execstack(8)						      System Manager's Manual						      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 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)