Commit 59649de9 authored by Jiaxun Yang's avatar Jiaxun Yang Committed by Thomas Bogendoerfer
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MIPS: Implement ieee754 NAN2008 emulation mode 



Implement ieee754 NAN2008 emulation mode.

When this mode is enabled, kernel will accept ELF file
compiled for both NaN 2008 and NaN legacy, but if hardware
does not have capability to match ELF's NaN mode, __own_fpu
will fail for corresponding thread and fpuemu will then kick
in.

This mode trade performance for correctness, while maintaining
support for both NaN mode regardless of hardware capability.
It is useful for multilib installation that have both types
of binary exist in system.

Reviewed-by: default avatarPhilippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: default avatarJiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: default avatarThomas Bogendoerfer <tsbogend@alpha.franken.de>
parent 9c7a86c9

Documentation/admin-guide/kernel-parameters.txt

+3 −1
Original line number Diff line number Diff line
@@ -2022,7 +2022,7 @@ 
			for the device. By default it is set to false (0).



	ieee754=	[MIPS] Select IEEE Std 754 conformance mode

			Format: { strict | legacy | 2008 | relaxed }

			Format: { strict | legacy | 2008 | relaxed | emulated }

			Default: strict



			Choose which programs will be accepted for execution
@@ -2042,6 +2042,8 @@ 
				by the FPU

			relaxed	accept any binaries regardless of whether

				supported by the FPU

			emulated accept any binaries but enable FPU emulator

				if binary mode is unsupported by the FPU.



			The FPU emulator is always able to support both NaN

			encodings, so if no FPU hardware is present or it has

arch/mips/include/asm/fpu.h

+15 −0
Original line number Diff line number Diff line
@@ -129,6 +129,18 @@ static inline int __own_fpu(void) 
	if (ret)

		return ret;



	if (current->thread.fpu.fcr31 & FPU_CSR_NAN2008) {

		if (!cpu_has_nan_2008) {

			ret = SIGFPE;

			goto failed;

		}

	} else {

		if (!cpu_has_nan_legacy) {

			ret = SIGFPE;

			goto failed;

		}

	}



	KSTK_STATUS(current) |= ST0_CU1;

	if (mode == FPU_64BIT || mode == FPU_HYBRID)

		KSTK_STATUS(current) |= ST0_FR;
@@ -137,6 +149,9 @@ static inline int __own_fpu(void) 


	set_thread_flag(TIF_USEDFPU);

	return 0;

failed:

	__disable_fpu();

	return ret;

}



static inline int own_fpu_inatomic(int restore)

arch/mips/kernel/elf.c

+4 −0
Original line number Diff line number Diff line
@@ -318,6 +318,10 @@ void mips_set_personality_nan(struct arch_elf_state *state) 
	t->thread.fpu.fcr31 = c->fpu_csr31;

	switch (state->nan_2008) {

	case 0:

		if (!(c->fpu_msk31 & FPU_CSR_NAN2008))

			t->thread.fpu.fcr31 &= ~FPU_CSR_NAN2008;

		if (!(c->fpu_msk31 & FPU_CSR_ABS2008))

			t->thread.fpu.fcr31 &= ~FPU_CSR_ABS2008;

		break;

	case 1:

		if (!(c->fpu_msk31 & FPU_CSR_NAN2008))

arch/mips/kernel/fpu-probe.c

+8 −1
Original line number Diff line number Diff line
@@ -144,7 +144,7 @@ static void cpu_set_fpu_2008(struct cpuinfo_mips *c) 
 * IEEE 754 conformance mode to use.  Affects the NaN encoding and the

 * ABS.fmt/NEG.fmt execution mode.

 */

static enum { STRICT, LEGACY, STD2008, RELAXED } ieee754 = STRICT;

static enum { STRICT, EMULATED, LEGACY, STD2008, RELAXED } ieee754 = STRICT;



/*

 * Set the IEEE 754 NaN encodings and the ABS.fmt/NEG.fmt execution modes
@@ -160,6 +160,7 @@ static void cpu_set_nofpu_2008(struct cpuinfo_mips *c) 


	switch (ieee754) {

	case STRICT:

	case EMULATED:

		if (c->isa_level & (MIPS_CPU_ISA_M32R1 | MIPS_CPU_ISA_M64R1 |

				    MIPS_CPU_ISA_M32R2 | MIPS_CPU_ISA_M64R2 |

				    MIPS_CPU_ISA_M32R5 | MIPS_CPU_ISA_M64R5 |
@@ -204,6 +205,10 @@ static void cpu_set_nan_2008(struct cpuinfo_mips *c) 
		mips_use_nan_legacy = !cpu_has_nan_2008;

		mips_use_nan_2008 = !!cpu_has_nan_2008;

		break;

	case EMULATED:

		/* Pretend ABS2008/NAN2008 options are dynamic */

		c->fpu_msk31 &= ~(FPU_CSR_NAN2008 | FPU_CSR_ABS2008);

		fallthrough;

	case RELAXED:

		mips_use_nan_legacy = true;

		mips_use_nan_2008 = true;
@@ -226,6 +231,8 @@ static int __init ieee754_setup(char *s) 
		return -1;

	else if (!strcmp(s, "strict"))

		ieee754 = STRICT;

	else if (!strcmp(s, "emulated"))

		ieee754 = EMULATED;

	else if (!strcmp(s, "legacy"))

		ieee754 = LEGACY;

	else if (!strcmp(s, "2008"))