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.
Signed-off-by: Paul Burton <[email protected]>
---
Changes in v2: None
arch/mips/include/uapi/asm/sigcontext.h | 9 +++++++++
arch/mips/kernel/signal.c | 15 +++++++++++----
2 files changed, 20 insertions(+), 4 deletions(-)
diff --git a/arch/mips/include/uapi/asm/sigcontext.h
b/arch/mips/include/uapi/asm/sigcontext.h
index ae78902..f28facd 100644
--- a/arch/mips/include/uapi/asm/sigcontext.h
+++ b/arch/mips/include/uapi/asm/sigcontext.h
@@ -12,6 +12,15 @@
#include <linux/types.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
struct sigcontext {
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 @@ int protected_save_fp_context(void __user *sc)
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 protected_restore_fp_context(void __user *sc)
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;
}
--
2.4.6
--
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