1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
|
//
// Copyright 2018 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#include "absl/debugging/internal/stack_consumption.h"
#ifdef ABSL_INTERNAL_HAVE_DEBUGGING_STACK_CONSUMPTION
#include <signal.h>
#include <sys/mman.h>
#include <unistd.h>
#include <string.h>
#include "absl/base/attributes.h"
#include "absl/base/internal/raw_logging.h"
namespace absl {
ABSL_NAMESPACE_BEGIN
namespace debugging_internal {
namespace {
// This code requires that we know the direction in which the stack
// grows. It is commonly believed that this can be detected by putting
// a variable on the stack and then passing its address to a function
// that compares the address of this variable to the address of a
// variable on the function's own stack. However, this is unspecified
// behavior in C++: If two pointers p and q of the same type point to
// different objects that are not members of the same object or
// elements of the same array or to different functions, or if only
// one of them is null, the results of p<q, p>q, p<=q, and p>=q are
// unspecified. Therefore, instead we hardcode the direction of the
// stack on platforms we know about.
#if defined(__i386__) || defined(__x86_64__) || defined(__ppc__) || \
defined(__aarch64__)
constexpr bool kStackGrowsDown = true;
#else
#error Need to define kStackGrowsDown
#endif
// To measure the stack footprint of some code, we create a signal handler
// (for SIGUSR2 say) that exercises this code on an alternate stack. This
// alternate stack is initialized to some known pattern (0x55, 0x55, 0x55,
// ...). We then self-send this signal, and after the signal handler returns,
// look at the alternate stack buffer to see what portion has been touched.
//
// This trick gives us the the stack footprint of the signal handler. But the
// signal handler, even before the code for it is exercised, consumes some
// stack already. We however only want the stack usage of the code inside the
// signal handler. To measure this accurately, we install two signal handlers:
// one that does nothing and just returns, and the user-provided signal
// handler. The difference between the stack consumption of these two signals
// handlers should give us the stack foorprint of interest.
void EmptySignalHandler(int) {}
// This is arbitrary value, and could be increase further, at the cost of
// memset()ting it all to known sentinel value.
constexpr int kAlternateStackSize = 64 << 10; // 64KiB
constexpr int kSafetyMargin = 32;
constexpr char kAlternateStackFillValue = 0x55;
// These helper functions look at the alternate stack buffer, and figure
// out what portion of this buffer has been touched - this is the stack
// consumption of the signal handler running on this alternate stack.
// This function will return -1 if the alternate stack buffer has not been
// touched. It will abort the program if the buffer has overflowed or is about
// to overflow.
int GetStackConsumption(const void* const altstack) {
const char* begin;
int increment;
if (kStackGrowsDown) {
begin = reinterpret_cast<const char*>(altstack);
increment = 1;
} else {
begin = reinterpret_cast<const char*>(altstack) + kAlternateStackSize - 1;
increment = -1;
}
for (int usage_count = kAlternateStackSize; usage_count > 0; --usage_count) {
if (*begin != kAlternateStackFillValue) {
ABSL_RAW_CHECK(usage_count <= kAlternateStackSize - kSafetyMargin,
"Buffer has overflowed or is about to overflow");
return usage_count;
}
begin += increment;
}
ABSL_RAW_LOG(FATAL, "Unreachable code");
return -1;
}
} // namespace
int GetSignalHandlerStackConsumption(void (*signal_handler)(int)) {
// The alt-signal-stack cannot be heap allocated because there is a
// bug in glibc-2.2 where some signal handler setup code looks at the
// current stack pointer to figure out what thread is currently running.
// Therefore, the alternate stack must be allocated from the main stack
// itself.
void* altstack = mmap(nullptr, kAlternateStackSize, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
ABSL_RAW_CHECK(altstack != MAP_FAILED, "mmap() failed");
// Set up the alt-signal-stack (and save the older one).
stack_t sigstk;
memset(&sigstk, 0, sizeof(sigstk));
sigstk.ss_sp = altstack;
sigstk.ss_size = kAlternateStackSize;
sigstk.ss_flags = 0;
stack_t old_sigstk;
memset(&old_sigstk, 0, sizeof(old_sigstk));
ABSL_RAW_CHECK(sigaltstack(&sigstk, &old_sigstk) == 0,
"sigaltstack() failed");
// Set up SIGUSR1 and SIGUSR2 signal handlers (and save the older ones).
struct sigaction sa;
memset(&sa, 0, sizeof(sa));
struct sigaction old_sa1, old_sa2;
sigemptyset(&sa.sa_mask);
sa.sa_flags = SA_ONSTACK;
// SIGUSR1 maps to EmptySignalHandler.
sa.sa_handler = EmptySignalHandler;
ABSL_RAW_CHECK(sigaction(SIGUSR1, &sa, &old_sa1) == 0, "sigaction() failed");
// SIGUSR2 maps to signal_handler.
sa.sa_handler = signal_handler;
ABSL_RAW_CHECK(sigaction(SIGUSR2, &sa, &old_sa2) == 0, "sigaction() failed");
// Send SIGUSR1 signal and measure the stack consumption of the empty
// signal handler.
// The first signal might use more stack space. Run once and ignore the
// results to get that out of the way.
ABSL_RAW_CHECK(kill(getpid(), SIGUSR1) == 0, "kill() failed");
memset(altstack, kAlternateStackFillValue, kAlternateStackSize);
ABSL_RAW_CHECK(kill(getpid(), SIGUSR1) == 0, "kill() failed");
int base_stack_consumption = GetStackConsumption(altstack);
// Send SIGUSR2 signal and measure the stack consumption of signal_handler.
ABSL_RAW_CHECK(kill(getpid(), SIGUSR2) == 0, "kill() failed");
int signal_handler_stack_consumption = GetStackConsumption(altstack);
// Now restore the old alt-signal-stack and signal handlers.
if (old_sigstk.ss_sp == nullptr && old_sigstk.ss_size == 0 &&
(old_sigstk.ss_flags & SS_DISABLE)) {
// https://git.musl-libc.org/cgit/musl/commit/src/signal/sigaltstack.c?id=7829f42a2c8944555439380498ab8b924d0f2070
// The original stack has ss_size==0 and ss_flags==SS_DISABLE, but some
// versions of musl have a bug that rejects ss_size==0. Work around this by
// setting ss_size to MINSIGSTKSZ, which should be ignored by the kernel
// when SS_DISABLE is set.
old_sigstk.ss_size = MINSIGSTKSZ;
}
ABSL_RAW_CHECK(sigaltstack(&old_sigstk, nullptr) == 0,
"sigaltstack() failed");
ABSL_RAW_CHECK(sigaction(SIGUSR1, &old_sa1, nullptr) == 0,
"sigaction() failed");
ABSL_RAW_CHECK(sigaction(SIGUSR2, &old_sa2, nullptr) == 0,
"sigaction() failed");
ABSL_RAW_CHECK(munmap(altstack, kAlternateStackSize) == 0, "munmap() failed");
if (signal_handler_stack_consumption != -1 && base_stack_consumption != -1) {
return signal_handler_stack_consumption - base_stack_consumption;
}
return -1;
}
} // namespace debugging_internal
ABSL_NAMESPACE_END
} // namespace absl
#endif // ABSL_INTERNAL_HAVE_DEBUGGING_STACK_CONSUMPTION
|
