1/*
2 * Simple C functions to supplement the C library
3 *
4 * Copyright (c) 2006 Fabrice Bellard
5 *
6 * Permission is hereby granted, free of charge, to any person obtaining a copy
7 * of this software and associated documentation files (the "Software"), to deal
8 * in the Software without restriction, including without limitation the rights
9 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
10 * copies of the Software, and to permit persons to whom the Software is
11 * furnished to do so, subject to the following conditions:
12 *
13 * The above copyright notice and this permission notice shall be included in
14 * all copies or substantial portions of the Software.
15 *
16 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
17 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
18 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
19 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
20 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
21 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
22 * THE SOFTWARE.
23 */
24#include "qemu/osdep.h"
25#include "qemu/cutils.h"
26#include "qemu/bswap.h"
27
28static bool
29buffer_zero_int(const void *buf, size_t len)
30{
31 if (unlikely(len < 8)) {
32 /* For a very small buffer, simply accumulate all the bytes. */
33 const unsigned char *p = buf;
34 const unsigned char *e = buf + len;
35 unsigned char t = 0;
36
37 do {
38 t |= *p++;
39 } while (p < e);
40
41 return t == 0;
42 } else {
43 /* Otherwise, use the unaligned memory access functions to
44 handle the beginning and end of the buffer, with a couple
45 of loops handling the middle aligned section. */
46 uint64_t t = ldq_he_p(buf);
47 const uint64_t *p = (uint64_t *)(((uintptr_t)buf + 8) & -8);
48 const uint64_t *e = (uint64_t *)(((uintptr_t)buf + len) & -8);
49
50 for (; p + 8 <= e; p += 8) {
51 __builtin_prefetch(p + 8);
52 if (t) {
53 return false;
54 }
55 t = p[0] | p[1] | p[2] | p[3] | p[4] | p[5] | p[6] | p[7];
56 }
57 while (p < e) {
58 t |= *p++;
59 }
60 t |= ldq_he_p(buf + len - 8);
61
62 return t == 0;
63 }
64}
65
66#if defined(CONFIG_AVX2_OPT) || defined(__SSE2__)
67/* Do not use push_options pragmas unnecessarily, because clang
68 * does not support them.
69 */
70#ifdef CONFIG_AVX2_OPT
71#pragma GCC push_options
72#pragma GCC target("sse2")
73#endif
74#include <emmintrin.h>
75
76/* Note that each of these vectorized functions require len >= 64. */
77
78static bool
79buffer_zero_sse2(const void *buf, size_t len)
80{
81 __m128i t = _mm_loadu_si128(buf);
82 __m128i *p = (__m128i *)(((uintptr_t)buf + 5 * 16) & -16);
83 __m128i *e = (__m128i *)(((uintptr_t)buf + len) & -16);
84 __m128i zero = _mm_setzero_si128();
85
86 /* Loop over 16-byte aligned blocks of 64. */
87 while (likely(p <= e)) {
88 __builtin_prefetch(p);
89 t = _mm_cmpeq_epi8(t, zero);
90 if (unlikely(_mm_movemask_epi8(t) != 0xFFFF)) {
91 return false;
92 }
93 t = p[-4] | p[-3] | p[-2] | p[-1];
94 p += 4;
95 }
96
97 /* Finish the aligned tail. */
98 t |= e[-3];
99 t |= e[-2];
100 t |= e[-1];
101
102 /* Finish the unaligned tail. */
103 t |= _mm_loadu_si128(buf + len - 16);
104
105 return _mm_movemask_epi8(_mm_cmpeq_epi8(t, zero)) == 0xFFFF;
106}
107#ifdef CONFIG_AVX2_OPT
108#pragma GCC pop_options
109#endif
110
111#ifdef CONFIG_AVX2_OPT
112/* Note that due to restrictions/bugs wrt __builtin functions in gcc <= 4.8,
113 * the includes have to be within the corresponding push_options region, and
114 * therefore the regions themselves have to be ordered with increasing ISA.
115 */
116#pragma GCC push_options
117#pragma GCC target("sse4")
118#include <smmintrin.h>
119
120static bool
121buffer_zero_sse4(const void *buf, size_t len)
122{
123 __m128i t = _mm_loadu_si128(buf);
124 __m128i *p = (__m128i *)(((uintptr_t)buf + 5 * 16) & -16);
125 __m128i *e = (__m128i *)(((uintptr_t)buf + len) & -16);
126
127 /* Loop over 16-byte aligned blocks of 64. */
128 while (likely(p <= e)) {
129 __builtin_prefetch(p);
130 if (unlikely(!_mm_testz_si128(t, t))) {
131 return false;
132 }
133 t = p[-4] | p[-3] | p[-2] | p[-1];
134 p += 4;
135 }
136
137 /* Finish the aligned tail. */
138 t |= e[-3];
139 t |= e[-2];
140 t |= e[-1];
141
142 /* Finish the unaligned tail. */
143 t |= _mm_loadu_si128(buf + len - 16);
144
145 return _mm_testz_si128(t, t);
146}
147
148#pragma GCC pop_options
149#pragma GCC push_options
150#pragma GCC target("avx2")
151#include <immintrin.h>
152
153static bool
154buffer_zero_avx2(const void *buf, size_t len)
155{
156 /* Begin with an unaligned head of 32 bytes. */
157 __m256i t = _mm256_loadu_si256(buf);
158 __m256i *p = (__m256i *)(((uintptr_t)buf + 5 * 32) & -32);
159 __m256i *e = (__m256i *)(((uintptr_t)buf + len) & -32);
160
161 if (likely(p <= e)) {
162 /* Loop over 32-byte aligned blocks of 128. */
163 do {
164 __builtin_prefetch(p);
165 if (unlikely(!_mm256_testz_si256(t, t))) {
166 return false;
167 }
168 t = p[-4] | p[-3] | p[-2] | p[-1];
169 p += 4;
170 } while (p <= e);
171 } else {
172 t |= _mm256_loadu_si256(buf + 32);
173 if (len <= 128) {
174 goto last2;
175 }
176 }
177
178 /* Finish the last block of 128 unaligned. */
179 t |= _mm256_loadu_si256(buf + len - 4 * 32);
180 t |= _mm256_loadu_si256(buf + len - 3 * 32);
181 last2:
182 t |= _mm256_loadu_si256(buf + len - 2 * 32);
183 t |= _mm256_loadu_si256(buf + len - 1 * 32);
184
185 return _mm256_testz_si256(t, t);
186}
187#pragma GCC pop_options
188#endif /* CONFIG_AVX2_OPT */
189
190/* Note that for test_buffer_is_zero_next_accel, the most preferred
191 * ISA must have the least significant bit.
192 */
193#define CACHE_AVX2 1
194#define CACHE_SSE4 2
195#define CACHE_SSE2 4
196
197/* Make sure that these variables are appropriately initialized when
198 * SSE2 is enabled on the compiler command-line, but the compiler is
199 * too old to support CONFIG_AVX2_OPT.
200 */
201#ifdef CONFIG_AVX2_OPT
202# define INIT_CACHE 0
203# define INIT_ACCEL buffer_zero_int
204#else
205# ifndef __SSE2__
206# error "ISA selection confusion"
207# endif
208# define INIT_CACHE CACHE_SSE2
209# define INIT_ACCEL buffer_zero_sse2
210#endif
211
212static unsigned cpuid_cache = INIT_CACHE;
213static bool (*buffer_accel)(const void *, size_t) = INIT_ACCEL;
214
215static void init_accel(unsigned cache)
216{
217 bool (*fn)(const void *, size_t) = buffer_zero_int;
218 if (cache & CACHE_SSE2) {
219 fn = buffer_zero_sse2;
220 }
221#ifdef CONFIG_AVX2_OPT
222 if (cache & CACHE_SSE4) {
223 fn = buffer_zero_sse4;
224 }
225 if (cache & CACHE_AVX2) {
226 fn = buffer_zero_avx2;
227 }
228#endif
229 buffer_accel = fn;
230}
231
232#ifdef CONFIG_AVX2_OPT
233#include "qemu/cpuid.h"
234
235static void __attribute__((constructor)) init_cpuid_cache(void)
236{
237 int max = __get_cpuid_max(0, NULL);
238 int a, b, c, d;
239 unsigned cache = 0;
240
241 if (max >= 1) {
242 __cpuid(1, a, b, c, d);
243 if (d & bit_SSE2) {
244 cache |= CACHE_SSE2;
245 }
246 if (c & bit_SSE4_1) {
247 cache |= CACHE_SSE4;
248 }
249
250 /* We must check that AVX is not just available, but usable. */
251 if ((c & bit_OSXSAVE) && (c & bit_AVX) && max >= 7) {
252 int bv;
253 __asm("xgetbv" : "=a"(bv), "=d"(d) : "c"(0));
254 __cpuid_count(7, 0, a, b, c, d);
255 if ((bv & 6) == 6 && (b & bit_AVX2)) {
256 cache |= CACHE_AVX2;
257 }
258 }
259 }
260 cpuid_cache = cache;
261 init_accel(cache);
262}
263#endif /* CONFIG_AVX2_OPT */
264
265bool test_buffer_is_zero_next_accel(void)
266{
267 /* If no bits set, we just tested buffer_zero_int, and there
268 are no more acceleration options to test. */
269 if (cpuid_cache == 0) {
270 return false;
271 }
272 /* Disable the accelerator we used before and select a new one. */
273 cpuid_cache &= cpuid_cache - 1;
274 init_accel(cpuid_cache);
275 return true;
276}
277
278static bool select_accel_fn(const void *buf, size_t len)
279{
280 if (likely(len >= 64)) {
281 return buffer_accel(buf, len);
282 }
283 return buffer_zero_int(buf, len);
284}
285
286#else
287#define select_accel_fn buffer_zero_int
288bool test_buffer_is_zero_next_accel(void)
289{
290 return false;
291}
292#endif
293
294/*
295 * Checks if a buffer is all zeroes
296 */
297bool buffer_is_zero(const void *buf, size_t len)
298{
299 if (unlikely(len == 0)) {
300 return true;
301 }
302
303 /* Fetch the beginning of the buffer while we select the accelerator. */
304 __builtin_prefetch(buf);
305
306 /* Use an optimized zero check if possible. Note that this also
307 includes a check for an unrolled loop over 64-bit integers. */
308 return select_accel_fn(buf, len);
309}
310