RE: X86 fpu registers in a signal handler's ucontext

From: Warlich, Christof
Date: Tue Apr 30 2013 - 09:45:38 EST

Mikael Pettersson <mikpe@xxxxxxxx> 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.

However, these elements seem to be available in the uc_mcontext definition of the
kernel, but I can't have a sigaction handler there, can I? Then, how does the
kernel's uc_mcontext definition help me in my (userspace) signal handler?
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