Re: [PATCH 2/4] target/arm: Move cortex-m related functions to new file v7m.c

[Peter Maydell]

On Mon, 23 Sep 2019 at 19:09, Thomas Huth <address@hidden> wrote:
> However, there's one thing I currently don't quite understand in this
> code (since I'm not an ARM guy, sorry) : There are references to "v8" in
> m_helper.c, too. Is that related to a separate CPU type, ie. should the
> v8 code also be available when CONFIG_ARM_V7M is disabled? Or can the
> code in m_helper.c be disabled completely if CONFIG_ARM_V7M is not set?

QEMU's naming conventions here is a bit confusing, for
historical reasons.

Architecturally what we have is:
 * "M-profile" -- this is the flavour of Arm architecture for
microcontrollers; it has some big differences from A and R
profile (eg the exception mechanism is different and it has
a built-in NVIC interrupt controller). All the Cortex-M<anything>
CPUs are M-profile
 * "Arm-v7M" -- this is the v7 flavour of the M-profile
architecture, eg Cortex-M3.
 * "Arm-v6M" -- this looks like it ought to mean "v6 flavour
of M-profile", but if you look at what features it has it's
more like "cut down version of v7M" (fewer instructions, cut
down exception model, etc, but some things which on A-profile
don't appear until v7A are present in v6M). Cortex-M0 and -M1.
 * "Arm-v8M" -- v8 flavour of M-profile. The big change here
is support for TrustZone. Cortex-M33. v8M comes in two
sub-profiles: "mainline", which has all the features like v7M,
and "baseline", which is cut-down in the same way v6M is a
cut-down v7M.

In QEMU, we implemented Cortex-M3 first, and then added -M0 and
-M33 later. So mostly our function naming convention uses
"v7m" when it means "any M-profile"; a few v8M-specific
functions use a "v8m" prefix. Everything in m_helper.c is
M-profile specific; most of it is used by all M-profile cores,
and a few bits are v8M-only or v7M-and-v8M-mainline only.

>From a CONFIG switch point of view I don't think it's
worth being able to #ifdef out the various flavours of
M-profile individually.

thanks
-- PMM