Check if there is a specific symbol in the executable file and its dependent libraries (simplified version)

Purpose

Sometimes you want to determine if a particular symbol is used in your current execution environment when debugging. (When you want to hook a specific function with LD_PRELOAD, etc. => Reference: Replace printf later with LD_PRELOAD --Qiita)

The investigation method in that case is summarized.

Execution source

Basically, I just use ldd and readelf, but I made it a tool because it was a big deal.

elf_symbol_searcher.sh

#!/bin/bash

APP=$1
SYMBOL=$2

LIST=$(echo $APP; ldd $APP \
    | grep -v -E 'ld-linux*.so' \
    | grep -v 'linux-vdso.so' \
    | grep -v 'linux-gate.so' \
    | awk '{print $3}')

for f in $LIST
do
    echo $f
    readelf -s -W $f | grep $SYMBOL
done

I'm getting the dependent libraries with ldd, but ld-linux * .so and Linux Virtual Dynamic Shared Objects (Reference library / l-lpic1-102-3 /)) is excluded. You can get the symbol with nm, but you can't see the symbol if it is strip, so we are using readelf this time.

The execution example is as follows. This time, the target is / usr / bin / weston, and the search target is ʻeglSwapBuffers`.

Execution result

$ ./elf_symbol_searcher.sh /usr/bin/weston eglSwapBuffers
/usr/bin/weston
   166: 0000000000000000     0 FUNC    GLOBAL DEFAULT  UND eglSwapBuffers
/usr/lib/x86_64-linux-gnu/libwayland-server.so.0
/usr/lib/x86_64-linux-gnu/libpixman-1.so.0
/usr/lib/x86_64-linux-gnu/mesa-egl/libEGL.so.1
   180: 0000000000006fb0   380 FUNC    GLOBAL DEFAULT   11 eglSwapBuffersRegionNOK
   187: 0000000000009850   339 FUNC    GLOBAL DEFAULT   11 eglSwapBuffers
   235: 00000000000079e0   427 FUNC    GLOBAL DEFAULT   11 eglSwapBuffersWithDamageEXT
/usr/lib/x86_64-linux-gnu/mesa-egl/libGLESv2.so.2
/usr/lib/x86_64-linux-gnu/libxkbcommon.so.0
/lib/x86_64-linux-gnu/libdl.so.2
/lib/x86_64-linux-gnu/libm.so.6
/lib/x86_64-linux-gnu/libc.so.6
/usr/lib/x86_64-linux-gnu/libffi.so.6
/lib/x86_64-linux-gnu/librt.so.1
/lib/x86_64-linux-gnu/libpthread.so.0
/usr/lib/x86_64-linux-gnu/libX11-xcb.so.1
/usr/lib/x86_64-linux-gnu/libX11.so.6
/usr/lib/x86_64-linux-gnu/libxcb-dri2.so.0
/usr/lib/x86_64-linux-gnu/libxcb-xfixes.so.0
/usr/lib/x86_64-linux-gnu/libxcb.so.1
/usr/lib/x86_64-linux-gnu/libwayland-client.so.0
/usr/lib/x86_64-linux-gnu/libgbm.so.1
/usr/lib/x86_64-linux-gnu/libdrm.so.2
/usr/lib/x86_64-linux-gnu/libglapi.so.0
/usr/lib/x86_64-linux-gnu/libXau.so.6
/usr/lib/x86_64-linux-gnu/libXdmcp.so.6

It's very simple, but I was able to find out that there are symbols in libEGL, which implements weston and ʻeglSwapBuffers` in the body.

The script is also published below. (I plan to write it in python to make it a little easier to use) https://github.com/koara-local/elf_symbol_searcher

TODO

The above can also be used for debugging purposes, but it would be nice if you could search in a little more detail.

• Specify multiple symbols + Search by regular expression
• Specify exclusion library
• Search before and after demangle in C ++

Such

reference

Linux 101 Exam Preparation: Managing Shared Libraries