prevent gcc from removing an unused variable

Question

In our source files we usually have a version string like that:

static const char srcvers[] = \"VERSION/foo.c/1.01/09.0         


        

Answer 1

As I understand your question, you need to add version string to every object file without touching sources. It can be done using next way.

Create header file, for example include/version.h:

#ifndef VERSION_H
#define VERSION_H

static const char _ver[] __attribute__((used)) = "VERSION/foo.c/1.01/09.04.15";

#endif /* VERSION_H */

Then in your Makefile (or whatever your build system is) add next gcc flag:

CPPFLAGS += -include include/version.h

Of course it should be passed to gcc, e.g. like this:

%.o: %.c
    $(CC) $(CFLAGS) $(CPPFLAGS) -o $(*).o -c $(*).c

Now you can observe your _ver string compiled to every object file:

$ objdump -DS src/main.o | grep _ver

Which will show you something like that:

Disassembly of section .rodata._ver:
00000000 <_ver>: