Add demo on GOT (and PLT) analysis

There are two source code files (`main.c` and `basket.c`), a header file
(`basket.h`) and a `Makefile`. The `bascket.c` file will be compiled
into a shared library (`libbasket.so`). The `main.c` will be compiled
and linked against the shared library, resulting in an executable
`main`. We investigate the resulting files: the `main` executable and
the `libbasket.so` library.

We used `nm`, `objdump` and `readelf` for static analysis and GDB for
dynamic analysis.

Author: razvand

got-plt/.gitignore

@@ -0,0 +1,2 @@
+/main
+/libbasket.so

got-plt/Makefile

@@ -0,0 +1,25 @@
+CFLAGS = -fPIC -fno-stack-protector -Wall -Wextra
+LDFLAGS = -pie
+LDLIBS = -lbasket
+
+.DEFAULT_GOAL := all
+
+.PHONY: all clean
+
+all: main
+
+main: main.o libbasket.so
+	$(CC) $(LDFLAGS) -Wl,-rpath=. -o $@ main.o -L. $(LDLIBS)
+
+main.o: main.c basket.h
+
+libbasket.so: basket.o
+	$(CC) -shared -o $@ $^
+
+basket.o: basket.c basket.h
+
+clean:
+	-rm -f basket.o main.o
+	-rm -f main
+	-rm -f libbasket.so
+	-rm -f *~

got-plt/README.md

@@ -0,0 +1,6 @@
+unsigned long basket_size = 3;
+
+void flowers(void)
+{
+	basket_size = 55;
+}

got-plt/basket.c

@@ -0,0 +1,8 @@
+#ifndef BASKET_H_
+#define BASKET_H_	1
+
+extern unsigned long basket_size;
+
+void flowers(void);
+
+#endif

got-plt/basket.h

@@ -0,0 +1,9 @@
+#include "basket.h"
+
+int main(void)
+{
+	flowers();
+	basket_size = 99;
+
+	return 0;
+}

got-plt/main.c

@@ -0,0 +1,2 @@
+/main
+/libbasket.so

got-plt/nostdlib/.gitignore

@@ -0,0 +1,30 @@
+CFLAGS = -fPIC -fno-stack-protector -Wall -Wextra
+LDFLAGS = -nostdlib -nostdinc -pie
+LDLIBS = -lbasket
+LD.SO = /lib/x86_64-linux-gnu/ld-linux-x86-64.so.2
+
+.DEFAULT_GOAL := all
+
+.PHONY: all clean
+
+all: main
+
+main: start.o main.o libbasket.so
+	$(LD) -e_start -pie -dynamic-linker=$(LD.SO) -rpath=. -o $@ start.o main.o -L. $(LDLIBS)
+#	$(CC) $(LDFLAGS) -Wl,-e_start -o $@ start.o main.o -L. $(LDLIBS)
+
+start.o: start.s
+
+main.o: main.c basket.h
+
+libbasket.so: basket.o
+	$(LD) -shared -o $@ $^
+#	$(CC) $(LDFLAGS) -shared -o $@ $^
+
+basket.o: basket.c basket.h
+
+clean:
+	-rm -f start.o basket.o main.o
+	-rm -f main
+	-rm -f libbasket.so
+	-rm -f *~

got-plt/nostdlib/Makefile

@@ -0,0 +1 @@
+../basket.c

got-plt/nostdlib/basket.c

@@ -0,0 +1 @@
+../basket.h