diff options
author | misterg <misterg@google.com> | 2017-09-19 16:54:40 -0400 |
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committer | misterg <misterg@google.com> | 2017-09-19 16:54:40 -0400 |
commit | c2e754829628d1e9b7a16b3389cfdace76950fdf (patch) | |
tree | 5a7f056f44e27c30e10025113b644f0b3b5801fc /absl/debugging/internal/vdso_support.cc |
Initial Commit
Diffstat (limited to 'absl/debugging/internal/vdso_support.cc')
-rw-r--r-- | absl/debugging/internal/vdso_support.cc | 177 |
1 files changed, 177 insertions, 0 deletions
diff --git a/absl/debugging/internal/vdso_support.cc b/absl/debugging/internal/vdso_support.cc new file mode 100644 index 00000000..5026e1c1 --- /dev/null +++ b/absl/debugging/internal/vdso_support.cc @@ -0,0 +1,177 @@ +// Copyright 2017 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. + +// Allow dynamic symbol lookup in the kernel VDSO page. +// +// VDSOSupport -- a class representing kernel VDSO (if present). + +#include "absl/debugging/internal/vdso_support.h" + +#ifdef ABSL_HAVE_VDSO_SUPPORT // defined in vdso_support.h + +#include <fcntl.h> +#include <sys/syscall.h> +#include <unistd.h> + +#include "absl/base/dynamic_annotations.h" +#include "absl/base/internal/raw_logging.h" +#include "absl/base/port.h" + +#ifndef AT_SYSINFO_EHDR +#define AT_SYSINFO_EHDR 33 // for crosstoolv10 +#endif + +namespace absl { +namespace debug_internal { + +std::atomic<const void *> VDSOSupport::vdso_base_( + debug_internal::ElfMemImage::kInvalidBase); +std::atomic<VDSOSupport::GetCpuFn> VDSOSupport::getcpu_fn_(&InitAndGetCPU); +VDSOSupport::VDSOSupport() + // If vdso_base_ is still set to kInvalidBase, we got here + // before VDSOSupport::Init has been called. Call it now. + : image_(vdso_base_.load(std::memory_order_relaxed) == + debug_internal::ElfMemImage::kInvalidBase + ? Init() + : vdso_base_.load(std::memory_order_relaxed)) {} + +// NOTE: we can't use GoogleOnceInit() below, because we can be +// called by tcmalloc, and none of the *once* stuff may be functional yet. +// +// In addition, we hope that the VDSOSupportHelper constructor +// causes this code to run before there are any threads, and before +// InitGoogle() has executed any chroot or setuid calls. +// +// Finally, even if there is a race here, it is harmless, because +// the operation should be idempotent. +const void *VDSOSupport::Init() { + if (vdso_base_.load(std::memory_order_relaxed) == + debug_internal::ElfMemImage::kInvalidBase) { + { + // Valgrind zaps AT_SYSINFO_EHDR and friends from the auxv[] + // on stack, and so glibc works as if VDSO was not present. + // But going directly to kernel via /proc/self/auxv below bypasses + // Valgrind zapping. So we check for Valgrind separately. + if (RunningOnValgrind()) { + vdso_base_.store(nullptr, std::memory_order_relaxed); + getcpu_fn_.store(&GetCPUViaSyscall, std::memory_order_relaxed); + return nullptr; + } + int fd = open("/proc/self/auxv", O_RDONLY); + if (fd == -1) { + // Kernel too old to have a VDSO. + vdso_base_.store(nullptr, std::memory_order_relaxed); + getcpu_fn_.store(&GetCPUViaSyscall, std::memory_order_relaxed); + return nullptr; + } + ElfW(auxv_t) aux; + while (read(fd, &aux, sizeof(aux)) == sizeof(aux)) { + if (aux.a_type == AT_SYSINFO_EHDR) { + vdso_base_.store(reinterpret_cast<void *>(aux.a_un.a_val), + std::memory_order_relaxed); + break; + } + } + close(fd); + } + if (vdso_base_.load(std::memory_order_relaxed) == + debug_internal::ElfMemImage::kInvalidBase) { + // Didn't find AT_SYSINFO_EHDR in auxv[]. + vdso_base_.store(nullptr, std::memory_order_relaxed); + } + } + GetCpuFn fn = &GetCPUViaSyscall; // default if VDSO not present. + if (vdso_base_.load(std::memory_order_relaxed)) { + VDSOSupport vdso; + SymbolInfo info; + if (vdso.LookupSymbol("__vdso_getcpu", "LINUX_2.6", STT_FUNC, &info)) { + fn = reinterpret_cast<GetCpuFn>(const_cast<void *>(info.address)); + } + } + // Subtle: this code runs outside of any locks; prevent compiler + // from assigning to getcpu_fn_ more than once. + getcpu_fn_.store(fn, std::memory_order_relaxed); + return vdso_base_.load(std::memory_order_relaxed); +} + +const void *VDSOSupport::SetBase(const void *base) { + ABSL_RAW_CHECK(base != debug_internal::ElfMemImage::kInvalidBase, + "internal error"); + const void *old_base = vdso_base_.load(std::memory_order_relaxed); + vdso_base_.store(base, std::memory_order_relaxed); + image_.Init(base); + // Also reset getcpu_fn_, so GetCPU could be tested with simulated VDSO. + getcpu_fn_.store(&InitAndGetCPU, std::memory_order_relaxed); + return old_base; +} + +bool VDSOSupport::LookupSymbol(const char *name, + const char *version, + int type, + SymbolInfo *info) const { + return image_.LookupSymbol(name, version, type, info); +} + +bool VDSOSupport::LookupSymbolByAddress(const void *address, + SymbolInfo *info_out) const { + return image_.LookupSymbolByAddress(address, info_out); +} + +// NOLINT on 'long' because this routine mimics kernel api. +long VDSOSupport::GetCPUViaSyscall(unsigned *cpu, // NOLINT(runtime/int) + void *, void *) { +#ifdef SYS_getcpu + return syscall(SYS_getcpu, cpu, nullptr, nullptr); +#else + // x86_64 never implemented sys_getcpu(), except as a VDSO call. + errno = ENOSYS; + return -1; +#endif +} + +// Use fast __vdso_getcpu if available. +long VDSOSupport::InitAndGetCPU(unsigned *cpu, // NOLINT(runtime/int) + void *x, void *y) { + Init(); + GetCpuFn fn = getcpu_fn_.load(std::memory_order_relaxed); + ABSL_RAW_CHECK(fn != &InitAndGetCPU, "Init() did not set getcpu_fn_"); + return (*fn)(cpu, x, y); +} + +// This function must be very fast, and may be called from very +// low level (e.g. tcmalloc). Hence I avoid things like +// GoogleOnceInit() and ::operator new. +ABSL_ATTRIBUTE_NO_SANITIZE_MEMORY +int GetCPU() { + unsigned cpu; + int ret_code = (*VDSOSupport::getcpu_fn_)(&cpu, nullptr, nullptr); + return ret_code == 0 ? cpu : ret_code; +} + +// We need to make sure VDSOSupport::Init() is called before +// InitGoogle() does any setuid or chroot calls. If VDSOSupport +// is used in any global constructor, this will happen, since +// VDSOSupport's constructor calls Init. But if not, we need to +// ensure it here, with a global constructor of our own. This +// is an allowed exception to the normal rule against non-trivial +// global constructors. +static class VDSOInitHelper { + public: + VDSOInitHelper() { VDSOSupport::Init(); } +} vdso_init_helper; + +} // namespace debug_internal +} // namespace absl + +#endif // ABSL_HAVE_VDSO_SUPPORT |