execstack(8)               System Manager's Manual              execstack(8)

NAME         top

       execstack - tool to set, clear, or query executable stack flag of ELF
       binaries and shared libraries

SYNOPSIS         top

       execstack [OPTION...] [FILES]

DESCRIPTION         top

       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         top

       -s --set-execstack
              Mark binary or shared library as requiring executable stack.

       -c --clear-execstack
              Mark binary or shared library as not requiring executable

       -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.

              Print a short usage message.

ARGUMENTS         top

       Command line arguments should be names of ELF binaries and shared
       libraries which should be modified or queried.

EXAMPLES         top

              # execstack -s ~/lib/
       will mark ~/lib/ as requiring executable stack.
              # execstack -c ~/bin/bar
       will mark ~/bin/bar as not requiring executable stack.
              # execstack -q ~/lib/ ~/bin/bar
       will query executable stack marking of the given files.

SEE ALSO         top

BUGS         top

       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         top

       Jakub Jelinek <>.

COLOPHON         top

       This page is part of the prelink (prelink ELF shared libraries and
       binaries) project.  Information about the project can be found at 
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       COLOPHON (which is not part of the original manual page), send a mail

                               28 October 2003                  execstack(8)