Add prctl

prctl/prctl_mm_map.c

@@ -0,0 +1,157 @@
+#include <sys/prctl.h>
+#include <errno.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <syscall.h>
+
+/*
+ * Sets the process title to the specified title. Note that this may fail if
+ * the kernel doesn't support PR_SET_MM_MAP (kernels <3.18).
+ */
+int setproctitle(char *title)
+{
+	FILE *f = NULL;
+	int i, fd, len;
+	char *buf_ptr, *tmp_proctitle;
+	char buf[4096];
+	int ret = 0;
+	ssize_t bytes_read = 0;
+	static char *proctitle = NULL;
+
+	/*
+	 * We don't really need to know all of this stuff, but unfortunately
+	 * PR_SET_MM_MAP requires us to set it all at once, so we have to
+	 * figure it out anyway.
+	 */
+	unsigned long start_data, end_data, start_brk, start_code, end_code,
+		start_stack, arg_start, arg_end, env_start, env_end, brk_val;
+	struct prctl_mm_map prctl_map;
+
+	f = fopen("/proc/self/stat", "r");
+	if (!f) {
+		fprintf(stderr, "fopen(stat): '%m' (%d)\n", errno);
+		return -1;
+	}
+
+	fd = fileno(f);
+	if (fd < 0) {
+		fprintf(stderr, "fileno(%p): '%m' (%d)\n", f, errno);
+		fclose(f);
+		return -1;
+	}
+
+	bytes_read = read(fd, buf, sizeof(buf) - 1);
+	if (bytes_read <= 0) {
+		fprintf(stderr, "read(): '%m' (%d)\n", errno);
+		fclose(f);
+		return -1;
+	}
+
+	buf[bytes_read] = '\0';
+
+	/* Skip the first 25 fields, column 26-28 are start_code, end_code,
+	 * and start_stack */
+	buf_ptr = strchr(buf, ' ');
+	for (i = 0; i < 24; i++) {
+		if (!buf_ptr) {
+			fclose(f);
+			return -1;
+		}
+		buf_ptr = strchr(buf_ptr + 1, ' ');
+	}
+	if (!buf_ptr) {
+		fclose(f);
+		return -1;
+	}
+
+	i = sscanf(buf_ptr, "%lu %lu %lu", &start_code, &end_code, &start_stack);
+	if (i != 3) {
+		fclose(f);
+		return -1;
+	}
+
+	/* Skip the next 19 fields, column 45-51 are start_data to arg_end */
+	for (i = 0; i < 19; i++) {
+		if (!buf_ptr) {
+			fclose(f);
+			return -1;
+		}
+		buf_ptr = strchr(buf_ptr + 1, ' ');
+	}
+
+	if (!buf_ptr) {
+		fclose(f);
+		return -1;
+	}
+
+	i = sscanf(buf_ptr, "%lu %lu %lu %*u %*u %lu %lu", &start_data,
+		   &end_data, &start_brk, &env_start, &env_end);
+	if (i != 5) {
+		fclose(f);
+		return -1;
+	}
+
+	/* Include the null byte here, because in the calculations below we
+	 * want to have room for it. */
+	len = strlen(title) + 1;
+
+	tmp_proctitle = realloc(proctitle, len);
+	if (!tmp_proctitle) {
+		fclose(f);
+		return -1;
+	}
+
+	proctitle = tmp_proctitle;
+
+	arg_start = (unsigned long)proctitle;
+	arg_end = arg_start + len;
+
+	brk_val = syscall(__NR_brk, 0);
+
+	prctl_map = (struct prctl_mm_map){
+		.start_code = start_code,
+		.end_code = end_code,
+		.start_stack = start_stack,
+		.start_data = start_data,
+		.end_data = end_data,
+		.start_brk = start_brk,
+		.brk = brk_val,
+		.arg_start = arg_start,
+		.arg_end = arg_end,
+		.env_start = env_start,
+		.env_end = env_end,
+		.auxv = NULL,
+		.auxv_size = 0,
+		.exe_fd = -1,
+	};
+
+	ret = prctl(PR_SET_MM, PR_SET_MM_MAP, &prctl_map,
+		    sizeof(prctl_map), 0);
+	if (ret == 0)
+		(void)strncpy((char *)arg_start, title, len);
+	else
+		fprintf(stderr, "Failed to set cmdline\n");
+
+	fclose(f);
+
+	return ret;
+}
+
+int main(int argc, char *argv[])
+{
+	// ...
+	// show pid to find the right process
+	pid_t pid = getpid();
+	printf("pid = %d\n", pid);
+
+	if (argv[1]) {
+		setproctitle(argv[1]);
+		// ...
+	}
+
+	sleep(1000);
+	return 0;
+}