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+//
+// 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
+//
+// http://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