Warlich, Christof writes:
> Mikael Pettersson <mi...@it.uu.se> writes:
> > Write to the fpstate ->mxcsr and ->swd fields in the sigaction handler's
> > uc_mcontext.
>
> To me, "sigaction handler's uc_mcontext" sounds like userspace, which really
> confuses me:
> Even in most recent glibc-2.17, uc_mcontext is of type mcontext_t, which us
> defined as:
>
> typedef struct {
> gregset_t gregs;
> fpregset_t fpregs;
> } mcontext_t;
>
> typedef struct fpregset {
> union {
> struct fpchip_state {
> int state[27];
> int status;
> } fpchip_state;
> struct fp_emul_space {
> char fp_emul[246];
> char fp_epad[2];
> } fp_emul_space;
> int f_fpregs[62];
> } fp_reg_set;
> long int f_wregs[33];
> } fpregset_t;
>
> So there is no fpstate whatsoever.
You're looking at the wrong header: glibc-2.17/sysdeps/i386/sys/ucontext.h is
legacy SVR4.
Instead look at glibc-2.17/sysdeps/unix/sysv/linux/x86/sys/ucontext.h.
(If the old one got installed on your system then something there is seriously
wrong.)
The only quirk is that to access ->mxcsr on 32-bit you have to check if the
high half of
->status contains FXSR_MAGIC and if so you need to cast that pointer to struct
_fpstate*.
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