Re: Declaring x86_64 registers as input in gcc inline assembler

"Johannes Singler" <spamtrap@xxxxxxxxxx> wrote in message news:e0b988$b3b$1@xxxxxxxxxxxxxxxxxxxxxxxxxxxx
the gcc inline assembler allows to declare input and output registers
with its extended syntax. Since I want to bind a variable to a specific
register, I have to use a constraint like "a", "b", "S" and so on. But
how can I constrain it to one of the new registers r8-r15. Is there any
new letter for those?

I can't find anything in the documentation* that mentions the possibility. This rather makes sense, since the main reason for register constraints is for instructions that implicitly use particular registers, and no instruction implicitly uses any of the high ones. You can get a low register with the "R" constraint, but there doesn't seem to be an opposite constraint.

If you don't need a particular low register, just use constraint "r" and let the compiler figure it out.

* http://gcc.gnu.org/onlinedocs/gcc-4.1.0/gcc/Machine-Constraints.html#Machine-Constraints

S

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