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>

1 files changed, 107 insertions, 0 deletions

diff --git a/arch/mips/include/asm/asmmacro.h b/arch/mips/include/asm/asmmacro.h
index 6c8342ae74db..3220c93ea981 100644
--- a/arch/mips/include/asm/asmmacro.h
+++ b/arch/mips/include/asm/asmmacro.h
@@ -62,6 +62,113 @@
 	.endm
 #endif /* CONFIG_MIPS_MT_SMTC */
 
+	.macro	fpu_save_16even thread tmp=t0
+	cfc1	\tmp, fcr31
+	sdc1	$f0,  THREAD_FPR0(\thread)
+	sdc1	$f2,  THREAD_FPR2(\thread)
+	sdc1	$f4,  THREAD_FPR4(\thread)
+	sdc1	$f6,  THREAD_FPR6(\thread)
+	sdc1	$f8,  THREAD_FPR8(\thread)
+	sdc1	$f10, THREAD_FPR10(\thread)
+	sdc1	$f12, THREAD_FPR12(\thread)
+	sdc1	$f14, THREAD_FPR14(\thread)
+	sdc1	$f16, THREAD_FPR16(\thread)
+	sdc1	$f18, THREAD_FPR18(\thread)
+	sdc1	$f20, THREAD_FPR20(\thread)
+	sdc1	$f22, THREAD_FPR22(\thread)
+	sdc1	$f24, THREAD_FPR24(\thread)
+	sdc1	$f26, THREAD_FPR26(\thread)
+	sdc1	$f28, THREAD_FPR28(\thread)
+	sdc1	$f30, THREAD_FPR30(\thread)
+	sw	\tmp, THREAD_FCR31(\thread)
+	.endm
+
+	.macro	fpu_save_16odd thread
+	.set	push
+	.set	mips64r2
+	sdc1	$f1,  THREAD_FPR1(\thread)
+	sdc1	$f3,  THREAD_FPR3(\thread)
+	sdc1	$f5,  THREAD_FPR5(\thread)
+	sdc1	$f7,  THREAD_FPR7(\thread)
+	sdc1	$f9,  THREAD_FPR9(\thread)
+	sdc1	$f11, THREAD_FPR11(\thread)
+	sdc1	$f13, THREAD_FPR13(\thread)
+	sdc1	$f15, THREAD_FPR15(\thread)
+	sdc1	$f17, THREAD_FPR17(\thread)
+	sdc1	$f19, THREAD_FPR19(\thread)
+	sdc1	$f21, THREAD_FPR21(\thread)
+	sdc1	$f23, THREAD_FPR23(\thread)
+	sdc1	$f25, THREAD_FPR25(\thread)
+	sdc1	$f27, THREAD_FPR27(\thread)
+	sdc1	$f29, THREAD_FPR29(\thread)
+	sdc1	$f31, THREAD_FPR31(\thread)
+	.set	pop
+	.endm
+
+	.macro	fpu_save_double thread status tmp
+#if defined(CONFIG_MIPS64) || defined(CONFIG_CPU_MIPS32_R2)
+	sll	\tmp, \status, 5
+	bgez	\tmp, 10f
+	fpu_save_16odd \thread
+10:
+#endif
+	fpu_save_16even \thread \tmp
+	.endm
+
+	.macro	fpu_restore_16even thread tmp=t0
+	lw	\tmp, THREAD_FCR31(\thread)
+	ldc1	$f0,  THREAD_FPR0(\thread)
+	ldc1	$f2,  THREAD_FPR2(\thread)
+	ldc1	$f4,  THREAD_FPR4(\thread)
+	ldc1	$f6,  THREAD_FPR6(\thread)
+	ldc1	$f8,  THREAD_FPR8(\thread)
+	ldc1	$f10, THREAD_FPR10(\thread)
+	ldc1	$f12, THREAD_FPR12(\thread)
+	ldc1	$f14, THREAD_FPR14(\thread)
+	ldc1	$f16, THREAD_FPR16(\thread)
+	ldc1	$f18, THREAD_FPR18(\thread)
+	ldc1	$f20, THREAD_FPR20(\thread)
+	ldc1	$f22, THREAD_FPR22(\thread)
+	ldc1	$f24, THREAD_FPR24(\thread)
+	ldc1	$f26, THREAD_FPR26(\thread)
+	ldc1	$f28, THREAD_FPR28(\thread)
+	ldc1	$f30, THREAD_FPR30(\thread)
+	ctc1	\tmp, fcr31
+	.endm
+
+	.macro	fpu_restore_16odd thread
+	.set	push
+	.set	mips64r2
+	ldc1	$f1,  THREAD_FPR1(\thread)
+	ldc1	$f3,  THREAD_FPR3(\thread)
+	ldc1	$f5,  THREAD_FPR5(\thread)
+	ldc1	$f7,  THREAD_FPR7(\thread)
+	ldc1	$f9,  THREAD_FPR9(\thread)
+	ldc1	$f11, THREAD_FPR11(\thread)
+	ldc1	$f13, THREAD_FPR13(\thread)
+	ldc1	$f15, THREAD_FPR15(\thread)
+	ldc1	$f17, THREAD_FPR17(\thread)
+	ldc1	$f19, THREAD_FPR19(\thread)
+	ldc1	$f21, THREAD_FPR21(\thread)
+	ldc1	$f23, THREAD_FPR23(\thread)
+	ldc1	$f25, THREAD_FPR25(\thread)
+	ldc1	$f27, THREAD_FPR27(\thread)
+	ldc1	$f29, THREAD_FPR29(\thread)
+	ldc1	$f31, THREAD_FPR31(\thread)
+	.set	pop
+	.endm
+
+	.macro	fpu_restore_double thread status tmp
+#if defined(CONFIG_MIPS64) || defined(CONFIG_CPU_MIPS32_R2)
+	sll	\tmp, \status, 5
+	bgez	\tmp, 10f				# 16 register mode?
+
+	fpu_restore_16odd \thread
+10:
+#endif
+	fpu_restore_16even \thread \tmp
+	.endm
+
 /*
  * Temporary until all gas have MT ASE support
  */