Merge tag 'nolibc-20250308-for-6.15-1' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu

Pull nolibc updates from Paul McKenney:
 - 32bit s390 support
 - opendir() and friends
 - openat() support
 - sscanf() support
 - various cleanups

[ Paul has just forwarded the pull request from Thomas Weißschuh, so
  the tag signature is from Thomas, not Paul   - Linus ]

* tag 'nolibc-20250308-for-6.15-1' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu: (26 commits)
  tools/nolibc: don't use asm/ UAPI headers
  selftests/nolibc: stop testing constructor order
  selftests/nolibc: use O_RDONLY flag instead of 0
  tools/nolibc: drop outdated example from overview comment
  tools/nolibc: process open() vararg as mode_t
  tools/nolibc: always use openat(2) instead of open(2)
  tools/nolibc: add support for openat(2)
  selftests/nolibc: add armthumb configuration
  selftests/nolibc: explicitly enable ARM mode
  Revert "selftests: kselftest: Fix build failure with NOLIBC"
  tools/nolibc: add support for [v]sscanf()
  tools/nolibc: add support for 32-bit s390
  selftests/nolibc: rename s390 to s390x
  selftests/nolibc: only run constructor tests on nolibc
  selftests/nolibc: split up architecture list in run-tests.sh
  tools/nolibc: add support for directory access
  tools/nolibc: add support for sys_llseek()
  selftests/nolibc: always keep test kernel configuration up to date
  selftests/nolibc: execute defconfig before other targets
  selftests/nolibc: drop call to mrproper target
  ...

Author: torvalds

tools/include/nolibc/Makefile

@@ -29,6 +29,7 @@ all_files := \
 		compiler.h \
 		crt.h \
 		ctype.h \
+		dirent.h \
 		errno.h \
 		nolibc.h \
 		signal.h \

tools/include/nolibc/arch-mips.h

@@ -179,6 +179,7 @@
 })
 
 /* startup code, note that it's called __start on MIPS */
+void __start(void);
 void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector __start(void)
 {
 	__asm__ volatile (

tools/include/nolibc/arch-s390.h

@@ -5,8 +5,8 @@
 
 #ifndef _NOLIBC_ARCH_S390_H
 #define _NOLIBC_ARCH_S390_H
-#include <asm/signal.h>
-#include <asm/unistd.h>
+#include <linux/signal.h>
+#include <linux/unistd.h>
 
 #include "compiler.h"
 #include "crt.h"
@@ -143,8 +143,13 @@
 void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _start(void)
 {
 	__asm__ volatile (
+#ifdef __s390x__
 		"lgr	%r2, %r15\n"          /* save stack pointer to %r2, as arg1 of _start_c */
 		"aghi	%r15, -160\n"         /* allocate new stackframe                        */
+#else
+		"lr	%r2, %r15\n"
+		"ahi	%r15, -96\n"
+#endif
 		"xc	0(8,%r15), 0(%r15)\n" /* clear backchain                                */
 		"brasl	%r14, _start_c\n"     /* transfer to c runtime                          */
 	);

tools/include/nolibc/arch.h

@@ -29,7 +29,7 @@
 #include "arch-powerpc.h"
 #elif defined(__riscv)
 #include "arch-riscv.h"
-#elif defined(__s390x__)
+#elif defined(__s390x__) || defined(__s390__)
 #include "arch-s390.h"
 #elif defined(__loongarch__)
 #include "arch-loongarch.h"

tools/include/nolibc/crt.h

@@ -10,6 +10,7 @@
 char **environ __attribute__((weak));
 const unsigned long *_auxv __attribute__((weak));
 
+void _start(void);
 static void __stack_chk_init(void);
 static void exit(int);
 
@@ -22,6 +23,7 @@ extern void (*const __init_array_end[])(int, char **, char**) __attribute__((wea
 extern void (*const __fini_array_start[])(void) __attribute__((weak));
 extern void (*const __fini_array_end[])(void) __attribute__((weak));
 
+void _start_c(long *sp);
 __attribute__((weak,used))
 void _start_c(long *sp)
 {

tools/include/nolibc/dirent.h

@@ -0,0 +1,98 @@
+/* SPDX-License-Identifier: LGPL-2.1 OR MIT */
+/*
+ * Directory access for NOLIBC
+ * Copyright (C) 2025 Thomas Weißschuh <linux@weissschuh.net>
+ */
+
+#ifndef _NOLIBC_DIRENT_H
+#define _NOLIBC_DIRENT_H
+
+#include "stdint.h"
+#include "types.h"
+
+#include <linux/limits.h>
+
+struct dirent {
+	ino_t	d_ino;
+	char	d_name[NAME_MAX + 1];
+};
+
+/* See comment of FILE in stdio.h */
+typedef struct {
+	char dummy[1];
+} DIR;
+
+static __attribute__((unused))
+DIR *fdopendir(int fd)
+{
+	if (fd < 0) {
+		SET_ERRNO(EBADF);
+		return NULL;
+	}
+	return (DIR *)(intptr_t)~fd;
+}
+
+static __attribute__((unused))
+DIR *opendir(const char *name)
+{
+	int fd;
+
+	fd = open(name, O_RDONLY);
+	if (fd == -1)
+		return NULL;
+	return fdopendir(fd);
+}
+
+static __attribute__((unused))
+int closedir(DIR *dirp)
+{
+	intptr_t i = (intptr_t)dirp;
+
+	if (i >= 0) {
+		SET_ERRNO(EBADF);
+		return -1;
+	}
+	return close(~i);
+}
+
+static __attribute__((unused))
+int readdir_r(DIR *dirp, struct dirent *entry, struct dirent **result)
+{
+	char buf[sizeof(struct linux_dirent64) + NAME_MAX + 1];
+	struct linux_dirent64 *ldir = (void *)buf;
+	intptr_t i = (intptr_t)dirp;
+	int fd, ret;
+
+	if (i >= 0)
+		return EBADF;
+
+	fd = ~i;
+
+	ret = sys_getdents64(fd, ldir, sizeof(buf));
+	if (ret < 0)
+		return -ret;
+	if (ret == 0) {
+		*result = NULL;
+		return 0;
+	}
+
+	/*
+	 * getdents64() returns as many entries as fit the buffer.
+	 * readdir() can only return one entry at a time.
+	 * Make sure the non-returned ones are not skipped.
+	 */
+	ret = lseek(fd, ldir->d_off, SEEK_SET);
+	if (ret == -1)
+		return errno;
+
+	entry->d_ino = ldir->d_ino;
+	/* the destination should always be big enough */
+	strlcpy(entry->d_name, ldir->d_name, sizeof(entry->d_name));
+	*result = entry;
+	return 0;
+}
+
+/* make sure to include all global symbols */
+#include "nolibc.h"
+
+#endif /* _NOLIBC_DIRENT_H */

tools/include/nolibc/errno.h

@@ -7,7 +7,7 @@
 #ifndef _NOLIBC_ERRNO_H
 #define _NOLIBC_ERRNO_H
 
-#include <asm/errno.h>
+#include <linux/errno.h>
 
 #ifndef NOLIBC_IGNORE_ERRNO
 #define SET_ERRNO(v) do { errno = (v); } while (0)

tools/include/nolibc/nolibc.h

@@ -31,8 +31,7 @@
  *   - The third level is the libc call definition. It exposes the lower raw
  *     sys_<name>() calls in a way that looks like what a libc usually does,
  *     takes care of specific input values, and of setting errno upon error.
- *     There can be minor variations compared to standard libc calls. For
- *     example the open() call always takes 3 args here.
+ *     There can be minor variations compared to standard libc calls.
  *
  * The errno variable is declared static and unused. This way it can be
  * optimized away if not used. However this means that a program made of
@@ -105,6 +104,7 @@
 #include "string.h"
 #include "time.h"
 #include "stackprotector.h"
+#include "dirent.h"
 
 /* Used by programs to avoid std includes */
 #define NOLIBC

tools/include/nolibc/signal.h

@@ -13,6 +13,7 @@
 #include "sys.h"
 
 /* This one is not marked static as it's needed by libgcc for divide by zero */
+int raise(int signal);
 __attribute__((weak,unused,section(".text.nolibc_raise")))
 int raise(int signal)
 {

tools/include/nolibc/stackprotector.h

@@ -18,6 +18,7 @@
  * triggering stack protector errors themselves
  */
 
+void __stack_chk_fail(void);
 __attribute__((weak,used,noreturn,section(".text.nolibc_stack_chk")))
 void __stack_chk_fail(void)
 {
@@ -28,6 +29,7 @@ void __stack_chk_fail(void)
 	for (;;);
 }
 
+void __stack_chk_fail_local(void);
 __attribute__((weak,noreturn,section(".text.nolibc_stack_chk")))
 void __stack_chk_fail_local(void)
 {