ltimer: indicate no support for more platforms

[midnightveil]

These were taken from the sel4test Sel4testHaveTimer config option.

Do not merge until #195 has been merged (as it will break sel4test for more platforms) ok now

[Indanz]

Moving the knowledge from sel4test to util_libs makes a lot of sense. But please don't use negated terms, use something like LIB_PLAT_SUPPORT_HAVE_LTIMER (it's fine to still use the blacklist, as that makes it easier to add a new timer without yet another subtle failure case).

It would be nice if we could add a define to each timer.h driver file to set a HAVE_TIMER define instead of hard-coding it in CMake, but it looks like the code structure won't allow it. That would automatically be up-to-date with the code. Oh well.

[Indanz]

To be fully portable you would need an if defined(__has_attribute), except if you rely on C23. At this point I'd get rid of the error thing altogether and just fall back to linker errors personally, but oh well, bit late for that.

[lsf37]

@midnightveil for some reason this line breaks the camkes timer component build. For all Arm platforms we're getting:

  /github/workspace/projects/global-components/components/TimeServer/src/time_server.c: In function ‘post_init’:
  /github/workspace/projects/global-components/components/TimeServer/src/time_server.c:230:13: error: call to ‘ltimer_default_init’ declared with attribute error: no ltimer support for this platform
    230 |     error = ltimer_default_init(&ltimer, io_ops, time_server_ltimer_handle, NULL);
        |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

(e.g. https://github.com/seL4/camkes-tool/actions/runs/15923333523/job/45177979627)

If I remove this line, everything builds and works fine. Either SIMULATION does not mean what it says or it is on for those builds even though they are hardware images. It does seem to work if I explicitly provide -DSIMULATION=OFF on the command line.

Are we actually sure that it is true for all Arm platforms that qemu does not provide an ltimer device? I thought that some of them have fairly extensive device simulation (but maybe not timer, I have not checked).

[lsf37]

SIMULATE does just seem to be on for those builds. It is actually generating a simulate script (which then says the platform is not supported for simulation).

So the right fix seems to be to make sure SIMULATE is not on for those builds, but it makes me wonder if we're braking other builds without intending to.

[lsf37]

Ok, so it does intentionally switch on SIMULATION by default in easy-settings.cmake

set(SIMULATION ON CACHE BOOL "Try and use simulable features")

So I'm not entirely sure how to proceed. Do we actually need to guard SIMULATION here in util_libs, or is it just to fail early?

[midnightveil]

This was copied from sel4test: https://github.com/seL4/sel4test/pull/142/files

[midnightveil]

What the issue is probably that it was previously an

if (qemu arm virt)
    if (timers) enable
    else disable
else (check this bunch of other conditions)
    disable

Now it is

if (qemu arm virt OR these other conditions)
   disable

[midnightveil]

Suggested change

	OR (SIMULATION AND (KernelArchRiscV OR KernelArchARM))
	OR ((NOT KernelPlatformQEMUArmVirt) AND SIMULATION AND (KernelArchRiscV OR KernelArchARM))

I think would be equivalent?

EDIT: Actually, no, it's still different. I'm going to go back to the original double if I guess.

[midnightveil]

#198