1 /* $NetBSD: convert_xmm_s87.c,v 1.8 2024/02/10 09:24:17 andvar Exp $ */
2
3 /*-
4 * Copyright (c) 1998, 2000, 2001, 2008 The NetBSD Foundation, Inc.
5 * All rights reserved.
6 *
7 * This code is derived from software contributed to The NetBSD Foundation
8 * by Charles M. Hannum; by Jason R. Thorpe of Wasabi Systems, Inc.
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
12 * are met:
13 * 1. Redistributions of source code must retain the above copyright
14 * notice, this list of conditions and the following disclaimer.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 * notice, this list of conditions and the following disclaimer in the
17 * documentation and/or other materials provided with the distribution.
18 *
19 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
20 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
21 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
22 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
23 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
24 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
25 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
26 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
27 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
28 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
29 * POSSIBILITY OF SUCH DAMAGE.
30 */
31
32 #include <sys/cdefs.h>
33 __KERNEL_RCSID(0, "$NetBSD: convert_xmm_s87.c,v 1.8 2024/02/10 09:24:17 andvar Exp $");
34
35
36 #include <sys/param.h>
37 #include <x86/fpu.h>
38
39 void
process_xmm_to_s87(const struct fxsave * sxmm,struct save87 * s87)40 process_xmm_to_s87(const struct fxsave *sxmm, struct save87 *s87)
41 {
42 unsigned int tag, ab_tag, st;
43 const struct fpaccfx *fx_reg;
44 struct fpacc87 *s87_reg;
45 int i;
46
47 /*
48 * For historic reasons core dumps and ptrace all use the old save87
49 * layout. Convert the important parts.
50 * getucontext gets what we give it.
51 * setucontext should return something given by getucontext, but
52 * we are (at the moment) willing to change it.
53 *
54 * It really isn't worth setting the 'tag' bits to 01 (zero) or
55 * 10 (NaN etc) since the processor will set any internal bits
56 * correctly when the value is loaded (the 287 believed them).
57 *
58 * Additionally the s87_tw and s87_tw are 'indexed' by the actual
59 * register numbers, whereas the registers themselves have ST(0)
60 * first. Pairing the values and tags can only be done with
61 * reference to the 'top of stack'.
62 *
63 * If any x87 registers are used, they will typically be from
64 * r7 downwards - so the high bits of the tag register indicate
65 * used registers. The conversions are not optimised for this.
66 *
67 * The ABI we use requires the FP stack to be empty on every
68 * function call. I think this means that the stack isn't expected
69 * to overflow - overflow doesn't drop a core in my testing.
70 *
71 * Note that this code writes to all of the 's87' structure that
72 * actually gets written to userspace.
73 */
74
75 /* FPU control/status */
76 s87->s87_cw = sxmm->fx_cw;
77 s87->s87_sw = sxmm->fx_sw;
78 /* tag word handled below */
79 s87->s87_ip = sxmm->fx_ip;
80 s87->s87_opcode = sxmm->fx_opcode;
81 s87->s87_dp = sxmm->fx_dp;
82
83 /* FP registers (in stack order) */
84 fx_reg = sxmm->fx_87_ac;
85 s87_reg = s87->s87_ac;
86 for (i = 0; i < 8; fx_reg++, s87_reg++, i++)
87 *s87_reg = fx_reg->r;
88
89 /* Tag word and registers. */
90 ab_tag = sxmm->fx_tw & 0xff; /* Bits set if valid */
91 if (ab_tag == 0) {
92 /* none used */
93 s87->s87_tw = 0xffff;
94 return;
95 }
96
97 /* For ST(i), i = fpu_reg - top, we start with fpu_reg=7. */
98 st = 7 - ((sxmm->fx_sw >> 11) & 7);
99 tag = 0;
100 for (i = 0x80; i != 0; i >>= 1) {
101 tag <<= 2;
102 if (ab_tag & i) {
103 unsigned int exp;
104 /* Non-empty - we need to check ST(i) */
105 fx_reg = &sxmm->fx_87_ac[st];
106 exp = fx_reg->r.f87_exp_sign & 0x7fff;
107 if (exp == 0) {
108 if (fx_reg->r.f87_mantissa == 0)
109 tag |= 1; /* Zero */
110 else
111 tag |= 2; /* Denormal */
112 } else if (exp == 0x7fff)
113 tag |= 2; /* Infinity or NaN */
114 } else
115 tag |= 3; /* Empty */
116 st = (st - 1) & 7;
117 }
118 s87->s87_tw = tag;
119 }
120
121 void
process_s87_to_xmm(const struct save87 * s87,struct fxsave * sxmm)122 process_s87_to_xmm(const struct save87 *s87, struct fxsave *sxmm)
123 {
124 unsigned int tag, ab_tag;
125 struct fpaccfx *fx_reg;
126 const struct fpacc87 *s87_reg;
127 int i;
128
129 /*
130 * ptrace gives us registers in the save87 format and
131 * we must convert them to the correct format.
132 *
133 * This code is normally used when overwriting the processes
134 * registers (in the pcb), so it mustn't change any other fields.
135 *
136 * There is a lot of pad in 'struct fxsave', if the destination
137 * is written to userspace, it must be zeroed first.
138 */
139
140 /* FPU control/status */
141 sxmm->fx_cw = s87->s87_cw;
142 sxmm->fx_sw = s87->s87_sw;
143 /* tag word handled below */
144 sxmm->fx_ip = s87->s87_ip;
145 sxmm->fx_opcode = s87->s87_opcode;
146 sxmm->fx_dp = s87->s87_dp;
147
148 /* Tag word */
149 tag = s87->s87_tw; /* 0b11 => unused */
150 if (tag == 0xffff) {
151 /* All unused - values don't matter, zero for safety */
152 sxmm->fx_tw = 0;
153 memset(&sxmm->fx_87_ac, 0, sizeof sxmm->fx_87_ac);
154 return;
155 }
156
157 tag ^= 0xffff; /* So 0b00 is unused */
158 tag |= tag >> 1; /* Look at even bits */
159 ab_tag = 0;
160 i = 1;
161 do
162 ab_tag |= tag & i;
163 while ((tag >>= 1) >= (i <<= 1));
164 sxmm->fx_tw = ab_tag;
165
166 /* FP registers (in stack order) */
167 fx_reg = sxmm->fx_87_ac;
168 s87_reg = s87->s87_ac;
169 for (i = 0; i < 8; fx_reg++, s87_reg++, i++)
170 fx_reg->r = *s87_reg;
171 }
172