add execvp

lib/emscripten/emtests/test_execvp.c

@@ -0,0 +1,17 @@
+#include <stdio.h>
+#include <unistd.h>
+
+int main() {
+    char command[] = "touch";
+    char arg1[] = "foo.txt";
+    char* argv[3];
+    argv[0] = command;
+    argv[1] = arg1;
+    argv[2] = 0;
+
+    printf("_execvp\n");
+    int result = execvp(command, argv);
+    // should not return, and not print this message
+    printf("error");
+    return 0;
+}

lib/emscripten/emtests/test_execvp.out

@@ -0,0 +1 @@
+_execvp

lib/emscripten/emtests/test_execvp_windows.c

@@ -0,0 +1,18 @@
+#include <stdio.h>
+#include <unistd.h>
+
+int main() {
+    char command[] = "C:\\Windows\\System32\\cmd.exe";
+    char arg1[] = "echo";
+    char arg2[] = "foo";
+    char* argv[4];
+    argv[0] = command;
+    argv[1] = arg1;
+    argv[2] = arg2;
+    argv[3] = 0;
+    printf("_execvp\n");
+    int result = execvp(command, argv);
+    // should not return, and not print this message
+    printf("error");
+    return 0;
+}

lib/emscripten/src/exec.rs

@@ -0,0 +1,40 @@
+use libc::execvp;
+use std::cell::Cell;
+use std::ffi::CString;
+use wasmer_runtime_core::vm::Ctx;
+
+pub fn _execvp(ctx: &mut Ctx, command_name_offset: u32, argv_offset: u32) -> i32 {
+    // a single reference to re-use
+    let emscripten_memory = ctx.memory(0);
+
+    // read command name as string
+    let command_name_string_vec: Vec<u8> = emscripten_memory.view()
+        [(command_name_offset as usize)..]
+        .iter()
+        .map(|cell| cell.get())
+        .take_while(|&byte| byte != 0)
+        .collect();
+    let command_name_string = CString::new(command_name_string_vec).unwrap();
+
+    // get the array of args
+    let mut argv: Vec<*const i8> = emscripten_memory.view()[((argv_offset / 4) as usize)..]
+        .iter()
+        .map(|cell: &Cell<u32>| cell.get())
+        .take_while(|&byte| byte != 0)
+        .map(|offset| {
+            let p: *const i8 = (emscripten_memory.view::<u8>()[(offset as usize)..])
+                .iter()
+                .map(|cell| cell.as_ptr() as *const i8)
+                .collect::<Vec<*const i8>>()[0];
+            p
+        })
+        .collect();
+
+    // push a nullptr on to the end of the args array
+    argv.push(std::ptr::null());
+
+    // construct raw pointers and hand them to `execvp`
+    let command_pointer = command_name_string.as_ptr() as *const i8;
+    let args_pointer = argv.as_ptr();
+    unsafe { execvp(command_pointer, args_pointer) }
+}

lib/emscripten/src/lib.rs

@@ -31,6 +31,7 @@ mod emscripten_target;
 mod env;
 mod errno;
 mod exception;
+mod exec;
 mod io;
 mod jmp;
 mod linking;
@@ -439,6 +440,9 @@ pub fn generate_emscripten_env(globals: &mut EmscriptenGlobals) -> ImportObject
             "___unlock" => func!(crate::lock::___unlock),
             "___wait" => func!(crate::lock::___wait),
 
+            // exec
+            "_execvp" => func!(crate::exec::_execvp),
+
             // Env
             "___assert_fail" => func!(crate::env::___assert_fail),
             "_getenv" => func!(crate::env::_getenv),

lib/emscripten/tests/emtests/mod.rs

@@ -43,6 +43,7 @@ mod test_exceptions_2;
 mod test_exceptions_multi;
 mod test_exceptions_std;
 mod test_exceptions_white_list;
+mod test_execvp;
 mod test_fast_math;
 mod test_flexarray_struct;
 mod test_float32_precise;

lib/emscripten/tests/emtests/test_execvp.rs

@@ -0,0 +1,17 @@
+#[test]
+fn test_execvp() {
+    #[cfg(not(target_os = "windows"))]
+    assert_emscripten_output!(
+        "../../emtests/test_execvp.wasm",
+        "test_execvp",
+        vec![],
+        "../../emtests/test_execvp.out"
+    );
+    #[cfg(target_os = "windows")]
+    assert_emscripten_output!(
+        "../../emtests/test_execvp_windows.wasm",
+        "test_execvp",
+        vec![],
+        "../../emtests/test_execvp.out"
+    );
+}