[wasm2c] Add rot13 example (#1384)

This example demonstrates how to use imported functions. The `rot13`
program takes each command line argument, and rot13-encodes it.

The exported `rot13` function has no arguments, and instead calls back
into the program (via `fill_buf`) with a buffer to fill in. When the
function finishes it calls `buf_done`.

(rot13.wat is the same as in src/test-interp.cc.)

12 files changed, 185 insertions, 55 deletions

diff --git a/src/prebuilt/wasm2c.include.c b/src/prebuilt/wasm2c.include.c
index b14cc435..d7b1df23 100644
--- a/src/prebuilt/wasm2c.include.c
+++ b/src/prebuilt/wasm2c.include.c
@@ -1,5 +1,6 @@
 /* Generated from 'wasm2c.c.tmpl' by wasm2c_tmpl.py, do not edit! */
 const char SECTION_NAME(includes)[] =
+"/* Automically generated by wasm2c */\n"
 "#include <math.h>\n"
 "#include <string.h>\n"
 ;
diff --git a/src/prebuilt/wasm2c.include.h b/src/prebuilt/wasm2c.include.h
index 23319cde..4ba24751 100644
--- a/src/prebuilt/wasm2c.include.h
+++ b/src/prebuilt/wasm2c.include.h
@@ -1,5 +1,6 @@
 /* Generated from 'wasm2c.h.tmpl' by wasm2c_tmpl.py, do not edit! */
 const char SECTION_NAME(top)[] =
+"/* Automically generated by wasm2c */\n"
 "#ifdef __cplusplus\n"
 "extern \"C\" {\n"
 "#endif\n"
diff --git a/src/wasm2c.c.tmpl b/src/wasm2c.c.tmpl
index 2d188c77..4465cf9a 100644
--- a/src/wasm2c.c.tmpl
+++ b/src/wasm2c.c.tmpl
@@ -1,4 +1,5 @@
 %%includes
+/* Automically generated by wasm2c */
 #include <math.h>
 #include <string.h>
 %%declarations
diff --git a/src/wasm2c.h.tmpl b/src/wasm2c.h.tmpl
index ac51cde9..8478d81b 100644
--- a/src/wasm2c.h.tmpl
+++ b/src/wasm2c.h.tmpl
@@ -1,4 +1,5 @@
 %%top
+/* Automically generated by wasm2c */
 #ifdef __cplusplus
 extern "C" {
 #endif
diff --git a/src/wasm2c_tmpl.py b/src/wasm2c_tmpl.py
index af3b953e..0da117a8 100755
--- a/src/wasm2c_tmpl.py
+++ b/src/wasm2c_tmpl.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 #
 # Copyright 2018 WebAssembly Community Group participants
 #
diff --git a/wasm2c/.gitignore b/wasm2c/.gitignore
new file mode 100644
index 00000000..47ea610d
--- /dev/null
+++ b/wasm2c/.gitignore
@@ -0,0 +1,10 @@
+wasm-rt-impl.o
+examples/fac/main.o
+examples/fac/fac
+examples/fac/fac.o
+examples/rot13/main.o
+examples/rot13/rot13
+examples/rot13/rot13.c
+examples/rot13/rot13.h
+examples/rot13/rot13.o
+examples/rot13/rot13.wasm
diff --git a/wasm2c/examples/fac/Makefile b/wasm2c/examples/fac/Makefile
new file mode 100644
index 00000000..f5b2a338
--- /dev/null
+++ b/wasm2c/examples/fac/Makefile
@@ -0,0 +1,9 @@
+# Use implicit rules for compiling C files.
+CFLAGS=-I../..
+fac: main.o fac.o ../../wasm-rt-impl.o
+
+fac.wasm: fac.wat
+	../../../bin/wat2wasm $< -o $@
+
+fac.c: fac.wasm
+	../../../bin/wasm2c $< -o $@
diff --git a/wasm2c/examples/fac/fac.c b/wasm2c/examples/fac/fac.c
index a954c363..acd8ed91 100644
--- a/wasm2c/examples/fac/fac.c
+++ b/wasm2c/examples/fac/fac.c
@@ -1,6 +1,5 @@
-#include <assert.h>
+/* Automically generated by wasm2c */
 #include <math.h>
-#include <stdlib.h>
 #include <string.h>
 
 #include "fac.h"
diff --git a/wasm2c/examples/fac/fac.h b/wasm2c/examples/fac/fac.h
index 0a58ef42..5e78f33b 100644
--- a/wasm2c/examples/fac/fac.h
+++ b/wasm2c/examples/fac/fac.h
@@ -1,17 +1,13 @@
 #ifndef FAC_H_GENERATED_
 #define FAC_H_GENERATED_
+/* Automically generated by wasm2c */
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-#ifndef WASM_RT_INCLUDED_
-#define WASM_RT_INCLUDED_
-
 #include <stdint.h>
 
-#ifndef WASM_RT_MAX_CALL_STACK_DEPTH
-#define WASM_RT_MAX_CALL_STACK_DEPTH 500
-#endif
+#include "wasm-rt.h"
 
 #ifndef WASM_RT_MODULE_PREFIX
 #define WASM_RT_MODULE_PREFIX
@@ -33,52 +29,6 @@ typedef int64_t s64;
 typedef float f32;
 typedef double f64;
 
-typedef enum {
-  WASM_RT_TRAP_NONE,
-  WASM_RT_TRAP_OOB,
-  WASM_RT_TRAP_INT_OVERFLOW,
-  WASM_RT_TRAP_DIV_BY_ZERO,
-  WASM_RT_TRAP_INVALID_CONVERSION,
-  WASM_RT_TRAP_UNREACHABLE,
-  WASM_RT_TRAP_CALL_INDIRECT,
-  WASM_RT_TRAP_EXHAUSTION,
-} wasm_rt_trap_t;
-
-typedef enum {
-  WASM_RT_I32,
-  WASM_RT_I64,
-  WASM_RT_F32,
-  WASM_RT_F64,
-} wasm_rt_type_t;
-
-typedef void (*wasm_rt_anyfunc_t)(void);
-
-typedef struct {
-  uint32_t func_type;
-  wasm_rt_anyfunc_t func;
-} wasm_rt_elem_t;
-
-typedef struct {
-  uint8_t* data;
-  uint32_t pages, max_pages;
-  uint32_t size;
-} wasm_rt_memory_t;
-
-typedef struct {
-  wasm_rt_elem_t* data;
-  uint32_t max_size;
-  uint32_t size;
-} wasm_rt_table_t;
-
-extern void wasm_rt_trap(wasm_rt_trap_t) __attribute__((noreturn));
-extern uint32_t wasm_rt_register_func_type(uint32_t params, uint32_t results, ...);
-extern void wasm_rt_allocate_memory(wasm_rt_memory_t*, uint32_t initial_pages, uint32_t max_pages);
-extern uint32_t wasm_rt_grow_memory(wasm_rt_memory_t*, uint32_t pages);
-extern void wasm_rt_allocate_table(wasm_rt_table_t*, uint32_t elements, uint32_t max_elements);
-extern uint32_t wasm_rt_call_stack_depth;
-
-#endif  /* WASM_RT_INCLUDED_ */
-
 extern void WASM_RT_ADD_PREFIX(init)(void);
 
 /* export: 'fac' */
diff --git a/wasm2c/examples/rot13/Makefile b/wasm2c/examples/rot13/Makefile
new file mode 100644
index 00000000..35483310
--- /dev/null
+++ b/wasm2c/examples/rot13/Makefile
@@ -0,0 +1,9 @@
+# Use implicit rules for compiling C files.
+CFLAGS=-I../..
+rot13: main.o rot13.o ../../wasm-rt-impl.o
+
+rot13.wasm: rot13.wat
+	../../../bin/wat2wasm $< -o $@
+
+rot13.c: rot13.wasm
+	../../../bin/wasm2c $< -o $@
diff --git a/wasm2c/examples/rot13/main.c b/wasm2c/examples/rot13/main.c
new file mode 100644
index 00000000..f99ee014
--- /dev/null
+++ b/wasm2c/examples/rot13/main.c
@@ -0,0 +1,93 @@
+/* Entry point for the rot13 example.
+ *
+ * This example shows how you can fulfill wasm module imports in your C
+ * program, and access linear memory.
+ *
+ * The program reads arguments from the command line, and [rot13] encodes them,
+ * e.g.:
+ *
+ * ```
+ * $ rot13 foo bar
+ * foo -> sbb
+ * bar -> one
+ * ```
+ *
+ * [rot13]: https://en.wikipedia.org/wiki/ROT13
+ */
+#include <stdio.h>
+#include <stdlib.h>
+
+/* Uncomment this to define rot13_init rot13_Z_rot13Z_vv instead. */
+/* #define WASM_RT_MODULE_PREFIX rot13_ */
+
+#include "rot13.h"
+
+/* Define the imports as declared in rot13.h. */
+wasm_rt_memory_t (*Z_hostZ_mem);
+u32 (*Z_hostZ_fill_bufZ_iii)(u32, u32);
+void (*Z_hostZ_buf_doneZ_vii)(u32, u32);
+
+/* Define the implementations of the imports. */
+static wasm_rt_memory_t s_memory;
+static u32 fill_buf(u32 ptr, u32 size);
+static void buf_done(u32 ptr, u32 size);
+
+/* The string that is currently being processed. This needs to be static
+ * because the buffer is filled in the callback. */
+static const char* s_input;
+
+int main(int argc, char** argv) {
+  /* Initialize the rot13 module. Since we didn't define WASM_RT_MODULE_PREFIX,
+  the initialization function is called `init`. */
+  init();
+
+  /* Allocate 1 page of wasm memory (64KiB). */
+  wasm_rt_allocate_memory(&s_memory, 1, 1);
+
+  /* Provide the imports expected by the module: "host.mem", "host.fill_buf"
+   * and "host.buf_done". Their mangled names are `Z_hostZ_mem`,
+   * `Z_hostZ_fill_bufZ_iii` and `Z_hostZ_buf_doneZ_vii`. */
+  Z_hostZ_mem = &s_memory;
+  Z_hostZ_fill_bufZ_iii = &fill_buf;
+  Z_hostZ_buf_doneZ_vii = &buf_done;
+
+  /* Call `rot13` on each argument, using the mangled name. */
+  while (argc > 1) {
+    /* Move to next arg. Do this first, so the program name is skipped. */
+    argc--; argv++;
+
+    s_input = argv[0];
+    Z_rot13Z_vv();
+  }
+  return 0;
+}
+
+/* Fill the wasm buffer with the input to be rot13'd.
+ *
+ * params:
+ *   ptr: The wasm memory address of the buffer to fill data.
+ *   size: The size of the buffer in wasm memory.
+ * result:
+ *   The number of bytes filled into the buffer. (Must be <= size).
+ */
+u32 fill_buf(u32 ptr, u32 size) {
+  for (size_t i = 0; i < size; ++i) {
+    if (s_input[i] == 0) {
+      return i;
+    }
+    s_memory.data[ptr + i] = s_input[i];
+  }
+  return size;
+}
+
+/* Called when the wasm buffer has been rot13'd.
+ *
+ * params:
+ *   ptr: The wasm memory address of the buffer.
+ *   size: The size of the buffer in wasm memory.
+ */
+void buf_done(u32 ptr, u32 size) {
+  /* The output buffer is not necessarily null-terminated, so use the %*.s
+   * printf format to limit the number of characters printed. */
+  printf("%s -> %.*s\n", s_input, (int)size, &s_memory.data[ptr]);
+}
diff --git a/wasm2c/examples/rot13/rot13.wat b/wasm2c/examples/rot13/rot13.wat
new file mode 100644
index 00000000..0a33d80e
--- /dev/null
+++ b/wasm2c/examples/rot13/rot13.wat
@@ -0,0 +1,56 @@
+(import "host" "mem" (memory $mem 1))
+(import "host" "fill_buf" (func $fill_buf (param i32 i32) (result i32)))
+(import "host" "buf_done" (func $buf_done (param i32 i32)))
+
+(func $rot13c (param $c i32) (result i32)
+  (local $uc i32)
+
+  ;; No change if < 'A'.
+  (if (i32.lt_u (get_local $c) (i32.const 65))
+    (return (get_local $c)))
+
+  ;; Clear 5th bit of c, to force uppercase. 0xdf = 0b11011111
+  (set_local $uc (i32.and (get_local $c) (i32.const 0xdf)))
+
+  ;; In range ['A', 'M'] return |c| + 13.
+  (if (i32.le_u (get_local $uc) (i32.const 77))
+    (return (i32.add (get_local $c) (i32.const 13))))
+
+  ;; In range ['N', 'Z'] return |c| - 13.
+  (if (i32.le_u (get_local $uc) (i32.const 90))
+    (return (i32.sub (get_local $c) (i32.const 13))))
+
+  ;; No change for everything else.
+  (return (get_local $c))
+)
+
+(func (export "rot13")
+  (local $size i32)
+  (local $i i32)
+
+  ;; Ask host to fill memory [0, 1024) with data.
+  (call $fill_buf (i32.const 0) (i32.const 1024))
+
+  ;; The host returns the size filled.
+  (set_local $size)
+
+  ;; Loop over all bytes and rot13 them.
+  (block $exit
+    (loop $top
+      ;; if (i >= size) break
+      (if (i32.ge_u (get_local $i) (get_local $size)) (br $exit))
+
+      ;; mem[i] = rot13c(mem[i])
+      (i32.store8
+        (get_local $i)
+        (call $rot13c
+          (i32.load8_u (get_local $i))))
+
+      ;; i++
+      (set_local $i (i32.add (get_local $i) (i32.const 1)))
+      (br $top)
+    )
+  )
+
+  (call $buf_done (i32.const 0) (get_local $size))
+)