"Julian Seward (Intl Vendor)"
Hmm, we're looking at this. However, I don't really know what C is or is not supposed to do here. Given
char fooble ( ... ) { return 'z'; }
on an x86, 'z' will be returned at the lowest 8 bits in %eax. What I don't know is, is the C compiler obliged to clear the upper 24 bits of %eax, or does that onus fall on the callee?
Yes, the callee is required to narrow <expr> in 'return <expr>;' to fit that of the specified return type -- see 9.8 of Harbison and Steele. So, a C compiler that cause f() to return 0x7fffffff for the following, unsigned char g() { return 0x7fffffff; } unsigned int f() { return g(); } is in the wrong. [Notice that narrowing for signed integral types is undefined in ISO C, but most current-day compilers implement such narrowing ops the same way, i.e., by masking off excess bits.]
Also, I don't even know where to look for the specification of details of the C calling conventions. Anyone got a clue?
Harbison & Steele Chapters 6 and 9 cover the conversion rules that apply to functions (and other expressions). As you no doubt already know, lower-level details are the domain of a platform's ABI. Sounds to me like unboxed sized Words and Ints is the (unavoidable) way to go. --sigbjorn