tools/nolibc: add abs() and friends

This is used in various selftests and will be handy when integrating
those with nolibc.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Acked-by: Willy Tarreau <w@1wt.eu>
Link: https://lore.kernel.org/r/20250428-nolibc-misc-v2-6-3c043eeab06c@linutronix.de
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>

5 files changed, 53 insertions, 0 deletions

diff --git a/tools/include/nolibc/Makefile b/tools/include/nolibc/Makefile
index 45beeecad52d..da4771ef8984 100644
--- a/tools/include/nolibc/Makefile
+++ b/tools/include/nolibc/Makefile
@@ -35,6 +35,7 @@ all_files := \
 		fcntl.h \
 		getopt.h \
 		limits.h \
+		math.h \
 		nolibc.h \
 		poll.h \
 		signal.h \
diff --git a/tools/include/nolibc/math.h b/tools/include/nolibc/math.h
new file mode 100644
index 000000000000..9df823ddd412
--- /dev/null
+++ b/tools/include/nolibc/math.h
@@ -0,0 +1,31 @@
+/* SPDX-License-Identifier: LGPL-2.1 OR MIT */
+/*
+ * math definitions for NOLIBC
+ * Copyright (C) 2025 Thomas Weißschuh <thomas.weissschuh@linutronix.de>
+ */
+
+/* make sure to include all global symbols */
+#include "nolibc.h"
+
+#ifndef _NOLIBC_SYS_MATH_H
+#define _NOLIBC_SYS_MATH_H
+
+static __inline__
+double fabs(double x)
+{
+	return x >= 0 ? x : -x;
+}
+
+static __inline__
+float fabsf(float x)
+{
+	return x >= 0 ? x : -x;
+}
+
+static __inline__
+long double fabsl(long double x)
+{
+	return x >= 0 ? x : -x;
+}
+
+#endif /* _NOLIBC_SYS_MATH_H */
diff --git a/tools/include/nolibc/nolibc.h b/tools/include/nolibc/nolibc.h
index 1d2f391ca4d0..966302c9e8e1 100644
--- a/tools/include/nolibc/nolibc.h
+++ b/tools/include/nolibc/nolibc.h
@@ -116,6 +116,7 @@
 #include "fcntl.h"
 #include "getopt.h"
 #include "poll.h"
+#include "math.h"
 
 /* Used by programs to avoid std includes */
 #define NOLIBC
diff --git a/tools/include/nolibc/stdlib.h b/tools/include/nolibc/stdlib.h
index 4790298f985c..5fd99a480f82 100644
--- a/tools/include/nolibc/stdlib.h
+++ b/tools/include/nolibc/stdlib.h
@@ -32,6 +32,24 @@ static __attribute__((unused)) char itoa_buffer[21];
  * As much as possible, please keep functions alphabetically sorted.
  */
 
+static __inline__
+int abs(int j)
+{
+	return j >= 0 ? j : -j;
+}
+
+static __inline__
+long labs(long j)
+{
+	return j >= 0 ? j : -j;
+}
+
+static __inline__
+long long llabs(long long j)
+{
+	return j >= 0 ? j : -j;
+}
+
 /* must be exported, as it's used by libgcc for various divide functions */
 void abort(void);
 __attribute__((weak,unused,noreturn,section(".text.nolibc_abort")))
diff --git a/tools/testing/selftests/nolibc/nolibc-test.c b/tools/testing/selftests/nolibc/nolibc-test.c
index df1cb3e62564..14a27bc6c83e 100644
--- a/tools/testing/selftests/nolibc/nolibc-test.c
+++ b/tools/testing/selftests/nolibc/nolibc-test.c
@@ -1318,6 +1318,8 @@ int run_stdlib(int min, int max)
 		CASE_TEST(tolower_noop);            EXPECT_EQ(1, tolower('a'), 'a'); break;
 		CASE_TEST(toupper);                 EXPECT_EQ(1, toupper('a'), 'A'); break;
 		CASE_TEST(toupper_noop);            EXPECT_EQ(1, toupper('A'), 'A'); break;
+		CASE_TEST(abs);                     EXPECT_EQ(1, abs(-10), 10); break;
+		CASE_TEST(abs_noop);                EXPECT_EQ(1, abs(10), 10); break;
 
 		case __LINE__:
 			return ret; /* must be last */