adri1mart1 / symbol-comparator

binary comparison tool based on nm

Symbol comparator

This python script has been created to ease symbol comparison between 2 binaries. When adjusting some compilation settings via CMake, the goal was find differences and understand it.

Symbol comparator just parse nm output and find all symbols that cannot be found, or symbols that have different types or sizes.

Running the example

Clone the project

git clone https://github.com/adri1mart1/symbol-comparator.git
cd symbol-comparator

Build the example:

cd example
mkdir build
cd build
cmake ..
ninja
cd ../..

Start the symbol comparison script:

python3 symbol-comparator.py --file example\symbol-comparator-example.json
comparing out files
generate nm files using: nm.exe -l -S --size-sort example/build/pgmA.exe > out\example\nm-file_A.txt
generate nm files using: nm.exe -l -S --size-sort example/build/pgmB.exe > out\example\nm-file_B.txt
 ***** file_A file *****
 * location: example/build/pgmA.exe
 * size: 122604
 * nm file number of line: 575
 * missing symbols num: 3
 ******************
 ***** file_B file *****
 * location: example/build/pgmB.exe
 * size: 122586
 * nm file number of line: 574
 * missing symbols num: 2
 ******************

The interesting output is under the out directory by default. You will find 4 files:

• the nm command output for file A.
• the nm command output for file B.
• the missing symbols in file A.
• the missing symbols in file B.

Output example

As an example, the missing-in-fileA.txt contains the following line:

Symbol s:000000000000001e t:T n:_Z3barv

Which is the symbol for the function (attribute T):

void bar() {
	std::puts("bar");
#ifdef REQUIREMENT
	std::puts("another");
#endif
}

In mainA.cpp, the REQUIREMENT is defined so the function is a bit bigger than in mainB.cpp.

The symbol in nm-fileB.txt is:

000000014000154e 000000000000002d T _Z3barv

Note the size difference 2d vs 1e.

Another example is in missing-in-fileB.txt

Symbol s:0000000000000010 t:d n:_ZL3qux

This stands for the static variable (attribute d) which is missing in mainB.cpp.

How to use

Copy and update the config-template.json file to your needs. Start the script.

You have change the default output directory which is hardcoded at the moment. You may also change the nm command to a cross compiled compatible version, so just replace the nm to arm-none-eabi-nm in the Python script.

Known limitations

• Unit tests are inexistant
• Dupplicated symbols are not well handled