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)