| // Copyright (c) 2008, Google Inc. |
| // All rights reserved. |
| // |
| // Redistribution and use in source and binary forms, with or without |
| // modification, are permitted provided that the following conditions are |
| // met: |
| // |
| // * Redistributions of source code must retain the above copyright |
| // notice, this list of conditions and the following disclaimer. |
| // * Redistributions in binary form must reproduce the above |
| // copyright notice, this list of conditions and the following disclaimer |
| // in the documentation and/or other materials provided with the |
| // distribution. |
| // * Neither the name of Google Inc. nor the names of its |
| // contributors may be used to endorse or promote products derived from |
| // this software without specific prior written permission. |
| // |
| // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
| // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
| // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR |
| // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT |
| // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, |
| // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT |
| // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
| // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
| // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
| // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE |
| // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
| |
| // --- |
| // Author: Paul Pluzhnikov |
| // |
| // Allow dynamic symbol lookup in the kernel VDSO page. |
| // |
| // VDSOSupport -- a class representing kernel VDSO (if present). |
| // |
| |
| #include "base/vdso_support.h" |
| |
| #ifdef HAVE_VDSO_SUPPORT // defined in vdso_support.h |
| |
| #include <fcntl.h> |
| #include <stddef.h> // for ptrdiff_t |
| |
| #include "base/atomicops.h" // for MemoryBarrier |
| #include "base/linux_syscall_support.h" |
| #include "base/logging.h" |
| #include "base/dynamic_annotations.h" |
| #include "base/basictypes.h" // for COMPILE_ASSERT |
| |
| using base::subtle::MemoryBarrier; |
| |
| #ifndef AT_SYSINFO_EHDR |
| #define AT_SYSINFO_EHDR 33 |
| #endif |
| |
| namespace base { |
| |
| const void *VDSOSupport::vdso_base_ = ElfMemImage::kInvalidBase; |
| 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_ == ElfMemImage::kInvalidBase ? Init() : vdso_base_) { |
| } |
| |
| // 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_ == 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_ = NULL; |
| return NULL; |
| } |
| int fd = open("/proc/self/auxv", O_RDONLY); |
| if (fd == -1) { |
| // Kernel too old to have a VDSO. |
| vdso_base_ = NULL; |
| return NULL; |
| } |
| ElfW(auxv_t) aux; |
| while (read(fd, &aux, sizeof(aux)) == sizeof(aux)) { |
| if (aux.a_type == AT_SYSINFO_EHDR) { |
| COMPILE_ASSERT(sizeof(vdso_base_) == sizeof(aux.a_un.a_val), |
| unexpected_sizeof_pointer_NE_sizeof_a_val); |
| vdso_base_ = reinterpret_cast<void *>(aux.a_un.a_val); |
| break; |
| } |
| } |
| close(fd); |
| if (vdso_base_ == ElfMemImage::kInvalidBase) { |
| // Didn't find AT_SYSINFO_EHDR in auxv[]. |
| vdso_base_ = NULL; |
| } |
| } |
| return vdso_base_; |
| } |
| |
| const void *VDSOSupport::SetBase(const void *base) { |
| CHECK(base != ElfMemImage::kInvalidBase); |
| const void *old_base = vdso_base_; |
| vdso_base_ = base; |
| image_.Init(base); |
| 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); |
| } |
| |
| // We need to make sure VDSOSupport::Init() is called before |
| // the main() runs, since it might do something like setuid or |
| // chroot. 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; |
| } |
| |
| #endif // HAVE_VDSO_SUPPORT |