tools/testing/selftests/rcutorture/bin/mkinitrd.sh

#!/bin/bash
# SPDX-License-Identifier: GPL-2.0+
#
# Create an initrd directory if one does not already exist.
#
# Copyright (C) IBM Corporation, 2013
#
# Author: Connor Shu <Connor.Shu@ibm.com>

D=tools/testing/selftests/rcutorture

# Prerequisite checks
[ -z "$D" ] && echo >&2 "No argument supplied" && exit 1
if [ ! -d "$D" ]; then
    echo >&2 "$D does not exist: Malformed kernel source tree?"
    exit 1
fi
if [ -s "$D/initrd/init" ]; then
    echo "$D/initrd/init already exists, no need to create it"
    exit 0
fi

# Create a C-language initrd/init infinite-loop program and statically
# link it.  This results in a very small initrd.
echo "Creating a statically linked C-language initrd"
cd $D
mkdir -p initrd
cd initrd
cat > init.c << '___EOF___'
#ifndef NOLIBC
#include <unistd.h>
#include <sys/time.h>
#endif

volatile unsigned long delaycount;

int main(int argc, int argv[])
{
	int i;
	struct timeval tv;
	struct timeval tvb;

	for (;;) {
		sleep(1);
		/* Need some userspace time. */
		if (gettimeofday(&tvb, NULL))
			continue;
		do {
			for (i = 0; i < 1000 * 100; i++)
				delaycount = i * i;
			if (gettimeofday(&tv, NULL))
				break;
			tv.tv_sec -= tvb.tv_sec;
			if (tv.tv_sec > 1)
				break;
			tv.tv_usec += tv.tv_sec * 1000 * 1000;
			tv.tv_usec -= tvb.tv_usec;
		} while (tv.tv_usec < 1000);
	}
	return 0;
}
___EOF___

# build using nolibc on supported archs (smaller executable) and fall
# back to regular glibc on other ones.
if echo -e "#if __x86_64__||__i386__||__i486__||__i586__||__i686__" \
           "||__ARM_EABI__||__aarch64__\nyes\n#endif" \
   | ${CROSS_COMPILE}gcc -E -nostdlib -xc - \
   | grep -q '^yes'; then
	# architecture supported by nolibc
        ${CROSS_COMPILE}gcc -fno-asynchronous-unwind-tables -fno-ident \
		-nostdlib -include ../../../../include/nolibc/nolibc.h \
		-s -static -Os -o init init.c -lgcc
else
	${CROSS_COMPILE}gcc -s -static -Os -o init init.c
fi

rm init.c
echo "Done creating a statically linked C-language initrd"

exit 0