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