third_party/tcmalloc/chromium/src/base/vdso_support.h

   1 // Copyright (c) 2008, Google Inc.
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  29
  30 // ---
  31 // Author: Paul Pluzhnikov
  32 //
  33 // Allow dynamic symbol lookup in the kernel VDSO page.
  34 //
  35 // VDSO stands for "Virtual Dynamic Shared Object" -- a page of
  36 // executable code, which looks like a shared library, but doesn't
  37 // necessarily exist anywhere on disk, and which gets mmap()ed into
  38 // every process by kernels which support VDSO, such as 2.6.x for 32-bit
  39 // executables, and 2.6.24 and above for 64-bit executables.
  40 //
  41 // More details could be found here:
  42 // http://www.trilithium.com/johan/2005/08/linux-gate/
  43 //
  44 // VDSOSupport -- a class representing kernel VDSO (if present).
  45 //
  46 // Example usage:
  47 //  VDSOSupport vdso;
  48 //  VDSOSupport::SymbolInfo info;
  49 //  typedef (*FN)(unsigned *, void *, void *);
  50 //  FN fn = NULL;
  51 //  if (vdso.LookupSymbol("__vdso_getcpu", "LINUX_2.6", STT_FUNC, &info)) {
  52 //     fn = reinterpret_cast<FN>(info.address);
  53 //  }
  54
  55 #ifndef BASE_VDSO_SUPPORT_H_
  56 #define BASE_VDSO_SUPPORT_H_
  57
  58 #include <config.h>
  59 #include "base/basictypes.h"
  60 #include "base/elf_mem_image.h"
  61
  62 #ifdef HAVE_ELF_MEM_IMAGE
  63
  64 #define HAVE_VDSO_SUPPORT 1
  65
  66 #include <stdlib.h>     // for NULL
  67
  68 namespace base {
  69
  70 // NOTE: this class may be used from within tcmalloc, and can not
  71 // use any memory allocation routines.
  72 class VDSOSupport {
  73  public:
  74   VDSOSupport();
  75
  76   typedef ElfMemImage::SymbolInfo SymbolInfo;
  77   typedef ElfMemImage::SymbolIterator SymbolIterator;
  78
  79   // Answers whether we have a vdso at all.
  80   bool IsPresent() const { return image_.IsPresent(); }
  81
  82   // Allow to iterate over all VDSO symbols.
  83   SymbolIterator begin() const { return image_.begin(); }
  84   SymbolIterator end() const { return image_.end(); }
  85
  86   // Look up versioned dynamic symbol in the kernel VDSO.
  87   // Returns false if VDSO is not present, or doesn't contain given
  88   // symbol/version/type combination.
  89   // If info_out != NULL, additional details are filled in.
  90   bool LookupSymbol(const char *name, const char *version,
  91                     int symbol_type, SymbolInfo *info_out) const;
  92
  93   // Find info about symbol (if any) which overlaps given address.
  94   // Returns true if symbol was found; false if VDSO isn't present
  95   // or doesn't have a symbol overlapping given address.
  96   // If info_out != NULL, additional details are filled in.
  97   bool LookupSymbolByAddress(const void *address, SymbolInfo *info_out) const;
  98
  99   // Used only for testing. Replace real VDSO base with a mock.
 100   // Returns previous value of vdso_base_. After you are done testing,
 101   // you are expected to call SetBase() with previous value, in order to
 102   // reset state to the way it was.
 103   const void *SetBase(const void *s);
 104
 105   // Computes vdso_base_ and returns it. Should be called as early as
 106   // possible; before any thread creation, chroot or setuid.
 107   static const void *Init();
 108
 109  private:
 110   // image_ represents VDSO ELF image in memory.
 111   // image_.ehdr_ == NULL implies there is no VDSO.
 112   ElfMemImage image_;
 113
 114   // Cached value of auxv AT_SYSINFO_EHDR, computed once.
 115   // This is a tri-state:
 116   //   kInvalidBase   => value hasn't been determined yet.
 117   //              0   => there is no VDSO.
 118   //           else   => vma of VDSO Elf{32,64}_Ehdr.
 119   //
 120   // When testing with mock VDSO, low bit is set.
 121   // The low bit is always available because vdso_base_ is
 122   // page-aligned.
 123   static const void *vdso_base_;
 124
 125   // NOLINT on 'long' because these routines mimic kernel api.
 126   // The 'cache' parameter may be used by some versions of the kernel,
 127   // and should be NULL or point to a static buffer containing at
 128   // least two 'long's.
 129   static long InitAndGetCPU(unsigned *cpu, void *cache,     // NOLINT 'long'.
 130                             void *unused);
 131   static long GetCPUViaSyscall(unsigned *cpu, void *cache,  // NOLINT 'long'.
 132                                void *unused);
 133   typedef long (*GetCpuFn)(unsigned *cpu, void *cache,      // NOLINT 'long'.
 134                            void *unused);
 135
 136   // This function pointer may point to InitAndGetCPU,
 137   // GetCPUViaSyscall, or __vdso_getcpu at different stages of initialization.
 138   static GetCpuFn getcpu_fn_;
 139
 140   friend int GetCPU(void);  // Needs access to getcpu_fn_.
 141
 142   DISALLOW_COPY_AND_ASSIGN(VDSOSupport);
 143 };
 144
 145 // Same as sched_getcpu() on later glibc versions.
 146 // Return current CPU, using (fast) __vdso_getcpu@LINUX_2.6 if present,
 147 // otherwise use syscall(SYS_getcpu,...).
 148 // May return -1 with errno == ENOSYS if the kernel doesn't
 149 // support SYS_getcpu.
 150 int GetCPU();
 151 }  // namespace base
 152
 153 #endif  // HAVE_ELF_MEM_IMAGE
 154
 155 #endif  // BASE_VDSO_SUPPORT_H_