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 for running custom OSes since the icache might hold outdated data.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.
~Bryan
> 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
~Bryan
