1 files changed, 129 insertions, 0 deletions
diff --git a/libc/bionic/vdso.cpp b/libc/bionic/vdso.cpp
new file mode 100644
index 0000000..0875ee6
--- /dev/null
+++ b/libc/bionic/vdso.cpp
@@ -0,0 +1,129 @@
+/*
+ * Copyright (C) 2014 The Android Open Source Project
+ *
+ * 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 <link.h>
+#include <sys/auxv.h>
+#include <unistd.h>
+
+// x86 has a vdso, but there's nothing useful to us in it.
+#if defined(__aarch64__) || defined(__x86_64__)
+
+#if defined(__aarch64__)
+#define VDSO_CLOCK_GETTIME_SYMBOL "__kernel_clock_gettime"
+#define VDSO_GETTIMEOFDAY_SYMBOL  "__kernel_gettimeofday"
+#elif defined(__x86_64__)
+#define VDSO_CLOCK_GETTIME_SYMBOL "__vdso_clock_gettime"
+#define VDSO_GETTIMEOFDAY_SYMBOL  "__vdso_gettimeofday"
+#endif
+
+#include <time.h>
+
+extern "C" int __clock_gettime(int, timespec*);
+extern "C" int __gettimeofday(timeval*, struct timezone*);
+
+struct vdso_entry {
+  const char* name;
+  void* fn;
+};
+
+enum {
+  VDSO_CLOCK_GETTIME = 0,
+  VDSO_GETTIMEOFDAY,
+  VDSO_END
+};
+
+static vdso_entry vdso_entries[] = {
+  [VDSO_CLOCK_GETTIME] = { VDSO_CLOCK_GETTIME_SYMBOL, reinterpret_cast<void*>(__clock_gettime) },
+  [VDSO_GETTIMEOFDAY] = { VDSO_GETTIMEOFDAY_SYMBOL, reinterpret_cast<void*>(__gettimeofday) },
+};
+
+int clock_gettime(int clock_id, timespec* tp) {
+  static int (*vdso_clock_gettime)(int, timespec*) =
+      (int (*)(int, timespec*)) vdso_entries[VDSO_CLOCK_GETTIME].fn;
+  return vdso_clock_gettime(clock_id, tp);
+}
+
+int gettimeofday(timeval* tv, struct timezone* tz) {
+  static int (*vdso_gettimeofday)(timeval*, struct timezone*) =
+      (int (*)(timeval*, struct timezone*)) vdso_entries[VDSO_GETTIMEOFDAY].fn;
+  return vdso_gettimeofday(tv, tz);
+}
+
+void __libc_init_vdso() {
+  // Do we have a vdso?
+  uintptr_t vdso_ehdr_addr = getauxval(AT_SYSINFO_EHDR);
+  ElfW(Ehdr)* vdso_ehdr = reinterpret_cast<ElfW(Ehdr)*>(vdso_ehdr_addr);
+  if (vdso_ehdr == NULL) {
+    return;
+  }
+
+  // How many symbols does it have?
+  size_t symbol_count = 0;
+  ElfW(Shdr)* vdso_shdr = reinterpret_cast<ElfW(Shdr)*>(vdso_ehdr_addr + vdso_ehdr->e_shoff);
+  for (size_t i = 0; i < vdso_ehdr->e_shnum; ++i) {
+    if (vdso_shdr[i].sh_type == SHT_DYNSYM) {
+      symbol_count = vdso_shdr[i].sh_size / sizeof(ElfW(Sym));
+    }
+  }
+  if (symbol_count == 0) {
+    return;
+  }
+
+  // Where's the dynamic table?
+  ElfW(Addr) vdso_addr = 0;
+  ElfW(Dyn)* vdso_dyn = NULL;
+  ElfW(Phdr)* vdso_phdr = reinterpret_cast<ElfW(Phdr)*>(vdso_ehdr_addr + vdso_ehdr->e_phoff);
+  for (size_t i = 0; i < vdso_ehdr->e_phnum; ++i) {
+    if (vdso_phdr[i].p_type == PT_DYNAMIC) {
+      vdso_dyn = reinterpret_cast<ElfW(Dyn)*>(vdso_ehdr_addr + vdso_phdr[i].p_offset);
+    } else if (vdso_phdr[i].p_type == PT_LOAD) {
+      vdso_addr = vdso_ehdr_addr + vdso_phdr[i].p_offset - vdso_phdr[i].p_vaddr;
+    }
+  }
+  if (vdso_addr == 0 || vdso_dyn == NULL) {
+    return;
+  }
+
+  // Where are the string and symbol tables?
+  const char* strtab = NULL;
+  ElfW(Sym)* symtab = NULL;
+  for (ElfW(Dyn)* d = vdso_dyn; d->d_tag != DT_NULL; ++d) {
+    if (d->d_tag == DT_STRTAB) {
+      strtab = reinterpret_cast<const char*>(vdso_addr + d->d_un.d_ptr);
+    } else if (d->d_tag == DT_SYMTAB) {
+      symtab = reinterpret_cast<ElfW(Sym)*>(vdso_addr + d->d_un.d_ptr);
+    }
+  }
+  if (strtab == NULL || symtab == NULL) {
+    return;
+  }
+
+  // Are there any symbols we want?
+  for (size_t i = 0; i < symbol_count; ++i) {
+    for (size_t j = 0; j < VDSO_END; ++j) {
+      if (strcmp(vdso_entries[j].name, strtab + symtab[i].st_name) == 0) {
+        vdso_entries[j].fn = reinterpret_cast<void*>(vdso_addr + symtab[i].st_value);
+      }
+    }
+  }
+}
+
+#else
+
+void __libc_init_vdso() {
+}
+
+#endif