when is a static variable initialized

Proc USENIX Conf on Usenix Annual Technical Conf, p.377389. Does the conduit for a wall oven need to be pulled inside the cabinet? SNPSFuzzer: a fast grey-box fuzzer for stateful network protocols using snapshots. So to implicitly initialize a local variable the compiler would need to generate code without the programmer explicitly commanding it to do so, which is quite against that "philosophy". But can we mark members of a class, static? On the other hand, the memory for local variables is allocated at run time. That actually eases writing correct programs in the long run ;-). Part of Springer Nature. What's the idea of Dirichlets Theorem on Arithmetic Progressions proof? https://doi.org/10.1631/FITEE.2200275, DOI: https://doi.org/10.1631/FITEE.2200275. It is allocated for the lifetime of program. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, Its not specific to language, but its all about concepts? https://doi.org/10.1145/3319535.3363247, College of Computer Science and Technology, National University of Defense Technology, Changsha, 410073, China, Jianxin Huang Jockey: a user-space library for record-replay debugging. If you do not explicitly initialize a static (or external) variable, it will have a value of zero of the appropriate type, unless it is a pointer, in which case it will be initialized to NULL. Note though that the assignment to the static . Proc 24th Annual Network and Distributed System Security Symp. Accelerating dynamic detection of uses of undefined values with static value-flow analysis. Normally, you would put code to initialize an instance variable in a constructor. Two attempts of an if with an "and" are failing: if [ ] -a [ ] , if [[ && ]] Why? Aviram A, Weng SC, Hu S, et al., 2012. Is it correct that when a class is loaded, static vars are created (allocated), then static initializers and initializations in declarations are executed? And why this is not true for local variables? https://doi.org/10.1007/978-3-030-29962-0_4, Giuffrida C, Cavallaro L, Tanenbaum AS, 2013. For local variables there's no way to initialize them without code because they are not initialized once, they should be initialized every time you enter their scope; also they are allocated in the stack, and when the allocation occurs the initial value in the stack in the general case is simply what was there before (except those rare moments you grow the stack more than it has grown before). The core idea is that a stateful variable features information of the communication entities and the software states, so it will exist in the form of a global or static variable during program execution. In this paper, we propose a novel method that could automatically discover the use of stateful variables in network protocol software. Initialisation of Static variables in java, Import complex numbers from a CSV file created in Matlab. It contains statements to be evaluated during class initialization. In Java, static variables are also called class variables. However, there are still ways of seeing the fields before assignments (not true with locals). In Portrait of the Artist as a Young Man, how can the reader intuit the meaning of "champagne" in the first chapter? IEEE Access, 7:1849018499. Variables with a native type can't get a null value, so non-local variables are initialized with 0 or false, as a fallback. The compiler checks for you, if the variable is definitly set. The only significant difference between them is that the scope of static variables is the entire program. Empir Softw Eng, 27(7):191. https://doi.org/10.1007/s10664-022-10233-3. ACM SIGARCH Comput Archit News, 36(3):289300. ;-). Runhao LIU helped implement the computer code in the experiments. Speaking for java: local variables must be initialized before you can access it, because it's a safety gain. This assume that compilers are really dumb. end example. Repeatable reverse engineering with PANDA. For more info, please refer to these other questions: Paragraph 8.5.6 of the C++ standard states that: "Every object of static storage duration shall be zero-initialized at program startup", (The standard also says that the initialization of local variables is undefined). https://doi.org/10.14722/ndss.2017.23183, Montesinos P, Ceze L, Torrellas J, 2008. your institution. When do function-level static variables get allocated/initialized? https://doi.org/10.1145/1085130.1085139, Song CX, Yu B, Zhou X, et al., 2019. I have no idea about java and I doubt it's different for statics/locals in java. In this paper, we propose a novel method that could automatically discover the use of stateful variables in network protocol software. Provided by the Springer Nature SharedIt content-sharing initiative, Over 10 million scientific documents at your fingertips, Not logged in You can quite easily explain why 0 is used (although indeed it sounds slightly arbitrary), but explaining -1 or 1024 seems to be even harder (especially that the variable may not be large enough to hold that value, etc). https://doi.org/10.1145/2544137.2544154, Yu B, Wang PF, Yue T, et al., 2019. Poster: fuzzing IoT firmware via multi-stage message generation. Garmany B, Stoffel M, Gawlik R, et al., 2019. AFLNET: a greybox fuzzer for network protocols. Proc Int Symp on Computer Architecture, p.265276. static or class variables (with an Object type) are initialized with null, because the compiler can't check if they are initialized at compile time. With the help of available open-source code, the evaluation results show that the average true positive rate (TPR) can reach 82% and the average precision can be approximately up to 96%. This permits more flexible initialization logic than static properties, such as using try.catch or setting multiple fields from a single value. It makes sense to initialize all of them to their default values. But then, what should that value be? Syntax: static data_type var_name = var_value; Following are some interesting facts about static variables in C: Correspondence to (),Runhao Liu When static keyword is used, variable or data members or functions can not be modified again. How much of the power drawn by a chip turns into heat? A static local variable is different from a local variable as a static local variable is initialized only once no matter how many times the function in which it resides is called and its value is retained and accessible through many calls to the function in which it is declared, e.g. ()&Jinshu Su Thanks for contributing an answer to Stack Overflow! For static variables, an initialization can be made without generating code. You initialize a static object with a constant expression, or an expression that reduces to the address of a previously declared extern or static object, possibly modified by a constant expression. See how the static variables are implemented. Not sure what you want. @Tom - The answer to your "open" question is that it would be exceedingly difficult to come up with JLS rules for this that 1) don't require analysis of all classes in a program, and 2) cope with dynamic loading. Towards automatic discovery of deviations in binary implementations with applications to error detection and fingerprint generation. You could create a static boolean variable. For local variables, none of these apply; they are allocated "on the fly" (typically on a stack) and it would be a waste of resources to clear them, since they're typically going to be assigned to very soon anyway. Is there a faster algorithm for max(ctz(x), ctz(y))? OK, but why are static variables initialized to zero, and not some other value? ReVirt: enabling intrusion analysis through virtual-machine logging and replay. Well, you generally want to do something with that variable. Does substituting electrons with muons change the atomic shell configuration? Proc 43rd Annual IEEE/IFIP Int Conf on Dependable Systems and Networks, p.112. The Static statement is used to declare specific variables within nonstatic procedures to preserve their value for as long as the program is running. Proc 33rd IFIP Int Conf on ICT Systems Security and Privacy Protection, p.141155. In contrast, a class's instance will initialize the instance variables (non-static variables). Proc Annual IEEE/ACM Int Symp on Code Generation and Optimization, p.154164. (). Anyone you share the following link with will be able to read this content: Sorry, a shareable link is not currently available for this article. https://doi.org/10.1145/1394608.1382146. The data that support the findings of this study are available from the corresponding authors upon reasonable request. Engineering record and replay for deployability. yes I agreed that the memory of static variables is alllocated at link time, but why it is zero by default. Proc 4th ACM SIGPLAN/SIGOPS Int Conf on Virtual Execution Environments, p.121130. Hence, a static variable preserves its previous value in its previous scope and is not initialized again in the new scope. As for c and c++, it's about programmers caring about their code effect and loving being in control. Network protocol software is usually characterized by complicated functions and a vast state space. Proc ACM SIGSAC Conf on Computer and Communications Security, p.25252527. Compiler persist the variable till the end of the program. Initialization of static variables should be simple, but off course it isn't. And, as always, you can do a lot of self damage if you are not careful. See 6.7.8/10 in the C99 Standard (PDF document) If an object that has automatic storage duration is not initialized explicitly, its value is indeterminate. - 5.135.136.57. The compiler checks for you, if the variable is definitly set. In this article, we will be Jianxin HUANG and Bo YU designed the research. Initializer blocks for instance variables look just like static initializer blocks, but without the static keyword: What answer are you looking for? Does the policy change for AI-generated content affect users who (want to) why global variable in C takes zero as initial value? In Germany, does an academic position after PhD have an age limit? But then how do you know if it has been initialized? If you reject this, I'd expect you to accept Andreas' answer. IEEE Trans Inform Forens Secur, 17:26732687. Proc 5th Program Protection and Reverse Engineering Workshop, Article 4. https://doi.org/10.1145/2843859.2843867, Dunlap GW, King ST, Cinar S, et al., 2002. 576), AI/ML Tool examples part 3 - Title-Drafting Assistant, We are graduating the updated button styling for vote arrows. Safelnit: comprehensive and practical mitigation of uninitialized read vulnerabilities. The static variable declaration only runs the initializer if the static variable has not been initialized. Jianxin HUANG processed the data and drafted the paper. To learn more, see our tips on writing great answers. I expanded my answer, hopefully it has the info you're interested in. We draw up some rules from multiple dimensions by taking full advantage of the existing vulnerability knowledge to determine whether the data stored in critical memory areas have stateful characteristics. As a result, class initialization will initialize static variables. Node classification with random labels for GNNs. https://doi.org/10.1109/ISCA.2008.26, Lee C, Bae J, Lee H, 2018. The semantics of initialization could still be considered sane if the default value is something other than 0, but still deterministic. Static variables are initialized only once. Actually, from the JVM point of view, the local variable simply doesn't exist until it is initialized. It has some other data members inside. x is a static variable, y is an instance variable, v[0] is an array element, a is a value parameter, b is a reference parameter, c is an output parameter, and i is a local variable. All the instances of a class share the class's static variables. https://doi.org/10.1145/1346256.1346273. ACM SIGARCH Comput Archit News, 41(3):643654. PubMedGoogle Scholar. Why does bunched up aluminum foil become so extremely hard to compress? Rationale for sending manned mission to another star? The Two Stages of Static Variable Initialization As discussed, variables with static storage duration must be initialized once before the program starts and destroyed after execution terminates. for local variables, giving them no default allows for the rule that forces the programmer to set some value before the variable is read, which can actually be useful in allowing the compiler to spot certain errors. ACM SIGOPS Oper Syst Rev, 36(SI):211224. Front Inform Technol Electron Eng 24, 403416 (2023). OCallahan R, Jones C, Froyd N, et al., 2017. Why file scope static variables have to be zero-initialized? A static variable comes into existence before execution of the . N.B. Bo Yu Connect and share knowledge within a single location that is structured and easy to search. Asking for help, clarification, or responding to other answers. This leads to the problem of forward reference. Proc 13th Int Conf on Software Testing, Validation and Verification, p.460465. #include<stdio.h> int initializer (void) { return 50; } int main () { static int i = initializer (); printf(" value of i = %d", i); getchar(); Proc 9th USENIX Symp on Operating Systems Design and Implementation, p.177191. For frequently called functions that may be a disaster. And the flip side is that default initialization of locals would result in a performance hit. When the initializer calls the current function recursively this check will be reached before the function has been initialized. Practical automated vulnerability monitoring using program state invariants. (), Academy of Military Science, Beijing, 100091, China, You can also search for this author in This is not really a technical requirement. Static functions can be called directly by using class name. This has to do with the concept of "only pay for what you use" in C/C++. MemorySanitizer: fast detector of uninitialized memory use in C++. We also implement a prototype system that can discover stateful variables automatically and then perform it on nine programs in ProFuzzBench and two complex real-world software programs. Proc 30th USENIX Security Symp, p.28292846. Jianxin HUANG, Bo YU, Runhao LIU, and Jinshu SU declare that they have no conflict of interest. For example, following program fails in compilation. Ask Question Asked 14 years, 8 months ago Modified 1 year, 4 months ago Viewed 78k times 104 I'm quite confident that globally declared variables get allocated (and initialized, if applicable) at program start time. Yes, all members are initialized for objects with static storage. In C/C++, "static" variables mean a different thing to static variables in Java! Well written ,but thats not an answer to my question. Dolan-Gavitt B, Hodosh J, Hulin P, et al., 2015. Non-final static fields should be exceedingly rare (. A static variable may also . How about a struct/record? He cites standard and I give you the reason behind it. Proc 1st Conf on Symp on Networked Systems Design and Implementation, p.112. Not the answer you're looking for? local variables must be initialized before you can access it, because it's a safety gain. You'd rather want it initialized to NULL than some random garbage. Find centralized, trusted content and collaborate around the technologies you use most. for static/member variables, if you're going to initialise them to something, then zero is a convenient value because (a) it's generally a suitable value to mean "not set to anything else special", and is the value you would have picked anyway in some cases such as counters; and (b) internally, it's likely that zero can be used for "special" values, notably to represent null in the case of an object reference. The answer is Yes. And not only performance. This is just a guess, but it might be the way it is for statics since it's easy to implement, and useful. In almost all cases it is easy to see whether a variable is assigned before use. You don't know what was there before. The object file contains the initial values for the variables in the data segment and when the OS loads the executable it loads and maps this data segment before the program starts executing. (),Bo Yu Building a safer community: Announcing our new Code of Conduct, Balancing a PhD program with a startup career (Ep. But for simplicity, if you use the "initialize to 0" strategy, you don't have to inspect the individual members and check their types. Bruening D, Zhao Q, 2011. https://doi.org/10.1109/DSN.2013.6575318, Hower DR, Hill MD, 2008. int globalgarbage; unsigned int anumber = 42; How about a pointer? Jinshu SU took the oversight and leadership responsibility for the research. Instead of letting the program fail if it accesses a non-initialized variable, it will be initialized implicit with null. Fioraldi A, DElia DC, Balzarotti D, 2021. At what point are the default values are given? StateAFL: greybox fuzzing for stateful network servers. What does it have to do with the assumption you accuse me of? That is, they belong to a class and not a particular instance. SPFuzz: a hierarchical scheduling framework for stateful network protocol fuzzing. Proc Int Symp on Code Generation and Optimization, p.213223. https://doi.org/10.1145/2160718.2160742, Article If the initialization of a non-local variable with static or thread storage duration exits via an exception, std::terminate is called. Execution replay of multiprocessor virtual machines. https://doi.org/10.1109/ICST46399.2020.00062, Pokam G, Danne K, Pereira C, et al., 2013. There are two alternatives to using a constructor to initialize instance variables: initializer blocks and final methods. https://doi.org/10.1109/CGO.2011.5764689. The compiler can co-allocate all the variables into one contigous memory area, and then either emit code (a single memset() call) to clear it before main() is called. Learn more about Institutional subscriptions. The memory for them is allocated at link time, and the initial value for them is also provided at link time. In all the languages C, C++, Java, the default initialisation of static variable is zero. () or Jinshu Su https://doi.org/10.1109/ACCESS.2019.2895025, Stepanov E, Serebryany K, 2015. Project supported by the National Natural Science Foundation of China (Nos. How can an accidental cat scratch break skin but not damage clothes? The compiler checks that final fields are assigned and not obviously used before assigned. In this type of program, a massive number of stateful variables that are used to represent the evolution of the states and store some information about the sessions are prone to potential flaws caused by violations of protocol specification requirements and program logic. But the probable reasons for these decisions in Java are: In the case of local variables, it's also conceivable that a local variable could be declared (which at the bytecode/machine code level essentially means allocating stack space/moving the stack pointer) but then never actually written/read in a particular code path. Should convert 'k' and 't' sounds to 'g' and 'd' sounds when they follow 's' in a word for pronunciation? Efficient system-enforced deterministic parallelism. Automatic discovery of stateful variables in network protocol software based on replay analysis. your institution, https://doi.org/10.1007/978-3-030-29962-0_4, https://doi.org/10.1007/978-3-319-99828-2_11, https://doi.org/10.1109/TIFS.2022.3192991, https://doi.org/10.1007/s10664-022-10233-3, https://doi.org/10.1109/ICST46399.2020.00062, https://doi.org/10.1109/ACCESS.2019.2895025, Automatic discovery of stateful variables in network protocol software based on replay analysis. Why do front gears become harder when the cassette becomes larger but opposite for the rear ones? Model checking large network protocol implementations. The use of likely invariants as feedback for fuzzers. Proc 16th USENIX Security Symp, p.213228. Static variables are commonly used in C. Since C++ is a better C, static variables are also present there. Brumley D, Caballero J, Liang ZK, et al., 2007. Google Scholar. This is a preview of subscription content, access via Bergan T, Hunt N, Ceze L, et al., 2010. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. PRETT: protocol reverse engineering using binary tokens and network traces. About Java, as far as I know, variables are always initialized when the program enters their scope, no matter if they are static or not. rev2023.6.2.43474. But then it also has to be reliably initialized to something (preferably false). static or class variables (with an Object type) are initialized with null, because the compiler can't check if they are initialized at compile time. So not having a default avoids doing unnecessary work of setting a default in those cases. This saves space in the executable, you could have. You can just initialize the entire memory area to 0. I want to know why exactly static variables in C, C++ and Java are initialized by zero by default? He probably wants to know why this choice was made. Making statements based on opinion; back them up with references or personal experience. In many cases it can also rely on features of the operating system's executable file format, if that format supports "bss sections", which are cleared by the loader instead. Frontiers of Information Technology & Electronic Engineering When variables are initialized, a numeric variable is initialized to 0, a variable-length string is initialized to a zero-length string (""), and a fixed-length string is filled with zeros. QuickRec: prototyping an Intel architecture extension for record and replay of multithreaded programs. https://doi.org/10.1007/978-3-319-99828-2_11, Li JQ, Li SY, Sun G, et al., 2022. I repeat, though, these are design decisions to some extent. Initialization is performed in the context of the current class declaration, with access to private state, which allows the . The stack has to grow. Static detection of uninitialized stack variables in binary code. 102 I am wondering when static variables are initialized to their default values. So to some extent these are just design decisions on the part of the language designers. The compilers are allowed to initialize dynamically-initialized variables as part of static initialization (essentially, at compile time), if the following conditions are both true: Why the static variables are deterministically initialized and local variables aren't? No, Ton, static variables are default-initialized. There is no runtime overhead. It's not best solution, sure, but I don't know a better one. Natella R, 2022. By clicking Post Your Answer, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct. Discovering such variables is significant in discovering and exploiting vulnerabilities in protocol software, and still needs massive manual verifications. Musuvathi M, Engler DR, 2004. And you can always initialize the variable explicitly. As to why, the standard doesn't say ;) One guess is that it's reasonably easy to implement without any additional downsides. Initializing local variables would imply execution of extra code each time program enters the scope. , , , , , , , , , , , , , , , ProFuzzBench92, (TPR)82%, 96%. https://doi.org/10.1109/TIFS.2022.3192991, Milburn A, Bos H, Giuffrida C, 2017. Based on recording and replaying a protocol programs execution, varieties of variables in the life cycle can be tracked with the technique of dynamic instrument. and the executable would not grow by a megabyte. Jianxin HUANG and Bo YU revised and finalized the paper. The C++ philosophy is "you don't pay for things you don't use", so it doesn't zero that memory by default. How to deal with "online" status competition at work? Stephen C, not so much performance as control over performance. 9.2.2 Static variables. what about a class object, sure its constructor won't be called at link time, then if it is initialized in link time, it is just initialized as a POD, which seems make no sense? Frontiers of Information Technology & Electronic Engineering, access via Commun ACM, 55(5):111119. In general relativity, why is Earth able to accelerate? Proc 24th European Symp on Research in Computer Security, p.6887. Initialization of static variables in C Read Discuss (70+) Courses Practice In C, static variables can only be initialized using constant literals. This means that the initializer will be called multiple times. The core idea is that a stateful variable features information of the communication entities and the software states, so it will exist in the form of a global or static variable during program execution. Is the order of variables defined by the standard? Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. to be used as a count variable. Practical memory checking with Dr.Memory. A static class can be used as a convenient container for sets of methods that just operate on input parameters and do not have to get or set any internal instance fields. Proc IEEE/ACM Int Symp on Code Generation and Optimization, p.4655. What maths knowledge is required for a lab-based (molecular and cell biology) PhD? And the C++ designers are more focused on performance than ease of writing correct programs. 2023 Springer Nature Switzerland AG. How are these two pieces of code different? https://doi.org/10.1145/844128.844148, Dunlap GW, Lucchetti DG, Fetterman MA, et al., 2008. https://doi.org/10.1109/CGO.2015.7054186, Ye D, Sui YL, Xue JL, 2014. volume24,pages 403416 (2023)Cite this article. 2019JJ50729), Huang, J., Yu, B., Liu, R. et al. They're essentially a tradeoff between what's likely to be convenient for JVM implementations and convenient for programmers. A field declared with the static modifier is a static variable. If an object that has static storage duration is not initialized explicitly, then: if it is a union, the first named . Pham V, Bhme M, Roychoudhury A, 2020. 61902416 and 61902412) and the Natural Science Foundation of Hunan Province, China (No. Rerun: exploiting episodes for lightweight memory race recording. Given that, the behavior is consistent among all of them. Proc 6th Int Symp on Automated Analysis-Driven Debugging, p.6976. @hacker, I want to know why exactly static variables are initialized by zero? Deterministic process groups in DoS. https://doi.org/10.1145/2508148.2485977, Saito Y, 2005. If you want, you can clear that memory (zero it), but that would incur a runtime overhead. And you always have paragraph 8.5.6 of the C++ standard which says "Every object of static storage duration shall be zero-initialized at program startup". Static variables have the property of preserving their value even after they are out of their scope! To subscribe to this RSS feed, copy and paste this URL into your RSS reader. DeLorean: recording and deterministically replaying shared-memory multiprocessor execution efficiently. What do the following phrases mean in C++: zero-, default- and value-initialization? Early dynamic initialization. Static initialization blocks are declared within a class.

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