lib/commonio.h: Use [[gnu::copy()]] and typeof() for function pointers compatible with libc

lib/attr.h

@@ -10,27 +10,49 @@
 #endif
 
 
-#if (__GNUC__ >= 10)
-# define MAYBE_UNUSED                [[gnu::unused]]
-# define NORETURN                    [[gnu::__noreturn__]]
-# define format_attr(type, fmt, va)  [[gnu::format(type, fmt, va)]]
-# define ATTR_ACCESS(...)            [[gnu::access(__VA_ARGS__)]]
-# define ATTR_ALLOC_SIZE(...)        [[gnu::alloc_size(__VA_ARGS__)]]
+#if __has_c_attribute(maybe_unused)
+# define MAYBE_UNUSED                [[maybe_unused]]
 #else
 # define MAYBE_UNUSED
+#endif
+
+#if __has_c_attribute(noreturn)
+# define NORETURN                    [[noreturn]]
+#else
 # define NORETURN
+#endif
+
+#if __has_c_attribute(gnu::format)
+# define format_attr(type, fmt, va)  [[gnu::format(type, fmt, va)]]
+#else
 # define format_attr(type, fmt, va)
+#endif
+
+#if __has_c_attribute(gnu::access)
+# define ATTR_ACCESS(...)            [[gnu::access(__VA_ARGS__)]]
+#else
 # define ATTR_ACCESS(...)
+#endif
+
+#if __has_c_attribute(gnu::alloc_size)
+# define ATTR_ALLOC_SIZE(...)        [[gnu::alloc_size(__VA_ARGS__)]]
+#else
 # define ATTR_ALLOC_SIZE(...)
 #endif
 
+#if __has_c_attribute(gnu::copy)
+# define ATTR_COPY(x)            [[gnu::copy(x)]]
+#else
+# define ATTR_COPY(x)
+#endif
+
 #if (__GNUC__ >= 11) && !defined(__clang__)
 # define ATTR_MALLOC(deallocator)    [[gnu::malloc(deallocator)]]
 #else
 # define ATTR_MALLOC(deallocator)
 #endif
 
-#if (__GNUC__ >= 14)
+#if __has_c_attribute(gnu::null_terminated_string_arg)
 # define ATTR_STRING(i)              [[gnu::null_terminated_string_arg(i)]]
 #else
 # define ATTR_STRING(i)

lib/commonio.h

@@ -12,6 +12,10 @@
 #define COMMONIO_H
 
 
+#include <config.h>
+
+#include <stdio.h>
+
 #include "attr.h"
 #include "defines.h" /* bool */
 
@@ -64,10 +68,8 @@ struct commonio_ops {
 	 * fgets and fputs (can be replaced by versions that
 	 * understand line continuation conventions).
 	 */
-	ATTR_ACCESS(write_only, 1, 2)
-	/*@null@*/char *(*cio_fgets)(/*@returned@*/char *restrict s, int n,
-	                         FILE *restrict stream);
-	int (*cio_fputs)(const char *, FILE *);
+	ATTR_COPY(fgets) typeof(fgets)  *cio_fgets;
+	ATTR_COPY(fputs) typeof(fputs)  *cio_fputs;
 
 	/*
 	 * open_hook and close_hook.

src/get_subid_owners.c

@@ -4,6 +4,7 @@
 #include <stdio.h>
 
 #include "atoi/getnum.h"
+#include "attr.h"
 #include "prototypes.h"
 #include "shadowlog.h"
 #include "stdlib.h"
@@ -14,13 +15,8 @@
 static const char Prog[] = "get_subid_owners";
 
 
-static void usage(void)
-{
-	fprintf(stderr, "Usage: [-g] %s subuid\n", Prog);
-	fprintf(stderr, "    list uids who own the given subuid\n");
-	fprintf(stderr, "    pass -g to query a subgid\n");
-	exit(EXIT_FAILURE);
-}
+NORETURN static void usage(void);
+
 
 int main(int argc, char *argv[])
 {
@@ -52,3 +48,13 @@ int main(int argc, char *argv[])
 	free(uids);
 	return 0;
 }
+
+
+static void
+usage(void)
+{
+	fprintf(stderr, "Usage: [-g] %s subuid\n", Prog);
+	fprintf(stderr, "    list uids who own the given subuid\n");
+	fprintf(stderr, "    pass -g to query a subgid\n");
+	exit(EXIT_FAILURE);
+}

src/getsubids.c

@@ -4,20 +4,17 @@
 #include <stdlib.h>
 #include <string.h>
 
+#include "attr.h"
 #include "prototypes.h"
 #include "shadowlog.h"
 #include "string/strcmp/streq.h"
 #include "subid.h"
 
 static const char Prog[] = "getsubids";
 
-static void usage(void)
-{
-	fprintf(stderr, "Usage: %s [-g] user\n", Prog);
-	fprintf(stderr, "    list subuid ranges for user\n");
-	fprintf(stderr, "    pass -g to list subgid ranges\n");
-	exit(EXIT_FAILURE);
-}
+
+NORETURN static void usage(void);
+
 
 int main(int argc, char *argv[])
 {
@@ -49,3 +46,13 @@ int main(int argc, char *argv[])
 	subid_free(ranges);
 	return 0;
 }
+
+
+static void
+usage(void)
+{
+	fprintf(stderr, "Usage: %s [-g] user\n", Prog);
+	fprintf(stderr, "    list subuid ranges for user\n");
+	fprintf(stderr, "    pass -g to list subgid ranges\n");
+	exit(EXIT_FAILURE);
+}