On Mon, Dec 16, 2013 at 10:47 PM, Florian Weimer <fweimer@xxxxxxxxxx> wrote: > Isn't it specific to a subset of all the architectures? If it's generic, it > makes sense to add it to the Extended Asm documentation. If I am to give opinion, here it is: I have only used the x86/x64 architecture so far and don't know if it is architecture specific or generic. AFAIK the $ sign for immediate operands is for all architectures, so i'd guess the feature is generic. This feature is not a constraint modifier and has nothing to do with the constraints because it is written in the assembly string itself and not in the constraint descriptor string: asm ( "... %0 ..." : "+r" (...) : ); // the '+' here is a constraint modifier asm ( "... %a0 ..." : : "i" (...) ); // the 'a' here is NOT a constraint modifier so I would say it's documentation should be located in Extended Asm (or probably in a new section about "operand modifiers" or whatever they are called) but not in the constraint section. Best regards Lucho.