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>
diff --git a/arch/mips/kernel/signal.c b/arch/mips/kernel/signal.c
index 08f5215..9cb75e9 100644
--- a/arch/mips/kernel/signal.c
+++ b/arch/mips/kernel/signal.c
@@ -133,9 +133,16 @@
unsigned int used;
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);
- if (err || !used)
+ if (err || !(used & USED_FP))
return err;
/*
@@ -177,13 +184,13 @@
int err, sig, tmp __maybe_unused;
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
* doesn't want it following sigreturn.
*/
- if (err || !used) {
+ if (err || !(used & USED_FP)) {
lose_fpu(0);
return err;
}