1 // Protocol Buffers - Google's data interchange format
2 // Copyright 2012 Google Inc.  All rights reserved.
3 // https://developers.google.com/protocol-buffers/
4 //
5 // Redistribution and use in source and binary forms, with or without
6 // modification, are permitted provided that the following conditions are
7 // met:
8 //
9 //     * Redistributions of source code must retain the above copyright
10 // notice, this list of conditions and the following disclaimer.
11 //     * Redistributions in binary form must reproduce the above
12 // copyright notice, this list of conditions and the following disclaimer
13 // in the documentation and/or other materials provided with the
14 // distribution.
15 //     * Neither the name of Google Inc. nor the names of its
16 // contributors may be used to endorse or promote products derived from
17 // this software without specific prior written permission.
18 //
19 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
20 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
21 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
22 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
23 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
24 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
25 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
26 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
27 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
28 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
29 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
30 
31 // This module gets enough CPU information to optimize the
32 // atomicops module on x86.
33 
34 #include <cstring>
35 
36 #include <google/protobuf/stubs/atomicops.h>
37 
38 // This file only makes sense with atomicops_internals_x86_gcc.h -- it
39 // depends on structs that are defined in that file.  If atomicops.h
40 // doesn't sub-include that file, then we aren't needed, and shouldn't
41 // try to do anything.
42 #ifdef GOOGLE_PROTOBUF_ATOMICOPS_INTERNALS_X86_GCC_H_
43 
44 // Inline cpuid instruction.  In PIC compilations, %ebx contains the address
45 // of the global offset table.  To avoid breaking such executables, this code
46 // must preserve that register's value across cpuid instructions.
47 #if defined(__i386__)
48 #define cpuid(a, b, c, d, inp) \
49   asm("mov %%ebx, %%edi\n"     \
50       "cpuid\n"                \
51       "xchg %%edi, %%ebx\n"    \
52       : "=a" (a), "=D" (b), "=c" (c), "=d" (d) : "a" (inp))
53 #elif defined(__x86_64__)
54 #define cpuid(a, b, c, d, inp) \
55   asm("mov %%rbx, %%rdi\n"     \
56       "cpuid\n"                \
57       "xchg %%rdi, %%rbx\n"    \
58       : "=a" (a), "=D" (b), "=c" (c), "=d" (d) : "a" (inp))
59 #endif
60 
61 #if defined(cpuid)        // initialize the struct only on x86
62 
63 namespace google {
64 namespace protobuf {
65 namespace internal {
66 
67 // Set the flags so that code will run correctly and conservatively, so even
68 // if we haven't been initialized yet, we're probably single threaded, and our
69 // default values should hopefully be pretty safe.
70 struct AtomicOps_x86CPUFeatureStruct AtomicOps_Internalx86CPUFeatures = {
71   false,          // bug can't exist before process spawns multiple threads
72   false,          // no SSE2
73 };
74 
75 namespace {
76 
77 // Initialize the AtomicOps_Internalx86CPUFeatures struct.
AtomicOps_Internalx86CPUFeaturesInit()78 void AtomicOps_Internalx86CPUFeaturesInit() {
79   uint32_t eax;
80   uint32_t ebx;
81   uint32_t ecx;
82   uint32_t edx;
83 
84   // Get vendor string (issue CPUID with eax = 0)
85   cpuid(eax, ebx, ecx, edx, 0);
86   char vendor[13];
87   memcpy(vendor, &ebx, 4);
88   memcpy(vendor + 4, &edx, 4);
89   memcpy(vendor + 8, &ecx, 4);
90   vendor[12] = 0;
91 
92   // get feature flags in ecx/edx, and family/model in eax
93   cpuid(eax, ebx, ecx, edx, 1);
94 
95   int family = (eax >> 8) & 0xf;        // family and model fields
96   int model = (eax >> 4) & 0xf;
97   if (family == 0xf) {                  // use extended family and model fields
98     family += (eax >> 20) & 0xff;
99     model += ((eax >> 16) & 0xf) << 4;
100   }
101 
102   // Opteron Rev E has a bug in which on very rare occasions a locked
103   // instruction doesn't act as a read-acquire barrier if followed by a
104   // non-locked read-modify-write instruction.  Rev F has this bug in
105   // pre-release versions, but not in versions released to customers,
106   // so we test only for Rev E, which is family 15, model 32..63 inclusive.
107   if (strcmp(vendor, "AuthenticAMD") == 0 &&       // AMD
108       family == 15 &&
109       32 <= model && model <= 63) {
110     AtomicOps_Internalx86CPUFeatures.has_amd_lock_mb_bug = true;
111   } else {
112     AtomicOps_Internalx86CPUFeatures.has_amd_lock_mb_bug = false;
113   }
114 
115   // edx bit 26 is SSE2 which we use to tell use whether we can use mfence
116   AtomicOps_Internalx86CPUFeatures.has_sse2 = ((edx >> 26) & 1);
117 }
118 
119 class AtomicOpsx86Initializer {
120  public:
AtomicOpsx86Initializer()121   AtomicOpsx86Initializer() {
122     AtomicOps_Internalx86CPUFeaturesInit();
123   }
124 };
125 
126 // A global to get use initialized on startup via static initialization :/
127 AtomicOpsx86Initializer g_initer;
128 
129 }  // namespace
130 
131 }  // namespace internal
132 }  // namespace protobuf
133 }  // namespace google
134 
135 #endif  // __i386__
136 
137 #endif  // GOOGLE_PROTOBUF_ATOMICOPS_INTERNALS_X86_GCC_H_
138