Add system calls for describing preopened directory handles.

Author: sunfishcode

expected/wasm32-wasi/predefined-macros.txt

@@ -3523,6 +3523,7 @@
 #define __WASI_O_DIRECTORY (UINT16_C(0x0002))
 #define __WASI_O_EXCL (UINT16_C(0x0004))
 #define __WASI_O_TRUNC (UINT16_C(0x0008))
+#define __WASI_PREOPENTYPE_DIR (UINT8_C(0))
 #define __WASI_RIGHT_FD_ADVISE (UINT64_C(0x0000000000000080))
 #define __WASI_RIGHT_FD_ALLOCATE (UINT64_C(0x0000000000000100))
 #define __WASI_RIGHT_FD_DATASYNC (UINT64_C(0x0000000000000001))

expected/wasm32-wasi/undefined-symbols.txt

@@ -39,6 +39,8 @@ __wasi_fd_filestat_get
 __wasi_fd_filestat_set_size
 __wasi_fd_filestat_set_times
 __wasi_fd_pread
+__wasi_fd_prestat_dir_name
+__wasi_fd_prestat_get
 __wasi_fd_pwrite
 __wasi_fd_read
 __wasi_fd_readdir

libc-bottom-half/crt/crt1.c

@@ -1,6 +1,7 @@
 #include <stdlib.h>
 #include <sysexits.h>
 #include <wasi/core.h>
+#include <wasi/libc.h>
 
 extern char **__environ;
 extern void __wasm_call_ctors(void);
@@ -64,7 +65,53 @@ static __wasi_errno_t populate_environ(void) {
     return __wasi_environ_get(__environ, environ_buf);
 }
 
+static __wasi_errno_t populate_libpreopen(void) {
+    __wasilibc_init_preopen();
+
+    // Skip stdin, stdout, and stderr, and count up until we reach an invalid
+    // file descriptor.
+    for (__wasi_fd_t fd = 3; fd != 0; ++fd) {
+        __wasi_prestat_t prestat;
+        __wasi_errno_t ret = __wasi_fd_prestat_get(fd, &prestat);
+        if (ret == __WASI_EBADF)
+            break;
+        if (ret != __WASI_ESUCCESS)
+            return ret;
+        switch (prestat.pr_type) {
+        case __WASI_PREOPENTYPE_DIR: {
+            char *path = malloc(prestat.u.dir.pr_name_len + 1);
+            if (path == NULL)
+                return __WASI_ENOMEM;
+
+            ret = __wasi_fd_prestat_dir_name(fd, path, prestat.u.dir.pr_name_len);
+            if (ret != __WASI_ESUCCESS) {
+                free(path);
+                return ret;
+            }
+            path[prestat.u.dir.pr_name_len] = '\0';
+
+            if (__wasilibc_register_preopened_fd(fd, path) != 0) {
+                free(path);
+                return __WASI_ENOMEM;
+            }
+
+            free(path);
+            break;
+        }
+        default:
+            break;
+        }
+    }
+
+    return __WASI_ESUCCESS;
+}
+
 void _start(void) {
+    /* Record the preopened resources. */
+    if (populate_libpreopen() != __WASI_ESUCCESS) {
+        _Exit(EX_OSERR);
+    }
+
     /* Fill in the environment from WASI syscalls. */
     if (populate_environ() != __WASI_ESUCCESS) {
         _Exit(EX_OSERR);

libc-bottom-half/headers/public/wasi/core.h

@@ -270,6 +270,9 @@ typedef uint8_t __wasi_whence_t;
 #define __WASI_WHENCE_END (UINT8_C(1))
 #define __WASI_WHENCE_SET (UINT8_C(2))
 
+typedef uint8_t __wasi_preopentype_t;
+#define __WASI_PREOPENTYPE_DIR              (UINT8_C(0))
+
 typedef struct __wasi_dirent_t {
     __wasi_dircookie_t d_next;
     __wasi_inode_t d_ino;
@@ -304,6 +307,28 @@ _Static_assert(
 _Static_assert(sizeof(__wasi_event_t) == 32, "non-wasi data layout");
 _Static_assert(_Alignof(__wasi_event_t) == 8, "non-wasi data layout");
 
+typedef struct __wasi_prestat_t {
+    __wasi_preopentype_t pr_type;
+    union __wasi_prestat_u {
+        struct __wasi_prestat_u_dir_t {
+            size_t pr_name_len;
+        } dir;
+    } u;
+} __wasi_prestat_t;
+_Static_assert(offsetof(__wasi_prestat_t, pr_type) == 0, "non-wasi data layout");
+_Static_assert(sizeof(void *) != 4 ||
+    offsetof(__wasi_prestat_t, u.dir.pr_name_len) == 4, "non-wasi data layout");
+_Static_assert(sizeof(void *) != 8 ||
+    offsetof(__wasi_prestat_t, u.dir.pr_name_len) == 8, "non-wasi data layout");
+_Static_assert(sizeof(void *) != 4 ||
+    sizeof(__wasi_prestat_t) == 8, "non-wasi data layout");
+_Static_assert(sizeof(void *) != 8 ||
+    sizeof(__wasi_prestat_t) == 16, "non-wasi data layout");
+_Static_assert(sizeof(void *) != 4 ||
+    _Alignof(__wasi_prestat_t) == 4, "non-wasi data layout");
+_Static_assert(sizeof(void *) != 8 ||
+    _Alignof(__wasi_prestat_t) == 8, "non-wasi data layout");
+
 typedef struct __wasi_fdstat_t {
     __wasi_filetype_t fs_filetype;
     __wasi_fdflags_t fs_flags;
@@ -457,6 +482,17 @@ __wasi_errno_t __wasi_environ_sizes_get(
     size_t *environ_buf_size
 ) __WASI_SYSCALL_NAME(environ_sizes_get) __attribute__((__warn_unused_result__));
 
+__wasi_errno_t __wasi_fd_prestat_get(
+    __wasi_fd_t fd,
+    __wasi_prestat_t *buf
+) __WASI_SYSCALL_NAME(fd_prestat_get) __attribute__((__warn_unused_result__));
+
+__wasi_errno_t __wasi_fd_prestat_dir_name(
+    __wasi_fd_t fd,
+    char *path,
+    size_t path_len
+) __WASI_SYSCALL_NAME(fd_prestat_dir_name) __attribute__((__warn_unused_result__));
+
 __wasi_errno_t __wasi_fd_close(
     __wasi_fd_t fd
 ) __WASI_SYSCALL_NAME(fd_close) __attribute__((__warn_unused_result__));

libc-bottom-half/headers/public/wasi/libc.h

@@ -5,6 +5,7 @@
 extern "C" {
 #endif
 
+void __wasilibc_init_preopen(void);
 int __wasilibc_register_preopened_fd(int fd, const char *path);
 int __wasilibc_fd_renumber(int fd, int newfd);
 int __wasilibc_rmfileat(int fd, const char *path);

libc-top-half/musl/src/stdio/fopen.c

@@ -28,11 +28,11 @@ FILE *fopen(const char *restrict filename, const char *restrict mode)
 	fd = open(filename, flags, 0666);
 #endif
 	if (fd < 0) return 0;
-	if (flags & O_CLOEXEC)
 #ifdef __wasilibc_unmodified_upstream
+	if (flags & O_CLOEXEC)
 		__syscall(SYS_fcntl, fd, F_SETFD, FD_CLOEXEC);
 #else
-		/* Avoid __syscall, but also, FD_CLOEXEC is not supported in WASI. */
+	/* Avoid __syscall, but also, FD_CLOEXEC is not supported in WASI. */
 #endif
 
 	f = __fdopen(fd, mode);