more getcpu

userland/linux/getcpu.c

@@ -14,7 +14,7 @@
 /* man getcpu says this exists since glibc 2.29, but I can't find it in Ubuntu 20.04 glibc 2.31 not even with locate
  * (there is a hit under /usr/src/linux-headers-5.4.0-29/include/linux/getcpu.h but it only defines `struct getcpu_cache`
  * and nothing else:
- * https://stackoverflow.com/questions/23224607/how-do-i-include-linux-header-files-like-linux-getcpu-h
+ * https://stackoverflow.com/questions/23224607/how-do-i-include-linux-header-files-like-linux-getcpu-h/61774312#61774312
  * Furthermore, there is already a prototype in sched.h, so we can't define our own either. */
 #if 0
 #include <linux/getcpu.h>
@@ -23,7 +23,7 @@
 void* main_thread(void *arg) {
     (void)arg;
     unsigned cpu, numa;
-    getcpu(&cpu, &numa);
+    assert(!getcpu(&cpu, &numa));
     printf("%u %u\n", cpu, numa);
     return NULL;
 }

userland/linux/getcpu_syscall.c

@@ -0,0 +1,48 @@
+/* https://cirosantilli.com/linux-kernel-module-cheat#getcpu */
+
+#define _GNU_SOURCE
+#include <assert.h>
+#include <errno.h>
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sys/syscall.h>
+
+void* main_thread(void *arg) {
+    (void)arg;
+    unsigned cpu = 1, numa;
+    int err, ret;
+    assert(!syscall(SYS_getcpu, &cpu, &numa, NULL));
+    err = errno;
+    if (ret == -1) {
+        printf("%d\n", err);
+        perror("getcpu");
+    }
+    printf("%d %u %u\n", ret, cpu, numa);
+    return NULL;
+}
+
+int main(int argc, char **argv) {
+    pthread_t *threads;
+    unsigned int nthreads, i;
+    if (argc > 1) {
+        nthreads = strtoll(argv[1], NULL, 0);
+    } else {
+        nthreads = 1;
+    }
+    threads = malloc(nthreads * sizeof(*threads));
+    for (i = 0; i < nthreads; ++i) {
+        assert(pthread_create(
+            &threads[i],
+            NULL,
+            main_thread,
+            NULL
+        ) == 0);
+    }
+    for (i = 0; i < nthreads; ++i) {
+        pthread_join(threads[i], NULL);
+    }
+    free(threads);
+    return EXIT_SUCCESS;
+}