hw7: initial HW7 commit

.gitignore

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+*.so

07_DebuggingTracing/Makefile

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+GENERATES = preloader.so testfile testFIXfile
+TRASH = *.o *~ o.*
+
+all: lib test
+
+lib:
+	gcc -g -fPIC -shared  preloader.c -o preloader.so -ldl
+
+test:
+	touch testfile
+	LD_PRELOAD="./preloader.so" rm testfile
+	[ ! -f testfile ]
+	touch testFIXfile
+	-LD_PRELOAD="./preloader.so" rm testFIXfile
+	[ -f testFIXfile ]
+	rm testFIXfile
+
+clean:
+	rm -f $(TRASH)
+
+distclean: clean
+	rm -rf $(GENERATES)

07_DebuggingTracing/preloader.c

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+#define _GNU_SOURCE
+#include <dlfcn.h>
+#include <errno.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+static int (*real_unlinkat)(int dirfd, const char* pathname, int flags) = NULL;
+
+int unlinkat(int dirfd, const char* pathname, int flags) {
+    printf("unlinkat: %s\n", pathname);
+    real_unlinkat = dlsym(RTLD_NEXT, "unlinkat");
+    if (strstr(pathname, "FIX") != NULL)
+        return EPERM;
+    return real_unlinkat(dirfd, pathname, flags);
+}