Re: [PATCH] hw/arm/bcm2835_property: Implement "get command line" message

[Peter Maydell <peter.maydell@linaro.org>]

On Tue, 25 Apr 2023 at 11:34, Daniel Bertalan <dani@danielbertalan.dev> wrote:
>
> This query copies the kernel command line into the message buffer. It
> was previously stubbed out to return empty, this commit makes it reflect
> the arguments specified with `-append`.
>
> I observed the following peculiarities on my Pi 3B+:
> - If the buffer is shorter than the string, the response header gives
>   the full length, but no data is actually copied.
> - No NUL terminator is added: even if the buffer is long enough to fit
>   one, the buffer's original contents are preserved past the string's
>   end.
> - The VC firmware adds the following extra parameters beside the
>   user-supplied ones (via /boot/cmdline.txt): `video`, `vc_mem.mem_base`
>   and `vc_mem.mem_size`. This is currently not implemented in qemu.

Are there any particularly interesting bits of guest software
that try to read this property ?

I added a brief comment to the code about the no-NUL-terminator
and short-buffer handling so that future readers of the code
don't have to refer back to the commit message:
+            /*
+             * We follow the firmware behaviour: no NUL terminator is
+             * written to the buffer, and if the buffer is too short
+             * we report the required length in the response header
+             * and copy nothing to the buffer.
+             */

and have applied this to target-arm.next; thanks.

-- PMM