various: add -Dbuild-static and alternatives to libc functions

When we try to build with -static, the linker refuses dlopen and
various functions related to nss. This commit adds the basic support
to compile with -static and allow the link to pass.

src/basic/dlfcn-util.c

@@ -101,6 +101,10 @@ void block_dlopen(void) {
 }
 
 int dlopen_safe(const char *filename, void **ret, const char **reterr_dlerror) {
+#if BUILD_STATIC
+        return log_debug_errno(SYNTHETIC_ERRNO(EOPNOTSUPP),
+                               "dlopen is not supported in static builds, cannot load %s.", filename);
+#else
         _cleanup_(dlclosep) void *dl = NULL;
         int r;
 
@@ -142,4 +146,5 @@ int dlopen_safe(const char *filename, void **ret, const char **reterr_dlerror) {
                 *ret = TAKE_PTR(dl);
 
         return 0;
+#endif
 }

src/basic/user-util.c

@@ -1171,6 +1171,9 @@ int lookup_pwent_in_files(
 
         return -ESRCH;
 }
+
+#if !BUILD_STATIC
+
 static size_t getpw_buffer_size(void) {
         long bufsize = sysconf(_SC_GETPW_R_SIZE_MAX);
         return bufsize <= 0 ? 4096U : (size_t) bufsize;
@@ -1182,15 +1185,25 @@ static bool errno_is_user_doesnt_exist(int error) {
         return IN_SET(abs(error), ENOENT, ESRCH, EBADF, EPERM);
 }
 
+#endif
+
 int getpwnam_malloc(const char *name, struct passwd **ret) {
+        /* For static builds use a very simplistic implementation that looks at 'passwd' in /etc/
+         * and /usr/lib/, and for non-static builds use NSS. The first matching entry wins. The
+         * same logic is implemented in getpwnam_malloc, getpwuid_malloc, getgrnam_malloc, and
+         * getgrgid_malloc. */
+
+        if (isempty(name))
+                return -EINVAL;
+
+#if BUILD_STATIC
+        return lookup_pwent_in_files(PASSWD_FILES, name, UID_INVALID, ret);
+#else
         size_t bufsize = getpw_buffer_size();
         int r;
 
         /* A wrapper around getpwnam_r() that allocates the necessary buffer on the heap. The caller must
-         * free() the returned structures! */
-
-        if (isempty(name))
-                return -EINVAL;
+         * free() the returned structure! */
 
         for (;;) {
                 _cleanup_free_ void *buf = NULL;
@@ -1226,15 +1239,19 @@ int getpwnam_malloc(const char *name, struct passwd **ret) {
                         return -ENOMEM;
                 bufsize *= 2;
         }
+#endif
 }
 
 int getpwuid_malloc(uid_t uid, struct passwd **ret) {
-        size_t bufsize = getpw_buffer_size();
-        int r;
-
         if (!uid_is_valid(uid))
                 return -EINVAL;
 
+#if BUILD_STATIC
+        return lookup_pwent_in_files(PASSWD_FILES, /* name= */ NULL, uid, ret);
+#else
+        size_t bufsize = getpw_buffer_size();
+        int r;
+
         for (;;) {
                 _cleanup_free_ void *buf = NULL;
 
@@ -1267,6 +1284,7 @@ int getpwuid_malloc(uid_t uid, struct passwd **ret) {
                         return -ENOMEM;
                 bufsize *= 2;
         }
+#endif
 }
 
 static int copy_struct_group(const struct group *gr, struct group **ret) {
@@ -1427,18 +1445,25 @@ ssize_t lookup_groups_in_files(
         return n_arr;
 }
 
+#if !BUILD_STATIC
+
 static size_t getgr_buffer_size(void) {
         long bufsize = sysconf(_SC_GETGR_R_SIZE_MAX);
         return bufsize <= 0 ? 4096U : (size_t) bufsize;
 }
 
-int getgrnam_malloc(const char *name, struct group **ret) {
-        size_t bufsize = getgr_buffer_size();
-        int r;
+#endif
 
+int getgrnam_malloc(const char *name, struct group **ret) {
         if (isempty(name))
                 return -EINVAL;
 
+#if BUILD_STATIC
+        return lookup_grent_in_files(GROUP_FILES, name, GID_INVALID, ret);
+#else
+        size_t bufsize = getgr_buffer_size();
+        int r;
+
         for (;;) {
                 _cleanup_free_ void *buf = NULL;
 
@@ -1471,15 +1496,19 @@ int getgrnam_malloc(const char *name, struct group **ret) {
                         return -ENOMEM;
                 bufsize *= 2;
         }
+#endif
 }
 
 int getgrgid_malloc(gid_t gid, struct group **ret) {
-        size_t bufsize = getgr_buffer_size();
-        int r;
-
         if (!gid_is_valid(gid))
                 return -EINVAL;
 
+#if BUILD_STATIC
+        return lookup_grent_in_files(GROUP_FILES, /* name= */ NULL, gid, ret);
+#else
+        size_t bufsize = getgr_buffer_size();
+        int r;
+
         for (;;) {
                 _cleanup_free_ void *buf = NULL;
 
@@ -1512,4 +1541,5 @@ int getgrgid_malloc(gid_t gid, struct group **ret) {
                         return -ENOMEM;
                 bufsize *= 2;
         }
+#endif
 }

src/basic/user-util.h

@@ -159,6 +159,10 @@ static inline bool hashed_password_is_locked_or_invalid(const char *password) {
         return password && password[0] != '$';
 }
 
+/* Places where we will try to load account data from */
+#define PASSWD_FILES STRV_MAKE("/etc/passwd", "/usr/lib/passwd")
+#define GROUP_FILES STRV_MAKE("/etc/group", "/usr/lib/group")
+
 /* A locked *and* invalid password for "struct spwd"'s .sp_pwdp and "struct passwd"'s .pw_passwd field */
 #define PASSWORD_LOCKED_AND_INVALID "!*"