Add implementation of memfd_create

Makefile

@@ -109,6 +109,7 @@ LIBC_TOP_HALF_MUSL_SOURCES = \
 	misc/realpath.c \
         misc/syslog.c \
         mman/shm_open.c \
+        mman/memfd_create.c \
         errno/strerror.c \
         \
         network/services.c \

Makefile-eh

@@ -117,6 +117,7 @@ LIBC_TOP_HALF_MUSL_SOURCES = \
 	misc/realpath.c \
         misc/syslog.c \
         mman/shm_open.c \
+        mman/memfd_create.c \
         errno/strerror.c \
         \
         network/services.c \

expected/wasm32-wasi-eh/defined-symbols.txt

@@ -1203,6 +1203,7 @@ memccpy
 memchr
 memcmp
 memcpy
+memfd_create
 memmem
 memmove
 mempcpy

expected/wasm32-wasi-ehpic/defined-symbols.txt

@@ -1211,6 +1211,7 @@ memccpy
 memchr
 memcmp
 memcpy
+memfd_create
 memmem
 memmove
 mempcpy

expected/wasm32-wasi-threads/defined-symbols.txt

@@ -1133,6 +1133,7 @@ memccpy
 memchr
 memcmp
 memcpy
+memfd_create
 memmem
 memmove
 mempcpy

expected/wasm32-wasi/defined-symbols.txt

@@ -1209,6 +1209,7 @@ memccpy
 memchr
 memcmp
 memcpy
+memfd_create
 memmem
 memmove
 mempcpy

expected/wasm64-wasi/defined-symbols.txt

@@ -1167,6 +1167,7 @@ memccpy
 memchr
 memcmp
 memcpy
+memfd_create
 memmem
 memmove
 mempcpy

libc-top-half/musl/src/mman/memfd_create.c

@@ -0,0 +1,93 @@
+#define _GNU_SOURCE
+
+#include <ctype.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <unistd.h>
+
+#define MEMFD_NAME_MAX 249
+
+static int create_unlinked_temp(char *template_path, unsigned int flags) {
+  int fd;
+  if (flags & MFD_CLOEXEC) {
+    fd = mkostemp(template_path, O_CLOEXEC);
+  } else {
+    fd = mkstemp(template_path);
+  }
+  if (fd < 0)
+    return -1;
+
+  if (unlink(template_path) != 0) {
+    int saved_errno = errno;
+    close(fd);
+    errno = saved_errno;
+    return -1;
+  }
+
+  return fd;
+}
+
+// Returns the number of characters copied, excluding any null terminator.
+// If the returned length == dst_len, src contained at least dst_len
+// non-null characters and dst is not null-terminated (no room for a terminator).
+static int sanitize_name(char *dst, size_t dst_len, const char *src) {
+  size_t i = 0;
+
+  while (i < dst_len && src[i] != '\0') {
+    unsigned char c = (unsigned char)src[i];
+    if (isalnum(c) || c == '_' || c == '-' || c == '.') {
+      dst[i] = (char)c;
+    } else {
+      dst[i] = '_';
+    }
+    i++;
+  }
+
+  return i;
+}
+
+int memfd_create(const char *name, unsigned int flags) {
+  if (flags & ~(MFD_CLOEXEC | MFD_ALLOW_SEALING | MFD_HUGETLB)) {
+    errno = EINVAL;
+    return -1;
+  }
+
+  if (flags & (MFD_HUGETLB | MFD_ALLOW_SEALING)) {
+    /* Seals are not currently supported by the WASIX fcntl subset. */
+    /* hugetlbfs is not currently supported by the WASIX filesystem subset. */
+    errno = ENOTSUP;
+    return -1;
+  }
+
+  if (name == NULL) {
+    errno = EFAULT;
+    return -1;
+  }
+
+  // Construct a string like "/tmp/.memfd-<name>-XXXXXX"
+  char tmp_template[sizeof("/tmp/.memfd-") - 1 + MEMFD_NAME_MAX +
+                    sizeof("-XXXXXX") - 1 + 1];
+  memcpy(tmp_template, "/tmp/.memfd-", sizeof("/tmp/.memfd-") - 1);
+  int name_len = sanitize_name(tmp_template + sizeof("/tmp/.memfd-") - 1,
+                               MEMFD_NAME_MAX + 1, name);
+  if (name_len > MEMFD_NAME_MAX) {
+    errno = EINVAL;
+    return -1;
+  }
+  memcpy(tmp_template + sizeof("/tmp/.memfd-") - 1 + name_len, "-XXXXXX",
+         sizeof("-XXXXXX"));
+
+  int fd = create_unlinked_temp(tmp_template, flags);
+  if (fd >= 0)
+    return fd;
+
+  // If that failed, try ".memfd-<name>-XXXXXX" in the current working
+  // directory. Restore the -XXXXXX placeholder because it got overwritten by
+  // the previous call to mkstemp.
+  memcpy(tmp_template + sizeof("/tmp/.memfd-") - 1 + name_len, "-XXXXXX",
+         sizeof("-XXXXXX"));
+  return create_unlinked_temp(tmp_template + sizeof("/tmp/") - 1, flags);
+}