[wasm] add asyncify based setjmp, fiber, register scan emulation

configure.ac: setup build tools and register objects

main.c: wrap main with rb_wasm_rt_start to handle asyncify unwinds

tool/m4/ruby_wasm_tools.m4: setup default command based on WASI_SDK_PATH
environment variable. checks wasm-opt which is used for asyncify.

tool/wasm-clangw wasm/wasm-opt: a clang wrapper which replaces real
wasm-opt with do-nothing wasm-opt to avoid misoptimization before
asyncify. asyncify is performed at POSTLINK, but clang linker driver
tries to run optimization by wasm-opt unconditionally. inlining pass
at wasm level breaks asyncify's assumption, so should not optimize
before POSTLIK.

wasm/GNUmakefile.in: wasm specific rules to compile objects

1 files changed, 83 insertions, 0 deletions

diff --git a/wasm/fiber.c b/wasm/fiber.c
new file mode 100644
index 0000000000..ecc481b0ee
--- /dev/null
+++ b/wasm/fiber.c
@@ -0,0 +1,83 @@
+/*
+ This is a ucontext-like userland context switching API for WebAssembly based on Binaryen's Asyncify.
+
+ * NOTE:
+ * This mechanism doesn't take care of stack state. Just save and restore program counter and
+ * registers (rephrased as locals by Wasm term). So use-site need to save and restore the C stack pointer.
+ * This Asyncify based implementation is not much efficient and will be replaced with future stack-switching feature.
+ */
+
+#include <stdlib.h>
+#include "wasm/fiber.h"
+#include "wasm/asyncify.h"
+
+#ifdef RB_WASM_ENABLE_DEBUG_LOG
+# include <stdio.h>
+# define RB_WASM_DEBUG_LOG(...) fprintf(stderr, __VA_ARGS__)
+#else
+# define RB_WASM_DEBUG_LOG(...)
+#endif
+
+void
+rb_wasm_init_context(rb_wasm_fiber_context *fcp, void (*func)(void *, void *), void *arg0, void *arg1)
+{
+    fcp->asyncify_buf.top = &fcp->asyncify_buf.buffer[0];
+    fcp->asyncify_buf.end = &fcp->asyncify_buf.buffer[WASM_FIBER_STACK_BUFFER_SIZE];
+    fcp->is_rewinding = false;
+    fcp->is_started = false;
+    fcp->entry_point = func;
+    fcp->arg0 = arg0;
+    fcp->arg1 = arg1;
+    RB_WASM_DEBUG_LOG("[%s] fcp->asyncify_buf %p\n", __func__, &fcp->asyncify_buf);
+}
+
+static rb_wasm_fiber_context *_rb_wasm_active_next_fiber;
+
+void
+rb_wasm_swapcontext(rb_wasm_fiber_context *ofcp, rb_wasm_fiber_context *fcp)
+{
+    RB_WASM_DEBUG_LOG("[%s] enter ofcp = %p fcp = %p\n", __func__, ofcp, fcp);
+    if (ofcp->is_rewinding) {
+        asyncify_stop_rewind();
+        ofcp->is_rewinding = false;
+        return;
+    }
+    _rb_wasm_active_next_fiber = fcp;
+    RB_WASM_DEBUG_LOG("[%s] start unwinding asyncify_buf = %p\n", __func__, &ofcp->asyncify_buf);
+    asyncify_start_unwind(&ofcp->asyncify_buf);
+}
+
+void *
+rb_wasm_handle_fiber_unwind(void (**new_fiber_entry)(void *, void *),
+                            void **arg0, void **arg1, bool *is_new_fiber_started)
+{
+    rb_wasm_fiber_context *next_fiber;
+    if (!_rb_wasm_active_next_fiber) {
+        RB_WASM_DEBUG_LOG("[%s] no next fiber\n", __func__);
+        *is_new_fiber_started = false;
+        return NULL;
+    }
+
+    next_fiber = _rb_wasm_active_next_fiber;
+    _rb_wasm_active_next_fiber = NULL;
+
+    RB_WASM_DEBUG_LOG("[%s] next_fiber->asyncify_buf = %p\n", __func__, &next_fiber->asyncify_buf);
+
+    *new_fiber_entry = next_fiber->entry_point;
+    *arg0 = next_fiber->arg0;
+    *arg1 = next_fiber->arg1;
+
+    if (!next_fiber->is_started) {
+        RB_WASM_DEBUG_LOG("[%s] new fiber started\n", __func__);
+        // start a new fiber if not started yet.
+        next_fiber->is_started = true;
+        *is_new_fiber_started = true;
+        return NULL;
+    } else {
+        RB_WASM_DEBUG_LOG("[%s] resume a fiber\n", __func__);
+        // resume a fiber again
+        next_fiber->is_rewinding = true;
+        *is_new_fiber_started = false;
+        return &next_fiber->asyncify_buf;
+    }
+}