1execstack(8) System Manager's Manual execstack(8)
2
6 execstack - tool to set, clear, or query executable stack flag of ELF
7 binaries and shared libraries
8
10 execstack [OPTION...] [FILES]
11
13 execstack is a program which sets, clears, or queries executable stack
14 flag of ELF binaries and shared libraries. Linux has in the past
15 allowed execution of instructions on the stack and there are lots of
16 binaries and shared libraries assuming this behaviour. Furthermore,
17 GCC trampoline code for e.g. nested functions requires executable stack
18 on many architectures. To avoid breaking binaries and shared libraries
19 which need executable stack, ELF binaries and shared libraries now can
20 be marked as requiring executable stack or not requiring it. This
21 marking is done through the p_flags field in the PT_GNU_STACK program
22 header entry. If the marking is missing, kernel or dynamic linker need
23 to assume it might need executable stack. The marking is done automat‐
24 ically by recent GCC versions (objects using trampolines on the stack
25 are marked as requiring executable stack, all other newly built objects
26 are marked as not requiring it) and linker collects these markings into
27 marking of the whole binary or shared library. The user can override
28 this at assembly time (through --execstack or --noexecstack assembler
29 options), at link time (through -z execstack or -z noexecstack linker
30 options) and using the execstack tool also on an already linker binary
31 or shared library. This tool is especially useful for third party
32 shared libraries where it is known that they don't need executable
33 stack or testing proves it.
34
36 -s --set-execstack
37 Mark binary or shared library as requiring executable stack.
38 -c --clear-execstack
40 Mark binary or shared library as not requiring executable stack.
41 -q --query
43 Query executable stack marking of binaries and shared libraries.
44 For each file it prints either - when executable stack is not
45 required, X when executable stack is required or ? when it is
46 unknown whether the object requires or doesn't require exe‐
47 cutable stack (the marking is missing).
48 -V Print execstack version and exit.
50 -? --help
52 Print help message.
53 --usage
55 Print a short usage message.
56
58 Command line arguments should be names of ELF binaries and shared
59 libraries which should be modified or queried.
60
62 # execstack -s ~/lib/libfoo.so.1
63 will mark ~/lib/libfoo.so.1 as requiring executable stack.
64 # execstack -c ~/bin/bar
65 will mark ~/bin/bar as not requiring executable stack.
66 # execstack -q ~/lib/libfoo.so.1 ~/bin/bar
67 will query executable stack marking of the given files.
68
70 ld.so(8).
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73 execstack doesn't support yet marking of executables if they do not
74 have PT_GNU_STACK program header entry nor they have room for program
75 segment header table growth.
76
78 Jakub Jelinek <jakub@redhat.com>.
79 28 October 2003 execstack(8)