[libc] Add the `<endian.h>` header. #125168

c8ef · 2025-01-31T05:03:13Z

Closes #124631.
ref: https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/endian.h.html

This patch adds the implementation of endian.h, which includes the header itself and three related macros. These macros in the header rely on the compiler preprocessor, similar to how https://github.com/llvm/llvm-project/blob/main/libc/src/__support/endian_internal.h does. Hopefully this will meet the requirements for compiling llvm with llvm-libc.

llvmbot · 2025-01-31T05:36:07Z

@llvm/pr-subscribers-libc

Author: None (c8ef)

Changes

Closes #124631.
ref: https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/endian.h.html

This patch adds the implementation of endian.h, which includes the header itself and three related macros. These macros in the header rely on the compiler preprocessor, similar to how https://github.com/llvm/llvm-project/blob/main/libc/src/__support/endian_internal.h does. Hopefully this will meet the requirements for compiling llvm with llvm-libc.

Full diff: https://github.com/llvm/llvm-project/pull/125168.diff

7 Files Affected:

(modified) libc/config/linux/aarch64/headers.txt (+1)
(modified) libc/config/linux/x86_64/headers.txt (+1)
(modified) libc/include/CMakeLists.txt (+9)
(added) libc/include/endian.h.def (+17)
(added) libc/include/endian.yaml (+9)
(modified) libc/include/llvm-libc-macros/CMakeLists.txt (+6)
(added) libc/include/llvm-libc-macros/endian-macros.h (+16)

diff --git a/libc/config/linux/aarch64/headers.txt b/libc/config/linux/aarch64/headers.txt
index 05f15a0e4e5cbb..7ff55899805508 100644
--- a/libc/config/linux/aarch64/headers.txt
+++ b/libc/config/linux/aarch64/headers.txt
@@ -4,6 +4,7 @@ set(TARGET_PUBLIC_HEADERS
     libc.include.ctype
     libc.include.dlfcn
     libc.include.elf
+    libc.include.endian
     libc.include.errno
     libc.include.features
     libc.include.fenv
diff --git a/libc/config/linux/x86_64/headers.txt b/libc/config/linux/x86_64/headers.txt
index 8750100302ea7e..fe1fd596960dd3 100644
--- a/libc/config/linux/x86_64/headers.txt
+++ b/libc/config/linux/x86_64/headers.txt
@@ -5,6 +5,7 @@ set(TARGET_PUBLIC_HEADERS
     libc.include.dirent
     libc.include.dlfcn
     libc.include.elf
+    libc.include.endian
     libc.include.errno
     libc.include.fcntl
     libc.include.features
diff --git a/libc/include/CMakeLists.txt b/libc/include/CMakeLists.txt
index e5ceea360d3965..96d715cde9de9d 100644
--- a/libc/include/CMakeLists.txt
+++ b/libc/include/CMakeLists.txt
@@ -73,6 +73,15 @@ add_header_macro(
     .llvm_libc_common_h
 )
 
+add_header_macro(
+  endian
+  ../libc/include/endian.yaml
+  endian.h
+  DEPENDS
+    .llvm-libc-macros.endian_macros
+    .llvm_libc_common_h
+)
+
 add_header_macro(
   features
   ../libc/include/features.yaml
diff --git a/libc/include/endian.h.def b/libc/include/endian.h.def
new file mode 100644
index 00000000000000..8448d93a86acc3
--- /dev/null
+++ b/libc/include/endian.h.def
@@ -0,0 +1,17 @@
+//===-- System V header endian.h ------------------------------------------===//
+//
+// 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_ENDIAN_H
+#define LLVM_LIBC_ENDIAN_H
+
+#include "__llvm-libc-common.h"
+#include "llvm-libc-macros/endian-macros.h"
+
+%%public_api()
+
+#endif // LLVM_LIBC_ENDIAN_H
diff --git a/libc/include/endian.yaml b/libc/include/endian.yaml
new file mode 100644
index 00000000000000..6497f897b63933
--- /dev/null
+++ b/libc/include/endian.yaml
@@ -0,0 +1,9 @@
+header: endian.h
+header_template: endian.h.def
+standards:
+  - POSIX
+macros: []
+types: []
+enums: []
+objects: []
+functions: []
diff --git a/libc/include/llvm-libc-macros/CMakeLists.txt b/libc/include/llvm-libc-macros/CMakeLists.txt
index 9d5d9f65442889..d165ada6612c84 100644
--- a/libc/include/llvm-libc-macros/CMakeLists.txt
+++ b/libc/include/llvm-libc-macros/CMakeLists.txt
@@ -310,6 +310,12 @@ add_macro_header(
     elf-macros.h
 )
 
+add_macro_header(
+  endian_macros
+  HDR
+    endian-macros.h
+)
+
 add_macro_header(
   locale_macros
   HDR
diff --git a/libc/include/llvm-libc-macros/endian-macros.h b/libc/include/llvm-libc-macros/endian-macros.h
new file mode 100644
index 00000000000000..94e1d60f8ff404
--- /dev/null
+++ b/libc/include/llvm-libc-macros/endian-macros.h
@@ -0,0 +1,16 @@
+//===-- Definition of macros from endian.h --------------------------------===//
+//
+// 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_MACROS_ENDIAN_MACROS_H
+#define LLVM_LIBC_MACROS_ENDIAN_MACROS_H
+
+#define LITTLE_ENDIAN __ORDER_LITTLE_ENDIAN__
+#define BIG_ENDIAN __ORDER_BIG_ENDIAN__
+#define BYTE_ORDER __BYTE_ORDER__
+
+#endif // LLVM_LIBC_MACROS_ENDIAN_MACROS_H

c8ef · 2025-02-04T05:53:50Z

Friendly ping!

libc/include/endian.yaml

nickdesaulniers

While you're here, do you mind wiring up docgen so we generate documentation for this newly added header? d398c0c is a good example.

c8ef · 2025-02-05T14:01:28Z

While you're here, do you mind wiring up docgen so we generate documentation for this newly added header? d398c0c is a good example.

Thank you for your guidance! Done.

nickdesaulniers · 2025-02-05T17:48:05Z

libc/utils/docgen/endian.yaml

+    in-latest-posix: ''
+  BYTE_ORDER:
+    in-latest-posix: ''
+


Do you mind stubbing out the rest of the functions listed at https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/endian.h.html? Otherwise, we will render a doc where it looks like our implementation of endian.h is complete; it's not, since we don't have the functions defined. That way, folks know what to expect, and can find more places to contribute.

Done.

I added these as macros because glibc, musl, and FreeBSD all implement them as macros. According to the POSIX standard, they can be either functions or macros.

I would like to implement these in following patches : )

SGTM; thanks! I wonder what happens if someone needs to link against them as strong symbols...

Closes [llvm#124631](llvm#124631). ref: https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/endian.h.html This patch adds the implementation of `endian.h`, which includes the header itself and three related macros. These macros in the header rely on the compiler preprocessor, similar to how https://github.com/llvm/llvm-project/blob/main/libc/src/__support/endian_internal.h does. Hopefully this will meet the requirements for compiling llvm with llvm-libc.

Follow up of #125168. This patch adds endian-related macros to `endian.h`. We utilize compiler built-ins for byte swap functions, which are already included in our minimal supported compiler version.

Follow up of llvm#125168. This patch adds endian-related macros to `endian.h`. We utilize compiler built-ins for byte swap functions, which are already included in our minimal supported compiler version.

add endian

b3630d6

c8ef changed the title ~~Draft~~ [libc] Add the <endian.h> header. Jan 31, 2025

c8ef marked this pull request as ready for review January 31, 2025 05:35

llvmbot added the libc label Jan 31, 2025

c8ef requested review from nickdesaulniers, SchrodingerZhu, jhuber6 and michaelrj-google January 31, 2025 05:35

treat it as POSIX header, NFC

5650441

RossComputerGuy reviewed Feb 4, 2025

View reviewed changes

libc/include/endian.yaml Show resolved Hide resolved

nickdesaulniers reviewed Feb 4, 2025

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add doc for endian

5fcc927

c8ef requested a review from nickdesaulniers February 5, 2025 14:59

nickdesaulniers reviewed Feb 5, 2025

View reviewed changes

nickdesaulniers mentioned this pull request Feb 5, 2025

[libc] provide sysexits.h #124640

Open

address review comments

2cfed7c

c8ef requested a review from nickdesaulniers February 6, 2025 14:57

nickdesaulniers approved these changes Feb 6, 2025

View reviewed changes

c8ef merged commit 6807164 into llvm:main Feb 7, 2025
15 checks passed

c8ef deleted the endian branch February 7, 2025 01:20

c8ef mentioned this pull request Feb 8, 2025

[libc] implement endian related macros #126368

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[libc] Add the `<endian.h>` header. #125168

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