I seem to be getting a sigabrt crash every once in a while (not every time).
malloc: *** error for object 0x7ff8884644c0: incorrect checksum for freed object - object was probably modified after being freed.
*** set a breakpoint in malloc_error_break to debug.
Now, I know that means I'm probably attempting to access, or change an object after calling free() on it, but I was wondering how to find out what object it's referring to, using the memory address listed above. Thanks!
This is what I see before it crashes (It crashes on NSLog):
One option might be to use a debug malloc replacement such as dmalloc that can help you track source file & line number of malloc/free calls.
Related
When i run my program, I have this error :
a.out(56815,0x10bb2c5c0) malloc: *** error for object 0x7fe5ea402a90: pointer being freed was not allocated
a.out(56815,0x10bb2c5c0) malloc: *** set a breakpoint in malloc_error_break to debug
how i can set a breakpoint to malloc_error_break with lldb ?
thanks for the help
(lldb) break set -n malloc_error_break
is the lldb command for setting a breakpoint by symbol name.
That breakpoint will stop you at the point where the errant free occurred, which is some information. It may be for instance that you have a code path where you don't initialize something that you later free. The backtrace when you hit malloc_error_break will show you what you are trying to free, so you can trace back why it didn't get initialized.
If the problem ends up being more complicated (a double-free for instance), that's going to be a little harder to track down from the stop point, since you can't tell from there where the first free was. In that case, it's definitely worthwhile to rebuild your program with ASAN enabled and run it again in the debugger. In the case of double free's and such-like since ASAN records the whole malloc history of the program, it can tell you every time the errant pointer was handled by the malloc system, making the error easier to spot. It also does a bunch of pre-flight checks and can often catch memory errors early on. And at a surprisingly small performance cost as well...
There's more on ASAN here:
https://clang.llvm.org/docs/AddressSanitizer.html
If it's too difficult to rebuild with ASAN you can use the MallocStackLoggingNoCompact environment variable and then use the malloc_history program to print the errors. There's more info about that in the "malloc" manpage, e.g.:
https://developer.apple.com/library/archive/documentation/System/Conceptual/ManPages_iPhoneOS/man3/malloc.3.html
But if you are planning to do more than a little development, it's a good idea to get familiar with ASAN. It makes tracking down allocation & deallocation errors much easier.
I am coding in C and receiving a malloc error with the error message:
malloc: *** error for object 0x7fe9d44026d8: incorrect checksum for freed object - object was probably modified after being freed.
*** set a breakpoint in malloc_error_break to debug
The objective of my code is to store a generated maze into a 2D array from a string that stores the maze using the read() function. I am not having trouble reading the maze into the string but when I pass the string, number of rows, and number of columns as parameters to a function
What exactly does this malloc error mean? And how can I determine which part of my code is creating this error?
Your implementation of malloc() does additional checks not required by the C language standard. In this case, it seems to detect that some data in a memory block was modified after it was marked as free (by a call to free()). That's a bug in your program.
To find the culprit, use a memory debugging tool. For *nix systems, there is valgrind. On windows, you can use drmemory. These tools replace the memory management functions of your standard library and will notify you instantly about errors such as writing to some memory that was already free()d.
Let's say I've got a program foo that allocates and frees memory. I run it like this:
./foo something.foo
It works perfectly, exits with no errors. Now, if I set the first line of the file to #!/path/foo, change the permissions, and run it as ./something.foo, the program runs correctly, but before exiting, I see this:
*** Error in '/path/foo': free(): invalid next size(fast): 0x019e2008 ***
Aborted
I've seen a lot of questions about free(): invalid next sign(fast), all with specific code examples. So I've got two questions:
Why might the error appear when using #!/path/foo instead of ./foo?
What exactly does the error mean - what conditions must be present for it to appear?
Huh, fixed this by changing
some_var = malloc(sizeof(char *));
to
some_var = malloc(CONSTANT);
It means you have heap corruption in your program. The message is telling you how the C library detected the corruption, not how the corruption occurred.
Heap corruption is a particularly insidious bug to track down as it generally does not manifest at the point where the bug occurs, but rather at some later point. Its quite possible for the program to continue to work despite the corruption, meaning it might be a bug that has been present in your code for weeks or months and has nothing to do with any recent changes you are testing and debugging.
The best response to heap corruption is usually a tool like valgrind, which can run along with your program and will often (though not always) be able to pinpoint where the offending code is.
First, a little background so you won't think I'm attempting to do something insane:
I'm trying to debug a crash in a C library that was written by someone else. The crash looks like this:
TheProgram(44365,0x7fff75996310) malloc: *** error for object 0x7fb8d4b9d440: pointer being freed was not allocated
The crash occurs on a system where I can't run valgrind, alas. The first thing I did was wrap debug-print-macros around all of the library's calls to malloc(), calloc(), realloc(), and free() so that I see printf() output whenever memory is allocated/reallocated/freed by the library. From that debug output, it appears that the pointer that makes free() crashing was indeed allocated previously in the program, and that it wasn't freed before the problem free() call:
JJ_CHECK_MALLOC at [fastgr.c : 265] malloc() returned 0x7fb8d4b9d440
[...]
JJ_CHECK_FREE at [dotinit.c : 204] about to call free(0x7fb8d4b9d440)
TheProgram(44365,0x7fff75996310) malloc: *** error for object 0x7fb8d4b9d440: pointer being freed was not allocated
So presumably what must be happening is that somewhere after the call to malloc() and before the call to free(), the heap must be getting corrupted in such a way that free() no longer thinks that that pointer is valid.
What I need to do, then, is track down the routine that is causing the heap corruption. One way I could do this is to query the validity of the pointer at various places along the execution path, and narrow down where its status changes from "valid heap pointer" to "the heap manager doesn't know what this pointer is". But the only way I know of to find out whether the heap manager thinks the pointer is free-able is to call free(), which I obviously can't do while the program still wants to use the pointer. Is there some way to call the check-if-pointer-is-in-heap function that free() uses, without actually freeing the data?
In general: No.
There are "debugging heaps" which surround allocated blocks with additional "fence" information to help detect bad-pointer errors. These will fairly reliably complain if you try to free something that wasn't allocated through them, since the fences will be missing. (They'll also complain if you've overwritten the end of the buffer and damaged the fence, of course.) In environments where code changed frequently, I've sometimes run with these heaps permanently enabled despite the performance costs... but one would hope that they could normally be turned off before the code ships to customers.
First of all, I'm not sure this is a specific platform error. I'm using openssl library to generate big prime number and private/public keys. It ran fine when prime number is relatively small (128 bits), but I can't compile and got an error when the prime number was getting bigger (256, 512 bits).
DH * params = DH_new();
params = DH_generate_parameters(512, 5, NULL, NULL);
DH_generate_key(params); // can't get through this point when prime bits getting bigger
above code produced an error:
malloc: *** error for object 0x7ffba8403c88: incorrect checksum for freed object - object was probably modified after being freed.
*** set a breakpoint in malloc_error_break to debug
I'm using openssl 1.0.1 on MAC OX 10.8.2. I'd appreciate for any advices.
UPDATE: Another way to produce this kind's error is creating a thread before above code. Either way, it always gave me error at sub-routine DH_generate_key.
Error messages related to heap corruption such as this message from malloc() indicate that you have memory management bugs, such as using memory after freeing it, or overrunning the allocated memory. It is normal for such malloc() error messages to occur at different locations than where the actual programming error happened. Run your application in Valgrind to get some useful information on what's going wrong.
Unrelated to the error, but you have a memory leak in these two lines of your code above:
DH * params = DH_new();
params = DH_generate_parameters(512, 5, NULL, NULL);
The pointer to the allocated DH structure is overwritten in the second line with a new DH structure returned by DH_generate_parameters(). The buffer allocated by DH_new() is lost. This is not the cause of the error message though.