Inline assembler: Pass a constant

Question

I have the following problem: I want to use the following assembler code from my C source files using inline assembler:

.word 1

The closest I've gotten is using this inline assembler code:

asm(".word %0\n": : "i"(1));

However, this results in the following code in the generated assembler file:

.word #1

So I need a way to pass a constant that is known at compile time without adding the '#' in front of it. Is this possible using inline assembler?

Edit:

To make it more clear why I need this, this is how it will be used:

#define LABELS_PUT(b) asm(".word %0\n": : "i"((b)));

int func(void) {
    LABELS_PUT(1 + 2);

    return 0;
}

I can't use ".word 1" because the value will be different every time the macro LABELS_PUT is called.

Answer 1

Your macro has a ; at the end. So it's a whole statement, not just an expression. Don't do that.

A .word mixed in with the code of your function is usually going to be an illegal instruction, isn't it? Are you actually planning to run this binary?

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You should be able to get the preprocessor to stringify your macro parameter, and let string-concatenation join it up. Then the assembler can evaluate 1+2.

#define LABELS_PUT(b) asm(".word " #b  "\n")


LABELS_PUT(1+2);   // becomes:
asm(".word " "1+2" "\n");

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There's also https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html#x86Operandmodifiers, some of which might work for other architectures:

asm (".word %c0" : : "i" (b))