Fix implementation on arm64v8

[npmccallum]

https://travis-ci.org/enarx/frenetic

At the above link you can see that tests fail for arm64v8. It is not currently known why. In order to solve this bug you need to:

1. Remove arm64v8 from allow_failures.
2. Make all required tests pass.
3. Submit a pull request.

[haraldh]

I tried hard, but could not get it to work. Looking at the assembler looks like setjmp and longjmp are not implemented.

Even trying to compile the following with clang gave me:

extern void jump_stack(void *stack, void *coro, void *func);

void jump_init(void *from[5], void *stack, void *coro, void *func) {
    if(__builtin_setjmp(from) == 0) {
        jump_stack(stack, coro, func);
    }
}

void jump_swap(void *from[5], void *into[5]) {
    if(__builtin_setjmp(from) == 0) {
        __builtin_longjmp(into, 1);
    }
}

void jump_into(void *into[5]) {
    __builtin_longjmp(into, 1);
}

Output:

running: "clang" "-Wall" "-Wextra" "-fPIC" "-o" "/tmp/build/target/debug/build/frenetic-0386846fb8b83b73/out/src/jump.o" "-c" "src/jump.c"
cargo:warning=src/jump.c:6:8: error: __builtin_setjmp is not supported for the current target
cargo:warning=    if(__builtin_setjmp(from) == 0) {
cargo:warning=       ^~~~~~~~~~~~~~~~~~~~~~
cargo:warning=src/jump.c:12:8: error: __builtin_setjmp is not supported for the current target
cargo:warning=    if(__builtin_setjmp(from) == 0) {
cargo:warning=       ^~~~~~~~~~~~~~~~~~~~~~
cargo:warning=src/jump.c:13:9: error: __builtin_longjmp is not supported for the current target
cargo:warning=        __builtin_longjmp(into, 1);
cargo:warning=        ^~~~~~~~~~~~~~~~~~~~~~~~~~
cargo:warning=src/jump.c:18:5: error: __builtin_longjmp is not supported for the current target
cargo:warning=    __builtin_longjmp(into, 1);
cargo:warning=    ^~~~~~~~~~~~~~~~~~~~~~~~~~

cargo:warning=4 errors generated.

[haraldh]

I would suggest using https://github.com/zonyitoo/context-rs

[haraldh]

a history of all my tries could be found on https://github.com/haraldh/frenetic