halfx / ElfHacks

Dive into ELF files using simple self-contained examples

ElfHacks

Dive into ELF files using simple self-contained examples.

Examples

#	Program	Description
backtrace	gcc	backtrace(3)
bss-section-in-c-and-c++	gcc/g++	.bss
hot-swapping	g++	hot swapping of C++ programs
gcc-attribute-alias	gcc	alias attribute emits an alias for another symbol
gcc-builtin_return_address	gcc	__builtin_return_address
gcc-finstrument-functions	gcc	generate instrumentation calls for entry and exit to functions
gcc-nostdlib	gcc	do not use standard system startup files or libraries
gcc-pie	gcc	produce a position independent executable (IMHO, like PIC+Bsymbolic)
gcc-static	gcc	statically linked executable
get-got-address	readelf,objdump	get GOT address of functions or variables
get-plt-address	readelf,objdump	get PLT address of functions
g++-inline-means-weak-symbol	g++	inline functions translated to weak symbols
implicit-inline-member-function	g++	member functions defined in classes are implicitly inline
ld-Bsymbolic	ld	-Bsymbolic binds references to local symbols
ld-dy-dn	ld	-dn makes ld link against static libraries
ld-execstack	ld	-z execstack and NX bit
ld-export-dynamic	ld	--export-dynamic makes executables export dynamic symbols
ld-now	ld	-z now tells ld.so to resolve symbols immediately
ld-relro	ld	RELocation Read-Only
ld-rpath	ld	-rpath sets DT_RUNPATH which adds a directory to runtime library search path
ld-whole-archive	ld	--whole-archive includes every object files (not only those which are required)
ld-wrap	ld	--wrap makes undefined references to SYMBOL be resolved to __wrap_SYMBOL
LD_BIND_NOW	ld.so	resolve all symbols at startup instead of deferring resolution to the first call
LD_PROFILE	ld.so	profile a shared library
LD_TRACE_LOADED_OBJECTS	ld.so	list dynamic library dependencies rather than running
as-syscall	as	make syscalls in x86-64 assembly
as-syscall-i386	as	make syscalls in i386 assembly
shellcode-in-c	gcc,objcopy	write shellcode in c using gcc & objcopy
objcopy-link-blob	objcopy	link blob into executable
libSegFault	glibc
version-script-hiding-c++-dynsym	ld	hide C++ dynamic symbols using a version script

Dynamic linker

The man page ld.so(8) specifies directories are searched in which order when resolving library dependencies:

• DT_RPATH attribute in dynamic section is DT_RUNPATH does not exist
• environment variable LD_LIBRARY_PATH
• DT_RUNPATH attribute in dynamic section
• /etc/ld.so.cache
• /lib, /usr/lib