[libc] implement sys/uio/writev (#122233)

implement sys/uio/writev according to POSIX standard. This vectorized IO
API is needed by many logging libraries to achieve atomic logging
multiple strings.

Author: SchrodingerZhu

libc/config/linux/aarch64/entrypoints.txt

@@ -350,6 +350,9 @@ set(TARGET_LIBC_ENTRYPOINTS
 
     # wchar.h entrypoints
     libc.src.wchar.wctob
+
+    # sys/uio.h entrypoints
+    libc.src.sys.uio.writev
 )
 
 if(LLVM_LIBC_INCLUDE_SCUDO)

libc/config/linux/x86_64/entrypoints.txt

@@ -350,6 +350,9 @@ set(TARGET_LIBC_ENTRYPOINTS
     # wchar.h entrypoints
     libc.src.wchar.wctob
     libc.src.wchar.btowc
+
+    # sys/uio.h entrypoints
+    libc.src.sys.uio.writev
 )
 
 if(LLVM_LIBC_INCLUDE_SCUDO)

libc/hdr/types/CMakeLists.txt

@@ -333,3 +333,12 @@ add_proxy_header_library(
   FULL_BUILD_DEPENDS
     libc.include.llvm-libc-types.uid_t
 )
+
+add_proxy_header_library(
+  struct_iovec
+  HDRS
+    struct_iovec.h
+  FULL_BUILD_DEPENDS
+    libc.include.llvm-libc-types.struct_iovec
+    libc.include.sys_uio
+)

libc/hdr/types/struct_iovec.h

@@ -0,0 +1,21 @@
+//===-- Proxy for struct iovec  -------------------------------------------===//
+//
+// 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_HDR_TYPES_STRUCT_IOVEC_H
+#define LLVM_LIBC_HDR_TYPES_STRUCT_IOVEC_H
+
+#ifdef LIBC_FULL_BUILD
+
+#include "include/llvm-libc-types/struct_iovec.h"
+
+#else
+
+#include <sys/uio.h>
+
+#endif // LIBC_FULL_BUILD
+
+#endif // LLVM_LIBC_HDR_TYPES_STRUCT_IOVEC_H

libc/include/CMakeLists.txt

@@ -632,6 +632,16 @@ add_header_macro(
     .llvm-libc-types.struct_utsname
 )
 
+add_header_macro(
+  sys_uio
+  ../libc/include/sys/uio.yaml
+  sys/uio.h
+  DEPENDS
+    .llvm_libc_common_h
+    .llvm-libc-types.struct_iovec
+    .llvm-libc-types.ssize_t
+)
+
 add_header_macro(
   sys_wait
   ../libc/include/sys/wait.yaml

libc/include/sys/uio.h.def

@@ -0,0 +1,16 @@
+//===-- POSIX header uio.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_SYS_UIO_H
+#define LLVM_LIBC_SYS_UIO_H
+
+#include "__llvm-libc-common.h"
+
+%%public_api()
+
+#endif // LLVM_LIBC_SYS_UIO_H

libc/include/sys/uio.yaml

@@ -0,0 +1,17 @@
+header: sys/uio.h
+header_template: uio.h.def
+macros: []
+types: 
+  - type_name: struct_iovec
+  - type_name: ssize_t
+enums: []
+objects: []
+functions:
+  - name: writev
+    standards:
+      - POSIX
+    return_type: ssize_t
+    arguments:
+      - type: int
+      - type: const struct iovec *
+      - type: int

libc/src/sys/CMakeLists.txt

@@ -11,3 +11,4 @@ add_subdirectory(statvfs)
 add_subdirectory(utsname)
 add_subdirectory(wait)
 add_subdirectory(prctl)
+add_subdirectory(uio)

libc/src/sys/uio/CMakeLists.txt

@@ -0,0 +1,10 @@
+if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
+  add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
+endif()
+
+add_entrypoint_object(
+  writev
+  ALIAS
+  DEPENDS
+    .${LIBC_TARGET_OS}.writev
+)

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

@@ -0,0 +1,14 @@
+add_entrypoint_object(
+  writev
+  SRCS
+    writev.cpp
+  HDRS
+    ../writev.h
+  DEPENDS
+    libc.include.sys_syscall
+    libc.src.__support.OSUtil.osutil
+    libc.src.__support.common
+    libc.src.errno.errno
+    libc.hdr.types.ssize_t
+    libc.hdr.types.struct_iovec
+)