llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT--> @llvm/pr-subscribers-clang Author: Aaron Ballman (AaronBallman) <details> <summary>Changes</summary> This adds some initial documentation about freestanding requirements for Clang. The most critical part of the documentation is spelling out that a conforming freestanding C Standard Library is required; Clang will not be providing the headers for <string.h> in C23 which expose a number of symbols in freestanding mode. The docs also make it clear that in addition to a conforming freestanding C standard library, the library must provide some additional symbols which LLVM requires. These docs are not comprehensive, this is just getting the bare bones in place so that they can be expanded later. This also updates the C status page to make it clear that we don't have anything to do for WG14 N2524 which adds string interfaces to freestanding mode. --- Full diff: https://github.com/llvm/llvm-project/pull/132232.diff 3 Files Affected: - (modified) clang/docs/CommandGuide/clang.rst (+4-3) - (modified) clang/docs/UsersManual.rst (+24) - (modified) clang/www/c_status.html (-5) ``````````diff diff --git a/clang/docs/CommandGuide/clang.rst b/clang/docs/CommandGuide/clang.rst index f0d94a4e628b0..dfe28fc5d2bcb 100644 --- a/clang/docs/CommandGuide/clang.rst +++ b/clang/docs/CommandGuide/clang.rst @@ -262,9 +262,10 @@ Language Selection and Mode Options .. option:: -ffreestanding Indicate that the file should be compiled for a freestanding, not a hosted, - environment. Note that it is assumed that a freestanding environment will - additionally provide `memcpy`, `memmove`, `memset` and `memcmp` - implementations, as these are needed for efficient codegen for many programs. + environment. Note that a freestanding build still requires linking against a C + Standard Library which supports the freestanding interfaces for the specified + language mode and target environment. This includes functions like `memcpy`, + `memmove`, `memset` and `memcmp`. .. option:: -fno-builtin diff --git a/clang/docs/UsersManual.rst b/clang/docs/UsersManual.rst index 2ea4b9d90ad34..d73e8eb78dbf6 100644 --- a/clang/docs/UsersManual.rst +++ b/clang/docs/UsersManual.rst @@ -1073,6 +1073,30 @@ inputs. Here is some example of ``$``-prefixed options: Language and Target-Independent Features ======================================== +Freestanding Builds +------------------- +Passing the ``-ffreestanding`` flag causes Clang to build for a freestanding +(rather than a hosted) environment. The ``__STDC_HOSTED__`` predefined macro +will expand to ``0`` in a freestanding environment. In such an environment, +execution of the program may happen without an operating system and so a +startup function (e.g., ``main``) may not be automatically called, though file +scope objects which need to run startup code (constructors in C++, +``__attribute__((constructor))``, etc) are executed via implementation-defined +means such as ``__cxx_global_var_init``. + +A freestanding environment is not one which has no C standard library support. +A conforming freestanding C standard library implementation is required. Clang +supplies some of the header files needed for a freestanding execution, such as +``<stdarg.h>``, ``<limits.h>``, ``<stdint.h>``, etc. However, Clang still +requires the runtime freestanding library to provide the interfaces required by +Clause 4 (Conformance) of the C standard. Additionally, Clang requires the +following runtime interfaces to be provided: + + * `memcpy`, + * `memmove`, + * `memset`, and + * `memcmp`. + Controlling Errors and Warnings ------------------------------- diff --git a/clang/www/c_status.html b/clang/www/c_status.html index c9e2eda4304f3..ee0cd057916ba 100644 --- a/clang/www/c_status.html +++ b/clang/www/c_status.html @@ -534,11 +534,6 @@ <h2 id="c2x">C23 implementation status</h2> <td class="full" align="center">Clang 16</td> </tr> <!-- Apr 2021 Papers --> - <tr> - <td>String functions for freestanding implementations</td> - <td><a href="https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2524.htm";>N2524</a></td> - <td class="none" align="center">No</td> - </tr> <tr> <td>Digit separators</td> <td><a href="https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2626.pdf";>N2626</a></td> `````````` </details> https://github.com/llvm/llvm-project/pull/132232 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
