How many memory pages do C compilers on desktop OSes use to detect stack overflows?

Question

This question is related to but different from this one about variable length arrays in C99.

The answers point out that one danger with allocating variable length ar

Answer 1

On Windows, it's one 4KB page (at least on x86): See Description of the stack checking for Windows NT-based applications.

This automatic growth method uses a guard page, a reserved, uncommitted, memory page that is contiguous with the committed portion of memory. When the application touches the guard page, the operating system commits that page and the next uncommitted page becomes the new guard page. Automatic stack growth works only for the guard page and stack memory must grow in 4K, or one page, increments. If the application touches another reserved but uncommitted page of stack memory before it touches the guard page, a normal page fault exception occurs and unpredictable behavior can result.

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To prevent the fault, the compiler calls the __chkstk() function each time the local allocation exceeds 4K. The Windows NT __chkstk() function does not explicitly check for stack overflow as the MS-DOS version does. It simply touches memory addresses every 4K from the current stack pointer location to the requested allocation. This triggers the guard pages in the proper sequence and commits additional memory to the stack as required.

For GCC, GCC Stack checking

I'm not sure how/if C99's VLA's would change the WinNT behaviour.

Answer 2

I'm pretty sure the most common practice is using just one page, usually 4k. A good compiler, however, will sequentially attempt to access each page of a stack frame larger than the page size on function entry (or on VLA/alloca allocation) to ensure that a guard page is hit. GCC can optionally do this; see: http://gcc.gnu.org/onlinedocs/gcc/Code-Gen-Options.html#Code-Gen-Options and the -fstack-check option.