um: add extended processor state save/restore support

This patch extends save_fp_registers() and restore_fp_registers() to use
PTRACE_GETREGSET and PTRACE_SETREGSET with the XSTATE note type, adding
support for new processor state extensions between context switches.

When the new ptrace requests are unavailable, it falls back to the old
PTRACE_GETFPREGS and PTRACE_SETFPREGS methods, which have been renamed to
save_i387_registers() and restore_i387_registers().

Now these functions expect *fp_regs to have the space of an _xstate struct.
Thus, this also makes ptrace in UML responde to PTRACE_GETFPREGS/_SETFPREG
requests with a user_i387_struct (thus independent from HOST_FP_SIZE), and
by calling save_i387_registers() and restore_i387_registers() instead of
the extended save_fp_registers() and restore_fp_registers() functions.

Signed-off-by: Eli Cooper <elicooper@gmx.com>

arch/um/include/shared/registers.h

@@ -9,6 +9,8 @@
 #include <sysdep/ptrace.h>
 #include <sysdep/archsetjmp.h>
 
+extern int save_i387_registers(int pid, unsigned long *fp_regs);
+extern int restore_i387_registers(int pid, unsigned long *fp_regs);
 extern int save_fp_registers(int pid, unsigned long *fp_regs);
 extern int restore_fp_registers(int pid, unsigned long *fp_regs);
 extern int save_fpx_registers(int pid, unsigned long *fp_regs);

arch/um/kernel/process.c

@@ -402,6 +402,6 @@ int elf_core_copy_fpregs(struct task_struct *t, elf_fpregset_t *fpu)
 {
 	int cpu = current_thread_info()->cpu;
 
-	return save_fp_registers(userspace_pid[cpu], (unsigned long *) fpu);
+	return save_i387_registers(userspace_pid[cpu], (unsigned long *) fpu);
 }