--- /dev/null
+//
+// 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
+//
+// 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.
+//
+
+// Allow dynamic symbol lookup in the kernel VDSO page.
+//
+// VDSO stands for "Virtual Dynamic Shared Object" -- a page of
+// executable code, which looks like a shared library, but doesn't
+// necessarily exist anywhere on disk, and which gets mmap()ed into
+// every process by kernels which support VDSO, such as 2.6.x for 32-bit
+// executables, and 2.6.24 and above for 64-bit executables.
+//
+// More details could be found here:
+// http://www.trilithium.com/johan/2005/08/linux-gate/
+//
+// VDSOSupport -- a class representing kernel VDSO (if present).
+//
+// Example usage:
+// VDSOSupport vdso;
+// VDSOSupport::SymbolInfo info;
+// typedef (*FN)(unsigned *, void *, void *);
+// FN fn = nullptr;
+// if (vdso.LookupSymbol("__vdso_getcpu", "LINUX_2.6", STT_FUNC, &info)) {
+// fn = reinterpret_cast<FN>(info.address);
+// }
+
+#ifndef ABSL_DEBUGGING_INTERNAL_VDSO_SUPPORT_H_
+#define ABSL_DEBUGGING_INTERNAL_VDSO_SUPPORT_H_
+
+#include <atomic>
+
+#include "absl/base/attributes.h"
+#include "absl/debugging/internal/elf_mem_image.h"
+
+#ifdef ABSL_HAVE_ELF_MEM_IMAGE
+
+#ifdef ABSL_HAVE_VDSO_SUPPORT
+#error ABSL_HAVE_VDSO_SUPPORT cannot be directly set
+#else
+#define ABSL_HAVE_VDSO_SUPPORT 1
+#endif
+
+namespace absl {
+namespace debugging_internal {
+
+// NOTE: this class may be used from within tcmalloc, and can not
+// use any memory allocation routines.
+class VDSOSupport {
+ public:
+ VDSOSupport();
+
+ typedef ElfMemImage::SymbolInfo SymbolInfo;
+ typedef ElfMemImage::SymbolIterator SymbolIterator;
+
+ // On PowerPC64 VDSO symbols can either be of type STT_FUNC or STT_NOTYPE
+ // depending on how the kernel is built. The kernel is normally built with
+ // STT_NOTYPE type VDSO symbols. Let's make things simpler first by using a
+ // compile-time constant.
+#ifdef __powerpc64__
+ enum { kVDSOSymbolType = STT_NOTYPE };
+#else
+ enum { kVDSOSymbolType = STT_FUNC };
+#endif
+
+ // Answers whether we have a vdso at all.
+ bool IsPresent() const { return image_.IsPresent(); }
+
+ // Allow to iterate over all VDSO symbols.
+ SymbolIterator begin() const { return image_.begin(); }
+ SymbolIterator end() const { return image_.end(); }
+
+ // Look up versioned dynamic symbol in the kernel VDSO.
+ // Returns false if VDSO is not present, or doesn't contain given
+ // symbol/version/type combination.
+ // If info_out != nullptr, additional details are filled in.
+ bool LookupSymbol(const char *name, const char *version,
+ int symbol_type, SymbolInfo *info_out) const;
+
+ // Find info about symbol (if any) which overlaps given address.
+ // Returns true if symbol was found; false if VDSO isn't present
+ // or doesn't have a symbol overlapping given address.
+ // If info_out != nullptr, additional details are filled in.
+ bool LookupSymbolByAddress(const void *address, SymbolInfo *info_out) const;
+
+ // Used only for testing. Replace real VDSO base with a mock.
+ // Returns previous value of vdso_base_. After you are done testing,
+ // you are expected to call SetBase() with previous value, in order to
+ // reset state to the way it was.
+ const void *SetBase(const void *s);
+
+ // Computes vdso_base_ and returns it. Should be called as early as
+ // possible; before any thread creation, chroot or setuid.
+ static const void *Init();
+
+ private:
+ // image_ represents VDSO ELF image in memory.
+ // image_.ehdr_ == nullptr implies there is no VDSO.
+ ElfMemImage image_;
+
+ // Cached value of auxv AT_SYSINFO_EHDR, computed once.
+ // This is a tri-state:
+ // kInvalidBase => value hasn't been determined yet.
+ // 0 => there is no VDSO.
+ // else => vma of VDSO Elf{32,64}_Ehdr.
+ //
+ // When testing with mock VDSO, low bit is set.
+ // The low bit is always available because vdso_base_ is
+ // page-aligned.
+ static std::atomic<const void *> vdso_base_;
+
+ // NOLINT on 'long' because these routines mimic kernel api.
+ // The 'cache' parameter may be used by some versions of the kernel,
+ // and should be nullptr or point to a static buffer containing at
+ // least two 'long's.
+ static long InitAndGetCPU(unsigned *cpu, void *cache, // NOLINT 'long'.
+ void *unused);
+ static long GetCPUViaSyscall(unsigned *cpu, void *cache, // NOLINT 'long'.
+ void *unused);
+ typedef long (*GetCpuFn)(unsigned *cpu, void *cache, // NOLINT 'long'.
+ void *unused);
+
+ // This function pointer may point to InitAndGetCPU,
+ // GetCPUViaSyscall, or __vdso_getcpu at different stages of initialization.
+ ABSL_CONST_INIT static std::atomic<GetCpuFn> getcpu_fn_;
+
+ friend int GetCPU(void); // Needs access to getcpu_fn_.
+
+ VDSOSupport(const VDSOSupport&) = delete;
+ VDSOSupport& operator=(const VDSOSupport&) = delete;
+};
+
+// Same as sched_getcpu() on later glibc versions.
+// Return current CPU, using (fast) __vdso_getcpu@LINUX_2.6 if present,
+// otherwise use syscall(SYS_getcpu,...).
+// May return -1 with errno == ENOSYS if the kernel doesn't
+// support SYS_getcpu.
+int GetCPU();
+
+} // namespace debugging_internal
+} // namespace absl
+
+#endif // ABSL_HAVE_ELF_MEM_IMAGE
+
+#endif // ABSL_DEBUGGING_INTERNAL_VDSO_SUPPORT_H_
git://repos.xcallymotion.com / motion2.git / blobdiff