Thanks. We will try this.
FWIW git blame says this inline asm is 11 years old and the new GCC
reported this. :)
--joel
On Sun, Apr 19, 2020 at 2:55 AM Uros Bizjak <ubiz...@gmail.com> wrote:
> Hello!
>
> > Over at RTEMS, we have had a report that this very old code has quit
> > compiling:
> >
> > #ifdef __SSE__
> > #define _CPU_Context_restore_fp(fp_context_pp) \
> > do { \
> > __asm__ __volatile__( \
> > "fldcw %0" \
> > ::"m"((*(fp_context_pp))->fpucw) \
> > :"fpcr" \
> > ); \
> > __builtin_ia32_ldmxcsr(_Thread_Executing->fp_context->mxcsr); \
> > } while (0)
> > #else
> >
> > The error is "error: unknown register name 'fpcr' in 'asm'"
>
> Just remove the fpcr clobber. FP control register was never properly
> handled.
>
> Please also note gcc manual section "6.47.2.1 Volatile", where the
> manual discusses similar case of a system register that controls the
> rounding mode of floating-point operations. You have to add an
> artificial dependency to the asm by referencing a variable in the
> subsequent code, otherwise the compiler may move the access to system
> register across the arithmetic insn.
>
> Uros.
>
