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, 70 insertions, 4 deletions

diff --git a/arch/mips/kernel/r4k_fpu.S b/arch/mips/kernel/r4k_fpu.S
index 55ffe149dae9..253b2fb52026 100644
--- a/arch/mips/kernel/r4k_fpu.S
+++ b/arch/mips/kernel/r4k_fpu.S
@@ -35,7 +35,15 @@
 LEAF(_save_fp_context)
         cfc1    t1, fcr31
 
-#ifdef CONFIG_64BIT
+#if defined(CONFIG_64BIT) || defined(CONFIG_MIPS32_R2)
+        .set    push
+#ifdef CONFIG_MIPS32_R2
+        .set    mips64r2
+        mfc0    t0, CP0_STATUS
+        sll     t0, t0, 5
+        bgez    t0, 1f                  # skip storing odd if FR=0
+         nop
+#endif
         /* Store the 16 odd double precision registers */
         EX      sdc1 $f1, SC_FPREGS+8(a0)
         EX      sdc1 $f3, SC_FPREGS+24(a0)
@@ -53,6 +61,7 @@ LEAF(_save_fp_context)
         EX      sdc1 $f27, SC_FPREGS+216(a0)
         EX      sdc1 $f29, SC_FPREGS+232(a0)
         EX      sdc1 $f31, SC_FPREGS+248(a0)
+1:      .set    pop
 #endif
 
         /* Store the 16 even double precision registers */
@@ -82,7 +91,31 @@ LEAF(_save_fp_context)
 LEAF(_save_fp_context32)
         cfc1    t1, fcr31
 
-        EX      sdc1 $f0, SC32_FPREGS+0(a0)
+        mfc0    t0, CP0_STATUS
+        sll     t0, t0, 5
+        bgez    t0, 1f                  # skip storing odd if FR=0
+         nop
+
+        /* Store the 16 odd double precision registers */
+        EX      sdc1 $f1, SC32_FPREGS+8(a0)
+        EX      sdc1 $f3, SC32_FPREGS+24(a0)
+        EX      sdc1 $f5, SC32_FPREGS+40(a0)
+        EX      sdc1 $f7, SC32_FPREGS+56(a0)
+        EX      sdc1 $f9, SC32_FPREGS+72(a0)
+        EX      sdc1 $f11, SC32_FPREGS+88(a0)
+        EX      sdc1 $f13, SC32_FPREGS+104(a0)
+        EX      sdc1 $f15, SC32_FPREGS+120(a0)
+        EX      sdc1 $f17, SC32_FPREGS+136(a0)
+        EX      sdc1 $f19, SC32_FPREGS+152(a0)
+        EX      sdc1 $f21, SC32_FPREGS+168(a0)
+        EX      sdc1 $f23, SC32_FPREGS+184(a0)
+        EX      sdc1 $f25, SC32_FPREGS+200(a0)
+        EX      sdc1 $f27, SC32_FPREGS+216(a0)
+        EX      sdc1 $f29, SC32_FPREGS+232(a0)
+        EX      sdc1 $f31, SC32_FPREGS+248(a0)
+
+        /* Store the 16 even double precision registers */
+1:      EX      sdc1 $f0, SC32_FPREGS+0(a0)
         EX      sdc1 $f2, SC32_FPREGS+16(a0)
         EX      sdc1 $f4, SC32_FPREGS+32(a0)
         EX      sdc1 $f6, SC32_FPREGS+48(a0)
@@ -114,7 +147,16 @@ LEAF(_save_fp_context32)
  */
 LEAF(_restore_fp_context)
         EX      lw t0, SC_FPC_CSR(a0)
-#ifdef CONFIG_64BIT
+
+#if defined(CONFIG_64BIT) || defined(CONFIG_MIPS32_R2)
+        .set    push
+#ifdef CONFIG_MIPS32_R2
+        .set    mips64r2
+        mfc0    t0, CP0_STATUS
+        sll     t0, t0, 5
+        bgez    t0, 1f                  # skip loading odd if FR=0
+         nop
+#endif
         EX      ldc1 $f1, SC_FPREGS+8(a0)
         EX      ldc1 $f3, SC_FPREGS+24(a0)
         EX      ldc1 $f5, SC_FPREGS+40(a0)
@@ -131,6 +173,7 @@ LEAF(_restore_fp_context)
         EX      ldc1 $f27, SC_FPREGS+216(a0)
         EX      ldc1 $f29, SC_FPREGS+232(a0)
         EX      ldc1 $f31, SC_FPREGS+248(a0)
+1:      .set pop
 #endif
         EX      ldc1 $f0, SC_FPREGS+0(a0)
         EX      ldc1 $f2, SC_FPREGS+16(a0)
@@ -157,7 +200,30 @@ LEAF(_restore_fp_context)
 LEAF(_restore_fp_context32)
         /* Restore an o32 sigcontext.  */
         EX      lw t0, SC32_FPC_CSR(a0)
-        EX      ldc1 $f0, SC32_FPREGS+0(a0)
+
+        mfc0    t0, CP0_STATUS
+        sll     t0, t0, 5
+        bgez    t0, 1f                  # skip loading odd if FR=0
+         nop
+
+        EX      ldc1 $f1, SC32_FPREGS+8(a0)
+        EX      ldc1 $f3, SC32_FPREGS+24(a0)
+        EX      ldc1 $f5, SC32_FPREGS+40(a0)
+        EX      ldc1 $f7, SC32_FPREGS+56(a0)
+        EX      ldc1 $f9, SC32_FPREGS+72(a0)
+        EX      ldc1 $f11, SC32_FPREGS+88(a0)
+        EX      ldc1 $f13, SC32_FPREGS+104(a0)
+        EX      ldc1 $f15, SC32_FPREGS+120(a0)
+        EX      ldc1 $f17, SC32_FPREGS+136(a0)
+        EX      ldc1 $f19, SC32_FPREGS+152(a0)
+        EX      ldc1 $f21, SC32_FPREGS+168(a0)
+        EX      ldc1 $f23, SC32_FPREGS+184(a0)
+        EX      ldc1 $f25, SC32_FPREGS+200(a0)
+        EX      ldc1 $f27, SC32_FPREGS+216(a0)
+        EX      ldc1 $f29, SC32_FPREGS+232(a0)
+        EX      ldc1 $f31, SC32_FPREGS+248(a0)
+
+1:      EX      ldc1 $f0, SC32_FPREGS+0(a0)
         EX      ldc1 $f2, SC32_FPREGS+16(a0)
         EX      ldc1 $f4, SC32_FPREGS+32(a0)
         EX      ldc1 $f6, SC32_FPREGS+48(a0)