Re: Porting to RISC-V

[Khem Raj <raj.khem@gmail.com>]

Hi Palmer

I think move it to riscv github handle and then I can help with
upstreaming in 1.21 timeframe.

Thanks
-Khem
On Wed, May 2, 2018 at 1:51 PM Palmer Dabbelt <palmer@dabbelt.com> wrote:
>
> On Wed, 02 May 2018 13:37:13 PDT (-0700), michaeljclark@mac.com wrote:
> >
> >
> >> On 3/05/2018, at 7:45 AM, Rich Felker <dalias@libc.org> wrote:
> >>
> >> On Wed, May 02, 2018 at 03:40:04PM -0400, Dean Michael Ancajas wrote:
> >>> Can you send a link of the wiki?
> >>
> >> https://wiki.musl-libc.org/
> >> https://wiki.musl-libc.org/porting.html
> >
> > Here’s a pointer to my fork of Aric Belsito’s tree, including several fixes to get threads and atomics passing libc-tests.
> >
> >       - https://github.com/michaeljclark/musl-riscv
> >
> > This is the list of contributors as far as I know, but I might have to do a deeper inspection of the git history:
> >
> >       Aric Belsito <lluixhi@gmail.com>
> >       Alex Suykov <alex.suykov@gmail.com>
> >       Michael Clark <michaeljclark@mac.com>
> >
> > I’ve talked to Palmer Dabbelt about moving the port to the riscv github organisation retaining all of the contributor history. Typically riscv repos are prefixed with riscv- versus suffixed however that is a minor detail. We’ll need to squash the port into some more logical commits as there is quite a bit of churn in the history, however we’ll tag the repo in its current state to keep the contributor history.
>
> I can move it whenever you want.
>
> > Threads and mutexes are working. I need to sync with latest musl and run libc-tests again and we need to run the tests in RISC-V Linux versus RISC-V QEMU linux-user. Running against linux-kernel will give more accurate results compared to QEMU’s linux-user emulation which may not be 100% accurate. This is easier to do now as there are several glibc based full Linux distros that can be run in QEMU RISC-V and on real hardware with networking and block storage. i.e. we can rsync binaries in over ssh in the QEMU virt machine. Indeed folk have been running self-hosted GCC bootstraps in the Fedora RISC-V port which has toolchain packages. Now there is a Debian port, and iirc there may even be a SUSE port (Palmer?)
> >
> > Here is some recent info on QEMU for RISC-V, which might help with the porting effort:
> >
> >       - https://github.com/riscv/riscv-qemu/wiki
> >       - https://www.sifive.com/blog/2018/04/25/risc-v-qemu-part-2-the-risc-v-qemu-port-is-upstream/
> >
> > Here is the last update I sent regarding the RISC-V musl port…
> >
> > Issues fixed since picking up GSoC musl-riscv branch:
> >
> >       • gcc patch to set the musl dynamic linker name (ELF interp) is upstream
> >               • /lib/ld-musl-riscv32.so.1 (-mabi=ilp32d, default, hard float)
> >               • /lib/ld-musl-riscv64.so.1 (-mabi=lp64d, default, hard float)
> >               • /lib/ld-musl-riscv32-sf.so.1 (-mabi=ilp32, soft float)
> >               • /lib/ld-musl-riscv64-sf.so.1 (-mabi=lp64, soft float)
> >               • /lib/ld-musl-riscv32-sp.so.1 (-mabi=ilp32f, single precision)
> >               • /lib/ld-musl-riscv64-sp.so.1 (-mabi=lp64f, single precision)
> >       • fixed failing pthread tests.
> >               • a_cas was deadlocking (updated a_cas in atomic_a.h, fixed missing inline asm constraint)
> >               • defined the minimal set of atomics required by the musl library
> >       • fixed failing sigaltstack tests (update sigaltstack and ucontext in signal.h)
> >       • fixed failing ipc_sem tests (added struct semid_ds in sem.h)
> >       • fixed failing stat tests (defined blksize_t and nlink_t in alltypes.h.in)
> >       • rename sigcontext __regs to gregs so that gcc would compile
> >       • rename _gp to __global_pointer$ in the crt to work with current binutils
> >       • change definition of long double to quadruple precision
> >       • update syscalls.h.in to use asm-generic syscall definitions
> >       • update stat.h to use asm-generic stat definition
> >
> > Remaining issues:
> >
> >       • rebase to current musl-libc
> >       • audit arch/riscv32 and arch/riscv64 headers to make sure they match linux-4.16
> >       • check results of tests that are expected to fail (compare with other architectures)
> >       • ELF thread local variables are not being initialised
> >               • tls_init test is failing
> >
> > Note: riscv32 glibc is not yet upstream so the 32-bit ABI is not yet frozen.
> >
> > Rich, BTW It seems the TLS offset is directly above the thread pointer (tp).
> >
> >       $ cat foo.c
> >       __thread int i = 42;
> >
> >       void foo()
> >       {
> >               i++;
> >       }
> >
> >       0000000000010226 <foo>:
> >          10226:       00022703                lw      a4,0(tp) # 0 <i>
> >          1022a:       2705                    addiw   a4,a4,1
> >          1022c:       00e22023                sw      a4,0(tp) # 0 <i>
> >          10230:       8082                    ret
> >
> >       0000000000010a7a <__set_thread_area>:
> >          10a7a:       822a                    mv      tp,a0
> >          10a7c:       4501                    li      a0,0
> >          10a7e:       8082                    ret
> >
> > Michael.