CODEWITHSUNDEEP
c++visual-studio-2008assembly
Junling
Junling

Reputation: 37

How to use asm code in C++ & Visual Studio 2008

I am doing some cross-platform work, porting code from Linux to Win32, but when it comes to some assembly code, I cannot get it to work. This code compiles normally in Linux gcc, but will not work in VS2008 --win32.

Some of my code is below. What do I need to do if I want to compile it using VS2008 --win32 platform:

static inline void spin_wait(int n)
{
    int    tmp = n;
    while(tmp > 0) { tmp--; asm("" ::: "memory", "cc"); }
}

__asm__ __volatile__(
    "xorq        %%rdx, %%rdx    \n"
    "xorq        %%rax, %%rax    \n"
    "incq        %%rdx        \n"
    "lock cmpxchgq    %%rdx, (%1)    \n"
    "decq        %%rax        \n"
: "=a" (not_set) : "r" (n) : "%rdx");

Upvotes: 0

Views: 1529

Answers (2)

snemarch
snemarch

Reputation: 5018

A thing like "spin_wait" isn't portable, and should be (re)written to what's appropriate for the target platform. It's been a while since I've dealt with the horrible GAS syntax, but xorq means the snippet is for x86-64, right? The Microsoft compilers don't support inline assembly for 64bit targets.

Will _AcquireSpinLock perhaps do the trick?

For larger blocks of assembly (the parts that generally make sense to write in assembly), I'd advise you to use an external assembly module with a cross-platform assembler with sane syntax and a good feature set (for instance yasm, fasm or nasm). Of course that's not viable for something as critical and must-be-inline as a spinlock, though :)

Upvotes: 1

Konrad
Konrad

Reputation: 41027

If your question is about the use of inline assembly, you can still use it in Visual Studio (MSDN link) although you may need to tweak it for the platform of course.

For example:

__asm {
   mov al, 2
   mov dx, 0xD007
   out dx, al
}

Upvotes: 2

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