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 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 --exec-
       stack 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 .



			       28 October 2003			 execstack(8)

UNIX/Linux commands referenced on this page:

1. clear
2. which
3. as
4. at
5. time
6. link
7. file