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

   1 #!/bin/bash
   2 # SPDX-License-Identifier: GPL-2.0+
   3 #
   4 # Create an initrd directory if one does not already exist.
   5 #
   6 # Copyright (C) IBM Corporation, 2013
   7 #
   8 # Author: Connor Shu <Connor.Shu@ibm.com>
   9
  10 D=tools/testing/selftests/rcutorture
  11
  12 # Prerequisite checks
  13 [ -z "$D" ] && echo >&2 "No argument supplied" && exit 1
  14 if [ ! -d "$D" ]; then
  15     echo >&2 "$D does not exist: Malformed kernel source tree?"
  16     exit 1
  17 fi
  18 if [ -s "$D/initrd/init" ]; then
  19     echo "$D/initrd/init already exists, no need to create it"
  20     exit 0
  21 fi
  22
  23 T=${TMPDIR-/tmp}/mkinitrd.sh.$$
  24 trap 'rm -rf $T' 0 2
  25 mkdir $T
  26
  27 cat > $T/init << '__EOF___'
  28 #!/bin/sh
  29 # Run in userspace a few milliseconds every second.  This helps to
  30 # exercise the NO_HZ_FULL portions of RCU.  The 192 instances of "a" was
  31 # empirically shown to give a nice multi-millisecond burst of user-mode
  32 # execution on a 2GHz CPU, as desired.  Modern CPUs will vary from a
  33 # couple of milliseconds up to perhaps 100 milliseconds, which is an
  34 # acceptable range.
  35 #
  36 # Why not calibrate an exact delay?  Because within this initrd, we
  37 # are restricted to Bourne-shell builtins, which as far as I know do not
  38 # provide any means of obtaining a fine-grained timestamp.
  39
  40 a4="a a a a"
  41 a16="$a4 $a4 $a4 $a4"
  42 a64="$a16 $a16 $a16 $a16"
  43 a192="$a64 $a64 $a64"
  44 while :
  45 do
  46         q=
  47         for i in $a192
  48         do
  49                 q="$q $i"
  50         done
  51         sleep 1
  52 done
  53 __EOF___
  54
  55 # Try using dracut to create initrd
  56 if command -v dracut >/dev/null 2>&1
  57 then
  58         echo Creating $D/initrd using dracut.
  59         # Filesystem creation
  60         dracut --force --no-hostonly --no-hostonly-cmdline --module "base" $T/initramfs.img
  61         cd $D
  62         mkdir -p initrd
  63         cd initrd
  64         zcat $T/initramfs.img | cpio -id
  65         cp $T/init init
  66         chmod +x init
  67         echo Done creating $D/initrd using dracut
  68         exit 0
  69 fi
  70
  71 # No dracut, so create a C-language initrd/init program and statically
  72 # link it.  This results in a very small initrd, but might be a bit less
  73 # future-proof than dracut.
  74 echo "Could not find dracut, attempting C initrd"
  75 cd $D
  76 mkdir -p initrd
  77 cd initrd
  78 cat > init.c << '___EOF___'
  79 #ifndef NOLIBC
  80 #include <unistd.h>
  81 #include <sys/time.h>
  82 #endif
  83
  84 volatile unsigned long delaycount;
  85
  86 int main(int argc, int argv[])
  87 {
  88         int i;
  89         struct timeval tv;
  90         struct timeval tvb;
  91
  92         for (;;) {
  93                 sleep(1);
  94                 /* Need some userspace time. */
  95                 if (gettimeofday(&tvb, NULL))
  96                         continue;
  97                 do {
  98                         for (i = 0; i < 1000 * 100; i++)
  99                                 delaycount = i * i;
 100                         if (gettimeofday(&tv, NULL))
 101                                 break;
 102                         tv.tv_sec -= tvb.tv_sec;
 103                         if (tv.tv_sec > 1)
 104                                 break;
 105                         tv.tv_usec += tv.tv_sec * 1000 * 1000;
 106                         tv.tv_usec -= tvb.tv_usec;
 107                 } while (tv.tv_usec < 1000);
 108         }
 109         return 0;
 110 }
 111 ___EOF___
 112
 113 # build using nolibc on supported archs (smaller executable) and fall
 114 # back to regular glibc on other ones.
 115 if echo -e "#if __x86_64__||__i386__||__i486__||__i586__||__i686__" \
 116            "||__ARM_EABI__||__aarch64__\nyes\n#endif" \
 117    | ${CROSS_COMPILE}gcc -E -nostdlib -xc - \
 118    | grep -q '^yes'; then
 119         # architecture supported by nolibc
 120         ${CROSS_COMPILE}gcc -fno-asynchronous-unwind-tables -fno-ident \
 121                 -nostdlib -include ../../../../include/nolibc/nolibc.h \
 122                 -lgcc -s -static -Os -o init init.c
 123 else
 124         ${CROSS_COMPILE}gcc -s -static -Os -o init init.c
 125 fi
 126
 127 rm init.c
 128 echo "Done creating a statically linked C-language initrd"
 129
 130 exit 0