[libc] implement vdso (#91572)

libc/hdr/CMakeLists.txt

@@ -143,4 +143,22 @@ add_proxy_header_library(
     libc.include.llvm-libc-macros.limits_macros
 )
 
+add_proxy_header_library(
+  link_macros
+  HDRS
+    link_macros.h
+  FULL_BUILD_DEPENDS
+    libc.include.llvm-libc-macros.link_macros
+    libc.include.link
+)
+
+add_proxy_header_library(
+  sys_auxv_macros
+  HDRS
+    sys_auxv_macros.h
+  FULL_BUILD_DEPENDS
+    libc.include.llvm-libc-macros.sys_auxv_macros
+    libc.include.sys_auxv
+)
+
 add_subdirectory(types)

libc/hdr/link_macros.h

@@ -0,0 +1,22 @@
+//===-- Definition of macros from link.h ----------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_HDR_LINK_MACROS_H
+#define LLVM_LIBC_HDR_LINK_MACROS_H
+
+#ifdef LIBC_FULL_BUILD
+
+#include "include/llvm-libc-macros/link-macros.h"
+
+#else // Overlay mode
+
+#include <link.h>
+
+#endif // LLVM_LIBC_FULL_BUILD
+
+#endif // LLVM_LIBC_HDR_LINK_MACROS_H

libc/hdr/sys_auxv_macros.h

@@ -0,0 +1,22 @@
+//===-- Definition of macros from sys/auxv.h ------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_HDR_SYS_AUXV_MACROS_H
+#define LLVM_LIBC_HDR_SYS_AUXV_MACROS_H
+
+#ifdef LIBC_FULL_BUILD
+
+#include "include/llvm-libc-macros/sys-auxv-macros.h"
+
+#else // Overlay mode
+
+#include <sys/auxv.h>
+
+#endif // LLVM_LIBC_FULL_BUILD
+
+#endif // LLVM_LIBC_HDR_SYS_AUXV_MACROS_H

libc/src/__support/OSUtil/linux/CMakeLists.txt

@@ -23,3 +23,33 @@ add_object_library(
     libc.hdr.types.struct_f_owner_ex
     libc.hdr.types.off_t
 )
+
+add_header_library(
+  vdso_sym
+  HDRS
+    vdso_sym.h
+  DEPENDS
+    libc.src.__support.common
+)
+
+add_object_library(
+  vdso
+  HDRS
+    vdso.h
+  SRCS
+    vdso.cpp
+  DEPENDS
+    .${LIBC_TARGET_ARCHITECTURE}.vdso
+    libc.src.__support.CPP.array
+    libc.src.__support.CPP.optional
+    libc.src.__support.CPP.string_view
+    libc.src.__support.threads.callonce
+    libc.src.__support.threads.linux.futex_word_type
+    libc.hdr.types.struct_timeval
+    libc.hdr.types.struct_timespec
+    libc.hdr.types.clockid_t
+    libc.hdr.types.time_t
+    libc.hdr.link_macros
+    libc.src.errno.errno
+    libc.src.sys.auxv.getauxval
+)

libc/src/__support/OSUtil/linux/aarch64/CMakeLists.txt

@@ -5,3 +5,13 @@ add_header_library(
   DEPENDS
     libc.src.__support.common
 )
+
+add_header_library(
+  vdso
+  HDRS
+    vdso.h
+  DEPENDS
+    libc.src.__support.common
+    libc.src.__support.CPP.string_view
+    libc.src.__support.OSUtil.linux.vdso_sym
+)

libc/src/__support/OSUtil/linux/aarch64/vdso.h

@@ -0,0 +1,37 @@
+//===---------- aarch64 vdso configuration ------------------------* C++ *-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+#ifndef LLVM_LIBC_SRC___SUPPORT_OSUTIL_LINUX_AARCH64_VDSO_H
+#define LLVM_LIBC_SRC___SUPPORT_OSUTIL_LINUX_AARCH64_VDSO_H
+#include "src/__support/CPP/string_view.h"
+#include "src/__support/OSUtil/linux/vdso_sym.h"
+namespace LIBC_NAMESPACE_DECL {
+namespace vdso {
+// translate VDSOSym to symbol names
+// https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm64/kernel/vdso/vdso.lds.S
+LIBC_INLINE constexpr cpp::string_view symbol_name(VDSOSym sym) {
+  switch (sym) {
+  case VDSOSym::RTSigReturn:
+    return "__kernel_rt_sigreturn";
+  case VDSOSym::GetTimeOfDay:
+    return "__kernel_gettimeofday";
+  case VDSOSym::ClockGetTime:
+    return "__kernel_clock_gettime";
+  case VDSOSym::ClockGetRes:
+    return "__kernel_clock_getres";
+  default:
+    return "";
+  }
+}
+
+// symbol versions
+LIBC_INLINE constexpr cpp::string_view symbol_version(VDSOSym) {
+  return "LINUX_2.6.39";
+}
+} // namespace vdso
+} // namespace LIBC_NAMESPACE_DECL
+#endif // LLVM_LIBC_SRC___SUPPORT_OSUTIL_LINUX_AARCH64_VDSO_H

libc/src/__support/OSUtil/linux/arm/CMakeLists.txt

@@ -5,3 +5,13 @@ add_header_library(
   DEPENDS
     libc.src.__support.common
 )
+
+add_header_library(
+  vdso
+  HDRS
+    vdso.h
+  DEPENDS
+    libc.src.__support.common
+    libc.src.__support.CPP.string_view
+    libc.src.__support.OSUtil.linux.vdso_sym
+)

libc/src/__support/OSUtil/linux/arm/vdso.h

@@ -0,0 +1,37 @@
+//===---------- arm vdso configuration ----------------------------* C++ *-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+#ifndef LLVM_LIBC_SRC___SUPPORT_OSUTIL_LINUX_ARM_VDSO_H
+#define LLVM_LIBC_SRC___SUPPORT_OSUTIL_LINUX_ARM_VDSO_H
+#include "src/__support/CPP/string_view.h"
+#include "src/__support/OSUtil/linux/vdso_sym.h"
+namespace LIBC_NAMESPACE_DECL {
+namespace vdso {
+// translate VDSOSym to symbol names
+// https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/vdso/vdso.lds.S
+LIBC_INLINE constexpr cpp::string_view symbol_name(VDSOSym sym) {
+  switch (sym) {
+  case VDSOSym::ClockGetTime:
+    return "__vdso_clock_gettime";
+  case VDSOSym::GetTimeOfDay:
+    return "__vdso_gettimeofday";
+  case VDSOSym::ClockGetRes:
+    return "__vdso_clock_getres";
+  case VDSOSym::ClockGetTime64:
+    return "__vdso_clock_gettime64";
+  default:
+    return "";
+  }
+}
+
+// symbol versions
+LIBC_INLINE constexpr cpp::string_view symbol_version(VDSOSym) {
+  return "LINUX_2.6";
+}
+} // namespace vdso
+} // namespace LIBC_NAMESPACE_DECL
+#endif // LLVM_LIBC_SRC___SUPPORT_OSUTIL_LINUX_ARM_VDSO_H

libc/src/__support/OSUtil/linux/riscv/CMakeLists.txt

@@ -5,3 +5,13 @@ add_header_library(
   DEPENDS
     libc.src.__support.common
 )
+
+add_header_library(
+  vdso
+  HDRS
+    vdso.h
+  DEPENDS
+    libc.src.__support.common
+    libc.src.__support.CPP.string_view
+    libc.src.__support.OSUtil.linux.vdso_sym
+)

libc/src/__support/OSUtil/linux/riscv/vdso.h

@@ -0,0 +1,43 @@
+//===---------- RISC-V vdso configuration -------------------------* C++ *-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+#ifndef LLVM_LIBC_SRC___SUPPORT_OSUTIL_LINUX_RISCV_VDSO_H
+#define LLVM_LIBC_SRC___SUPPORT_OSUTIL_LINUX_RISCV_VDSO_H
+#include "src/__support/CPP/string_view.h"
+#include "src/__support/OSUtil/linux/vdso_sym.h"
+namespace LIBC_NAMESPACE_DECL {
+namespace vdso {
+// translate VDSOSym to symbol names
+// https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/riscv/kernel/vdso/vdso.lds.S
+LIBC_INLINE constexpr cpp::string_view symbol_name(VDSOSym sym) {
+  switch (sym) {
+  case VDSOSym::RTSigReturn:
+    return "__vdso_rt_sigreturn";
+  case VDSOSym::GetTimeOfDay:
+    return "__vdso_gettimeofday";
+  case VDSOSym::ClockGetTime:
+    return "__vdso_clock_gettime";
+  case VDSOSym::ClockGetRes:
+    return "__vdso_clock_getres";
+  case VDSOSym::GetCpu:
+    return "__vdso_getcpu";
+  case VDSOSym::FlushICache:
+    return "__vdso_flush_icache";
+  case VDSOSym::RiscvHwProbe:
+    return "__vdso_riscv_hwprobe";
+  default:
+    return "";
+  }
+}
+
+// symbol versions
+LIBC_INLINE constexpr cpp::string_view symbol_version(VDSOSym) {
+  return "LINUX_4.15";
+}
+} // namespace vdso
+} // namespace LIBC_NAMESPACE_DECL
+#endif // LLVM_LIBC_SRC___SUPPORT_OSUTIL_LINUX_RISCV_VDSO_H

libc/src/__support/OSUtil/linux/vdso.cpp

@@ -0,0 +1,237 @@
+//===------------- Linux VDSO Implementation --------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+#include "src/__support/OSUtil/linux/vdso.h"
+#include "hdr/link_macros.h"
+#include "hdr/sys_auxv_macros.h"
+#include "src/__support/CPP/array.h"
+#include "src/__support/CPP/optional.h"
+#include "src/__support/CPP/string_view.h"
+#include "src/__support/threads/callonce.h"
+#include "src/__support/threads/linux/futex_word.h"
+#include "src/errno/libc_errno.h"
+#include "src/sys/auxv/getauxval.h"
+#include <linux/auxvec.h>
+
+// TODO: This is a temporary workaround to avoid including elf.h
+// Include our own headers for ElfW and friends once we have them.
+namespace LIBC_NAMESPACE_DECL {
+
+namespace vdso {
+
+Symbol::VDSOArray Symbol::global_cache{};
+CallOnceFlag Symbol::once_flag = callonce_impl::NOT_CALLED;
+
+namespace {
+// See https://refspecs.linuxfoundation.org/LSB_1.3.0/gLSB/gLSB/symverdefs.html
+struct Verdaux {
+  ElfW(Word) vda_name; /* Version or dependency names */
+  ElfW(Word) vda_next; /* Offset in bytes to next verdaux
+                          entry */
+};
+struct Verdef {
+  ElfW(Half) vd_version; /* Version revision */
+  ElfW(Half) vd_flags;   /* Version information */
+  ElfW(Half) vd_ndx;     /* Version Index */
+  ElfW(Half) vd_cnt;     /* Number of associated aux entries */
+  ElfW(Word) vd_hash;    /* Version name hash value */
+  ElfW(Word) vd_aux;     /* Offset in bytes to verdaux array */
+  ElfW(Word) vd_next;    /* Offset in bytes to next verdef entry */
+  Verdef *next() const {
+    if (vd_next == 0)
+      return nullptr;
+    return reinterpret_cast<Verdef *>(reinterpret_cast<uintptr_t>(this) +
+                                      vd_next);
+  }
+  Verdaux *aux() const {
+    return reinterpret_cast<Verdaux *>(reinterpret_cast<uintptr_t>(this) +
+                                       vd_aux);
+  }
+};
+
+// version search procedure specified by
+// https://refspecs.linuxfoundation.org/LSB_1.3.0/gLSB/gLSB/symversion.html#SYMVERTBL
+cpp::string_view find_version(Verdef *verdef, ElfW(Half) * versym,
+                              const char *strtab, size_t idx) {
+  constexpr ElfW(Half) VER_FLG_BASE = 0x1;
+  if (!versym)
+    return "";
+  ElfW(Half) identifier = versym[idx] & 0x7FFF;
+  // iterate through all version definitions
+  for (Verdef *def = verdef; def != nullptr; def = def->next()) {
+    // skip if this is a file-level version
+    if (def->vd_flags & VER_FLG_BASE)
+      continue;
+    // check if the version identifier matches. Highest bit is used to determine
+    // whether the symbol is local. Only lower 15 bits are used for version
+    // identifier.
+    if ((def->vd_ndx & 0x7FFF) == identifier) {
+      Verdaux *aux = def->aux();
+      return strtab + aux->vda_name;
+    }
+  }
+  return "";
+}
+
+size_t shdr_get_symbol_count(ElfW(Shdr) * vdso_shdr, size_t e_shnum) {
+  if (!vdso_shdr)
+    return 0;
+  // iterate all sections until we locate the dynamic symbol section
+  for (size_t i = 0; i < e_shnum; ++i) {
+    // dynamic symbol section is a table section
+    // therefore, the number of entries can be computed as the ratio
+    // of the section size to the size of a single entry
+    if (vdso_shdr[i].sh_type == SHT_DYNSYM)
+      return vdso_shdr[i].sh_size / vdso_shdr[i].sh_entsize;
+  }
+  return 0;
+}
+
+struct VDSOSymbolTable {
+  const char *strtab;
+  ElfW(Sym) * symtab;
+  // The following can be nullptr if the vDSO does not have versioning
+  ElfW(Half) * versym;
+  Verdef *verdef;
+
+  void populate_symbol_cache(Symbol::VDSOArray &symbol_table,
+                             size_t symbol_count, ElfW(Addr) vdso_addr) {
+    for (size_t i = 0, e = symbol_table.size(); i < e; ++i) {
+      Symbol sym = i;
+      cpp::string_view name = sym.name();
+      cpp::string_view version = sym.version();
+      if (name.empty())
+        continue;
+
+      for (size_t j = 0; j < symbol_count; ++j) {
+        if (name == strtab + symtab[j].st_name) {
+          // we find a symbol with desired name
+          // now we need to check if it has the right version
+          if (versym && verdef &&
+              version != find_version(verdef, versym, strtab, j))
+            continue;
+
+          // put the symbol address into the symbol table
+          symbol_table[i] =
+              reinterpret_cast<void *>(vdso_addr + symtab[j].st_value);
+        }
+      }
+    }
+  }
+};
+
+struct PhdrInfo {
+  ElfW(Addr) vdso_addr;
+  ElfW(Dyn) * vdso_dyn;
+  static cpp::optional<PhdrInfo> from(ElfW(Phdr) * vdso_phdr, size_t e_phnum,
+                                      uintptr_t vdso_ehdr_addr) {
+    constexpr ElfW(Addr) INVALID_ADDR = static_cast<ElfW(Addr)>(-1);
+    ElfW(Addr) vdso_addr = INVALID_ADDR;
+    ElfW(Dyn) *vdso_dyn = nullptr;
+    if (!vdso_phdr)
+      return cpp::nullopt;
+    // iterate through all the program headers until we get the desired pieces
+    for (size_t i = 0; i < 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);
+
+      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 && vdso_dyn)
+        return PhdrInfo{vdso_addr, vdso_dyn};
+    }
+
+    return cpp::nullopt;
+  }
+
+  cpp::optional<VDSOSymbolTable> populate_symbol_table() {
+    const char *strtab = nullptr;
+    ElfW(Sym) *symtab = nullptr;
+    ElfW(Half) *versym = nullptr;
+    Verdef *verdef = nullptr;
+    for (ElfW(Dyn) *d = vdso_dyn; d->d_tag != DT_NULL; ++d) {
+      switch (d->d_tag) {
+      case DT_STRTAB:
+        strtab = reinterpret_cast<const char *>(vdso_addr + d->d_un.d_ptr);
+        break;
+      case DT_SYMTAB:
+        symtab = reinterpret_cast<ElfW(Sym) *>(vdso_addr + d->d_un.d_ptr);
+        break;
+      case DT_VERSYM:
+        versym = reinterpret_cast<uint16_t *>(vdso_addr + d->d_un.d_ptr);
+        break;
+      case DT_VERDEF:
+        verdef = reinterpret_cast<Verdef *>(vdso_addr + d->d_un.d_ptr);
+        break;
+      }
+      if (strtab && symtab && versym && verdef)
+        break;
+    }
+    if (strtab == nullptr || symtab == nullptr)
+      return cpp::nullopt;
+
+    return VDSOSymbolTable{strtab, symtab, versym, verdef};
+  }
+};
+} // namespace
+
+void Symbol::initialize_vdso_global_cache() {
+  // first clear the symbol table
+  for (auto &i : global_cache)
+    i = nullptr;
+
+  // get the address of the VDSO, protect errno since getauxval may change
+  // it
+  int errno_backup = libc_errno;
+  uintptr_t vdso_ehdr_addr = getauxval(AT_SYSINFO_EHDR);
+  // Get the memory address of the vDSO ELF header.
+  auto vdso_ehdr = reinterpret_cast<ElfW(Ehdr) *>(vdso_ehdr_addr);
+  // leave the table unpopulated if we don't have vDSO
+  if (vdso_ehdr == nullptr) {
+    libc_errno = errno_backup;
+    return;
+  }
+
+  // locate the section header inside the elf using the section header
+  // offset
+  auto vdso_shdr =
+      reinterpret_cast<ElfW(Shdr) *>(vdso_ehdr_addr + vdso_ehdr->e_shoff);
+  size_t symbol_count = shdr_get_symbol_count(vdso_shdr, vdso_ehdr->e_shnum);
+
+  // early return if no symbol is found
+  if (symbol_count == 0)
+    return;
+
+  // We need to find both the loadable segment and the dynamic linking of
+  // the vDSO. compute vdso_phdr as the program header using the program
+  // header offset
+  ElfW(Phdr) *vdso_phdr =
+      reinterpret_cast<ElfW(Phdr) *>(vdso_ehdr_addr + vdso_ehdr->e_phoff);
+  cpp::optional<PhdrInfo> phdr_info =
+      PhdrInfo::from(vdso_phdr, vdso_ehdr->e_phnum, vdso_ehdr_addr);
+  // early return if either the dynamic linking or the loadable segment is
+  // not found
+  if (!phdr_info.has_value())
+    return;
+
+  // now, locate several more tables inside the dynmaic linking section
+  cpp::optional<VDSOSymbolTable> vdso_symbol_table =
+      phdr_info->populate_symbol_table();
+
+  // early return if we can't find any required fields of the symbol table
+  if (!vdso_symbol_table.has_value())
+    return;
+
+  // finally, populate the global symbol table cache
+  vdso_symbol_table->populate_symbol_cache(global_cache, symbol_count,
+                                           phdr_info->vdso_addr);
+}
+} // namespace vdso
+} // namespace LIBC_NAMESPACE_DECL

libc/src/__support/OSUtil/linux/vdso.h

@@ -0,0 +1,81 @@
+//===------------- Linux VDSO Header ----------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+#ifndef LLVM_LIBC_SRC___SUPPORT_OSUTIL_LINUX_VDSO_H
+#define LLVM_LIBC_SRC___SUPPORT_OSUTIL_LINUX_VDSO_H
+#include "src/__support/CPP/array.h"
+#include "src/__support/common.h"
+#include "src/__support/macros/attributes.h"
+#include "src/__support/macros/properties/architectures.h"
+#include "src/__support/threads/callonce.h"
+
+#if defined(LIBC_TARGET_ARCH_IS_X86)
+#include "x86_64/vdso.h"
+#elif defined(LIBC_TARGET_ARCH_IS_AARCH64)
+#include "aarch64/vdso.h"
+#elif defined(LIBC_TARGET_ARCH_IS_ARM)
+#include "arm/vdso.h"
+#elif defined(LIBC_TARGET_ARCH_IS_ANY_RISCV)
+#include "riscv/vdso.h"
+#else
+#error "unknown arch"
+#endif
+
+namespace LIBC_NAMESPACE_DECL {
+namespace vdso {
+
+class Symbol {
+  VDSOSym sym;
+
+public:
+  LIBC_INLINE_VAR static constexpr size_t COUNT =
+      static_cast<size_t>(VDSOSym::VDSOSymCount);
+  LIBC_INLINE constexpr explicit Symbol(VDSOSym sym) : sym(sym) {}
+  LIBC_INLINE constexpr Symbol(size_t idx) : sym(static_cast<VDSOSym>(idx)) {}
+  LIBC_INLINE constexpr cpp::string_view name() const {
+    return symbol_name(sym);
+  }
+  LIBC_INLINE constexpr cpp::string_view version() const {
+    return symbol_version(sym);
+  }
+  LIBC_INLINE constexpr operator size_t() const {
+    return static_cast<size_t>(sym);
+  }
+  LIBC_INLINE constexpr bool is_valid() const {
+    return *this < Symbol::global_cache.size();
+  }
+  using VDSOArray = cpp::array<void *, Symbol::COUNT>;
+
+private:
+  static CallOnceFlag once_flag;
+  static VDSOArray global_cache;
+  static void initialize_vdso_global_cache();
+
+  LIBC_INLINE void *get() const {
+    if (name().empty() || !is_valid())
+      return nullptr;
+
+    callonce(&once_flag, Symbol::initialize_vdso_global_cache);
+    return (global_cache[*this]);
+  }
+  template <VDSOSym sym> friend struct TypedSymbol;
+};
+
+template <VDSOSym sym> struct TypedSymbol {
+  LIBC_INLINE constexpr operator VDSOSymType<sym>() const {
+    return cpp::bit_cast<VDSOSymType<sym>>(Symbol{sym}.get());
+  }
+  template <typename... Args>
+  LIBC_INLINE auto operator()(Args &&...args) const {
+    return this->operator VDSOSymType<sym>()(cpp::forward<Args>(args)...);
+  }
+};
+
+} // namespace vdso
+
+} // namespace LIBC_NAMESPACE_DECL
+#endif // LLVM_LIBC_SRC___SUPPORT_OSUTIL_LINUX_VDSO_H

libc/src/__support/OSUtil/linux/vdso_sym.h

@@ -0,0 +1,70 @@
+//===------------- Linux VDSO Symbols ---------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+#include "hdr/types/clock_t.h"
+#include "hdr/types/clockid_t.h"
+#include "hdr/types/struct_timespec.h"
+#include "hdr/types/struct_timeval.h"
+#include "hdr/types/time_t.h"
+#include "src/__support/common.h"
+#include <stddef.h> // For size_t.
+
+// NOLINTBEGIN(llvmlibc-implementation-in-namespace)
+// TODO: some of the following can be defined via proxy headers.
+struct __kernel_timespec;
+struct timezone;
+struct riscv_hwprobe;
+struct getcpu_cache;
+struct cpu_set_t;
+// NOLINTEND(llvmlibc-implementation-in-namespace)
+
+namespace LIBC_NAMESPACE_DECL {
+namespace vdso {
+
+enum class VDSOSym {
+  ClockGetTime,
+  ClockGetTime64,
+  GetTimeOfDay,
+  GetCpu,
+  Time,
+  ClockGetRes,
+  RTSigReturn,
+  FlushICache,
+  RiscvHwProbe,
+  VDSOSymCount
+};
+
+template <VDSOSym sym> LIBC_INLINE constexpr auto dispatcher() {
+  if constexpr (sym == VDSOSym::ClockGetTime)
+    return static_cast<int (*)(clockid_t, timespec *)>(nullptr);
+  else if constexpr (sym == VDSOSym::ClockGetTime64)
+    return static_cast<int (*)(clockid_t, __kernel_timespec *)>(nullptr);
+  else if constexpr (sym == VDSOSym::GetTimeOfDay)
+    return static_cast<int (*)(timeval *__restrict, timezone *__restrict)>(
+        nullptr);
+  else if constexpr (sym == VDSOSym::GetCpu)
+    return static_cast<int (*)(unsigned *, unsigned *, getcpu_cache *)>(
+        nullptr);
+  else if constexpr (sym == VDSOSym::Time)
+    return static_cast<time_t (*)(time_t *)>(nullptr);
+  else if constexpr (sym == VDSOSym::ClockGetRes)
+    return static_cast<int (*)(clockid_t, timespec *)>(nullptr);
+  else if constexpr (sym == VDSOSym::RTSigReturn)
+    return static_cast<void (*)(void)>(nullptr);
+  else if constexpr (sym == VDSOSym::FlushICache)
+    return static_cast<void (*)(void *, void *, unsigned int)>(nullptr);
+  else if constexpr (sym == VDSOSym::RiscvHwProbe)
+    return static_cast<int (*)(riscv_hwprobe *, size_t, size_t, cpu_set_t *,
+                               unsigned)>(nullptr);
+  else
+    return static_cast<void *>(nullptr);
+}
+
+template <VDSOSym sym> using VDSOSymType = decltype(dispatcher<sym>());
+
+} // namespace vdso
+} // namespace LIBC_NAMESPACE_DECL

libc/src/__support/OSUtil/linux/x86_64/CMakeLists.txt

@@ -5,3 +5,13 @@ add_header_library(
   DEPENDS
     libc.src.__support.common
 )
+
+add_header_library(
+  vdso
+  HDRS
+    vdso.h
+  DEPENDS
+    libc.src.__support.common
+    libc.src.__support.CPP.string_view
+    libc.src.__support.OSUtil.linux.vdso_sym
+)

libc/src/__support/OSUtil/linux/x86_64/vdso.h

@@ -0,0 +1,43 @@
+//===---------- x86/x86_64 vdso configuration ---------------------* C++ *-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+#ifndef LLVM_LIBC_SRC___SUPPORT_OSUTIL_LINUX_X86_64_VDSO_H
+#define LLVM_LIBC_SRC___SUPPORT_OSUTIL_LINUX_X86_64_VDSO_H
+#include "src/__support/CPP/string_view.h"
+#include "src/__support/OSUtil/linux/vdso_sym.h"
+namespace LIBC_NAMESPACE_DECL {
+namespace vdso {
+// translate VDSOSym to symbol names
+// On x86, there are symbols defined without the __vdso_ prefix, however,
+// it is suggested that one should use the __vdso_ prefix.
+// Additionally, there is also an __vdso_sgx_enter_enclave, it is for the SGX
+// support, we do not include it here for now.
+// https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/x86/entry/vdso/vdso.lds.S
+LIBC_INLINE constexpr cpp::string_view symbol_name(VDSOSym sym) {
+  switch (sym) {
+  case VDSOSym::ClockGetTime:
+    return "__vdso_clock_gettime";
+  case VDSOSym::GetTimeOfDay:
+    return "__vdso_gettimeofday";
+  case VDSOSym::GetCpu:
+    return "__vdso_getcpu";
+  case VDSOSym::Time:
+    return "__vdso_time";
+  case VDSOSym::ClockGetRes:
+    return "__vdso_clock_getres";
+  default:
+    return "";
+  }
+}
+
+// symbol versions
+LIBC_INLINE constexpr cpp::string_view symbol_version(VDSOSym) {
+  return "LINUX_2.6";
+}
+} // namespace vdso
+} // namespace LIBC_NAMESPACE_DECL
+#endif // LLVM_LIBC_SRC___SUPPORT_OSUTIL_LINUX_X86_64_VDSO_H

libc/src/sys/auxv/getauxval.h

@@ -9,8 +9,8 @@
 #ifndef LLVM_LIBC_SRC_SYS_AUXV_GETAUXVAL_H
 #define LLVM_LIBC_SRC_SYS_AUXV_GETAUXVAL_H
 
+#include "hdr/sys_auxv_macros.h"
 #include "src/__support/macros/config.h"
-#include <sys/auxv.h>
 
 namespace LIBC_NAMESPACE_DECL {
 

libc/test/src/__support/OSUtil/linux/CMakeLists.txt

@@ -1,3 +1,21 @@
 if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_ARCHITECTURE})
   add_subdirectory(${LIBC_TARGET_ARCHITECTURE})
 endif()
+
+add_libc_test(
+  vdso_test
+  SUITE libc-osutil-tests
+  SRCS vdso_test.cpp
+  DEPENDS
+    libc.src.__support.OSUtil.linux.vdso
+    libc.src.__support.OSUtil.osutil
+    libc.hdr.types.struct_sigaction
+    libc.hdr.types.struct_timeval
+    libc.hdr.types.struct_timespec
+    libc.hdr.types.clockid_t
+    libc.hdr.types.time_t
+    libc.hdr.time_macros
+    libc.hdr.signal_macros
+    libc.src.signal.sigaction
+    libc.src.signal.raise
+)

libc/test/src/__support/OSUtil/linux/vdso_test.cpp

@@ -0,0 +1,162 @@
+//===-- Unittests for VDSO ------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "hdr/signal_macros.h"
+#include "hdr/time_macros.h"
+#include "hdr/types/clockid_t.h"
+#include "hdr/types/struct_sigaction.h"
+#include "hdr/types/struct_timespec.h"
+#include "hdr/types/struct_timeval.h"
+#include "hdr/types/time_t.h"
+#include "src/__support/OSUtil/linux/vdso.h"
+#include "src/__support/OSUtil/syscall.h"
+#include "src/__support/macros/properties/architectures.h"
+#include "src/signal/raise.h"
+#include "src/signal/sigaction.h"
+#include "test/UnitTest/ErrnoSetterMatcher.h"
+#include "test/UnitTest/LibcTest.h"
+#include "test/UnitTest/Test.h"
+#include <linux/time_types.h>
+#include <sys/syscall.h>
+
+struct riscv_hwprobe {
+  int64_t key;
+  uint64_t value;
+};
+
+namespace LIBC_NAMESPACE_DECL {
+// For x86_64, we explicitly test some traditional vdso symbols are indeed
+// available.
+
+TEST(LlvmLibcOSUtilVDSOTest, GetTimeOfDay) {
+  vdso::TypedSymbol<vdso::VDSOSym::GetTimeOfDay> symbol;
+  if (!symbol)
+    return;
+  timeval tv;
+  EXPECT_EQ(symbol(&tv, nullptr), 0);
+  // hopefully people are not building time machines using our libc.
+  EXPECT_GT(tv.tv_sec, static_cast<decltype(tv.tv_sec)>(0));
+}
+
+TEST(LlvmLibcOSUtilVDSOTest, Time) {
+  vdso::TypedSymbol<vdso::VDSOSym::Time> symbol;
+  if (!symbol)
+    return;
+  time_t a, b;
+  EXPECT_GT(symbol(&a), static_cast<time_t>(0));
+  EXPECT_GT(symbol(&b), static_cast<time_t>(0));
+  EXPECT_GE(b, a);
+}
+
+TEST(LlvmLibcOSUtilVDSOTest, ClockGetTime) {
+  vdso::TypedSymbol<vdso::VDSOSym::ClockGetTime> symbol;
+  if (!symbol)
+    return;
+  timespec a, b;
+  EXPECT_EQ(symbol(CLOCK_MONOTONIC, &a), 0);
+  EXPECT_EQ(symbol(CLOCK_MONOTONIC, &b), 0);
+  if (a.tv_sec == b.tv_sec) {
+    EXPECT_LT(a.tv_nsec, b.tv_nsec);
+  } else {
+    EXPECT_LT(a.tv_sec, b.tv_sec);
+  }
+}
+
+TEST(LlvmLibcOSUtilVDSOTest, ClockGetTime64) {
+  vdso::TypedSymbol<vdso::VDSOSym::ClockGetTime64> symbol;
+  if (!symbol)
+    return;
+  // See kernel API at
+  // https://elixir.bootlin.com/linux/latest/source/tools/testing/selftests/vDSO/vdso_test_correctness.c#L155
+  __kernel_timespec a, b;
+  EXPECT_EQ(symbol(CLOCK_MONOTONIC, &a), 0);
+  EXPECT_EQ(symbol(CLOCK_MONOTONIC, &b), 0);
+  if (a.tv_sec == b.tv_sec) {
+    EXPECT_LT(a.tv_nsec, b.tv_nsec);
+  } else {
+    EXPECT_LT(a.tv_sec, b.tv_sec);
+  }
+}
+
+TEST(LlvmLibcOSUtilVDSOTest, ClockGetRes) {
+  vdso::TypedSymbol<vdso::VDSOSym::ClockGetRes> symbol;
+  if (!symbol)
+    return;
+  timespec res{};
+  EXPECT_EQ(symbol(CLOCK_MONOTONIC, &res), 0);
+  EXPECT_TRUE(res.tv_sec > 0 || res.tv_nsec > 0);
+}
+
+TEST(LlvmLibcOSUtilVDSOTest, GetCpu) {
+  // The kernel system call has a third argument, which should be passed as
+  // nullptr.
+  vdso::TypedSymbol<vdso::VDSOSym::GetCpu> symbol;
+  if (!symbol)
+    return;
+  unsigned cpu = static_cast<unsigned>(-1), node = static_cast<unsigned>(-1);
+  EXPECT_EQ(symbol(&cpu, &node, nullptr), 0);
+  EXPECT_GE(cpu, 0u);
+  EXPECT_GE(node, 0u);
+}
+
+static bool flag = false;
+static void sigprof_handler [[gnu::used]] (int) { flag = true; }
+
+TEST(LlvmLibcOSUtilVDSOTest, RtSigReturn) {
+  using namespace testing::ErrnoSetterMatcher;
+  // must use struct since there is a function of the same name in the same
+  // scope.
+  struct sigaction sa {};
+  struct sigaction old_sa {};
+  sa.sa_handler = sigprof_handler;
+  sa.sa_flags = SA_RESTORER;
+  vdso::TypedSymbol<vdso::VDSOSym::RTSigReturn> symbol;
+  if (!symbol)
+    return;
+  sa.sa_restorer = symbol;
+  ASSERT_THAT(LIBC_NAMESPACE::sigaction(SIGPROF, &sa, &old_sa), Succeeds());
+  raise(SIGPROF);
+  ASSERT_TRUE(flag);
+  flag = false;
+  ASSERT_THAT(LIBC_NAMESPACE::sigaction(SIGPROF, &old_sa, nullptr), Succeeds());
+}
+
+TEST(LlvmLibcOSUtilVDSOTest, FlushICache) {
+  vdso::TypedSymbol<vdso::VDSOSym::FlushICache> symbol;
+  if (!symbol)
+    return;
+  char buf[512];
+  // we just check that the flush will not panic the program.
+  // the flags part only take 0/1 as up to kernel 6.10, which is used to
+  // indicate whether the flush is local to the core or global.
+  symbol(buf, buf + sizeof(buf), 0);
+  symbol(buf, buf + sizeof(buf), 1);
+}
+
+// https://docs.kernel.org/6.5/riscv/hwprobe.html
+TEST(LlvmLibcOSUtilVDSOTest, RiscvHwProbe) {
+  using namespace testing::ErrnoSetterMatcher;
+  vdso::TypedSymbol<vdso::VDSOSym::RiscvHwProbe> symbol;
+  if (!symbol)
+    return;
+  // If a key is unknown to the kernel, its key field will be cleared to -1, and
+  // its value set to 0. We expect probes.value are all 0.
+  // Usermode can supply NULL for cpus and 0 for cpu_count as a shortcut for all
+  // online CPUs
+  riscv_hwprobe probes[2] = {{-1, 1}, {-1, 1}};
+  ASSERT_THAT(symbol(/*pairs=*/probes, /*count=*/2, /*cpusetsize=*/0,
+                     /*cpuset=*/nullptr,
+                     /*flags=*/0),
+              Succeeds());
+  for (auto &probe : probes) {
+    EXPECT_EQ(probe.key, static_cast<decltype(probe.key)>(-1));
+    EXPECT_EQ(probe.value, static_cast<decltype(probe.value)>(0));
+  }
+}
+
+} // namespace LIBC_NAMESPACE_DECL