Causes Bus Error C
Contents |
here for a quick overview of the site Help Center Detailed answers to any questions you might have Meta Discuss the workings and policies of this site About Us Learn more about Stack Overflow the company Business Learn more about hiring developers
Causes Of Runtime Error In C
or posting ads with us Stack Overflow Questions Jobs Documentation Tags Users Badges Ask Question x bus error 10 c Dismiss Join the Stack Overflow Community Stack Overflow is a community of 4.7 million programmers, just like you, helping each other. Join them; it bus error in c program only takes a minute: Sign up What is a bus error? up vote 156 down vote favorite 49 What does the "bus error" message mean, and how does it differ from a segfault? c unix segmentation-fault bus-error share|improve this question
C Bus Error Core Dumped
edited Oct 18 '15 at 10:44 Cool Guy 15.8k51952 asked Oct 17 '08 at 14:48 raldi 7,244216178 add a comment| 15 Answers 15 active oldest votes up vote 151 down vote accepted Bus errors are rare nowadays on x86 and occur when your processor cannot even attempt the memory access requested, typically: using a processor instruction with an address that does not satisfy its alignment requirements. Segmentation faults occur when accessing memory which does not belong to your process, they are
Bus Error C++
very common and are typically the result of: using a pointer to something that was deallocated. using an uninitialized hence bogus pointer. using a null pointer. overflowing a buffer. PS: To be more precise this is not manipulating the pointer itself that will cause issues, it's accessing the memory it points to (dereferencing). share|improve this answer edited Oct 17 '08 at 15:18 answered Oct 17 '08 at 15:12 bltxd 5,72322336 52 They aren't rare; I'm just at Exercise 9 from How to Learn C the Hard Way and already encountered one... –11684 Mar 26 '13 at 20:12 5 Another cause of bus errors (on Linux anyway) is when the operating system can't back a virtual page with physical memory (e.g. low-memory conditions or out of huge pages when using huge page memory.) Typically mmap (and malloc) just reserve the virtual address space, and the kernel assigns the physical memory on demand (so called soft page faults.) Make a large enough malloc, and then write to enough of it and you'll get a bus error. –Eloff Jul 14 '15 at 0:09 add a comment| up vote 58 down vote A segfault is accessing memory that you're not allowed to access. It's read-only, you don't have permission, etc... A bus error is trying to access memory that can't possibly be there. You've used an address that's meaningless to the system, or the wrong kind of address for that o
here for a quick overview of the site Help Center Detailed answers to any questions you might have Meta Discuss the workings and policies of bus error linux this site About Us Learn more about Stack Overflow the company Business Learn
How To Debug Bus Error
more about hiring developers or posting ads with us Stack Overflow Questions Jobs Documentation Tags Users Badges Ask Question bus error vs segmentation fault x Dismiss Join the Stack Overflow Community Stack Overflow is a community of 4.7 million programmers, just like you, helping each other. Join them; it only takes a minute: Sign up http://stackoverflow.com/questions/212466/what-is-a-bus-error How to get a “bus error”? up vote 12 down vote favorite 1 I am trying very hard to get a bus error. One way is misaligned access and I have tried the examples given here and here, but no error for me - the programs execute just fine. Is there some situation which is sure to produce a bus error? c++ bus-error share|improve http://stackoverflow.com/questions/2069450/how-to-get-a-bus-error this question edited Jan 15 '10 at 9:50 asked Jan 15 '10 at 4:06 Lazer 25k65211309 2 What platform and hardware architecture are you using? –R Samuel Klatchko Jan 15 '10 at 5:32 it should be noted that by default x86 will not have a bus error, instead it will work but the memory access will be not as performant as an aligned read. on the other hand SPARC arches do have a bus error. –Evan Teran Jan 15 '10 at 6:50 1 No, see Michael Burr's comments and my answer. Even on x86, you can get a bus error by attempting to access memory which does not exist (as opposed to a segmentation fault, which comes from a violation of access policy). –ephemient Jan 16 '10 at 16:29 add a comment| 11 Answers 11 active oldest votes up vote 11 down vote accepted Bus errors can only be invoked on hardware platforms that: Require aligned access, and Don't compensate for an unaligned access by performing two aligned accesses and combining the results. You probably do not have access to such a system. share|improve
challenged and removed. (July 2015) (Learn how and when to remove this template message) In computing, a bus error is a fault raised by hardware, notifying an operating system (OS) that a process is trying to access memory that the CPU https://en.wikipedia.org/wiki/Bus_error cannot physically address: an invalid address for the address bus, hence the name. In http://www.glue.umd.edu/afs/glue.umd.edu/system/info/olh/Utilities/Unix_answers/unix_bus_or_seg.html modern use on most architectures these are much rarer than segmentation faults, which occur primarily due to memory access violations: problems in the logical address or permissions. On POSIX-compliant platforms, bus errors usually result in the SIGBUS signal being sent to the process that caused the error. SIGBUS can also be caused by any general device fault that the bus error computer detects, though a bus error rarely means that the computer hardware is physically broken—it is normally caused by a bug in a program's source code.[citation needed] Bus errors may also be raised for certain other paging errors; see below. Contents 1 Causes 1.1 Non-existent address 1.2 Unaligned access 1.3 Paging errors 2 Example 3 References Causes[edit] There are at least three main causes of bus errors: Non-existent address[edit] Software instructs the CPU bus error c to read or write a specific physical memory address. Accordingly, the CPU sets this physical address on its address bus and requests all other hardware connected to the CPU to respond with the results, if they answer for this specific address. If no other hardware responds, the CPU raises an exception, stating that the requested physical address is unrecognized by the whole computer system. Note that this only covers physical memory addresses. Trying to access an undefined virtual memory address is generally considered to be a segmentation fault rather than a bus error, though if the MMU is separate, the processor can't tell the difference. Unaligned access[edit] Most CPUs are byte-addressable, where each unique memory address refers to an 8-bit byte. Most CPUs can access individual bytes from each memory address, but they generally cannot access larger units (16 bits, 32 bits, 64 bits and so on) without these units being "aligned" to a specific boundary (the x86 platform being a notable exception). For example, if multi-byte accesses must be 16 bit-aligned, addresses (given in bytes) at 0, 2, 4, 6, and so on would be considered aligned and therefore accessible, while addresses 1, 3, 5, and so on would be considered unaligned. Similarly, if multi-byte accesses must be 32-bit aligned, addresses 0, 4, 8, 12, and
program yourself, you can skip the rest of this section. For College-supported software, you can report the bug by contacting a consultant through olc or "mail staff". ------------------------------------------------------------------------------- If the program displays this message: Bus error or Segmentation fault or Core dump ... then the program was trying to access a memory location outside its address space. The computer detected this problem and sent a signal to your program, which caused it to abort. Things that cause bus errors and segmentation violations are typically out-of-bounds array references and/or references through uninitialized or mangled pointers. Look very closely in your program for bizarre things like that. A common example in C is: int c; scanf("%d", c); instead of the correct version: int c; scanf("%d", &c); An example from C++ is: int* p=new int[100]; cout<< p[100]; instead of the correct version: int* p=new int[100]; cout << p[99] (remember array referances in C and C++ start with 0 ) There are a number of methods for finding out where the program went out of bounds. One method is to use printf() statements to determine how far the program is getting before it crashes, and to print out the contents of interesting variables. A more sophisticated method is using 'dbx', a source level symbolic debugger. C and C++ programmers can also use 'gdb'. To learn about 'dbx', you can read the manual pages by using the 'man' command, as in: man dbx To learn about 'gdb', you can read the manual node in the 'xinfo' program, or using 'M-x info' in Emacs. If you need to debug your program, you may want to enable a core dump. Usually, those two messages above would also have "(core dumped)" by them, indicating that the program wrote an image of its current memory into a file called "core" in that directory. You might want to type 'fs lq' and find out how many blocks (kilobytes) you have available in your quota. Then you can type, say: limit coredumpsize 100 .. to limit your core dump size to 100K for your current login. BE CAREFUL not to let yourself go over quota, as you would then not be able to create or edit files. You sh