[libc] add linux mman extension remap_file_pages

[SchrodingerZhu]

We need to create a remap_file_pages wrapper for linux targets, see https://www.man7.org/linux/man-pages/man2/remap_file_pages.2.html.

This requires:

• implement the entrypoint header similar to libc/src/sys/mman/mmap.h
  • modify libc/src/sys/mman/CMakeLists.txt accordingly
• implement the entrypoint similar to libc/src/sys/mman/linux/mmap.cpp
  • modify libc/src/sys/mman/linux/CMakeLists.txt accordingly
• add in the header spec
  • modify functions section in libc/newhdrgen/yaml/sys/mman.yaml
  • modify SysMMan section in libc/spec/linux.td
• add in test
  • similar to libc/test/src/sys/mman/linux/mmap_test.cpp
  • modify libc/test/src/sys/mman/linux/CMakeLists.txt accordingly

---

Misc:

• How to build libc for dev: https://libc.llvm.org/full_host_build.html
• Code style and dev guide: https://libc.llvm.org/dev/index.html

If you use vscode, sample settings are as the following (optional settings are useful in speeding up the compilation):

{
    "cmake.sourceDirectory": "${workspaceFolder}/runtimes",
    "cmake.configureSettings": {
        "CMAKE_EXPORT_COMPILE_COMMANDS": true,
        "LLVM_ENABLE_RUNTIMES": [
            "libc",
            "compiler-rt"
        ],
        "LLVM_LIBC_FULL_BUILD": true,
        "LLVM_USE_LINKER": "lld", // optional: requires installing lld
        "CMAKE_CXX_COMPILER_LAUNCHER": "sccache", // optional: requires installing sccache first
        "CMAKE_C_COMPILER_LAUNCHER": "sccache", // optional: requires installing sccache first
        "CMAKE_CXX_COMPILER": "/usr/bin/clang++",
        "CMAKE_C_COMPILER": "/usr/bin/clang",
        "LLVM_LIBC_INCLUDE_SCUDO": true,
        "COMPILER_RT_BUILD_SCUDO_STANDALONE_WITH_LLVM_LIBC": true,
        "COMPILER_RT_BUILD_GWP_ASAN": false,
        "COMPILER_RT_SCUDO_STANDALONE_BUILD_SHARED": false,
        "LIBC_USE_NEW_HEADER_GEN": true
    },
    "cmake.generator": "Ninja", // optional: requires installing Ninja
    "editor.formatOnSave": true,
    "files.insertFinalNewline": true,
    "clangd.arguments": [
        "--header-insertion=never"
    ]
}

[llvmbot]

@llvm/issue-subscribers-libc

Author: Schrodinger ZHU Yifan (SchrodingerZhu)

We need to create a `remap_file_pages` wrapper for linux targets, see https://www.man7.org/linux/man-pages/man2/remap_file_pages.2.html.

This requires:

• implement the entrypoint header similar to libc/src/sys/mman/mmap.h
  • modify libc/src/sys/mman/CMakeLists.txt accordingly
• implement the entrypoint similar to libc/src/sys/mman/linux/mmap.cpp
  • modify libc/src/sys/mman/linux/CMakeLists.txt accordingly
• add in the header spec
  • modify functions section in libc/newhdrgen/yaml/sys/mman.yaml
  • modify SysMMan section in libc/spec/linux.td
• add in test
  • similar to libc/test/src/sys/mman/linux/mmap_test.cpp
  • modify libc/test/src/sys/mman/linux/CMakeLists.txt accordingly

---

Misc:

• How to build libc for dev: https://libc.llvm.org/full_host_build.html
• Code style and dev guide: https://libc.llvm.org/dev/index.html

If you use vscode, sample settings are as the following (optional settings are useful in speeding up the compilation):

{
    "cmake.sourceDirectory": "${workspaceFolder}/runtimes",
    "cmake.configureSettings": {
        "CMAKE_EXPORT_COMPILE_COMMANDS": true,
        "LLVM_ENABLE_RUNTIMES": [
            "libc",
            "compiler-rt"
        ],
        "LLVM_LIBC_FULL_BUILD": true,
        "LLVM_USE_LINKER": "lld", // optional: requires installing lld
        "CMAKE_CXX_COMPILER_LAUNCHER": "sccache", // optional: requires installing sccache first
        "CMAKE_C_COMPILER_LAUNCHER": "sccache", // optional: requires installing sccache first
        "CMAKE_CXX_COMPILER": "/usr/bin/clang++",
        "CMAKE_C_COMPILER": "/usr/bin/clang",
        "LLVM_LIBC_INCLUDE_SCUDO": true,
        "COMPILER_RT_BUILD_SCUDO_STANDALONE_WITH_LLVM_LIBC": true,
        "COMPILER_RT_BUILD_GWP_ASAN": false,
        "COMPILER_RT_SCUDO_STANDALONE_BUILD_SHARED": false,
        "LIBC_USE_NEW_HEADER_GEN": true
    },
    "cmake.generator": "Ninja", // optional: requires installing Ninja
    "editor.formatOnSave": true,
    "files.insertFinalNewline": true,
    "clangd.arguments": [
        "--header-insertion=never"
    ]
}

[llvmbot]

Hi!

This issue may be a good introductory issue for people new to working on LLVM. If you would like to work on this issue, your first steps are:

1. Check that no other contributor has already been assigned to this issue. If you believe that no one is actually working on it despite an assignment, ping the person. After one week without a response, the assignee may be changed.
2. In the comments of this issue, request for it to be assigned to you, or just create a pull request after following the steps below. Mention this issue in the description of the pull request.
3. Fix the issue locally.
4. Run the test suite locally. Remember that the subdirectories under test/ create fine-grained testing targets, so you can e.g. use make check-clang-ast to only run Clang's AST tests.
5. Create a Git commit.
6. Run git clang-format HEAD~1 to format your changes.
7. Open a pull request to the upstream repository on GitHub. Detailed instructions can be found in GitHub's documentation. Mention this issue in the description of the pull request.

If you have any further questions about this issue, don't hesitate to ask via a comment in the thread below.

[llvmbot]

@llvm/issue-subscribers-good-first-issue

Author: Schrodinger ZHU Yifan (SchrodingerZhu)

We need to create a `remap_file_pages` wrapper for linux targets, see https://www.man7.org/linux/man-pages/man2/remap_file_pages.2.html.

This requires:

• implement the entrypoint header similar to libc/src/sys/mman/mmap.h
  • modify libc/src/sys/mman/CMakeLists.txt accordingly
• implement the entrypoint similar to libc/src/sys/mman/linux/mmap.cpp
  • modify libc/src/sys/mman/linux/CMakeLists.txt accordingly
• add in the header spec
  • modify functions section in libc/newhdrgen/yaml/sys/mman.yaml
  • modify SysMMan section in libc/spec/linux.td
• add in test
  • similar to libc/test/src/sys/mman/linux/mmap_test.cpp
  • modify libc/test/src/sys/mman/linux/CMakeLists.txt accordingly

---

Misc:

• How to build libc for dev: https://libc.llvm.org/full_host_build.html
• Code style and dev guide: https://libc.llvm.org/dev/index.html

If you use vscode, sample settings are as the following (optional settings are useful in speeding up the compilation):

{
    "cmake.sourceDirectory": "${workspaceFolder}/runtimes",
    "cmake.configureSettings": {
        "CMAKE_EXPORT_COMPILE_COMMANDS": true,
        "LLVM_ENABLE_RUNTIMES": [
            "libc",
            "compiler-rt"
        ],
        "LLVM_LIBC_FULL_BUILD": true,
        "LLVM_USE_LINKER": "lld", // optional: requires installing lld
        "CMAKE_CXX_COMPILER_LAUNCHER": "sccache", // optional: requires installing sccache first
        "CMAKE_C_COMPILER_LAUNCHER": "sccache", // optional: requires installing sccache first
        "CMAKE_CXX_COMPILER": "/usr/bin/clang++",
        "CMAKE_C_COMPILER": "/usr/bin/clang",
        "LLVM_LIBC_INCLUDE_SCUDO": true,
        "COMPILER_RT_BUILD_SCUDO_STANDALONE_WITH_LLVM_LIBC": true,
        "COMPILER_RT_BUILD_GWP_ASAN": false,
        "COMPILER_RT_SCUDO_STANDALONE_BUILD_SHARED": false,
        "LIBC_USE_NEW_HEADER_GEN": true
    },
    "cmake.generator": "Ninja", // optional: requires installing Ninja
    "editor.formatOnSave": true,
    "files.insertFinalNewline": true,
    "clangd.arguments": [
        "--header-insertion=never"
    ]
}

[AlyElashram]

You can Assign this one to me 👍

[AlyElashram]

@SchrodingerZhu I created the changes , but I'm a bit lost in Unit Testing at the moment.
I have a couple of question :

1. I assume the page size can be architecture dependent , so should I fetch the page size before using a sysconf call ?
2. To call remap_file_pages I should first allocate some memory , so is it safe to call mmap here given that it is already tested and succeeds on the main branch ? If not how should we allocate memory?
3. Is it necessary to test if each of the params fail/are invalid or would one of the following variables being invalid suffice
   EINVAL addr, size, prot, or pgoff is invalid. ?

[SchrodingerZhu]

1. I think u can use sysconf inside libc. It is already there in our codebase.

2. Using mmap is fine.

3. There is no need to exhaustively test kernel behaviors, and simple tests are fine.