From:	"Tanes Sriviroolchai" <Tanes DOT Sriviroolchai AT Thailand DOT NCR DOT COM>
Newsgroups:	comp.os.msdos.djgpp
References:	<7sul6k$l1n$1 AT dove DOT qut DOT edu DOT au>
Subject:	Re: asm errors compiling grx
Date:	Mon, 4 Oct 1999 11:02:25 +0700
Lines:	155
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To:	djgpp AT delorie DOT com
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Reply-To:	djgpp AT delorie DOT com

I think you are using gcc 2.95. If you use gcc 2.8.1 or gcc 2.7.2.x, you
will have no problem. Below is the explanation why gcc 2.95 issues error
while compiling those codes:

Regards,
Tanes Sriviroolchai

----- Start explanation -----
Why gcc 2.95 issues that error can explain by these statements that
extracted from http://gcc.gnu.org/faq.html

Problems with invalid `asm' statements
Previous releases of GCC (for example, GCC 2.7.2 or EGCS 1.1.2) did not
detect as invalid a clobber specifier that clobbered an operand. Instead, it
could spuriously and silently generate incorrect code for certain
non-obvious cases of source code. Even more unfortunately, the manual (Using
and Porting GCC, section Extended Asm, see the bug report entry) did not
explicitly say that it was invalid to specify clobber registers that were
destined to overlap operands; it could arguably be interpreted that it was
correct to clobber an input operand to mark it as not holding a usable value
after the asm.
For the general case, there is no way to tell whether a specified clobber is
intended to overlap with a specific (input) operand or is a program error,
where the choice of actual register for operands failed to avoid the
clobbered register. Such unavoidable overlap is detected by versions GCC
2.95 and newer, and flagged as an error rather than accepted. An error
message is given, such as:
  foo.c: In function `foo':
  foo.c:7: Invalid `asm' statement:
  foo.c:7: fixed or forbidden register 0 (ax) was spilled for class AREG.
Unfortunately, a lot of existing software, for example the Linux kernel
version 2.0.35 for the Intel x86, has constructs where input operands are
marked as clobbered.
The manual now describes how to write constructs with operands that are
modified by the construct, but not actually used. To write an asm which
modifies an input operand but does not output anything usable, specify that
operand as an output operand outputting to an unused dummy variable.
In the following example for the x86 architecture (taken from the Linux
2.0.35 kernel -- include/asm-i386/delay.h), the register-class constraint
"a" denotes a register class containing the single register "ax" (aka.
"eax"). It is therefore invalid to clobber "ax"; this operand has to be
specified as an output as well as an input. The following code is therefore
invalid:
extern __inline__ void
__delay (int loops)
{
  __asm__ __volatile__
    (".align 2,0x90\n1:\tdecl %0\n\tjns 1b"
     : /* no outputs */
     : "a" (loops)
     : "ax");
}
It could be argued that since the register class for "a" contains only a
single register, this could be detected as an "obvious" intended clobber of
the input operand. While that is feasible, it opens up for further "obvious"
cases, where the level of obviousness changes from person to person. As
there is a correct way to write such asm constructs, this
obviousness-detection is not needed other than for reasons of compatibility
with an existing code-base, and that code base can be corrected.
This corrected and clobber-less version, is valid for GCC 2.95 as well as
for previous versions of GCC and EGCS:
extern __inline__ void
__delay (int loops)
{
  int dummy;

  __asm__ __volatile__
    (".align 2,0x90\n1:\tdecl %0\n\tjns 1b"
     : "=a" (dummy)
     : "0" (loops));
}
Note that the asm construct now has an output operand, but it is unused.
Normally asm constructs with only unused output operands may be removed by
gcc, unless marked volatile as above

----- End explanation -----


Chris Ho-Stuart <hostuart AT sky DOT fit DOT qut DOT edu DOT au> wrote in message
news:7sul6k$l1n$1 AT dove DOT qut DOT edu DOT au...
> I am trying to compile the grx library on a pentium166 WindowsNT box
> using make from a dos command window.
>
> I unzip the files for grx23, cd to the src directory, and run
>
> make -f makefile.dj2
>
> After lots of compilation it ends up with
>
>
gcc -c -O6 -Wall -fomit-frame-pointer -I. -I./include -I../include -I../addo
ns/print -I../addons/bmp user/uellia.c -o user/uellia.o
> Load error: no DOS memory.
>
> But that is not the problem... I restart make, and it proceeds through
> the uellia just fine the second time.
>
> The real problem is at this point....
>
>
gcc -c -O6 -Wall -fomit-frame-pointer -I. -I./include -I../include -I../addo
ns/print -I../addons/bmp utils/shiftscl.c -o utils/shiftscl.o
> utils/shiftscl.c: In function `_GR_shift_scanline':
> utils/shiftscl.c:48: Invalidm' statement:
> utils/shiftscl.c:48: fixed or forbidden register 2 (cx) was spilled for
class CREG.
> utils/shiftscl.c:102: Invalidm' statement:
> utils/shiftscl.c:102: fixed or forbidden register 2 (cx) was spilled for
class CREG.
> make.exe: *** [utils/shiftscl.o] Error 1
>
> Any help gratefully accepted.
>
> Further info...
>
> Line 48 in utils/shiftscl.c is the asm statement in the following
> context...
>
> .
> .
> .
>       GR_int8u far *d = *(dst++) + ws;
> #     if defined(__GNUC__) && defined(__i386__)
>         int w = ws;
>         /* sad but true: the x86 bytesex forces this inefficient code
( */
>         asm volatile ("\n"
>           "   movb    (%3),%%ch    \n"
>           "   jmp     1f           \n"
>           "   .align  4,0x90       \n"
>           "1: decl    %3           \n"
>           "   movb    %%ch,%%al    \n"
>           "   movb    (%3),%%ah    \n"
>           "   movb    %%ah,%%ch    \n"
>           "   shrl    %%cl,%%eax   \n"
>           "   movb    %%al,(%4)    \n"
>           "   decl    %4           \n"
>           "   decl    %5           \n"
>           "   jne     1b           \n"
>           "   shrb    %%cl,%%ch    \n"
>           "   movb    %%ch,(%4)      "
>           : "=r" ((void *)s), "=r" ((void *)d), "=r" ((int)w)
>           : "0" ((void *)s), "1" ((void *)d), "2" ((int)w), "c"
((int)shift)
>           : "ax", "cx"
>         );
> #     elif defined(__TURBOC__)
> .
> .
> .
>
> Thanks -- Chris Ho-Stuart

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