diff options
| -rw-r--r-- | absl/debugging/BUILD.bazel | 26 | ||||
| -rw-r--r-- | absl/debugging/internal/stack_consumption.cc | 172 | ||||
| -rw-r--r-- | absl/debugging/internal/stack_consumption.h | 45 | ||||
| -rw-r--r-- | absl/debugging/internal/stack_consumption_test.cc | 48 |
4 files changed, 291 insertions, 0 deletions
diff --git a/absl/debugging/BUILD.bazel b/absl/debugging/BUILD.bazel index 7a56e496..d4cdf492 100644 --- a/absl/debugging/BUILD.bazel +++ b/absl/debugging/BUILD.bazel @@ -17,6 +17,7 @@ load( "//absl:copts.bzl", "ABSL_DEFAULT_COPTS", + "ABSL_TEST_COPTS", ) package( @@ -167,3 +168,28 @@ cc_test( "@com_google_googletest//:gtest_main", ], ) + +cc_library( + name = "stack_consumption", + testonly = 1, + srcs = ["internal/stack_consumption.cc"], + hdrs = ["internal/stack_consumption.h"], + copts = ABSL_DEFAULT_COPTS, + deps = [ + "//absl/base", + "//absl/base:core_headers", + ], + visibility = ["//visibility:private"], +) + +cc_test( + name = "stack_consumption_test", + srcs = ["internal/stack_consumption_test.cc"], + copts = ABSL_TEST_COPTS, + deps = [ + ":stack_consumption", + "//absl/base", + "//absl/base:core_headers", + "@com_google_googletest//:gtest_main", + ], +) diff --git a/absl/debugging/internal/stack_consumption.cc b/absl/debugging/internal/stack_consumption.cc new file mode 100644 index 00000000..2b3b972e --- /dev/null +++ b/absl/debugging/internal/stack_consumption.cc @@ -0,0 +1,172 @@ +// +// 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 diff --git a/absl/debugging/internal/stack_consumption.h b/absl/debugging/internal/stack_consumption.h new file mode 100644 index 00000000..5aa1a109 --- /dev/null +++ b/absl/debugging/internal/stack_consumption.h @@ -0,0 +1,45 @@ +// +// 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. + +// Helper function for measuring stack consumption of signal handlers. + +#ifndef ABSL_DEBUGGING_INTERNAL_STACK_CONSUMPTION_H_ +#define ABSL_DEBUGGING_INTERNAL_STACK_CONSUMPTION_H_ + +// The code in this module is not portable. +// Use this feature test macro to detect its availability. +#ifdef ABSL_INTERNAL_HAVE_DEBUGGING_STACK_CONSUMPTION +#error ABSL_INTERNAL_HAVE_DEBUGGING_STACK_CONSUMPTION cannot be set directly +#elif !defined(__APPLE__) && \ + (defined(__i386__) || defined(__x86_64__) || defined(__ppc__)) +#define ABSL_INTERNAL_HAVE_DEBUGGING_STACK_CONSUMPTION 1 + +namespace absl { +namespace debugging_internal { + +// Returns the stack consumption in bytes for the code exercised by +// signal_handler. To measure stack consumption, signal_handler is registered +// as a signal handler, so the code that it exercises must be async-signal +// safe. The argument of signal_handler is an implementation detail of signal +// handlers and should ignored by the code for signal_handler. Use global +// variables to pass information between your test code and signal_handler. +int GetSignalHandlerStackConsumption(void (*signal_handler)(int)); + +} // namespace debugging_internal +} // namespace absl + +#endif // ABSL_INTERNAL_HAVE_DEBUGGING_STACK_CONSUMPTION + +#endif // ABSL_DEBUGGING_INTERNAL_STACK_CONSUMPTION_H_ diff --git a/absl/debugging/internal/stack_consumption_test.cc b/absl/debugging/internal/stack_consumption_test.cc new file mode 100644 index 00000000..5ce3846e --- /dev/null +++ b/absl/debugging/internal/stack_consumption_test.cc @@ -0,0 +1,48 @@ +// +// 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 <string.h> + +#include "gtest/gtest.h" +#include "absl/base/internal/raw_logging.h" + +namespace absl { +namespace debugging_internal { +namespace { + +static void SimpleSignalHandler(int signo) { + char buf[100]; + memset(buf, 'a', sizeof(buf)); + + // Never true, but prevents compiler from optimizing buf out. + if (signo == 0) { + ABSL_RAW_LOG(INFO, "%p", static_cast<void*>(buf)); + } +} + +TEST(SignalHandlerStackConsumptionTest, MeasuresStackConsumption) { + // Our handler should consume reasonable number of bytes. + EXPECT_GE(GetSignalHandlerStackConsumption(SimpleSignalHandler), 100); +} + +} // namespace +} // namespace debugging_internal +} // namespace absl + +#endif // ABSL_INTERNAL_HAVE_DEBUGGING_STACK_CONSUMPTION |