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0e6d10de1c
Replace traditional `#ifndef`/`#define`/`#endif` include guards with
`#pragma` once.
`#pragma once` is a widely supported preprocessor directive that
prevents header files from being included multiple times. It is
supported by all toolchains used to build edk2: GCC, Clang/LLVM, and
MSVC.
Note: Some files in BaseTools are excluded from the change if they
are autogenerated or direcly related to a header from a subproject,
etc. In particular, headers in these directories were ignored:
- BaseTools/Source/C/LzmaCompress/Sdk/
- BaseTools/Source/C/VfrCompile/Pccts/
Compared to macro-based include guards, `#pragma once`:
- Eliminates the risk of macro name collisions or copy/paste errors
where two headers inadvertently use the same guard macro.
- Eliminate inconsistency in the way include guard macros are named
(e.g., some files use `__FILE_H__`, others use `FILE_H_`, etc.).
- Reduces boilerplate (three lines replaced by one).
- Avoids polluting the macro namespace with guard symbols.
- Can improve build times as the preprocessor can skip re-opening the
file entirely, rather than re-reading it to find the matching
`#endif` ("multiple-include optimization").
- Note that some compilers may already optimize traditional include
guards, by recognzining the idiomatic pattern.
This change is made acknowledging that overall portability of the
code will technically be reduced, as `#pragma once` is not part of the
C/C++ standards.
However, this is considered acceptable given:
1. edk2 already defines a subset of supported compilers in
BaseTools/Conf/tools_def.template, all of which have supported
`#pragma once` for over two decades.
2. There have been concerns raised to the project about inconsistent
include guard naming and potential macro collisions.
Approximate compiler support dates:
- MSVC: Supported since Visual C++ 4.2 (1996)
- GCC: Supported since 3.4 (2004)
(http://gnu.ist.utl.pt/software/gcc/gcc-3.4/changes.html)
- Clang (LLVM based): Since initial release in 2007
Signed-off-by: Michael Kubacki <michael.kubacki@microsoft.com>
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| .. | ||
| Bin | ||
| BinWrappers | ||
| Conf | ||
| Plugin | ||
| Scripts | ||
| Source | ||
| Tests | ||
| UserManuals | ||
| .gitignore | ||
| basetools_calling_path_env.yaml | ||
| basetools_path_env.yaml | ||
| BuildEnv | ||
| Edk2ToolsBuild.py | ||
| get_vsvars.bat | ||
| GNUmakefile | ||
| Makefile | ||
| ReadMe.rst | ||
| set_vsprefix_envs.bat | ||
| toolsetup.bat | ||
:: Note: New build instructions are available. It is recommended to start with the new instructions if learning how to build edk2 and/or BaseTools for the first time. This page is retained for reference. New instructions: `Build Instructions`_ .. _`Build Instructions`: https://github.com/tianocore/tianocore.github.io/wiki/Build-Instructions This directory contains the EDK II build tools and template files. Templates are located in the Conf directory, while the tools executables for Microsoft Windows Operating Systems are located in the Bin\\Win32 directory, other directory contains tools source. Build step to generate the binary tools --------------------------------------- Windows/Visual Studio Notes =========================== To build the BaseTools, you should run the standard vsvars32.bat script from your preferred Visual Studio installation or you can run get_vsvars.bat to use latest automatically detected version. In addition to this, you should set the following environment variables:: * EDK_TOOLS_PATH - Path to the BaseTools sub directory under the edk2 tree * BASE_TOOLS_PATH - The directory where the BaseTools source is located. (It is the same directory where this README.rst is located.) After this, you can run the toolsetup.bat file, which is in the same directory as this file. It should setup the remainder of the environment, and build the tools if necessary. Unix-like operating systems =========================== To build on Unix-like operating systems, you only need to type ``make`` in the base directory of the project. Ubuntu Notes ============ On Ubuntu, the following command should install all the necessary build packages to build all the C BaseTools:: sudo apt install build-essential uuid-dev