selftest: size: Add size test for Linux kernel

This test shows the amount of memory used by the system.
Note that this is dependent on the user-space that is loaded
when this program runs. Optimally, this program would be
run as the init program itself.

The program is optimized for size itself, to avoid conflating
its own execution with that of the system software.
The code is compiled statically, with no stdlibs. On my x86_64 system,
this results in a statically linked binary of less than 5K.

Signed-off-by: Tim Bird <[e-mail]>
Reviewed-by: Josh Triplett <[e-mail]>
Signed-off-by: Shuah Khan <[e-mail]>

tools/testing/selftests/Makefile

···
 TARGETS += sysctl
 TARGETS += firmware
 TARGETS += ftrace
+TARGETS += size
 
 TARGETS_HOTPLUG = cpu-hotplug
 TARGETS_HOTPLUG += memory-hotplug

tools/testing/selftests/size/.gitignore

···
+get_size

tools/testing/selftests/size/Makefile

···
+CC = $(CROSS_COMPILE)gcc
+
+all: get_size
+
+get_size: get_size.c
+	$(CC) -static -ffreestanding -nostartfiles -s $< -o $@
+
+run_tests: all
+	./get_size
+
+clean:
+	$(RM) get_size

tools/testing/selftests/size/get_size.c

···
+/*
+ * Copyright 2014 Sony Mobile Communications Inc.
+ *
+ * Licensed under the terms of the GNU GPL License version 2
+ *
+ * Selftest for runtime system size
+ *
+ * Prints the amount of RAM that the currently running system is using.
+ *
+ * This program tries to be as small as possible itself, to
+ * avoid perturbing the system memory utilization with its
+ * own execution.  It also attempts to have as few dependencies
+ * on kernel features as possible.
+ *
+ * It should be statically linked, with startup libs avoided.
+ * It uses no library calls, and only the following 3 syscalls:
+ *   sysinfo(), write(), and _exit()
+ *
+ * For output, it avoids printf (which in some C libraries
+ * has large external dependencies) by  implementing it's own
+ * number output and print routines, and using __builtin_strlen()
+ */
+
+#include <sys/sysinfo.h>
+#include <unistd.h>
+
+#define STDOUT_FILENO 1
+
+static int print(const char *s)
+{
+	return write(STDOUT_FILENO, s, __builtin_strlen(s));
+}
+
+static inline char *num_to_str(unsigned long num, char *buf, int len)
+{
+	unsigned int digit;
+
+	/* put digits in buffer from back to front */
+	buf += len - 1;
+	*buf = 0;
+	do {
+		digit = num % 10;
+		*(--buf) = digit + '0';
+		num /= 10;
+	} while (num > 0);
+
+	return buf;
+}
+
+static int print_num(unsigned long num)
+{
+	char num_buf[30];
+
+	return print(num_to_str(num, num_buf, sizeof(num_buf)));
+}
+
+static int print_k_value(const char *s, unsigned long num, unsigned long units)
+{
+	unsigned long long temp;
+	int ccode;
+
+	print(s);
+
+	temp = num;
+	temp = (temp * units)/1024;
+	num = temp;
+	ccode = print_num(num);
+	print("\n");
+	return ccode;
+}
+
+/* this program has no main(), as startup libraries are not used */
+void _start(void)
+{
+	int ccode;
+	struct sysinfo info;
+	unsigned long used;
+
+	print("Testing system size.\n");
+	print("1..1\n");
+
+	ccode = sysinfo(&info);
+	if (ccode < 0) {
+		print("not ok 1 get runtime memory use\n");
+		print("# could not get sysinfo\n");
+		_exit(ccode);
+	}
+	/* ignore cache complexities for now */
+	used = info.totalram - info.freeram - info.bufferram;
+	print_k_value("ok 1 get runtime memory use # size = ", used,
+		info.mem_unit);
+
+	print("# System runtime memory report (units in Kilobytes):\n");
+	print_k_value("#   Total:  ", info.totalram, info.mem_unit);
+	print_k_value("#   Free:   ", info.freeram, info.mem_unit);
+	print_k_value("#   Buffer: ", info.bufferram, info.mem_unit);
+	print_k_value("#   In use: ", used, info.mem_unit);
+
+	_exit(0);
+}