[PATCH v4 0/2] tools/nolibc: add err.h

[PATCH v4 0/2] tools/nolibc: add err.h

[Thomas Weißschuh]

Add a few convenient helpers to print error and warning messages.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
---
Changes in v4:
- #include <stdbool.h> from nolibc-test.c
- Link to v3: https://patch.msgid.link/20260316-nolibc-err-h-v3-0-6ef80c051ab7@weissschuh.net

Changes in v3:
- Make sure program_invocation_{short_,}name are never NULL.
- Provide dummy definitions of program_invocation_{short_,}name
  when NOLIBC_IGNORE_ERRNO is set.
- Drop Ack from Willy.
- Link to v2: https://patch.msgid.link/20260313-nolibc-err-h-v2-0-f4481053b07a@weissschuh.net

Changes in v2:
- Fix program_invocation_name test to handle test execution as /init
- Drop already applied patches
- Link to v1: https://patch.msgid.link/20260311-nolibc-err-h-v1-0-735a9de7f15d@weissschuh.net

---
Thomas Weißschuh (2):
      tools/nolibc: add support for program_invocation_{,short_}name
      tools/nolibc: add err.h

 tools/include/nolibc/Makefile                |  1 +
 tools/include/nolibc/crt.h                   | 26 +++++++++
 tools/include/nolibc/err.h                   | 87 ++++++++++++++++++++++++++++
 tools/include/nolibc/errno.h                 |  4 ++
 tools/include/nolibc/nolibc.h                |  1 +
 tools/testing/selftests/nolibc/nolibc-test.c | 34 +++++++++++
 6 files changed, 153 insertions(+)
---
base-commit: d59131de97ee69ab4e4b8926089a6e953d699b11
change-id: 20260311-nolibc-err-h-df36a75dddf8

Best regards,
-- 
Thomas Weißschuh <linux@weissschuh.net>

[PATCH v4 1/2] tools/nolibc: add support for program_invocation_{,short_}name

[Thomas Weißschuh]

Add support for the GNU extensions 'program_invocation_name' and
'program_invocation_short_name'. These are useful to print error
messages, which by convention include the program name.

As these are global variables which take up memory even if not used,
similar to 'errno', gate them behind NOLIBC_IGNORE_ERRNO.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
---
 tools/include/nolibc/crt.h                   | 26 +++++++++++++++++++++
 tools/include/nolibc/errno.h                 |  4 ++++
 tools/testing/selftests/nolibc/nolibc-test.c | 34 ++++++++++++++++++++++++++++
 3 files changed, 64 insertions(+)

diff --git a/tools/include/nolibc/crt.h b/tools/include/nolibc/crt.h
index d9262998dae9..5bb492555f13 100644
--- a/tools/include/nolibc/crt.h
+++ b/tools/include/nolibc/crt.h
@@ -17,6 +17,7 @@ const unsigned long *_auxv __attribute__((weak));
 void _start(void);
 static void __stack_chk_init(void);
 static void exit(int);
+static char *strrchr(const char *s, int c);
 
 extern void (*const __preinit_array_start[])(int, char **, char**) __attribute__((weak));
 extern void (*const __preinit_array_end[])(int, char **, char**) __attribute__((weak));
@@ -27,6 +28,24 @@ 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));
 
+#ifndef NOLIBC_IGNORE_ERRNO
+extern char *program_invocation_name __attribute__((weak));
+extern char *program_invocation_short_name __attribute__((weak));
+
+static __inline__
+char *__nolibc_program_invocation_short_name(char *long_name)
+{
+
+	char *short_name;
+
+	short_name = strrchr(long_name, '/');
+	if (!short_name || !short_name[0])
+		return long_name;
+
+	return short_name + 1;
+}
+#endif /* NOLIBC_IGNORE_ERRNO */
+
 void _start_c(long *sp);
 __attribute__((weak,used))
 #if __nolibc_has_feature(undefined_behavior_sanitizer)
@@ -76,6 +95,13 @@ void _start_c(long *sp)
 		;
 	_auxv = auxv;
 
+#ifndef NOLIBC_IGNORE_ERRNO
+	if (argc > 0 && argv[0]) {
+		program_invocation_name = argv[0];
+		program_invocation_short_name = __nolibc_program_invocation_short_name(argv[0]);
+	}
+#endif /* NOLIBC_IGNORE_ERRNO */
+
 	for (ctor_func = __preinit_array_start; ctor_func < __preinit_array_end; ctor_func++)
 		(*ctor_func)(argc, argv, envp);
 	for (ctor_func = __init_array_start; ctor_func < __init_array_end; ctor_func++)
diff --git a/tools/include/nolibc/errno.h b/tools/include/nolibc/errno.h
index 08a33c40ec0c..bab83692ea1c 100644
--- a/tools/include/nolibc/errno.h
+++ b/tools/include/nolibc/errno.h
@@ -15,8 +15,12 @@
 #ifndef NOLIBC_IGNORE_ERRNO
 #define SET_ERRNO(v) do { errno = (v); } while (0)
 int errno __attribute__((weak));
+char *program_invocation_name __attribute__((weak)) = "";
+char *program_invocation_short_name __attribute__((weak)) = "";
 #else
 #define SET_ERRNO(v) do { } while (0)
+#define program_invocation_name ""
+#define program_invocation_short_name ""
 #endif
 
 
diff --git a/tools/testing/selftests/nolibc/nolibc-test.c b/tools/testing/selftests/nolibc/nolibc-test.c
index 180611aabbfb..51da2f9e281b 100644
--- a/tools/testing/selftests/nolibc/nolibc-test.c
+++ b/tools/testing/selftests/nolibc/nolibc-test.c
@@ -42,6 +42,7 @@
 #include <unistd.h>
 #include <limits.h>
 #include <ctype.h>
+#include <stdbool.h>
 
 #pragma GCC diagnostic ignored "-Wmissing-prototypes"
 
@@ -702,6 +703,37 @@ static void constructor2(int argc, char **argv, char **envp)
 		constructor_test_value |= 1 << 1;
 }
 
+int test_program_invocation_name(void)
+{
+	char buf[100];
+	char *dirsep;
+	ssize_t r;
+	int fd;
+
+	fd = open("/proc/self/cmdline", O_RDONLY);
+	if (fd == -1)
+		return 1;
+
+	r = read(fd, buf, sizeof(buf));
+	close(fd);
+	if (r < 1 || r == sizeof(buf))
+		return 1;
+
+	buf[r - 1] = '\0';
+
+	if (strcmp(program_invocation_name, buf) != 0)
+		return 1;
+
+	dirsep = strrchr(buf, '/');
+	if (!dirsep || dirsep[1] == '\0')
+		return 1;
+
+	if (strcmp(program_invocation_short_name, dirsep + 1) != 0)
+		return 1;
+
+	return 0;
+}
+
 int run_startup(int min, int max)
 {
 	int test;
@@ -716,6 +748,7 @@ int run_startup(int min, int max)
 #ifdef NOLIBC
 	test_auxv = _auxv;
 #endif
+	bool proc = access("/proc", R_OK) == 0;
 
 	for (test = min; test >= 0 && test <= max; test++) {
 		int llen = 0; /* line length */
@@ -741,6 +774,7 @@ int run_startup(int min, int max)
 		CASE_TEST(constructor);      EXPECT_EQ(is_nolibc, constructor_test_value, 0x3); break;
 		CASE_TEST(linkage_errno);    EXPECT_PTREQ(1, linkage_test_errno_addr(), &errno); break;
 		CASE_TEST(linkage_constr);   EXPECT_EQ(1, linkage_test_constructor_test_value, 0x3); break;
+		CASE_TEST(prog_name);        EXPECT_ZR(proc, test_program_invocation_name()); break;
 		case __LINE__:
 			return ret; /* must be last */
 		/* note: do not set any defaults so as to permit holes above */

-- 
2.53.0

[PATCH v4 2/2] tools/nolibc: add err.h

[Thomas Weißschuh]

Add a few convenient helpers to print error and warning messages.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
---
 tools/include/nolibc/Makefile |  1 +
 tools/include/nolibc/err.h    | 87 +++++++++++++++++++++++++++++++++++++++++++
 tools/include/nolibc/nolibc.h |  1 +
 3 files changed, 89 insertions(+)

diff --git a/tools/include/nolibc/Makefile b/tools/include/nolibc/Makefile
index 1958dda98895..5d242312943f 100644
--- a/tools/include/nolibc/Makefile
+++ b/tools/include/nolibc/Makefile
@@ -30,6 +30,7 @@ all_files := \
 		ctype.h \
 		dirent.h \
 		elf.h \
+		err.h \
 		errno.h \
 		fcntl.h \
 		getopt.h \
diff --git a/tools/include/nolibc/err.h b/tools/include/nolibc/err.h
new file mode 100644
index 000000000000..e22ae87a7289
--- /dev/null
+++ b/tools/include/nolibc/err.h
@@ -0,0 +1,87 @@
+/* SPDX-License-Identifier: LGPL-2.1 OR MIT */
+/*
+ * formatted error message for NOLIBC
+ * Copyright (C) 2026 Thomas Weißschuh <linux@weissschuh.net>
+ */
+
+/* make sure to include all global symbols */
+#include "nolibc.h"
+
+#ifndef _NOLIBC_ERR_H
+#define _NOLIBC_ERR_H
+
+#include "errno.h"
+#include "stdarg.h"
+#include "sys.h"
+
+static __attribute__((unused))
+void vwarn(const char *fmt, va_list args)
+{
+	fprintf(stderr, "%s: ", program_invocation_short_name);
+	vfprintf(stderr, fmt, args);
+	fprintf(stderr, ": %m\n");
+}
+
+static __attribute__((unused))
+void vwarnx(const char *fmt, va_list args)
+{
+	fprintf(stderr, "%s: ", program_invocation_short_name);
+	vfprintf(stderr, fmt, args);
+	fprintf(stderr, "\n");
+}
+
+static __attribute__((unused))
+void warn(const char *fmt, ...)
+{
+	va_list args;
+
+	va_start(args, fmt);
+	vwarn(fmt, args);
+	va_end(args);
+}
+
+static __attribute__((unused))
+void warnx(const char *fmt, ...)
+{
+	va_list args;
+
+	va_start(args, fmt);
+	vwarnx(fmt, args);
+	va_end(args);
+}
+
+static __attribute__((noreturn, unused))
+void verr(int eval, const char *fmt, va_list args)
+{
+	vwarn(fmt, args);
+	exit(eval);
+}
+
+static __attribute__((noreturn, unused))
+void verrx(int eval, const char *fmt, va_list args)
+{
+	warnx(fmt, args);
+	exit(eval);
+}
+
+static __attribute__((noreturn, unused))
+void err(int eval, const char *fmt, ...)
+{
+	va_list args;
+
+	va_start(args, fmt);
+	verr(eval, fmt, args);
+	va_end(args);
+}
+
+static __attribute__((noreturn, unused))
+void errx(int eval, const char *fmt, ...)
+{
+	va_list args;
+
+	va_start(args, fmt);
+	verrx(eval, fmt, args);
+	va_end(args);
+}
+
+#endif /* _NOLIBC_ERR_H */
diff --git a/tools/include/nolibc/nolibc.h b/tools/include/nolibc/nolibc.h
index d1d08b7f8599..fe8195483b6d 100644
--- a/tools/include/nolibc/nolibc.h
+++ b/tools/include/nolibc/nolibc.h
@@ -130,6 +130,7 @@
 #include "getopt.h"
 #include "poll.h"
 #include "math.h"
+#include "err.h"
 
 /* Used by programs to avoid std includes */
 #define NOLIBC

-- 
2.53.0

Re: [PATCH v4 0/2] tools/nolibc: add err.h

[Willy Tarreau]

On Wed, Mar 18, 2026 at 04:50:15PM +0100, Thomas Weißschuh wrote:
> Add a few convenient helpers to print error and warning messages.
> 
> Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>

Thank you Thomas. For the whole series:

Acked-by: Willy Tarreau <w@1wt.eu>

willy