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process_start.md

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zx_process_start

SUMMARY

Start execution on a process.

DECLARATION

#include <zircon/syscalls.h>

zx_status_t zx_process_start(zx_handle_t handle,
                             zx_handle_t thread,
                             zx_vaddr_t entry,
                             zx_vaddr_t stack,
                             zx_handle_t arg1,
                             uintptr_t arg2);

DESCRIPTION

zx_process_start() is similar to zx_thread_start(), but is used for the purpose of starting the first thread in a process.

zx_process_start() causes a thread to begin execution at the program counter specified by entry and with the stack pointer set to stack. The arguments arg1 and arg2 are arranged to be in the architecture specific registers used for the first two arguments of a function call before the thread is started. All other registers are zero upon start.

The first argument (arg1) is a handle, which will be transferred from the process of the caller to the process being started, and an appropriate handle value will be placed in arg1 for the newly started thread. If zx_process_start() returns an error, arg1 is closed rather than transferred to the process being started.

Alternatively, arg1 can be ZX_HANDLE_INVALID instead of a handle. In this case the process starts with ZX_HANDLE_INVALID (i.e. zero) in its first argument register instead of a handle. This means there are no handles in the process and can never be any handles to any objects shared outside the process. zx_process_start() is the only way to transfer a handle into a process that doesn't involve the process making some system call using a handle it already has (arg1 is usually the "bootstrap" handle). A process with no handles can make the few system calls that don't require a handle, such as zx_process_exit(), if it's been provided with a vDSO mapping. It can create new kernel objects with system calls that don't require a handle, such as zx_vmo_create(), but there is no way to make use of those objects without more handles and no way to transfer them outside the process. Its only means of communication is via the memory mapped into its address space by others.

RIGHTS

handle must be of type ZX_OBJ_TYPE_PROCESS and have ZX_RIGHT_WRITE.

thread must be of type ZX_OBJ_TYPE_THREAD and have ZX_RIGHT_WRITE.

arg1 must have ZX_RIGHT_TRANSFER.

RETURN VALUE

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

ERRORS

ZX_ERR_BAD_HANDLE process or thread or arg1 is not a valid handle.

ZX_ERR_WRONG_TYPE process is not a process handle or thread is not a thread handle.

ZX_ERR_ACCESS_DENIED The handle thread lacks ZX_RIGHT_WRITE or thread does not belong to process, or the handle process lacks ZX_RIGHT_WRITE or arg1 lacks ZX_RIGHT_TRANSFER.

ZX_ERR_BAD_STATE process is already running or has exited.

ZX_ERR_INVALID_ARGS entry is not a userspace address, is not a canonical address, or is not 0.

SEE ALSO