execstack(8)                                                                                                        execstack(8)



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 assum-
       ing  this behaviour.  Furthermore, GCC trampoline code for e.g. nested functions requires executable stack on many archi-
       tectures.  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 <jakubATredhat.com>.



                                                         28 October 2003                                            execstack(8)