Notes and updated gitignore

.gitignore

 *.o
 *.d
 rlg327
-
+battleship

notes/4_26/myprintf.c

+#include <stdio.h>
+#include <stdarg.h>
+
+__attribute__((constructor))
+void init(void) {
+	//init the library
+	printf("About to replace printf.\n");
+}
+
+__attribute__((destructor))
+void destroy(void) {
+	printf("All done.\n");
+}
+
+int myprintf(const char *format, ...) {
+	int ret;
+	va_list ap;
+
+	printf("You are inside my nefarious printf!\n");
+
+	va_start(ap, format);
+	ret = vprintf(format, ap);
+	va_end(ap);
+
+	printf("Okay. Now leaving.\n");
+
+	return ret;
+}

notes/4_26/myprintf_test.c

+#include <stdio.h>
+#include <dlfcn.h>
+
+int main(int argc, char *argv[]) {
+	void *handle;
+	int (*printf)(const char *, ...);
+
+	if (!(handle = dlopen("./libmyprintf.so", RTLD_LAZY))) {
+		perror("dlopen");
+		return -1;
+	}
+
+	if (!(printf = dlsym(handle, "myprintf"))) {
+		perror("dlsym");
+		return -1;
+	}
+
+	printf("Hello World!\n");
+
+	dlclose(handle);
+
+	return 0;
+}
+

notes/4_26/notes.txt

+Static library
+ - required code is inserted into binary at compile time
+Dynamic library
+ - loaded at runtime, and only functionality needed by program is pulled
+   in on demand
+
+
+Compiling Static Library
+ar -cvq library.a file1.o file2.o
+
+Compiling Dynamic Library
+gcc with some .so output
+
+Static library is self-contained; dynamic library may implicitly depend on
+other libraries
+
+For our example DLL:
+gcc -fPIC -Wall myprintf.c -c
+gcc -shared -o libmyprintf.so myprintf.o
+gcc myprintf_test.c -o myprintf_test -l myprintf -L. -ldl
+
+Electric Fence -- malloc debugging tool
+Uses dynamic linking to replace malloc, related functions
+Allocates memory around each request and verifies it doesn't try to access
+Better tools in valgrind, gdb, so electric fence not used much any more