ELF Hacks
我喜欢基于代码片段的学习，之前学习过一些binutils和其他处理ELF的工具的奇技淫巧，了解到很多概念，比如weak symbol、common section、RPATH、把资源文件嵌入ELF等，昨天创建了一个项目https://github.com/MaskRay/ElfHacks整理了很多自包含的例子。
| # | Program | Description |
|---|---|---|
| backtrace | gcc | backtrace(3) |
| bss-section-in-c-and-c++ | gcc/g++ | .bss |
| gcc-attribute-alias | gcc | alias attribute emits an alias for another symbol |
| 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 |
| 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-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 |
每个例子都存放在单独的目录，里面有Makefile。在单独的目录里，执行make show可以看到说明，和所描述特性相关的输出用终端的红色字标出了。有些例子提供了make gdb，是用Expect脚本写的gdb的交互式会话，用来观察所描述的特性如何影响程序的运行时状态。
项目根目录也提供了Makefile，执行make show或make gdb会递归地在各例子目录里执行make。