[libc] Move the implementation of mmap and munmap into a linux specific area.

[sivachandra]

Summary

This allows us to get rid of the PAGE_SIZE macro and use EXEC_PAGESIZE
from linux/param.h.

Few other points about this change:

1. The linux syscall functions have been moved into a linux specific area

instead of src/unistd/syscall.h. The Linux syscall function from unistd.h
is a public vararg function. What we have currently are linux speciif internal
overloaded C++ functions. So, moving them to a Linux only area is more
meaningful.

2. The implementations of mmap and munmap are now in a 'linux' directory

within src/sys/mman. The idea here is that platform specific
implementations will live in a platform specific subdirectories like these.
Infrastructure common to a platform will live in the platform's config
directory. For example, the linux syscall implementations live in
config/linux.

[abrachet]

LGTM. Would it be appropriate for this patch to add non platform specific implementations that always fail and set errno to ENOSYS in libc/src/sys/mman?

[sivachandra]

In D73302#1837485, @abrachet wrote:

LGTM. Would it be appropriate for this patch to add non platform specific implementations that always fail and set errno to ENOSYS in libc/src/sys/mman?

Thats a good idea but I am not yet sure if we want to do this for every function for which we have platform specific implementations. As we add more items, we will see if it make sense to incorporate a pattern like this.

libc/config/linux/CMakeLists.txt

+add_gen_header(
+  linux_syscall_h
+  DEF_FILE syscall.h.def
+  GEN_HDR syscall.h
+  PARAMS
+    inline_syscalls=${LIBC_TARGET_MACHINE}/syscall.h.inc
+  DATA_FILES
+    ${LIBC_TARGET_MACHINE}/syscall.h.inc
+)
+
 add_subdirectory(x86_64)

libc/config/linux/platfrom_defs.h.inc

 //===----- Definition of platform specific macros for ELF paltforms -------===//
 //
 // 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
 //
 //===----------------------------------------------------------------------===//
 
 %%begin()
 
 #define ENTRYPOINT_SECTION_ATTRIBUTE(name) \
     __attribute__((section(".llvm.libc.entrypoint."#name)))
 #define LLVM_LIBC_ENTRYPOINT(name) ENTRYPOINT_SECTION_ATTRIBUTE(name) name
-
-// TODO: Get rid of the PAGE_SIZE macro. It is present only as an interim
-// measure until we can move the implementations of mmap and munmap to under
-// the config/linux directory. After that, the implementations can use
-// EXEC_PAGESIZE until page size can be read from the aux vector. 
-#define PAGE_SIZE 4096

libc/include/CMakeLists.txt

 file(MAKE_DIRECTORY "sys")
 
 add_gen_header(
   sys_mman_h
   DEF_FILE sys/mman.h.def
   GEN_HDR sys/mman.h
   DEPENDS
     libc_posix_types_h
+    llvm_libc_common_h
 )
 
 add_gen_header(
   sys_syscall_h
   DEF_FILE sys/syscall.h.def
   GEN_HDR sys/syscall.h
   PARAMS
     syscall_numbers=../config/${LIBC_TARGET_OS}/syscall_numbers.h.inc
   DATA_FILES
     ../config/${LIBC_TARGET_OS}/syscall_numbers.h.inc
 )

libc/src/CMakeLists.txt

 add_subdirectory(errno)
 add_subdirectory(math)
 add_subdirectory(string)
 # TODO: Add this target conditional to the target OS.
 add_subdirectory(sys)
-add_subdirectory(unistd)
 
 add_subdirectory(__support)

libc/src/sys/mman/CMakeLists.txt

-#TODO: The sources and target listed here should ideally live in config/linux.
-
-add_entrypoint_object(
-  mmap
-  SRCS
-    mmap.cpp
-  HDRS
-    mmap.h
-  DEPENDS
-    sys_mman_h
-    sys_syscall_h
-    syscall_impl_h
-    __errno_location
-)
-
-add_entrypoint_object(
-  munmap
-  SRCS
-    munmap.cpp
-  HDRS
-    munmap.h
-  DEPENDS
-    sys_mman_h
-    sys_syscall_h
-    syscall_impl_h
-    __errno_location
-)
+if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
+  add_subdirectory(${LIBC_TARGET_OS})
+endif()

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

-#TODO: The sources and target listed here should ideally live in config/linux.
-
 add_entrypoint_object(
   mmap
   SRCS
     mmap.cpp
   HDRS
-    mmap.h
+    ../mmap.h
   DEPENDS
     sys_mman_h
     sys_syscall_h
-    syscall_impl_h
+    linux_syscall_h
     __errno_location
 )
 
 add_entrypoint_object(
   munmap
   SRCS
     munmap.cpp
   HDRS
-    munmap.h
+    ../munmap.h
   DEPENDS
     sys_mman_h
     sys_syscall_h
-    syscall_impl_h
+    linux_syscall_h
     __errno_location
 )

libc/src/sys/mman/linux/mmap.cpp

-//===-------------- Implementation of the POSIX mmap function -------------===//
+//===---------- Linux implementation of the POSIX mmap 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/mman/mmap.h"
-#include "include/sys/syscall.h" // For syscall numbers.
+
+#include "config/linux/syscall.h" // For internal syscall function.
+#include "include/sys/syscall.h"  // For syscall numbers.
 #include "src/__support/common.h"
 #include "src/errno/llvmlibc_errno.h"
-#include "src/unistd/syscall.h" // For internal syscall function.
+
+#include <linux/param.h> // For EXEC_PAGESIZE.
 
 namespace __llvm_libc {
 
 // This function is currently linux only. It has to be refactored suitably if
 // mmap is to be supported on non-linux operating systems also.
 void *LLVM_LIBC_ENTRYPOINT(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 /= PAGE_SIZE;
+  offset /= EXEC_PAGESIZE;
   long syscall_number = SYS_mmap2;
 #elif SYS_mmap
   long syscall_number = SYS_mmap;
 #else
 #error "Target platform does not have SYS_mmap or SYS_mmap2 defined"
 #endif
 
   long ret_val =
       __llvm_libc::syscall(syscall_number, reinterpret_cast<long>(addr), size,
                            prot, flags, fd, 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 (ret_val < 0 && ret_val > -PAGE_SIZE) {
+  if (ret_val < 0 && ret_val > -EXEC_PAGESIZE) {
     llvmlibc_errno = -ret_val;
     return MAP_FAILED;
   }
 
   return reinterpret_cast<void *>(ret_val);
 }
 
 } // namespace __llvm_libc

libc/src/sys/mman/linux/munmap.cpp

-//===------------- Implementation of the POSIX munmap function ------------===//
+//===---------- Linux implementation of the POSIX munmap 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/mman/munmap.h"
-#include "include/sys/syscall.h" // For syscall numbers.
+
+#include "config/linux/syscall.h" // For internal syscall function.
+#include "include/sys/syscall.h"  // For syscall numbers.
 #include "src/__support/common.h"
 #include "src/errno/llvmlibc_errno.h"
-#include "src/unistd/syscall.h" // For internal syscall function.
 
 namespace __llvm_libc {
 
 // This function is currently linux only. It has to be refactored suitably if
 // mmap is to be supported on non-linux operating systems also.
 int LLVM_LIBC_ENTRYPOINT(munmap)(void *addr, size_t size) {
   long ret_val =
       __llvm_libc::syscall(SYS_munmap, reinterpret_cast<long>(addr), size);

libc/src/unistd/CMakeLists.txt

-add_gen_header(
-  syscall_impl_h
-  DEF_FILE syscall.h.def
-  GEN_HDR syscall.h
-  PARAMS
-    inline_syscalls=../../config/${LIBC_TARGET_OS}/${LIBC_TARGET_MACHINE}/syscall.h.inc
-  DATA_FILES
-    ../../config/${LIBC_TARGET_OS}/${LIBC_TARGET_MACHINE}/syscall.h.inc
-)

libc/test/config/linux/x86_64/CMakeLists.txt

 add_libc_unittest(
   libc_linux_x86_64_syscall_unittest
   SUITE libc_linux_tests
   SRCS syscall_test.cpp
   DEPENDS
-   syscall_impl_h
+   linux_syscall_h
    support_common_h
 )

libc/test/config/linux/x86_64/syscall_test.cpp

 //===------------------ Unittests for x86_64 syscalls ---------------------===//
 //
 // 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/unistd/syscall.h"
+#include "config/linux/syscall.h"
 #include "utils/UnitTest/Test.h"
 
 #include <functional>
 
 TEST(X86_64_SyscallTest, APITest) {
   // We only do a signature test here. Actual functionality tests are
   // done by the unit tests of the syscall wrappers like mmap.
 

libc/test/src/sys/mman/CMakeLists.txt

-add_libc_testsuite(libc_sys_mman_unittests)
-
-add_libc_unittest(
-  mmap_test
-  SUITE
-    libc_sys_mman_unittests
-  SRCS
-    mmap_test.cpp
-  DEPENDS
-    errno_h
-    sys_mman_h
-    mmap
-    munmap
-    __errno_location
-)
+if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
+  add_subdirectory(${LIBC_TARGET_OS})
+endif()