thesis: Complete 2.2

thesis/listings/intercept-preload.c

@@ -0,0 +1,35 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <errno.h>
+#include <string.h>
+#include <dlfcn.h>
+
+static void *(*__real_malloc)(size_t);
+
+static int mode = 0;
+
+static void fin(void) {
+    if (mode > 0) fprintf(stderr, "intercept: stopped\n");
+    mode = 0;
+}
+
+static void init(void) {
+    if (mode) return;
+    mode = -1;
+    if (((__real_malloc) = dlsym(RTLD_NEXT, "malloc")) == NULL) {
+        fprintf(stderr, "intercept: unable to load symbol '%s': %s",
+            "malloc", strerror(errno));
+        return;
+    }
+    atexit(fin);
+    fprintf(stderr, "intercept: intercepting function calls\n");
+    mode = 1;
+}
+
+void *malloc(size_t size) {
+    init();
+    // before call to malloc
+    void *ret = __real_malloc(size);
+    // after call to malloc
+    return ret;
+}

thesis/listings/intercept-wrap.c

@@ -0,0 +1,27 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+extern void *__real_malloc(size_t);
+
+static int mode = 0;
+
+static void fin(void) {
+    if (mode > 0) fprintf(stderr, "intercept: stopped\n");
+    mode = 0;
+}
+
+static void init(void) {
+    if (mode) return;
+    mode = -1;
+    atexit(fin);
+    fprintf(stderr, "intercept: intercepting function calls\n");
+    mode = 1;
+}
+
+void *__wrap_malloc(size_t size) {
+    init();
+    // before call to malloc
+    void *ret = __real_malloc(size);
+    // after call to malloc
+    return ret;
+}

thesis/listings/intercept.c

@@ -0,0 +1,47 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <errno.h>
+#include <string.h>
+#include <dlfcn.h>
+
+#ifdef INTERCEPT_PRELOAD
+#define load(name) \
+    if (((__real_ ## name) = dlsym(RTLD_NEXT, #name)) == NULL) { \
+        fprintf(stderr, "intercept: unable to load symbol '%s': %s", \
+            #name, strerror(errno)); \
+        return; \
+    }
+#define sym(name) name
+#define func_def(ret, name) static ret (*__real_ ## name)
+#else
+#define sym(name) __wrap_ ## name
+#define func_def(ret, name) extern ret __real_ ## name
+#endif
+
+func_def(void *, malloc)(size_t);
+
+static int mode = 0;
+
+static void fin(void) {
+    if (mode > 0) fprintf(stderr, "intercept: stopped\n");
+    mode = 0;
+}
+
+static void init(void) {
+    if (mode) return;
+    mode = -1;
+#ifdef INTERCEPT_PRELOAD
+    load(malloc);
+#endif
+    atexit(fin);
+    fprintf(stderr, "intercept: intercepting function calls\n");
+    mode = 1;
+}
+
+void *sym(malloc)(size_t size) {
+    init();
+    // before call to malloc
+    void *ret = __real_malloc(size);
+    // after call to malloc
+    return ret;
+}

thesis/listings/preload.c

@@ -0,0 +1,15 @@
+#include <stdlib.h>
+#include <dlfcn.h>
+#include <errno.h>
+
+void *malloc(size_t size) {
+    // before call to malloc
+    void *(*_malloc)(size_t);
+    if ((_malloc = dlsym(RTLD_NEXT, "malloc")) == NULL) {
+        errno = ENOSYS;
+        return NULL;
+    }
+    void *ret = _malloc(size);
+    // after call to malloc
+    return ret;
+}

thesis/listings/wrap.c

@@ -0,0 +1,10 @@
+#include <stddef.h>
+
+extern void *__real_malloc(size_t size);
+
+void *__wrap_malloc(size_t size) {
+    // before call to malloc
+    void *ret = __real_malloc(size);
+    // after call to malloc
+    return ret;
+}

thesis/src/02.intercept.tex

@@ -39,18 +39,7 @@ Also note that arguments to the calls are displayed in a ``pretty'' way.
 For example, string arguments would be simple pointers, but \texttt{strace} displays them as C-like strings.
 
 \begin{listing}[htbp]
-  \begin{minted}[linenos]{c}
+  \inputminted[linenos]{c}{listings/main.c}
-#include <stdlib.h>
-#include <stdio.h>
-#include <string.h>
-
-int main(const int argc, char *const argv[]) {
-    char *str = malloc(10);
-    strcpy(str, "Abc123");
-    printf("Hello World!\nString: %s\n", str);
-    free(str);
-}
-  \end{minted}
   \caption{Contents of \texttt{main.c}.}
   \label{lst:main.c}
 \end{listing}
@@ -149,18 +138,7 @@ To call the real function inside the wrapper, \texttt{\_\_real\_\textit{symbol}}
 Listings \ref{lst:wrap.c} and \ref{lst:wrap} try to illustrate this by overriding the \texttt{malloc} function of the C standard library.
 
 \begin{listing}[htbp]
-  \begin{minted}[linenos]{c}
+  \inputminted[linenos]{c}{listings/wrap.c}
-#include <stddef.h>
-
-extern void *__real_malloc(size_t size);
-
-void *__wrap_malloc(size_t size) {
-    // before call to malloc
-    void *ret = __real_malloc(size);
-    // after call to malloc
-    return ret;
-}
-  \end{minted}
   \caption{Contents of \texttt{wrap.c}.}
   \label{lst:wrap.c}
 \end{listing}
@@ -213,23 +191,7 @@ This means, by setting the environment variable \texttt{LD\_PRELOAD}, it is poss
 Listings \ref{lst:preload.c} and \ref{lst:preload} try to illustrate this by overriding the \texttt{malloc} function of the C standard library.
 
 \begin{listing}[htbp]
-  \begin{minted}[linenos]{c}
+  \inputminted[linenos]{c}{listings/preload.c}
-#include <stdlib.h>
-#include <dlfcn.h>
-#include <errno.h>
-
-void *malloc(size_t size) {
-    // before call to malloc
-    void *(*_malloc)(size_t);
-    if ((_malloc = dlsym(RTLD_NEXT, "malloc")) == NULL) {
-        errno = ENOSYS;
-        return NULL;
-    }
-    void *ret = _malloc(size);
-    // after call to malloc
-    return ret;
-}
-  \end{minted}
   \caption{Contents of \texttt{preload.c}.}
   \label{lst:preload.c}
 \end{listing}
@@ -264,9 +226,20 @@ because it is simple to use (``clean'' source code, easy to compile and run prog
 The following sections concern the next steps in what else is needed to create a powerful ``interceptor''.
 
 
-\section{Combining Preloading and Wrapper Functions}\label{sec:combining-preloading-and-wrapper-functions}
+\section{Fundamental Project Structure}\label{sec:structure}
+
+After deciding to use the preloading method to intercept function calls, a more detailed plan is needed to continue developing.
+It was decided to have one single \texttt{intercept.so} file as a resulting artifact which then may be loaded via the \texttt{LD\_PRELOAD} environment variable.
+The easiest and most straightforward way to structure the source code was to put all code in one single C file.
+Listing \ref{lst:intecept-preload.c} gives an overview over the grounding code structure.
+For each function that should be intercepted, this function simply has to be declared and defined as \texttt{malloc} was.
+
+\begin{listing}[htbp]
+  \inputminted[linenos]{c}{listings/intercept-preload.c}
+  \caption{Contents of \texttt{intercept-preload.c}.}
+  \label{lst:intecept-preload.c}
+\end{listing}
 
-Lorem Ipsum.
 
 \section{Retrieving Function Argument Values}\label{sec:Retrieving-function-argument-values}