[libc] Reapply ELF/LINK header changes (#102765)

This is based on @izaakschroeder previous patch but I only select macro
definitions for now. We need these definitions for VDSO work, which has
been delayed for a very long time.

Co-authored-by: Izaak Schroeder <izaak.schroeder@gmail.com>

libc/config/linux/aarch64/headers.txt

@@ -2,6 +2,7 @@ set(TARGET_PUBLIC_HEADERS
     libc.include.assert
     libc.include.ctype
     libc.include.dlfcn
+    libc.include.elf
     libc.include.errno
     libc.include.features
     libc.include.fenv
@@ -9,6 +10,7 @@ set(TARGET_PUBLIC_HEADERS
     libc.include.stdint
     libc.include.inttypes
     libc.include.limits
+    libc.include.link
     libc.include.math
     libc.include.pthread
     libc.include.signal

libc/config/linux/x86_64/headers.txt

@@ -3,6 +3,7 @@ set(TARGET_PUBLIC_HEADERS
     libc.include.ctype
     libc.include.dirent
     libc.include.dlfcn
+    libc.include.elf
     libc.include.errno
     libc.include.fcntl
     libc.include.features
@@ -11,6 +12,7 @@ set(TARGET_PUBLIC_HEADERS
     libc.include.stdint
     libc.include.inttypes
     libc.include.limits
+    libc.include.link
     libc.include.math
     libc.include.pthread
     libc.include.sched

libc/include/CMakeLists.txt

@@ -420,6 +420,23 @@ add_header_macro(
     .llvm-libc-types.posix_spawn_file_actions_t
 )
 
+add_gen_header(
+  link
+  DEF_FILE link.h.def
+  GEN_HDR link.h
+  DEPENDS
+    .llvm_libc_common_h
+    .llvm-libc-macros.link_macros
+)
+
+add_gen_header(
+  elf
+  DEF_FILE elf.h.def
+  GEN_HDR elf.h
+  DEPENDS
+    .llvm-libc-macros.elf_macros
+)
+
 # TODO: Not all platforms will have a include/sys directory. Add the sys
 # directory and the targets for sys/*.h files conditional to the OS requiring
 # them.

libc/include/elf.h.def

@@ -0,0 +1,17 @@
+//===-- System V header elf.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_ELF_H
+#define LLVM_LIBC_ELF_H
+
+#include "__llvm-libc-common.h"
+#include "llvm-libc-macros/elf-macros.h"
+
+%%public_api()
+
+#endif // LLVM_LIBC_ELF_H

libc/include/link.h.def

@@ -0,0 +1,17 @@
+//===-- GNU header link.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_LINK_H
+#define LLVM_LIBC_LINK_H
+
+#include "__llvm-libc-common.h"
+#include "llvm-libc-macros/link-macros.h"
+
+%%public_api()
+
+#endif // LLVM_LIBC_LINK_H

libc/include/llvm-libc-macros/CMakeLists.txt

@@ -289,3 +289,9 @@ add_macro_header(
   HDR
     dlfcn-macros.h
 )
+
+add_macro_header(
+  elf_macros
+  HDR
+    elf-macros.h
+)

libc/include/llvm-libc-macros/elf-macros.h

@@ -0,0 +1,18 @@
+//===-- Definition of macros from elf.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_ELF_MACROS_H
+#define LLVM_LIBC_MACROS_ELF_MACROS_H
+
+#if __has_include(<linux/elf.h>)
+#include <linux/elf.h>
+#else
+#error "cannot use <sys/elf.h> without proper system headers."
+#endif
+
+#endif // LLVM_LIBC_MACROS_ELF_MACROS_H

libc/include/llvm-libc-macros/link-macros.h

@@ -6,8 +6,15 @@
 //
 //===----------------------------------------------------------------------===//
 
+#ifndef LLVM_LIBC_MACROS_LINK_MACROS_H
+#define LLVM_LIBC_MACROS_LINK_MACROS_H
+
+#include "elf-macros.h"
+
 #ifdef __LP64__
-#define ElfW(type) Elf64_ ## type
+#define ElfW(type) Elf64_##type
 #else
-#define ElfW(type) Elf32_ ## type
+#define ElfW(type) Elf32_##type
+#endif
+
 #endif

libc/newhdrgen/yaml/elf.yaml

@@ -0,0 +1,8 @@
+header: elf.h
+standards:
+  - Linux
+macros: []
+types: []
+enums: []
+objects: []
+functions: []

libc/newhdrgen/yaml/link.yaml

@@ -0,0 +1,8 @@
+header: link.h
+standards:
+  - Linux
+macros: []
+types: []
+enums: []
+objects: []
+functions: []