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.
Mark binary or shared library as requiring executable
Mark binary or shared library as not requiring executable
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
-V Print execstack version and exit.
Print help message.
Print a short usage message.
# 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.
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28 October 2003 execstack(8)