[PATCH v1] arm: add call to cleanup_before_linux for go command

[Zixian Zeng]

On 25/04/30 01:32PM, Tom Rini wrote:
> On Wed, Apr 30, 2025 at 02:26:04PM -0500, Bryan Brattlof wrote:
> > On April 30, 2025 thus sayeth Tom Rini:
> > > On Wed, Apr 30, 2025 at 10:56:27PM +0530, Raghavendra, Vignesh wrote:
> > > >
> > > >
> > > > On 4/30/2025 10:01 PM, Tom Rini wrote:
> > > > > On Wed, Apr 30, 2025 at 11:29:04AM -0500, Bryan Brattlof wrote:
> > > > >> On April 30, 2025 thus sayeth Anshul Dalal:
> > > > >>> As discussed here[1], the go command causes undefined behavior when used
> > > > >>> for running custom OSes since the icache might hold outdated data. OSes
> > > > >>> usually also expect the MMU to be disabled upon execution.
> > > > >>>
> > > > >>> Therefore this patch adds a call to cleanup_before_linux before we jump
> > > > >>> to the loaded program/os which disables both the caches and the MMU.
> > > > >>> This makes the go command's behavior consistent with riscv platforms.
> > > > >>>
> > > > >>
> > > > >> I know quite a few other OSes are beginning to use U-Boot (QNX,
> > > > >> GreenHills or all the other RTOSes) each with their own requirements
> > > > >> from the bootloader. I'm curious if we should make boot* a little more
> > > > >> generic rather than abuse the 'go' command.
> > > >
> > > > VXworks has its own:
> > > > https://docs.u-boot.org/en/stable/usage/os/vxworks.html
> > > >
> > > > I suppose QNX and others should ideally have their own cmds as needed.
> > >
> > > Well, what's the QNX output file format (options?) again?
> >
> > I've only ever seen outputs in compressed binary formats but I've been
> > told there are tools to produce an ELF for the simulators
> >
> > >
> > > > > Well, that's what bootelf is for :)
> > > > >
> > > >
> > > > And if its not an elf but some .bin file "go" cmd should be used in
> > > > conjunction with "cache" cmd here to flush/disable cache, I guess?
> > >
> > > Well, what exactly are we talking about? Is this an "in theory" or some
> > > project(s) which exist today?
> > >
> >
> > I noticed this thread mainly because of the number of RTOS people asking
> > me about low level stuff U-Boot and TF-A is doing. I haven't seen any
> > 'In-Production' type bugs but I wouldn't be surprised if U-Boot is being
> > used in their CI environments today.
>
> A number of RTOSes are already supported via "bootm". If they've stopped
> working (as we don't have tests in CI for them) I'd love patches to fix
> and at least instructions on how to make it fail somewhere, ideally
> QEMU.
>
> > > There's a whole lot of reasons for either a legacy header and bootm or a
> > > not-legacy FIT image. The "go" command is for the "U-Boot is a debugger"
> > > side of the world, not how you should kick off some OS/application in
> > > production. It is all of the "this is dangerous" idioms.
> > >
> > > > If so, we should probably update the docs for this cmd appropriately so
> > > > as to avoid end users overloading like what RISC-V did?
> > >
> > > Yes, we should clarify things as needed and unwind, most likely, what
> > > RISC-V is doing. But not blindly so as perhaps there's now, sigh, a
> > > production / in-the-wild case here and we're now in a sticky spot.
> >
> > I like the idea of boot${OS} flags if only to standardize the interface
> > of how each OS should boot. I worry about situation where custom
> > scripting is being used to boot in production rather than stdboot
>
> Right. And that's part of why in this day and age, regular uses should
> not be using "go". We've had and supported RTOSes via "bootm" for what
> amounts to forever. We've had "bootelf" for arbitrary things for ages
> too (and in turn, your custom app/RTOS/whatever using the normal bare
> metal ELF linker script, target, etc makes it easier on that side too).
> In more recent times, having a whatever project spit out an EFI binary
> instead is also possible and done sometimes.
>
It might be a novice question, sorry..

I'm using uboot on riscv, and noticed that the "bootelf" command just
jumps to the entry point of the ELF file.  What if I want to boot
multiple harts?

bootm command calls "smp_call_functions" to change global variables
`gd->arch.ipi` which restores function addr and arguments
and sends IPI to each hart, but "bootelf" does not.

It might not be a problem on other arches such as x86, if I recall
correctly, x86 can specify the function address when sending IPI.

Thanks for your time.
> --
> Tom

Best regards,
Zixian