core: kernel: Add semihosting functions

Semihosting is a mechanism that enables target to communicate and use
I/O facilities on a host computer which is running a debugger, such as
GDB. The I/O faci

core: kernel: Add semihosting functions

Semihosting is a mechanism that enables target to communicate and use
I/O facilities on a host computer which is running a debugger, such as
GDB. The I/O facilities include character {read|write} {from|to} the
semihosting host side console or a file. In other words, OP-TEE OS can
output log to the host side console or the host side file, if there is a
semihosting host and OP-TEE OS requests the semihosting operations to
that host.

If CFG_SEMIHOSTING is enabled, some semihosting functions will be
compiled into OP-TEE kernel, including:
- semihosting_sys_readc()
- semihosting_sys_writec()
- semihosting_open()
- semihosting_read()
- semihosting_write()
- semihosting_close()

Note that the architectures which support semihosting should provide
their implementation of __do_semihosting(), which performs semihosting
instruction to raise the semihosting request.

Signed-off-by: Alvin Chang <alvinga@andestech.com>
Reviewed-by: Etienne Carriere <etienne.carriere@foss.st.com>
Reviewed-by: Jerome Forissier <jerome.forissier@linaro.org>
Reviewed-by: Jens Wiklander <jens.wiklander@linaro.org>

show more ...