Search for a pointer to a single-user postmart in GDB (C ++)

Question

I am doing a posthumous analysis of a broken program. I am on Linux (Ubuntu 12.04, x86), the code is written in C ++. The program uses some singletones that may contain valuable information. Is it possible to find a pointer to a singleton instance if it was created as follows:

SingletonType& SingletonType::getInstance(){ static SingletonType* instance = new SingletonType(); return *instance; } 

And if possible, how is this done in GDB?

Answer 1

Run gdb with the main file and run the command

 disassemble SingletonType::getInstance 

In my test program, I found the instruction mov 0x<addr>, %eax at the end of the method. A print *(*(SingletonType**) <0xaddr>) should print the contents of your singleton structure.

Answer 2

show modules ¹ should probably tell you the base addresses, and instance , being statically distributed, should be visible in some objdump / nm report. Yes, hairy math.

An alternative would be to parse SingletonType::getInstance() and see which effective address loads in the initialization / return path.

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¹ Mmm can't find the exact match that I remember. info sharedlibrary will provide you more information.

Answer 3

this is what i am doing and inside the kernel with gdb:

 (gdb) info var instance 

this will display all the addresses of all singleton instances, among which you will find one of SingletonType

 0x86aa960 SingletonType::getInstance()::instance 

Now that I have the address, you can print the reverse memory of your instance:

 (gdb) p *((SingletonType*)0x86aa960)