[libc][WIP] try to make sysconf work

libc/config/linux/aarch64/entrypoints.txt

@@ -166,6 +166,12 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.sys.wait.wait4
     libc.src.sys.wait.waitpid
 
+    # sys/auxv.h entrypoints
+    libc.src.sys.auxv.getauxval
+
+    # sys/prctl.h entrypoints
+    libc.src.sys.prctl.prctl
+
     # termios.h entrypoints
     libc.src.termios.cfgetispeed
     libc.src.termios.cfgetospeed

libc/config/linux/app.h

@@ -9,30 +9,32 @@
 #ifndef LLVM_LIBC_CONFIG_LINUX_APP_H
 #define LLVM_LIBC_CONFIG_LINUX_APP_H
 
+#include "src/__support/macros/attributes.h"
 #include "src/__support/macros/properties/architectures.h"
 
+#include <linux/auxvec.h>
 #include <stdint.h>
 
 namespace LIBC_NAMESPACE {
 
 // Data structure to capture properties of the linux/ELF TLS image.
 struct TLSImage {
   // The load address of the TLS.
-  uintptr_t address;
+  uintptr_t address = 0;
 
   // The byte size of the TLS image consisting of both initialized and
   // uninitialized memory. In ELF executables, it is size of .tdata + size of
   // .tbss. Put in another way, it is the memsz field of the PT_TLS header.
-  uintptr_t size;
+  uintptr_t size = 0;
 
   // The byte size of initialized memory in the TLS image. In ELF exectubles,
   // this is the size of .tdata. Put in another way, it is the filesz of the
   // PT_TLS header.
-  uintptr_t init_size;
+  uintptr_t init_size = 0;
 
   // The alignment of the TLS layout. It assumed that the alignment
   // value is a power of 2.
-  uintptr_t align;
+  uintptr_t align = 0;
 };
 
 #if defined(LIBC_TARGET_ARCH_IS_X86_64) ||                                     \
@@ -49,11 +51,19 @@ typedef uintptr_t ArgcType;
 typedef uintptr_t ArgVEntryType;
 
 typedef uintptr_t EnvironType;
-typedef uintptr_t AuxEntryType;
 #else
 #error "argc and argv types are not defined for the target platform."
 #endif
 
+// According the manpage associated to /proc/<pid>/auxv:
+// ... The format is one unsigned long ID plus one unsigned long
+// value for each entry ...
+// https://man7.org/linux/man-pages/man5/proc.5.html
+struct AuxEntryType {
+  unsigned long id;
+  unsigned long value;
+};
+
 struct Args {
   ArgcType argc;
 
@@ -69,18 +79,21 @@ struct Args {
 // Data structure which captures properties of a linux application.
 struct AppProperties {
   // Page size used for the application.
-  uintptr_t pageSize;
+  uintptr_t page_size = 0;
 
-  Args *args;
+  Args *args = nullptr;
 
   // The properties of an application's TLS image.
-  TLSImage tls;
+  TLSImage tls{};
 
   // Environment data.
-  EnvironType *envPtr;
+  EnvironType *env_ptr = nullptr;
+
+  // Auxiliary vector data.
+  const AuxEntryType *auxv_ptr = nullptr;
 };
 
-extern AppProperties app;
+LIBC_INLINE_VAR AppProperties app{};
 
 // The descriptor of a thread's TLS area.
 struct TLSDescriptor {

libc/config/linux/arm/entrypoints.txt

@@ -92,6 +92,12 @@ set(TARGET_LIBC_ENTRYPOINTS
     # sys/mman.h entrypoints
     libc.src.sys.mman.mmap
     libc.src.sys.mman.munmap
+
+    # sys/auxv.h entrypoints
+    libc.src.sys.auxv.getauxval
+
+    # sys/prctl.h entrypoints
+    libc.src.sys.prctl.prctl
 )
 
 set(TARGET_LIBM_ENTRYPOINTS

libc/config/linux/riscv/entrypoints.txt

@@ -172,6 +172,12 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.sys.wait.wait4
     libc.src.sys.wait.waitpid
 
+    # sys/auxv.h entrypoints
+    libc.src.sys.auxv.getauxval
+
+    # sys/prctl.h entrypoints
+    libc.src.sys.prctl.prctl
+
     # termios.h entrypoints
     libc.src.termios.cfgetispeed
     libc.src.termios.cfgetospeed

libc/config/linux/x86_64/entrypoints.txt

@@ -175,6 +175,12 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.sys.wait.wait4
     libc.src.sys.wait.waitpid
 
+    # sys/auxv.h entrypoints
+    libc.src.sys.auxv.getauxval
+
+    # sys/prctl.h entrypoints
+    libc.src.sys.prctl.prctl
+
     # termios.h entrypoints
     libc.src.termios.cfgetispeed
     libc.src.termios.cfgetospeed

libc/src/stdlib/getenv.cpp

@@ -16,7 +16,7 @@
 namespace LIBC_NAMESPACE {
 
 LLVM_LIBC_FUNCTION(char *, getenv, (const char *name)) {
-  char **env_ptr = reinterpret_cast<char **>(LIBC_NAMESPACE::app.envPtr);
+  char **env_ptr = reinterpret_cast<char **>(LIBC_NAMESPACE::app.env_ptr);
 
   if (name == nullptr || env_ptr == nullptr)
     return nullptr;

libc/src/sys/CMakeLists.txt

@@ -7,3 +7,5 @@ add_subdirectory(sendfile)
 add_subdirectory(stat)
 add_subdirectory(utsname)
 add_subdirectory(wait)
+add_subdirectory(auxv)
+add_subdirectory(prctl)

libc/src/sys/auxv/CMakeLists.txt

@@ -0,0 +1,10 @@
+if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
+  add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
+endif()
+
+add_entrypoint_object(
+  getauxval
+  ALIAS
+  DEPENDS
+    .${LIBC_TARGET_OS}.getauxval
+)

libc/src/sys/auxv/getauxval.h

@@ -0,0 +1,20 @@
+//===-- Implementation header for getauxval ----------------------*- 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_SYS_AUXV_GETAUXVAL_H
+#define LLVM_LIBC_SRC_SYS_AUXV_GETAUXVAL_H
+
+#include <sys/auxv.h>
+
+namespace LIBC_NAMESPACE {
+
+unsigned long getauxval(unsigned long id);
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_SYS_AUXV_GETAUXVAL_H

libc/src/sys/auxv/linux/CMakeLists.txt

@@ -0,0 +1,18 @@
+add_entrypoint_object(
+  getauxval
+  SRCS
+    getauxval.cpp
+  HDRS
+    ../getauxval.h
+  DEPENDS
+    libc.include.sys_auxv
+    libc.src.errno.errno
+    libc.src.fcntl.open
+    libc.src.unistd.read
+    libc.src.unistd.close
+    libc.src.sys.prctl.prctl
+    libc.src.sys.mman.mmap
+    libc.src.sys.mman.munmap
+    libc.config.linux.app_h
+    libc.src.__support.macros.optimization
+)

libc/src/sys/auxv/linux/getauxval.cpp

@@ -0,0 +1,141 @@
+//===---------- Linux implementation of the getauxval function ------------===//
+//
+// 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/sys/auxv/getauxval.h"
+#include "config/linux/app.h"
+#include "src/__support/common.h"
+#include "src/__support/macros/optimization.h"
+#include "src/errno/libc_errno.h"
+#include "src/fcntl/open.h"
+#include "src/sys/mman/mmap.h"
+#include "src/sys/mman/munmap.h"
+#include "src/sys/prctl/prctl.h"
+#include "src/unistd/close.h"
+#include "src/unistd/read.h"
+
+#include <linux/auxvec.h> // AT_NULL
+#include <sys/mman.h>     // MAP_FAILED, MAP_PRIVATE, MAP_ANONYMOUS
+
+namespace LIBC_NAMESPACE {
+
+constexpr size_t AUXV_MMAP_SIZE = sizeof(AuxEntryType) * 64;
+
+struct ErrorNo {
+  ErrorNo() : errno_backup(libc_errno), failure(false) {}
+  ~ErrorNo() { libc_errno = failure ? ENOENT : errno_backup; }
+  void mark_failure() { failure = true; }
+  int errno_backup;
+  bool failure;
+};
+
+struct TempAuxv {
+  TempAuxv() : ptr(nullptr) {}
+  ~TempAuxv() {
+    if (ptr != nullptr)
+      munmap(ptr, AUXV_MMAP_SIZE);
+  }
+  AuxEntryType *ptr;
+};
+
+struct TempFD {
+  TempFD(const char *path) : fd(open(path, O_RDONLY | O_CLOEXEC)) {}
+  ~TempFD() {
+    if (fd >= 0)
+      close(fd);
+  }
+  operator int() const { return fd; }
+  int fd;
+};
+
+static AuxEntryType read_entry(int fd) {
+  AuxEntryType buf;
+  ssize_t size = sizeof(AuxEntryType);
+  while (size > 0) {
+    ssize_t ret = read(fd, &buf, size);
+    if (ret < 0) {
+      if (libc_errno == EINTR)
+        continue;
+      buf.id = AT_NULL;
+      buf.value = AT_NULL;
+      break;
+    }
+    size -= ret;
+  }
+  return buf;
+}
+
+LLVM_LIBC_FUNCTION(unsigned long, getauxval, (unsigned long id)) {
+  // if llvm-libc's loader is applied, app.auxv_ptr should have been
+  // initialized, then we can directly get the auxillary vector
+  const AuxEntryType *auxv_ptr = app.auxv_ptr;
+  ErrorNo errno_holder;
+  TempAuxv temp_auxv;
+
+  // Compatible layer for the overlay mode.
+  // first check if PR_GET_AUXV is supported. Unfortunately, this is not
+  // supported until Linux 6.0+. We check this syscall first since it may be
+  // the case that /proc is not mounted.
+#ifdef PR_GET_AUXV
+  do {
+    if (LIBC_UNLIKELY(auxv_ptr == nullptr)) {
+      // no need to backup errno: once it has error, we will modify it
+      void *ptr = mmap(nullptr, AUXV_MMAP_SIZE, PROT_READ | PROT_WRITE,
+                       MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+
+      if (LIBC_UNLIKELY(ptr == MAP_FAILED))
+        break;
+
+      temp_auxv.ptr = reinterpret_cast<AuxEntryType *>(ptr);
+      for (size_t i = 0; i < AUXV_MMAP_SIZE / sizeof(AuxEntryType); ++i) {
+        temp_auxv.ptr[i].id = AT_NULL;
+        temp_auxv.ptr[i].value = AT_NULL;
+      }
+
+      // We keeps the last entry to be AT_NULL, so we can always terminate the
+      // loop.
+      int ret =
+          prctl(PR_GET_AUXV, reinterpret_cast<unsigned long>(temp_auxv.ptr),
+                AUXV_MMAP_SIZE - sizeof(AuxEntryType), 0, 0);
+      if (ret < 0)
+        break;
+
+      auxv_ptr = temp_auxv.ptr;
+    }
+  } while (0);
+#endif
+
+  if (LIBC_LIKELY(auxv_ptr != nullptr)) {
+    for (; auxv_ptr->id != AT_NULL; ++auxv_ptr) {
+      if (auxv_ptr->id == id)
+        return auxv_ptr->value;
+    }
+    errno_holder.mark_failure();
+    return 0;
+  }
+
+  // now attempt to read from /proc/self/auxv
+  do {
+    TempFD fd{"/proc/self/auxv"};
+    if (fd < 0)
+      break;
+
+    while (true) {
+      AuxEntryType buf = read_entry(fd);
+      if (buf.id == AT_NULL)
+        break;
+      if (buf.id == id)
+        return buf.value;
+    }
+
+  } while (0);
+
+  errno_holder.mark_failure();
+  return 0;
+}
+
+} // namespace LIBC_NAMESPACE

libc/src/sys/prctl/CMakeLists.txt

@@ -0,0 +1,10 @@
+if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
+  add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
+endif()
+
+add_entrypoint_object(
+  prctl
+  ALIAS
+  DEPENDS
+    .${LIBC_TARGET_OS}.prctl
+)

libc/src/sys/prctl/linux/CMakeLists.txt

@@ -0,0 +1,12 @@
+add_entrypoint_object(
+  prctl
+  SRCS
+    prctl.cpp
+  HDRS
+    ../prctl.h
+  DEPENDS
+    libc.include.sys_prctl
+    libc.include.sys_syscall
+    libc.src.__support.OSUtil.osutil
+    libc.src.errno.errno
+)