gcc7.2: argument range exceeds maximum object size 9..7 [-Werror=alloc-size-larger-than=]

Question

The program contains code like follows:

int size;
...
int *pi = (int*)calloc(size, sizeof(int));
...

Here is the error message when compiled with gcc7.2：

error: argument 1 range [18446744071562067968, 18446744073709551615] exceeds maximum object size 9223372036854775807 [-Werror=alloc-size-larger-than=]

When I change
int *pi = (int*)calloc(size, sizeof(int)); to
int *pi = (int*)calloc((unsigned int)size, sizeof(int));

The error disappeared.

However, in the program, there are many malloc and calloc used like my original version.

Why there is only one error detected by gcc?

Unrelated to your question, but you might want to read [this question about casting the result of `malloc` (and `calloc` too)](http://stackoverflow.com/questions/605845/do-i-cast-the-result-of-malloc). — Some programmer dude, Nov 23 '17 at 08:28
*"Should have been initialized"* usually means there's an execution path where it is not. I suggest you verify. — StoryTeller - Unslander Monica, Nov 23 '17 at 08:28
More related to your question, can you please try to create a [Minimal, **Complete**, and Verifiable Example](http://stackoverflow.com/help/mcve) and show us? — Some programmer dude, Nov 23 '17 at 08:28
The original code is too complicated, I haven't reproduced it with small case. — Yuan Wen, Nov 23 '17 at 08:32
Just in case someone met this problem before which may save me sometime — Yuan Wen, Nov 23 '17 at 08:36
18446744071562067968=2^64-2^31. 18446744073709551615=2^64-1. Make what you want of it. — n. m. could be an AI, Nov 23 '17 at 08:40

score 6 · Answer 1 · answered Jun 21 '19 at 12:23

6

I recently had the same problem on my GCC 9.1 build, and I found this discussion on the GCC Bugzilla:

https://gcc.gnu.org/bugzilla//show_bug.cgi?id=85783

As mentioned in the link discussion, I was able to suppress the warning by checking the size parameter against PTRDIFF_MAX.

answered Jun 21 '19 at 12:23

Kurt

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1
4

1

What's wrong with this answer? It answers the question by showing the link to the bug report and provides a workaround. I do not think it merits deletion. – L. F. Jun 22 '19 at 01:14

score 3 · Answer 2 · answered Aug 12 '20 at 08:34

The warning mentions a maximum object size of 9223372036854775807 (0x7FFFFFFFFFFFFFFF). It is an implementation defined value. size_t must be large enough to hold that value, and indeed, being unsigned, it can take the double of that number. The calloc() function multiplies two size_t values, its arguments nmemb and size. The resulting value can obviously exceed the maximum object size.

Well written programs are coded so as to never allow exceeding values in the arguments. However, if gcc is not able to locate such check, it issues a warning. Casting to a 4 byte integer would truncate exceeding values and make compiler happy.

score 1 · Answer 3 · answered Nov 23 '17 at 08:34

The warning depends on the range that GCC thinks size has. At that particular point in the program it is deemed to be in that (exceedingly large) range. At the other malloc/calloc callsites perhaps it wasn't so large.

It would largely depend on how size is calculated at different points in the program. Of course, making sure that it is actually initialised before any use is the first step.

gcc7.2: argument range exceeds maximum object size 9..7 [-Werror=alloc-size-larger-than=]

3 Answers3

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