Provided by: prelink_0.0.20050901-1_i386 bug

NAME

       execstack  -  tool to set, clear, or query executable stack flag of ELF
       binaries and shared libraries

SYNOPSIS

       execstack [OPTION...] [FILES]

DESCRIPTION

       execstack is a program which sets, clears, or queries executable  stack
       flag  of  ELF  binaries  and  shared  libraries.  Linux has in the past
       allowed execution of instructions on the stack and there  are  lots  of
       binaries  and  shared  libraries assuming this behaviour.  Furthermore,
       GCC trampoline code for e.g. nested functions requires executable stack
       on many architectures.  To avoid breaking binaries and shared libraries
       which need executable stack, ELF binaries and shared libraries now  can
       be  marked  as  requiring  executable  stack or not requiring it.  This
       marking is done through the p_flags field in the  PT_GNU_STACK  program
       header entry.  If the marking is missing, kernel or dynamic linker need
       to assume  it  might  need  executable  stack.   The  marking  is  done
       automatically  by recent GCC versions (objects using trampolines on the
       stack are marked as requiring executable stack, all other  newly  built
       objects  are  marked  as  not  requiring  it) and linker collects these
       markings into marking of the whole binary or shared library.  The  user
       can   override   this   at   assembly   time  (through  --execstack  or
       --noexecstack assembler options), at link time (through -z execstack or
       -z  noexecstack linker options) and using the execstack tool also on an
       already linker binary or  shared  library.   This  tool  is  especially
       useful  for  third  party  shared libraries where it is known that they
       don’t need executable stack or testing proves it.

OPTIONS

       -s --set-execstack
              Mark binary or shared library as requiring executable stack.

       -c --clear-execstack
              Mark binary or shared library as not requiring executable stack.

       -q --query
              Query executable stack marking of binaries and shared libraries.
              For each file it prints either - when executable  stack  is  not
              required,  X  when executable stack is required or ?  when it is
              unknown  whether  the  object  requires   or   doesn’t   require
              executable stack (the marking is missing).

       -V     Print execstack version and exit.

       -? --help
              Print help message.

       --usage
              Print a short usage message.

ARGUMENTS

       Command  line  arguments  should  be  names  of ELF binaries and shared
       libraries which should be modified or queried.

EXAMPLES

              # execstack -s ~/lib/libfoo.so.1
       will mark ~/lib/libfoo.so.1 as requiring executable stack.
              # execstack -c ~/bin/bar
       will mark ~/bin/bar as not requiring executable stack.
              # execstack -q ~/lib/libfoo.so.1 ~/bin/bar
       will query executable stack marking of the given files.

SEE ALSO

       ld.so(8).

BUGS

       execstack doesn’t support yet marking of executables  if  they  do  not
       have  PT_GNU_STACK  program header entry nor they have room for program
       segment header table growth.

AUTHORS

       Jakub Jelinek <jakub@redhat.com>.

                                28 October 2003                   execstack(8)