Raymend Chen has probably forgotten more about programming than I'll ever know, but aren't the first two blah() function examples either missing a } or have a superfluous { after the else?
I had fun exploiting this to detect the falling convention used by some code at runtime - there were two different options depending on OS version; one passed a jnienv* as the first param, the other did not. So if I called it with 0, I could tell which was being used based on whether the first argument was NULL or not. Only used for specific architectures with a defined ABI that behaved this way, of course.
It's not even possible to pass too few arguments to a function in C unless you go out of your way to write bad code.
You can write a function declaration that's inconsistent with its definition in another translation unit. Declaring the function in a shared header file avoids this.
You can use an old-style declaration that doesn't specify what parameters a function expects. Don't do that. Use prototypes.
You can use a cast to convert a function pointer to an incompatible type, and call through the resulting pointer. Don't do that.
You can call a function with no visible declaration if your compiler overly permissive or is operating in pre-C99 mode. Don't do that.
If you have 29 arguments, I assure that you some of them are on the stack in nearly every architecture in use. Also, certain types as parameters also get passed on the stack (usually types larger than a register, or in C++ code, objects with nontrivial constructors or destructors).
I had never considered the idea of passing too few register params so I didn't immediately think of the reuse problem. And I had no idea about Itanium's Not-a-thing bit! Always a good read from Raymond Chen.
Read the post - not all architectures behave the same!
Itanic had variable-sized register windows, plus extra tag bits for NaT ("not a thing") placeholder values. If you didn't set one of the argument registers the callee might trap in unexpected ways when it touches the register garbage.
If you compile with -std=c23, both gcc and clang will throw an error ( (*f)() is now the same as (*f)(void) )
Homer nods.
Kids these days!
You can write a function declaration that's inconsistent with its definition in another translation unit. Declaring the function in a shared header file avoids this.
You can use an old-style declaration that doesn't specify what parameters a function expects. Don't do that. Use prototypes.
You can use a cast to convert a function pointer to an incompatible type, and call through the resulting pointer. Don't do that.
You can call a function with no visible declaration if your compiler overly permissive or is operating in pre-C99 mode. Don't do that.
Itanium? Stone age
Itanic had variable-sized register windows, plus extra tag bits for NaT ("not a thing") placeholder values. If you didn't set one of the argument registers the callee might trap in unexpected ways when it touches the register garbage.