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)