Commit 0d071fa3 authored Jul 27, 2015 by Paul Burton Committed by Ralf Baechle Sep 03, 2015

MIPS: Indicate FP mode in sigcontext sc_used_math



The sc_used_math field of struct sigcontext & its variants has
traditionally been used as a boolean value indicating only whether or
not floating point context is saved within the sigcontext. With various
supported FP modes & the ability to switch between them this information
will no longer be enough to decode the meaning of the data stored in the
sc_fpregs fields of struct sigcontext.

To make that possible 3 bits are defined within sc_used_math:

  - Bit 0 (USED_FP) represents whether FP was used, essentially
    providing the boolean flag which sc_used_math as a whole provided
    previously.

  - Bit 1 (USED_FR1) provides the value of the Status.FR bit at the time
    the FP context was saved.

  - Bit 2 (USED_HYBRID_FPRS) indicates whether the FP context was saved
    under the hybrid FPR scheme. Essentially, when set the odd singles
    are located in bits 63:32 of the preceding even indexed sc_fpregs
    element.

Any userland that tests whether the sc_used_math field is zero or
non-zero will continue to function as expected. Having said that, I
could not find any userland which uses the sc_used_math field at all.

[ralf@linux-mips.org: Fixed rejects.]

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Matthew Fortune <matthew.fortune@imgtec.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: linux-kernel@vger.kernel.org
Cc: Richard Weinberger <richard@nod.at>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Maciej W. Rozycki <macro@codesourcery.com>
Patchwork: https://patchwork.linux-mips.org/patch/10794/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

parent 6a24432c

arch/mips/include/uapi/asm/sigcontext.h

+9 −0

Original line number	Original line	Diff line number	Diff line
	@@ -12,6 +12,15 @@
	#include <linux/types.h>		#include <linux/types.h>
	#include <asm/sgidefs.h>		#include <asm/sgidefs.h>

			/* scalar FP context was used */
			#define USED_FP (1 << 0)

			/* the value of Status.FR when context was saved */
			#define USED_FR1 (1 << 1)

			/* FR=1, but with odd singles in bits 63:32 of preceding even double */
			#define USED_HYBRID_FPRS (1 << 2)

	#if _MIPS_SIM == _MIPS_SIM_ABI32		#if _MIPS_SIM == _MIPS_SIM_ABI32

	/*		/*

arch/mips/kernel/signal.c

+11 −4

Original line number	Original line	Diff line number	Diff line
	@@ -133,9 +133,16 @@ int protected_save_fp_context(void __user *sc)
	unsigned int used;		unsigned int used;
	int err;		int err;

	used = !!used_math();		used = used_math() ? USED_FP : 0;
			if (used) {
			if (!test_thread_flag(TIF_32BIT_FPREGS))
			used \|= USED_FR1;
			if (test_thread_flag(TIF_HYBRID_FPREGS))
			used \|= USED_HYBRID_FPRS;
			}

	err = __put_user(used, used_math);		err = __put_user(used, used_math);
	if (err \|\| !used)		if (err \|\| !(used & USED_FP))
	return err;		return err;

	/*		/*
	@@ -177,13 +184,13 @@ int protected_restore_fp_context(void __user *sc)
	int err, sig, tmp __maybe_unused;		int err, sig, tmp __maybe_unused;

	err = __get_user(used, used_math);		err = __get_user(used, used_math);
	conditional_used_math(used);		conditional_used_math(used & USED_FP);

	/*		/*
	* The signal handler may have used FPU; give it up if the program		* The signal handler may have used FPU; give it up if the program
	* doesn't want it following sigreturn.		* doesn't want it following sigreturn.
	*/		*/
	if (err \|\| !used) {		if (err \|\| !(used & USED_FP)) {
	lose_fpu(0);		lose_fpu(0);
	return err;		return err;
	}		}