Name bla
OutFile bla.exe

!include Sections.nsh

InstallDir "$TEMP"

DirText bla
Page directory
Page instfiles
Page instfiles secInstPre

ShowInstDetails show

Section "" sec1
  DetailPrint "doing stuff..."
  Sleep 300
  DetailPrint "doing stuff..."
  Sleep 300
  DetailPrint "doing stuff..."
  Sleep 300
  DetailPrint "doing stuff..."
  Sleep 300
  DetailPrint "doing stuff..."
  Sleep 300
  DetailPrint "doing stuff..."
  Sleep 300
  DetailPrint "doing stuff..."
  Sleep 300
  DetailPrint "doing stuff..."
  Sleep 300

  # move on to the next page right away
  SetAutoClose true
  DetailPrint ""
  DetailPrint "Installtion failed!"
  # set the flag
  StrCpy $1 1
  MessageBox MB_OK "Prepare for rollback"
  # disable all sections
loop:
  SectionSetFlags $0 0
  IntOp $0 $0 + 1
  IfErrors 0 loop
  # stop executing anymore code in this section
  Return
SectionEnd

Section /o "" rollback
  SetAutoClose false
  MessageBox MB_OK "rolling back"
  DetailPrint "rolling back..."
  Sleep 300
  DetailPrint "rolling back..."
  Sleep 300
  DetailPrint "rolling back..."
  Sleep 300
  DetailPrint "rolling back..."
  Sleep 300
  DetailPrint "rolling back..."
  Sleep 300
  DetailPrint "rolling back..."
  Sleep 300
  Abort "installation failed, rollback completed"
SectionEnd

Function secInstPre
  StrCmp $1 1 0 +3
    SectionSetFlags ${rollback} ${SF_SELECTED}
    Return
  Abort
FunctionEnd