On Thu, Jul 30, 2015 at 5:03 AM, Geoffroy Couprie < [email protected]> wrote:
> Hi Len, > > On Wed, Jul 29, 2015 at 9:12 PM, Len Maxwell <[email protected]> wrote: > > > > Hi Geoffroy and Thomas, > > > > On Tue, Jul 28, 2015 at 4:29 AM, Thomas Leonard <[email protected]> > wrote: > >> > >> On 27 July 2015 at 15:54, Thomas Leonard <[email protected]> wrote: > >> > On 27 July 2015 at 09:36, Geoffroy Couprie < > [email protected]> > >> > wrote: > >> > >> [...] > >> > >> One other thing I should mention: Mini-OS runs in kernel mode and can > >> be interrupted at any time. On x86, the interrupt handler uses the > >> same stack as the rest of the code. Therefore, you must compile with > >> the Rust equivalent of -mno-red-zone so Rust doesn't assume it can > >> store things below the current stack pointer. > > > > > > I'm just starting to learn Rust, but I managed to create a simple static > lib > > and link it into a standalone Mini-OS build: > > > > * build Rust from git with static musl libc support [1] > > This is nice, I did not know about musl usage. This may be a bit big > for a unikernel, though. Do we need a full POSIX interface, with > threads and everything? > Hi, OK, now I see that targeting musl-static brings in too much additional/unnecessary code; that was my misguided way of working around linker errors between libhello and mini-os. Your "mm" package imports the "libc" crate; I suppose it adds the Rust stubs for libc functions, which are then linked to the implementations in mini-os? (which, in turn, are not needed for the trivial Rust code) It looks like mirage-platform/bindings [a] captures most of the interface between Mirage/OCaml and Mini-OS. It uses a few functions from time.h, string.h, and various Xen-related APIs. There's also main.c [b] which overrides start_kernel to kick off the OCaml runtime. Not sure if any additional functions are needed by OCaml itself? Rust and OCaml also have a common dependency on libm. For Mirage on Xen, it is pulled in via mirage-platform/xen-posix. [a] https://github.com/mirage/mirage-platform/tree/master/bindings [b] https://github.com/mirage/mirage-platform/blob/master/bindings/main.c > Thomas, what's mirage take on this? > > > * compile libhello.a from [2] > Those should be the correct compilation flags > > > * declare the Rust function as an extern in mini-os/kernel.c, call it > from > > start_kernel() > > * add -L... -lhello to the Mini-OS linker flags > > * make and run > > > > Geoffroy, how does this compare to your approach? > > See my code here: https://github.com/Geal/mini-os/compare/master...rust > > Basically, I'm trying to replace some parts of Mini-OS with Rust code, > as Thomas suggested. That way, we keep an architecture and a > bootloader that work well with Xen, and it can be tested right away > with Mirage. > > > > > To understand the interactions between Xen, Mini-OS, and MirageOS, I > found > > [3] and [4] useful starting points. > We will need a Rust implementation of clients for Xenbus and Xen > events. Once code is running from start_kernel, the next step is > interacting with Xen's devices. > I've started a learning exercise to see how much I can delete from Mini-OS while still supporting Mirage. Threading, POSIX emulation, HAVE_LIBC, and all of the front/back devs can go (except console), and then I might actually understand what's left. > > > > > The zinc.rs [5] project, a Rust RTOS for ARM, could provide some > inspiration > > for modeling low-level operations in a type-safe way. > > Zinc looks great, and they do something that I was planning to: > downloading the libcore part of Rust and linking to it directly. This > is the easiest way to get Rust features as needed, without having too > many dependencies. And once there's a libcore, making a libstd gets > easier. > Not knowing much about libcore vs. libstd -- which parts of libstd are important to the task of replacing C code in Mini-OS? Speaking of ARM, it would be interesting to see if the init_mm experiment runs on a Cubie: https://mirage.io/blog/introducing-xen-minios-arm > > > > [1]: https://doc.rust-lang.org/nightly/book/advanced-linking.html#linux > > [2]: https://gist.github.com/lnmx/e7a74bacafb7e38b8355 > > [3]: http://roscidus.com/blog/blog/2014/07/28/my-first-unikernel/ > > [4]: https://mirage.io/wiki/xen-events > > [5]: http://zinc.rs > > > > Geoffroy Couprie > -- Len
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