I’m fairly certain you’re being blocked by DEP. The x_CPUIDy_INSNS byte arrays are in a segment of memory marked as data and non-executable. EDIT: That being said, I’ve gotten a version that compiles and runs, but I don’t think gets the right values. Perhaps this will get you along your way. EDIT 2: I think … Read more
implementing alloca actually requires compiler assistance. A few people here are saying it’s as easy as: sub esp, <size> which is unfortunately only half of the picture. Yes that would “allocate space on the stack” but there are a couple of gotchas. if the compiler had emitted code which references other variables relative to esp … Read more
From your original question I did not realize gcc limited red-zone use to leaf functions. I don’t think that’s required by the x86_64 ABI, but it is a reasonable simplifying assumption for a compiler. In that case you only need to make the function calling your assembly routine a non-leaf for purposes of compilation: int … Read more
Editor’s note: this way of using a local register-asm variable is now documented by GCC as “not supported”. It still usually happens to work on GCC, but breaks with clang. (This wording in the documentation was added after this answer was posted, I think.) The global fixed-register variable version has a large performance cost for … Read more
According to the x86 ABI, EBX, ESI, EDI, and EBP are callee-save registers and EAX, ECX and EDX are caller-save registers. It means that functions can freely use and destroy previous values EAX, ECX, and EDX. For that reason, save values of EAX, ECX, EDX before calling functions if you don’t want their values to … Read more
A declaration of a local label is indeed a number followed by a colon. But a reference to a local label needs a suffix of f or b, depending on whether you want to look forwards or backwards – i.e. 1f refers to the next 1: label in the forwards direction. So declaring the label … Read more