Great day!! Finally I came to know, how to create a file which can act as both shared library and executable. You might not have observed it in your unix machines. In linux, execute /lib/libc.so as a command, it gives you all the version information. I have been trying to simulate the same feature in my shared libraries also. I have seen glibc source code and got to know that we have to use entry option of linker. With that knowledge, I have written a small program and tried for a complete working day, with the result ending up in Illegal instructions/ segmentation faults. Then I have just sent a mail to gcc mailing list and got the answers 1 ,2 ,3.
I am attaching a simple 5 line c program here. Commands that I have used are
# gcc -g -W -Wall -fPIC -o libtest.so -shared -Wl,-e,test1 test.c
#./ libtest.so
Hi dp! you finally made it
#
In our C program, we have to declare a char array for .interp section to hold the absolute path of the linker. In our entry function test1, after processing the logic, we should use exit() function instead of returning. I dont know the logic behind these 2 points.
In Solaris also, we can have this feature. But, I have not tried/tested it. If you are interested, you can look at this. Read the whole page and see the comment named “solaris 9 compile”.
