Checking for a variable in the executable

Question

Is there a way to know whether a variable is defined, by looking at the executable.

Lets say I declare

int i;

in the main function. By compiling and linking I get an executable my_program.exe.

Now, by looking inside my_program.exe, can I say if it has an int eger variable i ?

Answer 1

除非您在启用调试的情况下进行编译，否则不会这样做。

Answer 2

As others said, debugging information will show it. More specifically, for ELF files:

readelf -w binary-name

will have an entry like:

<2><58>: Abbrev Number: 4 (DW_TAG_variable)
 <59>     DW_AT_name        : i 
 <5b>     DW_AT_decl_file   : 1 
 <5c>     DW_AT_decl_line   : 2 
 <5d>     DW_AT_type        : <73>  
 <61>     DW_AT_location    : 2 byte block: 91 6c   (DW_OP_fbreg: -20)

Without debugging information, locals don't retain their names. If the variable is a global, there will be a symbol that points to it:

objdump -t binary-name

0804a010 g     O .data  00000004              i

Type information is lost there, but you can see the size is 4

Answer 3

如果使用调试符号（例如gcc -g）进行编译，则可以使用调试器查看几乎所有内容。

Answer 4

Local variables could be eliminated by the compiler during optimization process, so the initial value of variables will be hard to find out even with debugging symbols. That is platform specific though.