--- /dev/null	Sun Jun 21 11:00:58 2026
+++ /sys/src/libc/sparc/atom.c	Sun Jun 21 00:00:00 2026
@@ -0,0 +1,110 @@
+#include <u.h>
+#include <libc.h>
+
+static int atomlock;
+
+static void
+taslock(void)
+{
+	while(_tas(&atomlock))
+		;
+}
+
+static void
+tasunlock(void)
+{
+	atomlock = 0;
+}
+
+long
+ainc(long *p)
+{
+	long v;
+
+	taslock();
+	v = (*p += 1);
+	tasunlock();
+	return v;
+}
+
+long
+adec(long *p)
+{
+	long v;
+
+	taslock();
+	v = (*p -= 1);
+	tasunlock();
+	return v;
+}
+
+void
+_xinc(long *p)
+{
+	taslock();
+	*p += 1;
+	tasunlock();
+}
+
+long
+_xdec(long *p)
+{
+	long v;
+
+	taslock();
+	v = (*p -= 1);
+	tasunlock();
+	return v;
+}
+
+int
+cas(int *p, int ov, int nv)
+{
+	int r;
+
+	taslock();
+	r = *p == ov;
+	if(r)
+		*p = nv;
+	tasunlock();
+	return r;
+}
+
+int
+cas32(u32int *p, u32int ov, u32int nv)
+{
+	int r;
+
+	taslock();
+	r = *p == ov;
+	if(r)
+		*p = nv;
+	tasunlock();
+	return r;
+}
+
+int
+casp(void **p, void *ov, void *nv)
+{
+	int r;
+
+	taslock();
+	r = *p == ov;
+	if(r)
+		*p = nv;
+	tasunlock();
+	return r;
+}
+
+int
+casl(ulong *p, ulong ov, ulong nv)
+{
+	int r;
+
+	taslock();
+	r = *p == ov;
+	if(r)
+		*p = nv;
+	tasunlock();
+	return r;
+}
--- /n/sources/plan9/sys/src/libc/sparc/mkfile	Sun Nov 20 06:00:06 2005
+++ /sys/src/libc/sparc/mkfile	Sun Jun 21 00:00:00 2026
@@ -22,6 +22,7 @@
 	vlop.s
 
 CFILES=\
+	atom.c\
 	cycles.c\
 	notejmp.c\
 	sqrt.c\