idle hlt monkey patch for old solaris x86

sol-idle

#!/bin/sh
set -e
set -x

# idle hlt monkey patch for old solaris x86
# based on ian northeast's alt.solaris.x86 post from 2003
# https://groups.google.com/g/alt.solaris.x86/c/eCi8GKouFqg/m/jCnUnhhN7X4J

readval() # Usage: readval {adb address and verb} {type modifier}
{
  # TODO if adb has a mode without stdout spam use it instead of this marker business
  echo "$1\"marker \"$2" | adb -k /dev/ksyms /dev/mem | sed -n 's/^.*marker \(.*\)$/\1/p'
}

offset=0x34 # offset of call to idle_cpu in idle

# double check the offset by making sure the instruction there is
# what we expect

# If the offset is wrong for your system, go look at the disassembly of idle
#   echo "idle,25?ai" | adb -k /dev/ksyms /dev/mem
# and find the offset of the call instruction that calls idle_cpu
# TODO automate that

# check the opcode
if [ "`readval "idle+$offset?" x`" != "15ff" ] # call 32-bit literal
then
  exit 1
fi

# check the operand
idle_cpu=`readval idle_cpu= X` # address of idle_cpu()
if [ "`readval "idle+$offset+2?" X`" != "$idle_cpu" ]
then
  exit 1
fi

cat > /tmp/sol-idle <<eof
idle+$offset/"Inserting a temporary jmp 0x04"
idle+$offset/w 0x04e8
idle+$offset+2/"Smashing in the final NOP;NOP;NOP;NOP"
idle+$offset+2/W 0x90909090
idle+$offset/"Smashing in the initial HLT;NOP"
idle+$offset/w 0x90f4
idle+$offset/"Final result: call [idle_cpu] --> HLT;NOP;NOP;NOP;NOP;NOP"
eof

/usr/bin/adb -w -k /dev/ksyms /dev/mem < /tmp/sol-idle

rm /tmp/sol-idle

This probably works largely unmodified on whatever svr4's are close enough