[libc] Refactoring getauxval to use internal functions

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

@@ -9,6 +9,10 @@ add_object_library(
   SRCS
     exit.cpp
     fcntl.cpp
+    mmap.cpp
+    munmap.cpp
+    prctl.cpp
+    read.cpp
   HDRS
     io.h
     syscall.h
@@ -22,6 +26,10 @@ add_object_library(
     libc.hdr.types.struct_f_owner_ex
     libc.hdr.types.off_t
     libc.include.sys_syscall
+    libc.src.__support.macros.sanitizer
+    libc.hdr.types.size_t
+    libc.hdr.types.ssize_t
+    libc.include.unistd
 )
 
 add_header_library(

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

@@ -0,0 +1,66 @@
+//===------ Linux implementation of the POSIX mmap function -----*- 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/mmap.h"
+#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
+#include "src/__support/common.h"
+#include "src/__support/error_or.h"
+
+#include "src/__support/macros/config.h"
+#include <linux/param.h> // For EXEC_PAGESIZE.
+#include <sys/syscall.h> // For syscall numbers.
+#include "src/__support/macros/optimization.h" // LIBC_UNLIKELY
+
+namespace LIBC_NAMESPACE_DECL {
+namespace internal {
+
+// This function is currently linux only. It has to be refactored suitably if
+// mmap is to be supported on non-linux operating systems also.
+ErrorOr<void *> mmap(void *addr, size_t size, int prot, int flags, int fd,
+                     off_t offset) {
+  // A lot of POSIX standard prescribed validation of the parameters is not
+  // done in this function as modern linux versions do it in the syscall.
+  // TODO: Perform argument validation not done by the linux syscall.
+
+  // EXEC_PAGESIZE is used for the page size. While this is OK for x86_64, it
+  // might not be correct in general.
+  // TODO: Use pagesize read from the ELF aux vector instead of EXEC_PAGESIZE.
+
+#ifdef SYS_mmap2
+  offset /= EXEC_PAGESIZE;
+  long syscall_number = SYS_mmap2;
+#elif defined(SYS_mmap)
+  long syscall_number = SYS_mmap;
+#else
+#error "mmap or mmap2 syscalls not available."
+#endif
+
+  // We add an explicit cast to silence a "implicit conversion loses integer
+  // precision" warning when compiling for 32-bit systems.
+  long mmap_offset = static_cast<long>(offset);
+  long ret =
+      LIBC_NAMESPACE::syscall_impl(syscall_number, reinterpret_cast<long>(addr),
+                                   size, prot, flags, fd, mmap_offset);
+
+  // The mmap/mmap2 syscalls return negative values on error. These negative
+  // values are actually the negative values of the error codes. So, fix them
+  // up in case an error code is detected.
+  //
+  // A point to keep in mind for the fix up is that a negative return value
+  // from the syscall can also be an error-free value returned by the syscall.
+  // However, since a valid return address cannot be within the last page, a
+  // return value corresponding to a location in the last page is an error
+  // value.
+  if (LIBC_UNLIKELY(ret < 0 && ret > -EXEC_PAGESIZE))
+    return Error(static_cast<int>(-ret));
+
+  return reinterpret_cast<void *>(ret);
+}
+
+} // namespace internal
+} // namespace LIBC_NAMESPACE_DECL

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

@@ -0,0 +1,35 @@
+//===---- Linux implementation of the POSIX munmap function -----*- 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/munmap.h"
+
+#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
+#include "src/__support/common.h"
+
+#include "src/__support/error_or.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/macros/optimization.h" // LIBC_UNLIKELY
+#include <sys/syscall.h>                       // For syscall numbers.
+
+namespace LIBC_NAMESPACE_DECL {
+namespace internal {
+
+// This function is currently linux only. It has to be refactored suitably if
+// munmap is to be supported on non-linux operating systems also.
+ErrorOr<int> munmap(void *addr, size_t size) {
+  int ret = LIBC_NAMESPACE::syscall_impl<int>(
+      SYS_munmap, reinterpret_cast<long>(addr), size);
+
+  if (LIBC_UNLIKELY(ret < 0))
+    return Error(-ret);
+
+  return 0;
+}
+
+} // namespace internal
+} // namespace LIBC_NAMESPACE_DECL

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

@@ -0,0 +1,40 @@
+//===---- Linux implementation of the prctl function ------------*- 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/prctl.h"
+
+#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
+
+#include "src/__support/error_or.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/macros/optimization.h" // LIBC_UNLIKELY
+#include <sys/syscall.h> // For syscall numbers.
+
+namespace LIBC_NAMESPACE_DECL {
+namespace internal {
+
+ErrorOr<int> prctl(int option, unsigned long arg2, unsigned long arg3,
+                   unsigned long arg4, unsigned long arg5) {
+  long ret =
+      LIBC_NAMESPACE::syscall_impl(SYS_prctl, option, arg2, arg3, arg4, arg5);
+
+  // The manpage states that "... return the nonnegative values described
+  // above. All other option values return 0 on success. On error,
+  // -1 is returned, and errno is set to indicate the error."
+  // According to the kernel implementation
+  // (https://github.com/torvalds/linux/blob/bee0e7762ad2c6025b9f5245c040fcc36ef2bde8/kernel/sys.c#L2442),
+  // return value from the syscall is set to 0 on default so we do not need to
+  // set the value on success manually.
+  if (LIBC_UNLIKELY(ret < 0))
+    return Error(static_cast<int>(-ret));
+
+  return static_cast<int>(ret);
+}
+
+} // namespace internal
+} // namespace LIBC_NAMESPACE_DECL

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

@@ -0,0 +1,33 @@
+//===-- Linux implementation of read --------------------------------------===//
+//
+// 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/read.h"
+
+#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
+#include "src/__support/common.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/macros/optimization.h" // LIBC_UNLIKELY
+#include "src/__support/macros/sanitizer.h"    // for MSAN_UNPOISON
+#include <sys/syscall.h>                       // For syscall numbers.
+
+namespace LIBC_NAMESPACE_DECL {
+namespace internal {
+
+ErrorOr<ssize_t> read(int fd, void *buf, size_t count) {
+  ssize_t ret = LIBC_NAMESPACE::syscall_impl<ssize_t>(SYS_read, fd, buf, count);
+  if (LIBC_UNLIKELY(ret < 0))
+    return Error(static_cast<int>(-ret));
+
+  // The cast is important since there is a check that dereferences the pointer
+  // which fails on void*.
+  MSAN_UNPOISON(reinterpret_cast<char *>(buf), count);
+  return ret;
+}
+
+} // namespace internal
+} // namespace LIBC_NAMESPACE_DECL

libc/src/__support/OSUtil/mmap.h

@@ -0,0 +1,26 @@
+//===----------- Implementation header of the mmap function -----*- 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_MMAP_H
+#define LLVM_LIBC_SRC___SUPPORT_OSUTIL_MMAP_H
+
+#include "hdr/types/off_t.h"
+#include "hdr/types/size_t.h"
+#include "src/__support/error_or.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+namespace internal {
+
+ErrorOr<void *> mmap(void *addr, size_t size, int prot, int flags, int fd,
+                     off_t offset);
+
+} // namespace internal
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC___SUPPORT_OSUTIL_MMAP_H

libc/src/__support/OSUtil/munmap.h

@@ -0,0 +1,25 @@
+//===--------- Implementation header of the munmap function -----*- 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_MUNMAP_H
+#define LLVM_LIBC_SRC___SUPPORT_OSUTIL_MUNMAP_H
+
+#include "hdr/types/off_t.h"
+#include "hdr/types/size_t.h"
+#include "src/__support/error_or.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+namespace internal {
+
+ErrorOr<int> munmap(void *addr, size_t size);
+
+} // namespace internal
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC___SUPPORT_OSUTIL_MUNMAP_H

libc/src/__support/OSUtil/prctl.h

@@ -0,0 +1,26 @@
+//===--------- Implementation header of the prctl function -----*- 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_PRCTL_H
+#define LLVM_LIBC_SRC___SUPPORT_OSUTIL_PRCTL_H
+
+#include "src/__support/error_or.h"
+#include "src/__support/libc_errno.h"
+#include "src/__support/macros/config.h"
+#include <sys/prctl.h>
+
+namespace LIBC_NAMESPACE_DECL {
+namespace internal {
+
+ErrorOr<int> prctl(int option, unsigned long arg2, unsigned long arg3,
+                   unsigned long arg4, unsigned long arg5);
+
+} // namespace internal
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC___SUPPORT_OSUTIL_PRCTL_H

libc/src/__support/OSUtil/read.h

@@ -0,0 +1,26 @@
+//===--------- Implementation header of the read function -------*- 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_READ_H
+#define LLVM_LIBC_SRC___SUPPORT_OSUTIL_READ_H
+
+#include "hdr/types/size_t.h"
+#include "hdr/types/ssize_t.h"
+#include "hdr/unistd_macros.h"
+#include "src/__support/error_or.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+namespace internal {
+
+ErrorOr<ssize_t> read(int fd, void *buf, size_t count);
+
+} // namespace internal
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC___SUPPORT_OSUTIL_READ_H

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

@@ -6,10 +6,9 @@ add_entrypoint_object(
     ../getauxval.h
   DEPENDS
     libc.src.sys.prctl.prctl
-    libc.src.sys.mman.mmap
-    libc.src.sys.mman.munmap
     libc.src.__support.threads.callonce
     libc.src.__support.common
+    libc.src.__support.OSUtil.osutil
     libc.src.errno.errno
     libc.config.app_h
     libc.src.fcntl.open