Kernel: Use the Syscall string and buffer types more

While I was updating syscalls to stop passing null-terminated strings,
I added some helpful struct types:

    - StringArgument { const char*; size_t; }
    - ImmutableBuffer<Data, Size> { const Data*; Size; }
    - MutableBuffer<Data, Size> { Data*; Size; }

The Process class has some convenience functions for validating and
optionally extracting the contents from these structs:

    - get_syscall_path_argument(StringArgument)
    - validate_and_copy_string_from_user(StringArgument)
    - validate(ImmutableBuffer)
    - validate(MutableBuffer)

There's still so much code around this and I'm wondering if we should
generate most of it instead. Possible nice little project.

Libraries/LibC/fcntl.cpp

@@ -33,22 +33,30 @@ int creat_with_path_length(const char* path, size_t path_length, mode_t mode)
 
 int open_with_path_length(const char* path, size_t path_length, int options, mode_t mode)
 {
+    if (!path) {
+        errno = EFAULT;
+        return -1;
+    }
     if (path_length > INT32_MAX) {
         errno = EINVAL;
         return -1;
     }
-    Syscall::SC_open_params params { path, (int)path_length, options, mode };
+    Syscall::SC_open_params params { { path, path_length }, options, mode };
     int rc = syscall(SC_open, &params);
     __RETURN_WITH_ERRNO(rc, rc, -1);
 }
 
 int openat_with_path_length(int dirfd, const char* path, size_t path_length, int options, mode_t mode)
 {
+    if (!path) {
+        errno = EFAULT;
+        return -1;
+    }
     if (path_length > INT32_MAX) {
         errno = EINVAL;
         return -1;
     }
-    Syscall::SC_openat_params params { dirfd, path, (int)path_length, options, mode };
+    Syscall::SC_openat_params params { dirfd, { path, path_length }, options, mode };
     int rc = syscall(SC_openat, &params);
     __RETURN_WITH_ERRNO(rc, rc, -1);
 }

Libraries/LibC/mman.cpp

@@ -13,7 +13,7 @@ void* mmap(void* addr, size_t size, int prot, int flags, int fd, off_t offset)
 
 void* mmap_with_name(void* addr, size_t size, int prot, int flags, int fd, off_t offset, const char* name)
 {
-    Syscall::SC_mmap_params params { (u32)addr, size, prot, flags, fd, offset, name, name ? strlen(name) : 0 };
+    Syscall::SC_mmap_params params { (u32)addr, size, prot, flags, fd, offset, { name, name ? strlen(name) : 0 } };
     int rc = syscall(SC_mmap, &params);
     if (rc < 0 && -rc < EMAXERRNO) {
         errno = -rc;
@@ -40,7 +40,7 @@ int set_mmap_name(void* addr, size_t size, const char* name)
         errno = EFAULT;
         return -1;
     }
-    Syscall::SC_set_mmap_name_params params { addr, size, name, strlen(name) };
+    Syscall::SC_set_mmap_name_params params { addr, size, { name, strlen(name) } };
     int rc = syscall(SC_set_mmap_name, &params);
     __RETURN_WITH_ERRNO(rc, rc, -1);
 }

Libraries/LibC/stdlib.cpp

@@ -711,7 +711,7 @@ char* realpath(const char* pathname, char* buffer)
     size_t size = PATH_MAX;
     if (buffer == nullptr)
         buffer = (char*)malloc(size);
-    Syscall::SC_realpath_params params { pathname, strlen(pathname), buffer, size };
+    Syscall::SC_realpath_params params { { pathname, strlen(pathname) }, { buffer, size } };
     int rc = syscall(SC_realpath, &params);
     if (rc < 0) {
         errno = -rc;

Libraries/LibC/sys/socket.cpp

@@ -38,7 +38,7 @@ int connect(int sockfd, const sockaddr* addr, socklen_t addrlen)
 
 ssize_t sendto(int sockfd, const void* data, size_t data_length, int flags, const struct sockaddr* addr, socklen_t addr_length)
 {
-    Syscall::SC_sendto_params params { sockfd, data, data_length, flags, addr, addr_length };
+    Syscall::SC_sendto_params params { sockfd, { data, data_length }, flags, addr, addr_length };
     int rc = syscall(SC_sendto, &params);
     __RETURN_WITH_ERRNO(rc, rc, -1);
 }
@@ -50,7 +50,7 @@ ssize_t send(int sockfd, const void* data, size_t data_length, int flags)
 
 ssize_t recvfrom(int sockfd, void* buffer, size_t buffer_length, int flags, struct sockaddr* addr, socklen_t* addr_length)
 {
-    Syscall::SC_recvfrom_params params { sockfd, buffer, buffer_length, flags, addr, addr_length };
+    Syscall::SC_recvfrom_params params { sockfd, { buffer, buffer_length }, flags, addr, addr_length };
     int rc = syscall(SC_recvfrom, &params);
     __RETURN_WITH_ERRNO(rc, rc, -1);
 }

Libraries/LibPthread/pthread.cpp

@@ -539,11 +539,19 @@ int pthread_setspecific(pthread_key_t key, const void* value)
 }
 int pthread_setname_np(pthread_t thread, const char* buffer, int buffer_size)
 {
+    if (buffer_size < 0) {
+        errno = EINVAL;
+        return -1;
+    }
     return syscall(SC_set_thread_name, thread, buffer, buffer_size);
 }
 
 int pthread_getname_np(pthread_t thread, char* buffer, int buffer_size)
 {
+    if (buffer_size < 0) {
+        errno = EINVAL;
+        return -1;
+    }
     return syscall(SC_get_thread_name, thread, buffer, buffer_size);
 }