Try #481:

lib/runtime-c-api/src/lib.rs

@@ -95,6 +95,8 @@ pub mod instance;
 pub mod memory;
 pub mod module;
 pub mod table;
+#[cfg(all(unix, target_arch = "x86_64"))]
+pub mod trampoline;
 pub mod value;
 
 #[allow(non_camel_case_types)]

lib/runtime-c-api/src/trampoline.rs

@@ -0,0 +1,60 @@
+use std::ffi::c_void;
+use wasmer_runtime_core::trampoline::*;
+
+#[repr(C)]
+pub struct wasmer_trampoline_buffer_builder_t;
+
+#[repr(C)]
+pub struct wasmer_trampoline_buffer_t;
+
+#[repr(C)]
+pub struct wasmer_trampoline_callable_t;
+
+#[no_mangle]
+#[allow(clippy::cast_ptr_alignment)]
+pub extern "C" fn wasmer_trampoline_buffer_builder_new() -> *mut wasmer_trampoline_buffer_builder_t
+{
+    Box::into_raw(Box::new(TrampolineBufferBuilder::new())) as *mut _
+}
+
+#[no_mangle]
+#[allow(clippy::cast_ptr_alignment)]
+pub unsafe extern "C" fn wasmer_trampoline_buffer_builder_add_function(
+    b: *mut wasmer_trampoline_buffer_builder_t,
+    f: *const wasmer_trampoline_callable_t,
+    ctx: *const c_void,
+) -> usize {
+    let b = &mut *(b as *mut TrampolineBufferBuilder);
+    b.add_function(f as *const CallTarget, ctx as *const CallContext)
+}
+
+#[no_mangle]
+#[allow(clippy::cast_ptr_alignment)]
+pub unsafe extern "C" fn wasmer_trampoline_buffer_builder_build(
+    b: *mut wasmer_trampoline_buffer_builder_t,
+) -> *mut wasmer_trampoline_buffer_t {
+    let b = Box::from_raw(b as *mut TrampolineBufferBuilder);
+    Box::into_raw(Box::new(b.build())) as *mut _
+}
+
+#[no_mangle]
+#[allow(clippy::cast_ptr_alignment)]
+pub unsafe extern "C" fn wasmer_trampoline_buffer_destroy(b: *mut wasmer_trampoline_buffer_t) {
+    Box::from_raw(b);
+}
+
+#[no_mangle]
+#[allow(clippy::cast_ptr_alignment)]
+pub unsafe extern "C" fn wasmer_trampoline_buffer_get_trampoline(
+    b: *const wasmer_trampoline_buffer_t,
+    idx: usize,
+) -> *const wasmer_trampoline_callable_t {
+    let b = &*(b as *const TrampolineBuffer);
+    b.get_trampoline(idx) as _
+}
+
+#[no_mangle]
+#[allow(clippy::cast_ptr_alignment)]
+pub unsafe extern "C" fn wasmer_trampoline_get_context() -> *mut c_void {
+    get_context() as *const c_void as *mut c_void
+}

lib/runtime-c-api/tests/test-import-function.c

@@ -14,8 +14,15 @@ typedef struct {
   int value;
 } context_data;
 
+struct print_str_context {
+    int call_count;
+};
+
 void print_str(wasmer_instance_context_t *ctx, int32_t ptr, int32_t len)
 {
+    struct print_str_context *local_context = wasmer_trampoline_get_context();
+    local_context->call_count++;
+
     const wasmer_memory_t *memory = wasmer_instance_context_memory(ctx, 0);
     uint32_t mem_len = wasmer_memory_length(memory);
     uint8_t *mem_bytes = wasmer_memory_data(memory);
@@ -36,9 +43,22 @@ int main()
 {
     wasmer_value_tag params_sig[] = {WASM_I32, WASM_I32};
     wasmer_value_tag returns_sig[] = {};
+    struct print_str_context local_context = {
+        .call_count = 0
+    };
+
+    printf("Creating trampoline buffer\n");
+    wasmer_trampoline_buffer_builder_t *tbb = wasmer_trampoline_buffer_builder_new();
+    unsigned long print_str_idx = wasmer_trampoline_buffer_builder_add_function(
+        tbb,
+        (wasmer_trampoline_callable_t *) print_str,
+        (void *) &local_context
+    );
+    wasmer_trampoline_buffer_t *tb = wasmer_trampoline_buffer_builder_build(tbb);
+    const wasmer_trampoline_callable_t *print_str_callable = wasmer_trampoline_buffer_get_trampoline(tb, print_str_idx);
 
     printf("Creating new func\n");
-    wasmer_import_func_t *func = wasmer_import_func_new((void (*)(void *)) print_str, params_sig, 2, returns_sig, 0);
+    wasmer_import_func_t *func = wasmer_import_func_new((void (*)(void *)) print_str_callable, params_sig, 2, returns_sig, 0);
     wasmer_import_t import;
 
     char *module_name = "env";
@@ -95,7 +115,10 @@ int main()
     assert(ptr_len == 13);
     assert(0 == strcmp(actual_str, "Hello, World!"));
     assert(context_data_value == actual_context_data_value);
+    assert(local_context.call_count == 1);
 
+    printf("Destroying trampoline buffer\n");
+    wasmer_trampoline_buffer_destroy(tb);
     printf("Destroying func\n");
     wasmer_import_func_destroy(func);
     printf("Destroy instance\n");

lib/runtime-c-api/wasmer.h

@@ -133,6 +133,18 @@ typedef struct {
 
 } wasmer_serialized_module_t;
 
+typedef struct {
+
+} wasmer_trampoline_buffer_builder_t;
+
+typedef struct {
+
+} wasmer_trampoline_callable_t;
+
+typedef struct {
+
+} wasmer_trampoline_buffer_t;
+
 /**
  * Creates a new Module from the given wasm bytes.
  * Returns `wasmer_result_t::WASMER_OK` upon success.
@@ -584,6 +596,21 @@ uint32_t wasmer_table_length(wasmer_table_t *table);
  */
 wasmer_result_t wasmer_table_new(wasmer_table_t **table, wasmer_limits_t limits);
 
+uintptr_t wasmer_trampoline_buffer_builder_add_function(wasmer_trampoline_buffer_builder_t *b,
+                                                        const wasmer_trampoline_callable_t *f,
+                                                        const void *ctx);
+
+wasmer_trampoline_buffer_t *wasmer_trampoline_buffer_builder_build(wasmer_trampoline_buffer_builder_t *b);
+
+wasmer_trampoline_buffer_builder_t *wasmer_trampoline_buffer_builder_new(void);
+
+void wasmer_trampoline_buffer_destroy(wasmer_trampoline_buffer_t *b);
+
+const wasmer_trampoline_callable_t *wasmer_trampoline_buffer_get_trampoline(const wasmer_trampoline_buffer_t *b,
+                                                                            uintptr_t idx);
+
+void *wasmer_trampoline_get_context(void);
+
 /**
  * Returns true for valid wasm bytes and false for invalid bytes
  */

lib/runtime-c-api/wasmer.hh

@@ -131,6 +131,18 @@ struct wasmer_serialized_module_t {
 
 };
 
+struct wasmer_trampoline_buffer_builder_t {
+
+};
+
+struct wasmer_trampoline_callable_t {
+
+};
+
+struct wasmer_trampoline_buffer_t {
+
+};
+
 extern "C" {
 
 /// Creates a new Module from the given wasm bytes.
@@ -458,6 +470,21 @@ uint32_t wasmer_table_length(wasmer_table_t *table);
 /// and `wasmer_last_error_message` to get an error message.
 wasmer_result_t wasmer_table_new(wasmer_table_t **table, wasmer_limits_t limits);
 
+uintptr_t wasmer_trampoline_buffer_builder_add_function(wasmer_trampoline_buffer_builder_t *b,
+                                                        const wasmer_trampoline_callable_t *f,
+                                                        const void *ctx);
+
+wasmer_trampoline_buffer_t *wasmer_trampoline_buffer_builder_build(wasmer_trampoline_buffer_builder_t *b);
+
+wasmer_trampoline_buffer_builder_t *wasmer_trampoline_buffer_builder_new();
+
+void wasmer_trampoline_buffer_destroy(wasmer_trampoline_buffer_t *b);
+
+const wasmer_trampoline_callable_t *wasmer_trampoline_buffer_get_trampoline(const wasmer_trampoline_buffer_t *b,
+                                                                            uintptr_t idx);
+
+void *wasmer_trampoline_get_context();
+
 /// Returns true for valid wasm bytes and false for invalid bytes
 bool wasmer_validate(const uint8_t *wasm_bytes, uint32_t wasm_bytes_len);
 

lib/runtime-core/src/lib.rs

@@ -8,6 +8,10 @@ extern crate field_offset;
 #[macro_use]
 extern crate serde_derive;
 
+#[allow(unused_imports)]
+#[macro_use]
+extern crate lazy_static;
+
 #[macro_use]
 mod macros;
 #[doc(hidden)]
@@ -29,12 +33,16 @@ mod sig_registry;
 pub mod structures;
 mod sys;
 pub mod table;
+#[cfg(all(unix, target_arch = "x86_64"))]
+pub mod trampoline_x64;
 pub mod typed_func;
 pub mod types;
 pub mod units;
 pub mod vm;
 #[doc(hidden)]
 pub mod vmcalls;
+#[cfg(all(unix, target_arch = "x86_64"))]
+pub use trampoline_x64 as trampoline;
 
 use self::error::CompileResult;
 #[doc(inline)]

lib/runtime-core/src/trampoline_x64.rs

@@ -0,0 +1,130 @@
+//! Trampoline generator for carrying context with function pointer.
+//!
+//! This makes use of the `mm0` register to pass the context as an implicit "parameter" because `mm0` is
+//! not used to pass parameters and is almost never used by modern compilers. It's still better to call
+//! `get_context()` as early as possible in the callee function though, as a good practice.
+//!
+//! Variadic functions are not supported because `rax` is used by the trampoline code.
+
+use crate::loader::CodeMemory;
+
+lazy_static! {
+    static ref GET_CONTEXT: extern "C" fn () -> *const CallContext = {
+        static CODE: &'static [u8] = &[
+            0x48, 0x0f, 0x7e, 0xc0, // movq %mm0, %rax
+            0xc3, // retq
+        ];
+        let mut mem = CodeMemory::new(4096);
+        mem[..CODE.len()].copy_from_slice(CODE);
+        mem.make_executable();
+        let ptr = mem.as_ptr();
+        ::std::mem::forget(mem);
+        unsafe {
+            ::std::mem::transmute(ptr)
+        }
+    };
+}
+
+pub enum CallTarget {}
+pub enum CallContext {}
+pub enum Trampoline {}
+
+pub struct TrampolineBufferBuilder {
+    code: Vec<u8>,
+    offsets: Vec<usize>,
+}
+
+pub struct TrampolineBuffer {
+    code: CodeMemory,
+    offsets: Vec<usize>,
+}
+
+fn pointer_to_bytes<T>(ptr: &*const T) -> &[u8] {
+    unsafe {
+        ::std::slice::from_raw_parts(
+            ptr as *const *const T as *const u8,
+            ::std::mem::size_of::<*const T>(),
+        )
+    }
+}
+
+pub fn get_context() -> *const CallContext {
+    GET_CONTEXT()
+}
+
+impl TrampolineBufferBuilder {
+    pub fn new() -> TrampolineBufferBuilder {
+        TrampolineBufferBuilder {
+            code: vec![],
+            offsets: vec![],
+        }
+    }
+
+    pub fn add_function(
+        &mut self,
+        target: *const CallTarget,
+        context: *const CallContext,
+    ) -> usize {
+        let idx = self.offsets.len();
+        self.offsets.push(self.code.len());
+        self.code.extend_from_slice(&[
+            0x48, 0xb8, // movabsq ?, %rax
+        ]);
+        self.code.extend_from_slice(pointer_to_bytes(&context));
+        self.code.extend_from_slice(&[
+            0x48, 0x0f, 0x6e, 0xc0, // movq %rax, %mm0
+        ]);
+        self.code.extend_from_slice(&[
+            0x48, 0xb8, // movabsq ?, %rax
+        ]);
+        self.code.extend_from_slice(pointer_to_bytes(&target));
+        self.code.extend_from_slice(&[
+            0xff, 0xe0, // jmpq *%rax
+        ]);
+        idx
+    }
+
+    pub fn build(self) -> TrampolineBuffer {
+        get_context(); // ensure lazy initialization is completed
+
+        let mut code = CodeMemory::new(self.code.len());
+        code[..self.code.len()].copy_from_slice(&self.code);
+        code.make_executable();
+        TrampolineBuffer {
+            code,
+            offsets: self.offsets,
+        }
+    }
+}
+
+impl TrampolineBuffer {
+    pub fn get_trampoline(&self, idx: usize) -> *const Trampoline {
+        &self.code[self.offsets[idx]] as *const u8 as *const Trampoline
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_trampoline_call() {
+        struct TestContext {
+            value: i32,
+        }
+        extern "C" fn do_add(a: i32, b: f32) -> f32 {
+            let ctx = unsafe { &*(get_context() as *const TestContext) };
+            a as f32 + b + ctx.value as f32
+        }
+        let mut builder = TrampolineBufferBuilder::new();
+        let ctx = TestContext { value: 3 };
+        let idx = builder.add_function(
+            do_add as usize as *const _,
+            &ctx as *const TestContext as *const _,
+        );
+        let buf = builder.build();
+        let t = buf.get_trampoline(idx);
+        let ret =
+            unsafe { ::std::mem::transmute::<_, extern "C" fn(i32, f32) -> f32>(t)(1, 2.0) as i32 };
+        assert_eq!(ret, 6);
+    }
+}