fpu.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Save/restore floating point context for signal handlers.
 *
 * Copyright (C) 1999, 2000  Kaz Kojima & Niibe Yutaka
 *
 * FIXME! These routines can be optimized in big endian case.
 */
#include <linux/sched/signal.h>
#include <linux/signal.h>
#include <asm/processor.h>
#include <asm/io.h>
#include <asm/fpu.h>
#include <asm/traps.h>

/* The PR (precision) bit in the FP Status Register must be clear when
 * an frchg instruction is executed, otherwise the instruction is undefined.
 * Executing frchg with PR set causes a trap on some SH4 implementations.
 */

#define FPSCR_RCHG 0x00000000


/*
 * Save FPU registers onto task structure.
 */
void save_fpu(struct task_struct *tsk)
{
	unsigned long dummy;

	enable_fpu();
	asm volatile("sts.l	fpul, @-%0\n\t"
		     "sts.l	fpscr, @-%0\n\t"
		     "fmov.s	fr15, @-%0\n\t"
		     "fmov.s	fr14, @-%0\n\t"
		     "fmov.s	fr13, @-%0\n\t"
		     "fmov.s	fr12, @-%0\n\t"
		     "fmov.s	fr11, @-%0\n\t"
		     "fmov.s	fr10, @-%0\n\t"
		     "fmov.s	fr9, @-%0\n\t"
		     "fmov.s	fr8, @-%0\n\t"
		     "fmov.s	fr7, @-%0\n\t"
		     "fmov.s	fr6, @-%0\n\t"
		     "fmov.s	fr5, @-%0\n\t"
		     "fmov.s	fr4, @-%0\n\t"
		     "fmov.s	fr3, @-%0\n\t"
		     "fmov.s	fr2, @-%0\n\t"
		     "fmov.s	fr1, @-%0\n\t"
		     "fmov.s	fr0, @-%0\n\t"
		     "lds	%3, fpscr\n\t"
		     : "=r" (dummy)
		     : "0" ((char *)(&tsk->thread.xstate->hardfpu.status)),
		       "r" (FPSCR_RCHG),
		       "r" (FPSCR_INIT)
		     : "memory");

	disable_fpu();
}

void restore_fpu(struct task_struct *tsk)
{
	unsigned long dummy;

	enable_fpu();
	asm volatile("fmov.s	@%0+, fr0\n\t"
		     "fmov.s	@%0+, fr1\n\t"
		     "fmov.s	@%0+, fr2\n\t"
		     "fmov.s	@%0+, fr3\n\t"
		     "fmov.s	@%0+, fr4\n\t"
		     "fmov.s	@%0+, fr5\n\t"
		     "fmov.s	@%0+, fr6\n\t"
		     "fmov.s	@%0+, fr7\n\t"
		     "fmov.s	@%0+, fr8\n\t"
		     "fmov.s	@%0+, fr9\n\t"
		     "fmov.s	@%0+, fr10\n\t"
		     "fmov.s	@%0+, fr11\n\t"
		     "fmov.s	@%0+, fr12\n\t"
		     "fmov.s	@%0+, fr13\n\t"
		     "fmov.s	@%0+, fr14\n\t"
		     "fmov.s	@%0+, fr15\n\t"
		     "lds.l	@%0+, fpscr\n\t"
		     "lds.l	@%0+, fpul\n\t"
		     : "=r" (dummy)
		     : "0" (tsk->thread.xstate), "r" (FPSCR_RCHG)
		     : "memory");
	disable_fpu();
}

/*
 *	Emulate arithmetic ops on denormalized number for some FPU insns.
 */

/* denormalized float * float */
static int denormal_mulf(int hx, int hy)
{
	unsigned int ix, iy;
	unsigned long long m, n;
	int exp, w;

	ix = hx & 0x7fffffff;
	iy = hy & 0x7fffffff;
	if (iy < 0x00800000 || ix == 0)
		return ((hx ^ hy) & 0x80000000);

	exp = (iy & 0x7f800000) >> 23;
	ix &= 0x007fffff;
	iy = (iy & 0x007fffff) | 0x00800000;
	m = (unsigned long long)ix * iy;
	n = m;
	w = -1;
	while (n) { n >>= 1; w++; }

	/* FIXME: use guard bits */
	exp += w - 126 - 46;
	if (exp > 0)
		ix = ((int) (m >> (w - 23)) & 0x007fffff) | (exp << 23);
	else if (exp + 22 >= 0)
		ix = (int) (m >> (w - 22 - exp)) & 0x007fffff;
	else
		ix = 0;

	ix |= (hx ^ hy) & 0x80000000;
	return ix;
}

/* denormalized double * double */
static void mult64(unsigned long long x, unsigned long long y,
		unsigned long long *highp, unsigned long long *lowp)
{
	unsigned long long sub0, sub1, sub2, sub3;
	unsigned long long high, low;

	sub0 = (x >> 32) * (unsigned long) (y >> 32);
	sub1 = (x & 0xffffffffLL) * (unsigned long) (y >> 32);
	sub2 = (x >> 32) * (unsigned long) (y & 0xffffffffLL);
	sub3 = (x & 0xffffffffLL) * (unsigned long) (y & 0xffffffffLL);
	low = sub3;
	high = 0LL;
	sub3 += (sub1 << 32);
	if (low > sub3)
		high++;
	low = sub3;
	sub3 += (sub2 << 32);
	if (low > sub3)
		high++;
	low = sub3;
	high += (sub1 >> 32) + (sub2 >> 32);
	high += sub0;
	*lowp = low;
	*highp = high;
}

static inline long long rshift64(unsigned long long mh,
		unsigned long long ml, int n)
{
	if (n >= 64)
		return mh >> (n - 64);
	return (mh << (64 - n)) | (ml >> n);
}

static long long denormal_muld(long long hx, long long hy)
{
	unsigned long long ix, iy;
	unsigned long long mh, ml, nh, nl;
	int exp, w;

	ix = hx & 0x7fffffffffffffffLL;
	iy = hy & 0x7fffffffffffffffLL;
	if (iy < 0x0010000000000000LL || ix == 0)
		return ((hx ^ hy) & 0x8000000000000000LL);

	exp = (iy & 0x7ff0000000000000LL) >> 52;
	ix &= 0x000fffffffffffffLL;
	iy = (iy & 0x000fffffffffffffLL) | 0x0010000000000000LL;
	mult64(ix, iy, &mh, &ml);
	nh = mh;
	nl = ml;
	w = -1;
	if (nh) {
		while (nh) { nh >>= 1; w++;}
		w += 64;
	} else
		while (nl) { nl >>= 1; w++;}

	/* FIXME: use guard bits */
	exp += w - 1022 - 52 * 2;
	if (exp > 0)
		ix = (rshift64(mh, ml, w - 52) & 0x000fffffffffffffLL)
			| ((long long)exp << 52);
	else if (exp + 51 >= 0)
		ix = rshift64(mh, ml, w - 51 - exp) & 0x000fffffffffffffLL;
	else
		ix = 0;

	ix |= (hx ^ hy) & 0x8000000000000000LL;
	return ix;
}

/* ix - iy where iy: denormal and ix, iy >= 0 */
static int denormal_subf1(unsigned int ix, unsigned int iy)
{
	int frac;
	int exp;

	if (ix < 0x00800000)
		return ix - iy;

	exp = (ix & 0x7f800000) >> 23;
	if (exp - 1 > 31)
		return ix;
	iy >>= exp - 1;
	if (iy == 0)
		return ix;

	frac = (ix & 0x007fffff) | 0x00800000;
	frac -= iy;
	while (frac < 0x00800000) {
		if (--exp == 0)
			return frac;
		frac <<= 1;
	}

	return (exp << 23) | (frac & 0x007fffff);
}

/* ix + iy where iy: denormal and ix, iy >= 0 */
static int denormal_addf1(unsigned int ix, unsigned int iy)
{
	int frac;
	int exp;

	if (ix < 0x00800000)
		return ix + iy;

	exp = (ix & 0x7f800000) >> 23;
	if (exp - 1 > 31)
		return ix;
	iy >>= exp - 1;
	if (iy == 0)
	  return ix;

	frac = (ix & 0x007fffff) | 0x00800000;
	frac += iy;
	if (frac >= 0x01000000) {
		frac >>= 1;
		++exp;
	}

	return (exp << 23) | (frac & 0x007fffff);
}

static int denormal_addf(int hx, int hy)
{
	unsigned int ix, iy;
	int sign;

	if ((hx ^ hy) & 0x80000000) {
		sign = hx & 0x80000000;
		ix = hx & 0x7fffffff;
		iy = hy & 0x7fffffff;
		if (iy < 0x00800000) {
			ix = denormal_subf1(ix, iy);
			if ((int) ix < 0) {
				ix = -ix;
				sign ^= 0x80000000;
			}
		} else {
			ix = denormal_subf1(iy, ix);
			sign ^= 0x80000000;
		}
	} else {
		sign = hx & 0x80000000;
		ix = hx & 0x7fffffff;
		iy = hy & 0x7fffffff;
		if (iy < 0x00800000)
			ix = denormal_addf1(ix, iy);
		else
			ix = denormal_addf1(iy, ix);
	}

	return sign | ix;
}

/* ix - iy where iy: denormal and ix, iy >= 0 */
static long long denormal_subd1(unsigned long long ix, unsigned long long iy)
{
	long long frac;
	int exp;

	if (ix < 0x0010000000000000LL)
		return ix - iy;

	exp = (ix & 0x7ff0000000000000LL) >> 52;
	if (exp - 1 > 63)
		return ix;
	iy >>= exp - 1;
	if (iy == 0)
		return ix;

	frac = (ix & 0x000fffffffffffffLL) | 0x0010000000000000LL;
	frac -= iy;
	while (frac < 0x0010000000000000LL) {
		if (--exp == 0)
			return frac;
		frac <<= 1;
	}

	return ((long long)exp << 52) | (frac & 0x000fffffffffffffLL);
}

/* ix + iy where iy: denormal and ix, iy >= 0 */
static long long denormal_addd1(unsigned long long ix, unsigned long long iy)
{
	long long frac;
	long long exp;

	if (ix < 0x0010000000000000LL)
		return ix + iy;

	exp = (ix & 0x7ff0000000000000LL) >> 52;
	if (exp - 1 > 63)
		return ix;
	iy >>= exp - 1;
	if (iy == 0)
	  return ix;

	frac = (ix & 0x000fffffffffffffLL) | 0x0010000000000000LL;
	frac += iy;
	if (frac >= 0x0020000000000000LL) {
		frac >>= 1;
		++exp;
	}

	return (exp << 52) | (frac & 0x000fffffffffffffLL);
}

static long long denormal_addd(long long hx, long long hy)
{
	unsigned long long ix, iy;
	long long sign;

	if ((hx ^ hy) & 0x8000000000000000LL) {
		sign = hx & 0x8000000000000000LL;
		ix = hx & 0x7fffffffffffffffLL;
		iy = hy & 0x7fffffffffffffffLL;
		if (iy < 0x0010000000000000LL) {
			ix = denormal_subd1(ix, iy);
			if ((int) ix < 0) {
				ix = -ix;
				sign ^= 0x8000000000000000LL;
			}
		} else {
			ix = denormal_subd1(iy, ix);
			sign ^= 0x8000000000000000LL;
		}
	} else {
		sign = hx & 0x8000000000000000LL;
		ix = hx & 0x7fffffffffffffffLL;
		iy = hy & 0x7fffffffffffffffLL;
		if (iy < 0x0010000000000000LL)
			ix = denormal_addd1(ix, iy);
		else
			ix = denormal_addd1(iy, ix);
	}

	return sign | ix;
}

/**
 *	denormal_to_double - Given denormalized float number,
 *	                     store double float
 *
 *	@fpu: Pointer to sh_fpu_hard structure
 *	@n: Index to FP register
 */
static void
denormal_to_double (struct sh_fpu_hard_struct *fpu, int n)
{
	unsigned long du, dl;
	unsigned long x = fpu->fpul;
	int exp = 1023 - 126;

	if (x != 0 && (x & 0x7f800000) == 0) {
		du = (x & 0x80000000);
		while ((x & 0x00800000) == 0) {
			x <<= 1;
			exp--;
		}
		x &= 0x007fffff;
		du |= (exp << 20) | (x >> 3);
		dl = x << 29;

		fpu->fp_regs[n] = du;
		fpu->fp_regs[n+1] = dl;
	}
}

/**
 *	ieee_fpe_handler - Handle denormalized number exception
 *
 *	@regs: Pointer to register structure
 *
 *	Returns 1 when it's handled (should not cause exception).
 */
static int
ieee_fpe_handler (struct pt_regs *regs)
{
	unsigned short insn = *(unsigned short *) regs->pc;
	unsigned short finsn;
	unsigned long nextpc;
	int nib[4] = {
		(insn >> 12) & 0xf,
		(insn >> 8) & 0xf,
		(insn >> 4) & 0xf,
		insn & 0xf};

	if (nib[0] == 0xb ||
	    (nib[0] == 0x4 && nib[2] == 0x0 && nib[3] == 0xb)) /* bsr & jsr */
		regs->pr = regs->pc + 4;
	if (nib[0] == 0xa || nib[0] == 0xb) { /* bra & bsr */
		nextpc = regs->pc + 4 + ((short) ((insn & 0xfff) << 4) >> 3);
		finsn = *(unsigned short *) (regs->pc + 2);
	} else if (nib[0] == 0x8 && nib[1] == 0xd) { /* bt/s */
		if (regs->sr & 1)
			nextpc = regs->pc + 4 + ((char) (insn & 0xff) << 1);
		else
			nextpc = regs->pc + 4;
		finsn = *(unsigned short *) (regs->pc + 2);
	} else if (nib[0] == 0x8 && nib[1] == 0xf) { /* bf/s */
		if (regs->sr & 1)
			nextpc = regs->pc + 4;
		else
			nextpc = regs->pc + 4 + ((char) (insn & 0xff) << 1);
		finsn = *(unsigned short *) (regs->pc + 2);
	} else if (nib[0] == 0x4 && nib[3] == 0xb &&
		 (nib[2] == 0x0 || nib[2] == 0x2)) { /* jmp & jsr */
		nextpc = regs->regs[nib[1]];
		finsn = *(unsigned short *) (regs->pc + 2);
	} else if (nib[0] == 0x0 && nib[3] == 0x3 &&
		 (nib[2] == 0x0 || nib[2] == 0x2)) { /* braf & bsrf */
		nextpc = regs->pc + 4 + regs->regs[nib[1]];
		finsn = *(unsigned short *) (regs->pc + 2);
	} else if (insn == 0x000b) { /* rts */
		nextpc = regs->pr;
		finsn = *(unsigned short *) (regs->pc + 2);
	} else {
		nextpc = regs->pc + 2;
		finsn = insn;
	}

#define FPSCR_FPU_ERROR (1 << 17)

	if ((finsn & 0xf1ff) == 0xf0ad) { /* fcnvsd */
		struct task_struct *tsk = current;

		if ((tsk->thread.xstate->hardfpu.fpscr & FPSCR_FPU_ERROR)) {
			/* FPU error */
			denormal_to_double (&tsk->thread.xstate->hardfpu,
					    (finsn >> 8) & 0xf);
		} else
			return 0;

		regs->pc = nextpc;
		return 1;
	} else if ((finsn & 0xf00f) == 0xf002) { /* fmul */
		struct task_struct *tsk = current;
		int fpscr;
		int n, m, prec;
		unsigned int hx, hy;

		n = (finsn >> 8) & 0xf;
		m = (finsn >> 4) & 0xf;
		hx = tsk->thread.xstate->hardfpu.fp_regs[n];
		hy = tsk->thread.xstate->hardfpu.fp_regs[m];
		fpscr = tsk->thread.xstate->hardfpu.fpscr;
		prec = fpscr & (1 << 19);

		if ((fpscr & FPSCR_FPU_ERROR)
		     && (prec && ((hx & 0x7fffffff) < 0x00100000
				   || (hy & 0x7fffffff) < 0x00100000))) {
			long long llx, lly;

			/* FPU error because of denormal */
			llx = ((long long) hx << 32)
			       | tsk->thread.xstate->hardfpu.fp_regs[n+1];
			lly = ((long long) hy << 32)
			       | tsk->thread.xstate->hardfpu.fp_regs[m+1];
			if ((hx & 0x7fffffff) >= 0x00100000)
				llx = denormal_muld(lly, llx);
			else
				llx = denormal_muld(llx, lly);
			tsk->thread.xstate->hardfpu.fp_regs[n] = llx >> 32;
			tsk->thread.xstate->hardfpu.fp_regs[n+1] = llx & 0xffffffff;
		} else if ((fpscr & FPSCR_FPU_ERROR)
		     && (!prec && ((hx & 0x7fffffff) < 0x00800000
				   || (hy & 0x7fffffff) < 0x00800000))) {
			/* FPU error because of denormal */
			if ((hx & 0x7fffffff) >= 0x00800000)
				hx = denormal_mulf(hy, hx);
			else
				hx = denormal_mulf(hx, hy);
			tsk->thread.xstate->hardfpu.fp_regs[n] = hx;
		} else
			return 0;

		regs->pc = nextpc;
		return 1;
	} else if ((finsn & 0xf00e) == 0xf000) { /* fadd, fsub */
		struct task_struct *tsk = current;
		int fpscr;
		int n, m, prec;
		unsigned int hx, hy;

		n = (finsn >> 8) & 0xf;
		m = (finsn >> 4) & 0xf;
		hx = tsk->thread.xstate->hardfpu.fp_regs[n];
		hy = tsk->thread.xstate->hardfpu.fp_regs[m];
		fpscr = tsk->thread.xstate->hardfpu.fpscr;
		prec = fpscr & (1 << 19);

		if ((fpscr & FPSCR_FPU_ERROR)
		     && (prec && ((hx & 0x7fffffff) < 0x00100000
				   || (hy & 0x7fffffff) < 0x00100000))) {
			long long llx, lly;

			/* FPU error because of denormal */
			llx = ((long long) hx << 32)
			       | tsk->thread.xstate->hardfpu.fp_regs[n+1];
			lly = ((long long) hy << 32)
			       | tsk->thread.xstate->hardfpu.fp_regs[m+1];
			if ((finsn & 0xf00f) == 0xf000)
				llx = denormal_addd(llx, lly);
			else
				llx = denormal_addd(llx, lly ^ (1LL << 63));
			tsk->thread.xstate->hardfpu.fp_regs[n] = llx >> 32;
			tsk->thread.xstate->hardfpu.fp_regs[n+1] = llx & 0xffffffff;
		} else if ((fpscr & FPSCR_FPU_ERROR)
		     && (!prec && ((hx & 0x7fffffff) < 0x00800000
				   || (hy & 0x7fffffff) < 0x00800000))) {
			/* FPU error because of denormal */
			if ((finsn & 0xf00f) == 0xf000)
				hx = denormal_addf(hx, hy);
			else
				hx = denormal_addf(hx, hy ^ 0x80000000);
			tsk->thread.xstate->hardfpu.fp_regs[n] = hx;
		} else
			return 0;

		regs->pc = nextpc;
		return 1;
	}

	return 0;
}

BUILD_TRAP_HANDLER(fpu_error)
{
	struct task_struct *tsk = current;
	TRAP_HANDLER_DECL;

	__unlazy_fpu(tsk, regs);
	if (ieee_fpe_handler(regs)) {
		tsk->thread.xstate->hardfpu.fpscr &=
			~(FPSCR_CAUSE_MASK | FPSCR_FLAG_MASK);
		grab_fpu(regs);
		restore_fpu(tsk);
		task_thread_info(tsk)->status |= TS_USEDFPU;
		return;
	}

	force_sig(SIGFPE);
}