[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, 43 insertions, 0 deletions

diff --git a/wasm/fiber.h b/wasm/fiber.h
new file mode 100644
index 0000000000..0f3a336332
--- /dev/null
+++ b/wasm/fiber.h
@@ -0,0 +1,43 @@
+#ifndef RB_WASM_SUPPORT_FIBER_H
+#define RB_WASM_SUPPORT_FIBER_H
+
+#include <stdbool.h>
+
+#ifndef WASM_FIBER_STACK_BUFFER_SIZE
+# define WASM_FIBER_STACK_BUFFER_SIZE 6144
+#endif
+
+struct __rb_wasm_asyncify_fiber_ctx {
+    void* top;
+    void* end;
+    char buffer[WASM_FIBER_STACK_BUFFER_SIZE];
+};
+
+// Fiber execution context needed to perform context switch
+typedef struct {
+    // Fiber entry point called when the fiber started for the first time.
+    // NULL if the entry point is main
+    void (*entry_point)(void *, void *);
+    // Opaque argument pointers passed to the entry point function
+    void *arg0, *arg1;
+
+    // Internal asyncify buffer space
+    struct __rb_wasm_asyncify_fiber_ctx asyncify_buf;
+
+    bool is_rewinding;
+    bool is_started;
+} rb_wasm_fiber_context;
+
+// Initialize a given fiber context to be ready to pass to `rb_wasm_swapcontext`
+void rb_wasm_init_context(rb_wasm_fiber_context *fcp, void (*func)(void *, void *), void *arg0, void *arg1);
+
+// Swap the execution control with `target_fiber` and save the current context in `old_fiber`
+// NOTE: `old_fiber` must be the current executing fiber context
+void rb_wasm_swapcontext(rb_wasm_fiber_context *old_fiber, rb_wasm_fiber_context *target_fiber);
+
+// Returns the Asyncify buffer of next fiber if unwound for fiber context switch.
+// Used by the top level Asyncify handling in wasm/runtime.c
+void *rb_wasm_handle_fiber_unwind(void (**new_fiber_entry)(void *, void *),
+                                  void **arg0, void **arg1, bool *is_new_fiber_started);
+
+#endif