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>

arch/mips/Kconfig

@@ -2335,6 +2335,23 @@ config CC_STACKPROTECTOR
 
  This feature requires gcc version 4.2 or above.
 
+config MIPS_O32_FP64_SUPPORT
+ bool "Support for O32 binaries using 64-bit FP"
+ depends on 32BIT || MIPS32_O32
+ default y
+ help
+ When this is enabled, the kernel will support use of 64-bit floating
+ point registers with binaries using the O32 ABI along with the
+ EF_MIPS_FP64 ELF header flag (typically built with -mfp64). On
+ 32-bit MIPS systems this support is at the cost of increasing the
+ size and complexity of the compiled FPU emulator. Thus if you are
+ running a MIPS32 system and know that none of your userland binaries
+ will require 64-bit floating point, you may wish to reduce the size
+ of your kernel & potentially improve FP emulation performance by
+ saying N here.
+
+ If unsure, say Y.
+
 config USE_OF
  bool
  select OF

arch/mips/include/asm/asmmacro-32.h

@@ -12,27 +12,6 @@
 #include <asm/fpregdef.h>
 #include <asm/mipsregs.h>
 
- .macro fpu_save_double thread status tmp1=t0
- cfc1 \tmp1, 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 \tmp1, THREAD_FCR31(\thread)
- .endm
-
  .macro fpu_save_single thread tmp=t0
  cfc1 \tmp, fcr31
  swc1 $f0, THREAD_FPR0(\thread)
@@ -70,27 +49,6 @@
  sw \tmp, THREAD_FCR31(\thread)
  .endm
 
- .macro fpu_restore_double thread status 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_single thread tmp=t0
  lw \tmp, THREAD_FCR31(\thread)
  lwc1 $f0, THREAD_FPR0(\thread)

arch/mips/include/asm/asmmacro-64.h

@@ -13,102 +13,6 @@
 #include <asm/fpregdef.h>
 #include <asm/mipsregs.h>
 
- .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
- 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)
- .endm
-
- .macro fpu_save_double thread status tmp
- sll \tmp, \status, 5
- bgez \tmp, 2f
- fpu_save_16odd \thread
-2:
- 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
- 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)
- .endm
-
- .macro fpu_restore_double thread status tmp
- sll \tmp, \status, 5
- bgez \tmp, 1f # 16 register mode?
-
- fpu_restore_16odd \thread
-1: fpu_restore_16even \thread \tmp
- .endm
-
  .macro cpu_save_nonscratch thread
  LONG_S s0, THREAD_REG16(\thread)
  LONG_S s1, THREAD_REG17(\thread)

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
  */

arch/mips/include/asm/elf.h

@@ -36,6 +36,7 @@
 #define EF_MIPS_ABI2 0x00000020
 #define EF_MIPS_OPTIONS_FIRST 0x00000080
 #define EF_MIPS_32BITMODE 0x00000100
+#define EF_MIPS_FP64 0x00000200
 #define EF_MIPS_ABI 0x0000f000
 #define EF_MIPS_ARCH 0xf0000000
 
@@ -175,6 +176,18 @@ typedef elf_fpreg_t elf_fpregset_t[ELF_NFPREG];
 
 #ifdef CONFIG_32BIT
 
+/*
+ * In order to be sure that we don't attempt to execute an O32 binary which
+ * requires 64 bit FP (FR=1) on a system which does not support it we refuse
+ * to execute any binary which has bits specified by the following macro set
+ * in its ELF header flags.
+ */
+#ifdef CONFIG_MIPS_O32_FP64_SUPPORT
+# define __MIPS_O32_FP64_MUST_BE_ZERO 0
+#else
+# define __MIPS_O32_FP64_MUST_BE_ZERO EF_MIPS_FP64
+#endif
+
 /*
  * This is used to ensure we don't load something for the wrong architecture.
  */
@@ -191,6 +204,8 @@ typedef elf_fpreg_t elf_fpregset_t[ELF_NFPREG];
  __res = 0; \
  if (((__h->e_flags & EF_MIPS_ABI) != 0) && \
  ((__h->e_flags & EF_MIPS_ABI) != EF_MIPS_ABI_O32)) \
+ __res = 0; \
+ if (__h->e_flags & __MIPS_O32_FP64_MUST_BE_ZERO) \
  __res = 0; \
  \
  __res; \
@@ -249,6 +264,11 @@ extern struct mips_abi mips_abi_n32;
 
 #define SET_PERSONALITY(ex) \
 do { \
+ if ((ex).e_flags & EF_MIPS_FP64) \
+ clear_thread_flag(TIF_32BIT_FPREGS); \
+ else \
+ set_thread_flag(TIF_32BIT_FPREGS); \
+ \
  if (personality(current->personality) != PER_LINUX) \
  set_personality(PER_LINUX); \
  \
@@ -271,14 +291,18 @@ do { \
 #endif
 
 #ifdef CONFIG_MIPS32_O32
-#define __SET_PERSONALITY32_O32() \
+#define __SET_PERSONALITY32_O32(ex) \
  do { \
  set_thread_flag(TIF_32BIT_REGS); \
  set_thread_flag(TIF_32BIT_ADDR); \
+ \
+ if (!((ex).e_flags & EF_MIPS_FP64)) \
+ set_thread_flag(TIF_32BIT_FPREGS); \
+ \
  current->thread.abi = &mips_abi_32; \
  } while (0)
 #else
-#define __SET_PERSONALITY32_O32() \
+#define __SET_PERSONALITY32_O32(ex) \
  do { } while (0)
 #endif
 
@@ -289,7 +313,7 @@ do { \
  ((ex).e_flags & EF_MIPS_ABI) == 0) \
  __SET_PERSONALITY32_N32(); \
  else \
- __SET_PERSONALITY32_O32(); \
+ __SET_PERSONALITY32_O32(ex); \
 } while (0)
 #else
 #define __SET_PERSONALITY32(ex) do { } while (0)
@@ -300,6 +324,7 @@ do { \
  unsigned int p; \
  \
  clear_thread_flag(TIF_32BIT_REGS); \
+ clear_thread_flag(TIF_32BIT_FPREGS); \
  clear_thread_flag(TIF_32BIT_ADDR); \
  \
  if ((ex).e_ident[EI_CLASS] == ELFCLASS32) \