Re: [PATCH v2 2/7] semihosting: add the semihosting_exit_request function

[Eric Blake]

On Tue, Jun 21, 2022 at 02:59:11PM +0200, Luc Michel wrote:
> Add the semihosting_exit_request function to be used by targets when
> handling an `exit' semihosted syscall. This function calls gdb_exit to
> close existing GDB connections, and qemu_system_shutdown_request with
> the new `guest-semi-exit' exit reason. It sets the QEMU exit status
> given by the exit syscall parameter. Finally it stops the CPU to prevent
> further execution, and exit the CPU loop as the syscall caller expects
> this syscall to not return.
> 
> This function is meant to be used in place of a raw exit() call when
> handling semihosted `exit' syscalls. Such a call is not safe because
> it does not allow other CPU threads to exit properly, leading to e.g.
> at_exit callbacks being called while other CPUs still run. This can lead
> to strange bugs, especially in plugins with a registered at_exit function.
> 
> Signed-off-by: Luc Michel <lmichel@kalray.eu>
> ---
>  qapi/run-state.json            |  4 +++-
>  include/semihosting/semihost.h |  5 +++++
>  semihosting/config.c           | 16 ++++++++++++++++
>  3 files changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/qapi/run-state.json b/qapi/run-state.json
> index 6e2162d7b3..a4f08dd32e 100644
> --- a/qapi/run-state.json
> +++ b/qapi/run-state.json
> @@ -80,20 +80,22 @@
>  # @guest-reset: Guest reset request, and command line turns that into
>  #               a shutdown
>  #
>  # @guest-panic: Guest panicked, and command line turns that into a shutdown
>  #
> +# @guest-semi-exit: Guest exit request via a semi-hosted exit syscall

Should include a '(since 7.1)' notation.

> +#
>  # @subsystem-reset: Partial guest reset that does not trigger QMP events and
>  #                   ignores --no-reboot. This is useful for sanitizing
>  #                   hypercalls on s390 that are used during kexec/kdump/boot
>  #
>  ##

As it is, the overall enum is missing a 'Since: 1.0' section.

>  { 'enum': 'ShutdownCause',
>    # Beware, shutdown_caused_by_guest() depends on enumeration order
>    'data': [ 'none', 'host-error', 'host-qmp-quit', 'host-qmp-system-reset',
>              'host-signal', 'host-ui', 'guest-shutdown', 'guest-reset',
> -            'guest-panic', 'subsystem-reset'] }
> +            'guest-panic', 'guest-semi-exit', 'subsystem-reset'] }
>  
>  ##
>  # @StatusInfo:
>  #
>  # Information about VCPU run state

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org