Commit da0bac33 authored by David Daney's avatar David Daney Committed by Ralf Baechle
Browse files

MIPS: Fix emulation of 64-bit FPU on FPU-less 64-bit CPUs. 



Running a 64-bit kernel on a 64-bit CPU without an FPU would cause the
emulator to run in 32-bit mode.  The c0_Status.FR bit is wired to zero
on systems without an FPU, so using that bit to decide how the emulator
behaves doesn't allow for proper emulation on 64-bit FPU-less
processors.

Instead, we need to select the emulator mode based on the user-space
ABI.  Since the thread flag TIF_32BIT_REGS is used to set c0_Status.FR,
we can just use it to decide if the emulator should be in 32-bit or
64-bit mode.

Signed-off-by: default avatarDavid Daney <ddaney@caviumnetworks.com>
Signed-off-by: default avatarRalf Baechle <ralf@linux-mips.org>
parent 156171c7

arch/mips/math-emu/cp1emu.c

+21 −20
Original line number Diff line number Diff line
@@ -163,33 +163,34 @@ static int isBranchInstr(mips_instruction * i) 


/*

 * In the Linux kernel, we support selection of FPR format on the

 * basis of the Status.FR bit.  This does imply that, if a full 32

 * FPRs are desired, there needs to be a flip-flop that can be written

 * to one at that bit position.  In any case, O32 MIPS ABI uses

 * only the even FPRs (Status.FR = 0).

 * basis of the Status.FR bit.  If an FPU is not present, the FR bit

 * is hardwired to zero, which would imply a 32-bit FPU even for

 * 64-bit CPUs.  For 64-bit kernels with no FPU we use TIF_32BIT_REGS

 * as a proxy for the FR bit so that a 64-bit FPU is emulated.  In any

 * case, for a 32-bit kernel which uses the O32 MIPS ABI, only the

 * even FPRs are used (Status.FR = 0).

 */



#define CP0_STATUS_FR_SUPPORT



#ifdef CP0_STATUS_FR_SUPPORT

#define FR_BIT ST0_FR

static inline int cop1_64bit(struct pt_regs *xcp)

{

	if (cpu_has_fpu)

		return xcp->cp0_status & ST0_FR;

#ifdef CONFIG_64BIT

	return !test_thread_flag(TIF_32BIT_REGS);

#else

#define FR_BIT 0

	return 0;

#endif

}



#define SIFROMREG(si, x) ((si) = cop1_64bit(xcp) || !(x & 1) ? \

			(int)ctx->fpr[x] : (int)(ctx->fpr[x & ~1] >> 32))



#define SIFROMREG(si, x) ((si) = \

			(xcp->cp0_status & FR_BIT) || !(x & 1) ? \

			(int)ctx->fpr[x] : \

			(int)(ctx->fpr[x & ~1] >> 32 ))

#define SITOREG(si, x)	(ctx->fpr[x & ~((xcp->cp0_status & FR_BIT) == 0)] = \

			(xcp->cp0_status & FR_BIT) || !(x & 1) ? \

#define SITOREG(si, x)	(ctx->fpr[x & ~(cop1_64bit(xcp) == 0)] = \

			cop1_64bit(xcp) || !(x & 1) ? \

			ctx->fpr[x & ~1] >> 32 << 32 | (u32)(si) : \

			ctx->fpr[x & ~1] << 32 >> 32 | (u64)(si) << 32)



#define DIFROMREG(di, x) ((di) = \

			ctx->fpr[x & ~((xcp->cp0_status & FR_BIT) == 0)])

#define DITOREG(di, x)	(ctx->fpr[x & ~((xcp->cp0_status & FR_BIT) == 0)] \

			= (di))

#define DIFROMREG(di, x) ((di) = ctx->fpr[x & ~(cop1_64bit(xcp) == 0)])

#define DITOREG(di, x)	(ctx->fpr[x & ~(cop1_64bit(xcp) == 0)] = (di))



#define SPFROMREG(sp, x) SIFROMREG((sp).bits, x)

#define SPTOREG(sp, x)	SITOREG((sp).bits, x)

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