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I'm using mingw 4.7.2.

Could someone please tell me what's wrong in this MACRO All I want to do is a simple asm macro which add two int and puts the result into result variable

#define add(result,a,b) \ __asm__ __volatile__( \ " movl %1, %%eax \n" \ " addl %2, %%eax \n" \ " movl %%eax, %0 \n" \ " :"=r"(result) \ :"r"(a),"r"(b) )

The compiler says error: missing terminating " character

Thanks in advance

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  • 1
    I guess here *" :"=r"(result) * something is wrong with number of quotes Commented Jun 7, 2013 at 9:21
  • 2
    You should also marke eax in your clobber (or use the fact that %1 is already in a register, so you don't actually need to move it anywhere to add it to another register) Commented Jun 7, 2013 at 9:28
  • thanks sharptooth , i forgot to check the syntax , but really gcc inline asm is truly painful :( Commented Jun 7, 2013 at 9:31
  • 1
    Since it's tagged C++, everything is wrong with this macro, hrhrhr. Commented Jun 7, 2013 at 10:09

2 Answers 2

Reset to default
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#define add(result,a,b) \ __asm__ __volatile__( \ " movl %1, %%eax \n" \ " addl %2, %%eax \n" \ " movl %%eax, %0 \n" \ " :"=r"(result) \ // <---- This line starts with a " for no reason. :"r"(a),"r"(b) )

The line marked begins with a " which then offsets all the other strings to the end of the macro. Just get rid of this.

I.e. your last two lines are actually:

" :"=r"(result) :"r"(a),"r"(b) ) <----str-----> <----str---> <----> <-----.... No end

When you really meant

 :"=r"(result) :"r"(a),"r"(b) ) <--> <-> <->
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1 Comment

This still fails to inform the compiler that %eax is clobbered, nor does it prevent %0, %1 or %2 being substituted with %eax.
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Here's a much more flexible implementation:

__asm__ ("addl %2, %k0" : "=r" (result) : "%0" (a), "g" (b) : "cc")

Furthermore, the __volatile__ keyword is completely unnecessary in this context.

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1 Comment

Ah, me commenting before reading the entire thread ;-) This one is much better than the original, more compact, leaving more optimization possibilities to the compiler.

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