April 29, 2026
One missing input, maximum chaos
Consequences of passing too few register parameters to a C function
That “missing argument” shortcut? Commenters say it can blow up fast
TLDR: Skipping a function input in C can still corrupt memory or crash a program, even when that input seems unused. Commenters loved the bizarre Itanium trivia, argued over a possible code typo, and swapped stories about abusing this behavior to detect how software was wired underneath.
A delightfully nerdy warning about cutting corners in C code turned into a mini comment-section carnival: yes, even if a function looks like it won’t need the second input, calling it with only one can still go very wrong. The big takeaway is simple for non-coders: the program may still secretly rely on that “unused” slot as temporary workspace, so skipping it can scramble memory or produce random garbage. And on the famously strange Itanium chip, things get even messier: a leftover invalid value can trigger a crash just by being written down. In other words, the community’s mood was basically: do not try to outsmart the function.
The reactions were half admiration, half chaos. One reader praised Raymond Chen’s deep-cut hardware trivia, saying they’d never even considered missing register arguments or Itanium’s gloriously weird “Not a Thing” bit. Another chimed in with a mischievous confession: they’d actually exploited this behavior in the wild to figure out which calling style an operating system was using at runtime. That sent the vibe from “helpful lesson” to retro hacker campfire story real quick.
But because no tech thread is complete without side drama, someone immediately spotted what looked like a brace typo in the code sample and basically asked, "Uh, did anybody proofread this?" Meanwhile, another commenter dropped a standards-lawyer bombshell: in C23, an old loose way of declaring function pointers now gets rejected by modern compilers. So the thread had everything: warnings, nostalgia, nitpicks, and one very cursed processor cameo.
Key Points
- •The article states that calling a C or C++ function with the wrong number of parameters is formally undefined behavior.
- •If too few stack parameters are passed under a callee-clean calling convention, the callee may remove too many bytes from the stack, causing imbalance and possible corruption.
- •A compiler may reuse the storage allocated for an unused parameter as scratch space or for a local variable, so omitting that parameter can still corrupt memory.
- •On most processors, a missing register-passed argument results in the callee reading whatever uninitialized value is already in the expected register.
- •On Itanium, a missing register argument can cause a crash because a register in the NaT state may raise a NaT consumption exception when spilled to memory, and Itanium’s call mechanism also depends on the declared number of output registers.