MIPS: Support for 64-bit FP with O32 binaries
CPUs implementing MIPS32 R2 may include a 64-bit FPU, just as MIPS64 CPUs
do. In order to preserve backwards compatibility a 64-bit FPU will act
like a 32-bit FPU (by accessing doubles from the least significant 32
bits of an even-odd pair of FP registers) when the Status.FR bit is
zero, again just like a mips64 CPU. The standard O32 ABI is defined
expecting a 32-bit FPU, however recent toolchains support use of a
64-bit FPU from an O32 MIPS32 executable. When an ELF executable is
built to use a 64-bit FPU a new flag (EF_MIPS_FP64) is set in the ELF
header.
With this patch the kernel will check the EF_MIPS_FP64 flag when
executing an O32 binary, and set Status.FR accordingly. The addition
of O32 64-bit FP support lessens the opportunity for optimisation in
the FPU emulator, so a CONFIG_MIPS_O32_FP64_SUPPORT Kconfig option is
introduced to allow this support to be disabled for those that don't
require it.
Inspired by an earlier patch by Leonid Yegoshin, but implemented more
cleanly & correctly.
Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: Paul Burton <paul.burton@imgtec.com>
Patchwork: https://patchwork.linux-mips.org/patch/6154/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/include/asm/fpu.h b/arch/mips/include/asm/fpu.h
index 3bf023f..cfe092f 100644
--- a/arch/mips/include/asm/fpu.h
+++ b/arch/mips/include/asm/fpu.h
@@ -33,11 +33,48 @@
extern void _save_fp(struct task_struct *);
extern void _restore_fp(struct task_struct *);
-#define __enable_fpu() \
-do { \
- set_c0_status(ST0_CU1); \
- enable_fpu_hazard(); \
-} while (0)
+/*
+ * This enum specifies a mode in which we want the FPU to operate, for cores
+ * which implement the Status.FR bit. Note that FPU_32BIT & FPU_64BIT
+ * purposefully have the values 0 & 1 respectively, so that an integer value
+ * of Status.FR can be trivially casted to the corresponding enum fpu_mode.
+ */
+enum fpu_mode {
+ FPU_32BIT = 0, /* FR = 0 */
+ FPU_64BIT, /* FR = 1 */
+ FPU_AS_IS,
+};
+
+static inline int __enable_fpu(enum fpu_mode mode)
+{
+ int fr;
+
+ switch (mode) {
+ case FPU_AS_IS:
+ /* just enable the FPU in its current mode */
+ set_c0_status(ST0_CU1);
+ enable_fpu_hazard();
+ return 0;
+
+ case FPU_64BIT:
+#if !(defined(CONFIG_CPU_MIPS32_R2) || defined(CONFIG_MIPS64))
+ /* we only have a 32-bit FPU */
+ return SIGFPE;
+#endif
+ /* fall through */
+ case FPU_32BIT:
+ /* set CU1 & change FR appropriately */
+ fr = (int)mode;
+ change_c0_status(ST0_CU1 | ST0_FR, ST0_CU1 | (fr ? ST0_FR : 0));
+ enable_fpu_hazard();
+
+ /* check FR has the desired value */
+ return (!!(read_c0_status() & ST0_FR) == !!fr) ? 0 : SIGFPE;
+
+ default:
+ BUG();
+ }
+}
#define __disable_fpu() \
do { \
@@ -57,27 +94,46 @@
return cpu_has_fpu && __is_fpu_owner();
}
-static inline void __own_fpu(void)
+static inline int __own_fpu(void)
{
- __enable_fpu();
+ enum fpu_mode mode;
+ int ret;
+
+ mode = !test_thread_flag(TIF_32BIT_FPREGS);
+ ret = __enable_fpu(mode);
+ if (ret)
+ return ret;
+
KSTK_STATUS(current) |= ST0_CU1;
+ if (mode == FPU_64BIT)
+ KSTK_STATUS(current) |= ST0_FR;
+ else /* mode == FPU_32BIT */
+ KSTK_STATUS(current) &= ~ST0_FR;
+
set_thread_flag(TIF_USEDFPU);
+ return 0;
}
-static inline void own_fpu_inatomic(int restore)
+static inline int own_fpu_inatomic(int restore)
{
+ int ret = 0;
+
if (cpu_has_fpu && !__is_fpu_owner()) {
- __own_fpu();
- if (restore)
+ ret = __own_fpu();
+ if (restore && !ret)
_restore_fp(current);
}
+ return ret;
}
-static inline void own_fpu(int restore)
+static inline int own_fpu(int restore)
{
+ int ret;
+
preempt_disable();
- own_fpu_inatomic(restore);
+ ret = own_fpu_inatomic(restore);
preempt_enable();
+ return ret;
}
static inline void lose_fpu(int save)
@@ -93,16 +149,21 @@
preempt_enable();
}
-static inline void init_fpu(void)
+static inline int init_fpu(void)
{
+ int ret = 0;
+
preempt_disable();
if (cpu_has_fpu) {
- __own_fpu();
- _init_fpu();
+ ret = __own_fpu();
+ if (!ret)
+ _init_fpu();
} else {
fpu_emulator_init_fpu();
}
+
preempt_enable();
+ return ret;
}
static inline void save_fp(struct task_struct *tsk)