| // |
| // 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 { |
| 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__) |
| 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)); |
| stack_t old_sigstk; |
| sigstk.ss_sp = altstack; |
| sigstk.ss_size = kAlternateStackSize; |
| sigstk.ss_flags = 0; |
| 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. |
| 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 |
| } // namespace absl |
| |
| #endif // ABSL_INTERNAL_HAVE_DEBUGGING_STACK_CONSUMPTION |