86 FS.BASE or GS.BASE register, respectively. value must
be a canonical address. Attempting to set a noncanonical address will fail with
ZX_ERR_INVALID_ARGS.
This is a software substitute for the rdfsbase, wrfsbase and rdgsbase,
wrgsbase instruction pairs supported on newer x86-64 CPUs, and should behave
exactly the same as using the CPU instructions directly (except that
attempting to set a noncanonical address as the value just gets an error
return rather than generating a machine exception). When using a CPU that
supports these instructions (as reported by the cpuid instruction), it's
more efficient and simpler to use the machine instructions directly.
Only defined for x86-64. Returns ZX_ERR_NOT_SUPPORTED on other architectures.
Returns ZX_ERR_ACCESS_DENIED if not invoked from the current thread.
ZX_PROP_PROCESS_DEBUG_ADDR
handle type: Process
value type: uintptr_t
Allowed operations: get, set
The value of ld.so's _dl_debug_addr. This can be used by debuggers to
interrogate the state of the dynamic loader.
ZX_PROP_PROCESS_BREAK_ON_LOAD
handle type: Process
value type: uintptr_t
Allowed operations: get, set
Determines whether the dynamic loader will issue a debug trap on every load of a shared library. If set before the first thread of a process runs, it will also trigger a debug trap for the initial load.
The dynamic loader sets the expected value of ZX_PROP_PROCESS_DEBUG_ADDR before
triggering this debug trap. Exception handlers can use this property to query the
dynamic loader's state.
When the dynamic loader issues the debug trap, it also sets the value of
ZX_PROP_PROCESS_BREAK_ON_LOAD to the address of the debug trap, so that
a debugger could compare the value with the address of the exception to
determine whether the debug trap was triggered by the dynamic loader.
Any non-zero value is considered to activate this feature. Setting this property to zero will disable it. A debugger could also use this property to detect whether there's already another debugger attached to the same process.
ZX_PROP_PROCESS_VDSO_BASE_ADDRESS
handle type: Process
value type: uintptr_t
Allowed operations: get
The base address of the vDSO mapping, or zero.
ZX_PROP_PROCESS_HW_TRACE_CONTEXT_ID
handle type: Process
value type: uintptr_t
Allowed operations: get
The context ID distinguishes different processes in hardware instruction tracing. On Intel X86-64 this is the value of register CR3.
To obtain ZX_PROP_PROCESS_HW_TRACE_CONTEXT_ID, you must specify
kernel.enable-debugging-syscalls=true on the kernel command line. Otherwise,
the function returns ZX_ERR_NOT_SUPPORTED.
Currently only defined for X86.
ZX_PROP_SOCKET_RX_THRESHOLD
handle type: Socket
value type: size_t
Allowed operations: get, set
The size of the read threshold of a socket, in bytes. Setting this will
assert ZX_SOCKET_READ_THRESHOLD if the amount of data that can be read
is greater than or equal to the threshold. Setting this property to zero
will result in the deasserting of ZX_SOCKET_READ_THRESHOLD.
Setting to a value larger than the maximum permissible size supported by
sockets will fail with ZX_ERR_INVALID_ARGS.
ZX_PROP_SOCKET_TX_THRESHOLD
handle type: Socket
value type: size_t
Allowed operations: get, set
The size of the write threshold of a socket, in bytes. Setting this will
assert ZX_SOCKET_WRITE_THRESHOLD if the amount of space available for writing
is greater than or equal to the threshold. Setting this property to zero
will result in the deasserting of ZX_SOCKET_WRITE_THRESHOLD. Setting the
write threshold after the peer has closed is an error, and results in a
ZX_ERR_PEER_CLOSED error being returned.
Setting to a value larger than the maximum permissible size supported by
sockets will fail with ZX_ERR_INVALID_ARGS.
ZX_PROP_JOB_KILL_ON_OOM
handle type: Job
value type: size_t
Allowed operations: set
The value of 1 means the Job and its children will be terminated if the
system finds itself in a system-wide low memory situation. Called with 0
(which is the default) opts out the job from being terminated in this
scenario. Setting to any other value will fail with ZX_ERR_INVALID_ARGS.
ZX_PROP_EXCEPTION_STATE
handle type: Exception
value type: uint32_t
Allowed operations: get, set
When set to ZX_EXCEPTION_STATE_HANDLED, closing the exception handle will
finish exception processing and resume the underlying thread.
When set to ZX_EXCEPTION_STATE_TRY_NEXT, closing the exception handle will
continue exception processing by trying the next handler in order.
When set to ZX_EXCEPTION_STATE_THREAD_EXIT, closing the exception handle will
cause the thread that generated the exception to exit.
Setting to any other value will fail with ZX_ERR_INVALID_ARGS.
ZX_PROP_EXCEPTION_STRATEGY
handle type: Exception
value type: uint32_t
Allowed operations: get, set
If ZX_EXCEPTION_STRATEGY_SECOND_CHANCE is set, then the debugger gets a 'second
chance' at handling the exception if the process-level handler fails to do so.
If ZX_EXCEPTION_STRATEGY_FIRST_CHANCE is set, then the debugger does not get a
second chance at handling the exception.
Setting to any other value will fail with ZX_ERR_INVALID_ARGS.
This property can only be set when the handle corresponds to a debugger process
exception channel. Attempting to set this property when the exception channel
is any other type will result in ZX_ERR_BAD_STATE.
ZX_PROP_STREAM_MODE_APPEND
handle type: Stream
value type: uint8_t
Allowed operations: get, set
This property will have a value of 1 when the Stream is in append mode and a
value of 0 the Stream is not in append mode. A stream in append mode will
atomically set the seek offset of the stream to the content size of the stream
prior to writing data in zx_stream_writev().
Rights
handle must have ZX_RIGHT_GET_PROPERTY, and must be of a supported ZX_OBJ_TYPE_
for the property, as documented above in the description of individual properties.
Return value
zx_object_get_property() returns ZX_OK on success. In the event of
failure, a negative error value is returned.
Errors
Specific errors for individual property values are documented in their description above. Common errors are listed below:
ZX_ERR_BAD_HANDLE: handle is not a valid handle.
ZX_ERR_WRONG_TYPE: handle is not an appropriate type for property.
ZX_ERR_ACCESS_DENIED: handle does not have the necessary rights for the
operation.
ZX_ERR_INVALID_ARGS: value 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: value_size is too small for property.
ZX_ERR_NOT_SUPPORTED: property does not exist.