Make fnstcw work with emscripten

Make fnstcw work with emscripten

[Diomidis Spinellis]

When glibc is compiled with emscripten toolchain for compiling to asm.js 
and WebAssembly [1] (e.g. as part of groff), the compilation fails due 
to the inclusion of assembly code, as shown in the example below.

emcc groff.bc -o groff.html
In function vasnprintf()
void (i16*)* asm sideeffect "fnstcw $0", "=*m"
LLVM ERROR: asm() with non-empty content not supported, use EM_ASM() 
(see emscripten.h)

The following small change corrects this problem.

--- a/lib/fpucw.h  2019-10-12 15:27:25.810899880 +0300
+++ b/lib/fpucw.h 2019-10-12 14:25:30.875463263 +0300
@@ -62,7 +62,7 @@
   */

  /* Inline assembler like this works only with GNU C.  */
-#if (defined __i386__ || defined __x86_64__) && defined __GNUC__
+#if (defined __i386__ || defined __x86_64__) && defined __GNUC__ && 
!defined __EMSCRIPTEN__

  typedef unsigned short fpucw_t; /* glibc calls this fpu_control_t */


[1] https://emscripten.org/

Re: Make fnstcw work with emscripten

[Bruno Haible]

Hi Diomidis,

> When glibc is compiled with emscripten toolchain for compiling to asm.js 
> and WebAssembly [1] (e.g. as part of groff),

You mean gnulib, not glibc? glibc is not built when you compile groff.

> the compilation fails due 
> to the inclusion of assembly code, as shown in the example below.
> 
> emcc groff.bc -o groff.html
> In function vasnprintf()
> void (i16*)* asm sideeffect "fnstcw $0", "=*m"
> LLVM ERROR: asm() with non-empty content not supported, use EM_ASM() 
> (see emscripten.h)
> 
> The following small change corrects this problem.
> 
> --- a/lib/fpucw.h  2019-10-12 15:27:25.810899880 +0300
> +++ b/lib/fpucw.h 2019-10-12 14:25:30.875463263 +0300
> @@ -62,7 +62,7 @@
>    */
> 
>   /* Inline assembler like this works only with GNU C.  */
> -#if (defined __i386__ || defined __x86_64__) && defined __GNUC__
> +#if (defined __i386__ || defined __x86_64__) && defined __GNUC__ && 
> !defined __EMSCRIPTEN__
> 
>   typedef unsigned short fpucw_t; /* glibc calls this fpu_control_t */

This indicates that in the compilation, at this point, either the macro
__i386__ or __x86_64__ is defined as a preprocessor macro.

When you run
  $ touch empty.c; emcc -E -dM empty.c |grep '\(i386\|x86_64\)'
does is display such macro definitions?

If yes, your emcc compiler is misconfigured. For me, it does not
define __i386__ or __x86_64__; it defines __asmjs__ instead.

If not, it means that some file defines __i386__ or __x86_64__
during the compilation. But application files should not do this.
In this case, your groff.bc (or one of the files that it includes
directly or indirectly) is buggy.

Bruno

Re: Make fnstcw work with emscripten

[Diomidis Spinellis]

Hi Bruno,

On 13-Oct-19 3:21, Bruno Haible wrote:
>> When glibc is compiled with emscripten toolchain for compiling to asm.js
>> and WebAssembly [1] (e.g. as part of groff),
> 
> You mean gnulib, not glibc? glibc is not built when you compile groff.

Yes, I meant gnulib.

>> the compilation fails due
>> to the inclusion of assembly code, as shown in the example below.
[...]
> When you run
>    $ touch empty.c; emcc -E -dM empty.c |grep '\(i386\|x86_64\)'
> does is display such macro definitions?
> 
> If yes, your emcc compiler is misconfigured. For me, it does not
> define __i386__ or __x86_64__; it defines __asmjs__ instead.

Indeed I verified that emcc on its own defines __asmjs__, not __i386__ 
or __x86_64__.

> If not, it means that some file defines __i386__ or __x86_64__
> during the compilation. But application files should not do this.
> In this case, your groff.bc (or one of the files that it includesE
> directly or indirectly) is buggy.

By running gcc on lib/vasnprintf.c with the same flags as emcc (as shown 
with emmake make V=1) plus -E -fdirectives-only I found that groff's 
src/include/config.h defines __i386__.

#ifndef __i386__
#define __i386__ 1
#endif

Removing the definition fixes the problem.  So it's a bug of emconfigure 
or groff's autoconf.

Many thanks,

Diomidis