Stupid GCC inline assembler doesn't even support local variable

paulsm4 · 07-05-2010, 10:42 AM

Hi, guys -

1. I happened to use g++ (not gcc per se). G++ v4.1.2. The latest/greatest with CentOS 5.4:

Quote:

g++ --version
g++ (GCC) 4.1.2 20080704 (Red Hat 4.1.2-46)
Copyright (C) 2006 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

2. Yes, Gnu C/C++ inline assembler can access C/C++ local variables by name:

http://www.ibm.com/developerworks/library/l-ia.html

ntubski · 07-05-2010, 11:54 AM

Quote:

Originally Posted by paulsm4

1. I happened to use g++ (not gcc per se). G++ v4.1.2. The latest/greatest with CentOS 5.4:

Did you link the program and/or turn on warnings?

Quote:

2. Yes, Gnu C/C++ inline assembler can access C/C++ local variables by name:
http://www.ibm.com/developerworks/library/l-ia.html

Yes, but not in the way you showed.

Code:

% g++ --version                                                              ~/tmp
g++ (Debian 4.4.4-5) 4.4.4
Copyright (C) 2010 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

% cat asm.cc                                                                  ~/tmp
int myfunc(float f){
 int x;
 float fa[8];
  asm (
    "mov x,%eax\n"
    "movss f,%xmm1\n"
    "flds (fa+4)\n"
  );
}

int main() { return 0; }
% g++ -Wall -Wextra asm.cc -o asm                                             ~/tmp
asm.cc: In function ‘int myfunc(float)’:
asm.cc:2: warning: unused variable ‘x’
asm.cc:3: warning: unused variable ‘fa’
asm.cc:9: warning: no return statement in function returning non-void
asm.cc: At global scope:
asm.cc:1: warning: unused parameter ‘f’
/tmp/ccOA2oSl.o: In function `myfunc(float)':
asm.cc:(.text+0xc): undefined reference to `x'
asm.cc:(.text+0x15): undefined reference to `f'
asm.cc:(.text+0x1c): undefined reference to `fa'
collect2: ld returned 1 exit status

resetreset · 07-07-2010, 02:20 AM

I just wanted to say that I've known ASM since I was 12, and I *still* haven't learned C, because I can't stomach the concept of pointers, but - does anyone else think that C is sort of like, a high-level ASM?
Does anyone want to have a discussion, without hijacking the thread, about the *Science* of this?

pr_deltoid · 07-07-2010, 04:10 AM

I have read C is a high-level assembly, yes...

A portable assembly.