execstack - tool to set, clear, or query executable stack flag of ELF
binaries and shared libraries
execstack [OPTION...] [FILES]
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 automat-
ically 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 stack.
Mark binary or shared library as not requiring executable stack.
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 exe-
cutable stack (the marking is missing).
-V Print execstack version and exit.
Print help message.
Print a short usage message.
Command line arguments should be names of ELF binaries and shared
libraries which should be modified or queried.
# 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.
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.
Jakub Jelinek <firstname.lastname@example.org>.
28 October 2003 execstack(8)
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