The article explains how the alloca function allocates memory from the stack. Contrary to some assumptions, alloca does indeed perform necessary stack probing using the _chkstk() function to prevent large allocations from skipping guard pages. An assembly example shows that both local frame creation and alloca() invoke the same __chkstk() routine. On x86-64, the process involves pushing registers, calling __chkstks for initial local frame setup, then adjusting the stack pointer before allocating the buffer. Finally, consume() accesses the newly allocated memory and cleans up the local frame. This dual-probing mechanism ensures stack integrity for dynamic-sized allocations.

The same __chkstk() function serves two purposes here: first during local frame construction when setting up the stack frame, and second immediately afterward when recalculating the stack pointer after the alloca() adjustment. This ensures that if a guard page check fails, the system can detect and handle violations properly. The code snippet demonstrates this flow clearly in assembly language, showing how the compiler handles temporary buffers safely.