[libc] Define (stub) dl_iterate_phdr (#131436)

This fleshes out the <link.h> a little more, including the
`struct dl_phdr_info` type and declaring the dl_iterate_phdr
function.  There is only a no-op implementation without tests, as
for the existing dlfcn functions.

Author: frobtech

libc/config/linux/aarch64/entrypoints.txt

@@ -842,6 +842,9 @@ if(LLVM_LIBC_FULL_BUILD)
     libc.src.arpa.inet.ntohl
     libc.src.arpa.inet.ntohs
 
+    # link.h entrypoints
+    libc.src.link.dl_iterate_phdr
+
     # pthread.h entrypoints
     libc.src.pthread.pthread_atfork
     libc.src.pthread.pthread_attr_destroy

libc/config/linux/riscv/entrypoints.txt

@@ -795,6 +795,9 @@ if(LLVM_LIBC_FULL_BUILD)
     libc.src.arpa.inet.ntohl
     libc.src.arpa.inet.ntohs
 
+    # link.h entrypoints
+    libc.src.link.dl_iterate_phdr
+
     # pthread.h entrypoints
     libc.src.pthread.pthread_atfork
     libc.src.pthread.pthread_attr_destroy

libc/config/linux/x86_64/entrypoints.txt

@@ -960,6 +960,9 @@ if(LLVM_LIBC_FULL_BUILD)
     libc.src.arpa.inet.ntohl
     libc.src.arpa.inet.ntohs
 
+    # link.h entrypoints
+    libc.src.link.dl_iterate_phdr
+
     # pthread.h entrypoints
     libc.src.pthread.pthread_atfork
     libc.src.pthread.pthread_attr_destroy

libc/hdr/types/CMakeLists.txt

@@ -9,6 +9,14 @@ add_proxy_header_library(
     libc.include.stdlib
 )
 
+add_proxy_header_library(
+  struct_dl_phdr_info
+  HDRS
+    struct_dl_phdr_info.h
+  FULL_BUILD_DEPENDS
+    libc.include.llvm-libc-types.struct_dl_phdr_info
+)
+
 add_proxy_header_library(
   ldiv_t
   HDRS

libc/hdr/types/struct_dl_phdr_info.h

@@ -0,0 +1,21 @@
+//===-- Proxy for struct dl_phdr_info  -----------------------------------===//
+//
+// 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_DL_PHDR_INFO_H
+#define LLVM_LIBC_HDR_TYPES_STRUCT_DL_PHDR_INFO_H
+
+#ifdef LIBC_FULL_BUILD
+
+#include "include/llvm-libc-types/struct_dl_phdr_info.h"
+
+#else
+
+#include <link.h>
+
+#endif // LIBC_FULL_BUILD
+
+#endif // LLVM_LIBC_HDR_TYPES_STRUCT_DL_PHDR_INFO_H

libc/include/CMakeLists.txt

@@ -431,6 +431,8 @@ add_header_macro(
   DEPENDS
     .llvm_libc_common_h
     .llvm-libc-macros.link_macros
+    .llvm-libc-types.struct_dl_phdr_info
+    .llvm-libc-types.__dl_iterate_phdr_callback_t
 )
 
 add_header_macro(

libc/include/link.h.def

@@ -1,9 +1,20 @@
 header: link.h
-header_template: link.h.def
 standards:
-  - Linux
-macros: []
-types: []
-enums: []
-objects: []
-functions: []
+  - svid
+macros:
+  - macro_name: ElfW
+    standards:
+      - gnu
+    macro_header: link-macros.h
+types:
+  - type_name: struct_dl_phdr_info
+    standards:
+      - gnu
+functions:
+  - name: dl_iterate_phdr
+    standards:
+      - gnu
+    return_type: int
+    arguments:
+      - type: __dl_iterate_phdr_callback_t
+      - type: void *

libc/include/link.yaml

@@ -5,6 +5,7 @@ add_header(__atfork_callback_t HDR __atfork_callback_t.h)
 add_header(__bsearchcompare_t HDR __bsearchcompare_t.h)
 add_header(__lsearchcompare_t HDR __lsearchcompare_t.h)
 add_header(__call_once_func_t HDR __call_once_func_t.h)
+add_header(__dl_iterate_phdr_callback_t HDR __dl_iterate_phdr_callback_t.h DEPENDS .size_t)
 add_header(__exec_argv_t HDR __exec_argv_t.h)
 add_header(__exec_envp_t HDR __exec_envp_t.h)
 add_header(__futex_word HDR __futex_word.h)
@@ -69,6 +70,7 @@ add_header(sighandler_t HDR sighandler_t.h)
 add_header(stack_t HDR stack_t.h DEPENDS .size_t)
 add_header(suseconds_t HDR suseconds_t.h)
 add_header(struct_dirent HDR struct_dirent.h DEPENDS .ino_t .off_t)
+add_header(struct_dl_phdr_info HDR struct_dl_phdr_info.h DEPENDS .size_t libc.include.llvm-libc-macros.link_macros)
 add_header(struct_f_owner_ex HDR struct_f_owner_ex.h DEPENDS .pid_t)
 add_header(struct_flock HDR struct_flock.h DEPENDS .off_t .pid_t)
 add_header(struct_flock64 HDR struct_flock64.h DEPENDS .off64_t .pid_t)

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

@@ -0,0 +1,19 @@
+//===-- Definition of type __dl_iterate_phdr_callback_t ------------------===//
+//
+// 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_TYPES___DL_ITERATE_PHDR_CALLBACK_T_H
+#define LLVM_LIBC_TYPES___DL_ITERATE_PHDR_CALLBACK_T_H
+
+#include "size_t.h"
+
+struct dl_phdr_info;
+
+typedef int (*__dl_iterate_phdr_callback_t)(struct dl_phdr_info *, size_t,
+                                            void *);
+
+#endif // LLVM_LIBC_TYPES___DL_ITERATE_PHDR_CALLBACK_T_H

libc/include/llvm-libc-types/__dl_iterate_phdr_callback_t.h

@@ -0,0 +1,30 @@
+//===-- Definition of type struct dl_phdr_info ---------------------------===//
+//
+// 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_TYPES_STRUCT_DL_PHDR_INFO_H
+#define LLVM_LIBC_TYPES_STRUCT_DL_PHDR_INFO_H
+
+#include "../llvm-libc-macros/link-macros.h"
+#include "size_t.h"
+#include <elf.h>
+#include <stdint.h>
+
+struct dl_phdr_info {
+  ElfW(Addr) dlpi_addr;
+  const char *dlpi_name;
+  const ElfW(Phdr) * dlpi_phdr;
+  ElfW(Half) dlpi_phnum;
+
+  uint64_t dlpi_adds;
+  uint64_t dlpi_subs;
+
+  size_t dlpi_tls_modid;
+  void *dlpi_tls_data;
+};
+
+#endif // LLVM_LIBC_TYPES_STRUCT_DL_PHDR_INFO_H

libc/include/llvm-libc-types/struct_dl_phdr_info.h

@@ -6,16 +6,17 @@ add_subdirectory(dlfcn)
 add_subdirectory(errno)
 add_subdirectory(fenv)
 add_subdirectory(inttypes)
+add_subdirectory(link)
 add_subdirectory(math)
 add_subdirectory(stdbit)
 add_subdirectory(stdfix)
 add_subdirectory(stdio)
 add_subdirectory(stdlib)
 add_subdirectory(string)
 add_subdirectory(strings)
-add_subdirectory(wchar)
 add_subdirectory(time)
 add_subdirectory(unistd)
+add_subdirectory(wchar)
 
 if(${LIBC_TARGET_OS} STREQUAL "linux")
   add_subdirectory(dirent)

libc/src/CMakeLists.txt

@@ -0,0 +1,7 @@
+add_entrypoint_object(
+  dl_iterate_phdr
+  SRCS
+    dl_iterate_phdr.cpp
+  HDRS
+    dl_iterate_phdr.h
+)

libc/src/link/CMakeLists.txt

@@ -0,0 +1,25 @@
+//===-- Implementation of dl_iterate_phdr --------------------------------===//
+//
+// 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
+//
+//===---------------------------------------------------------------------===//
+
+#include "dl_iterate_phdr.h"
+
+#include "src/__support/common.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(int, dl_iterate_phdr,
+                   (__dl_iterate_phdr_callback_t callback, void *arg)) {
+  // FIXME: For pure static linking, this can report just the executable with
+  // info from __ehdr_start or AT_{PHDR,PHNUM} decoding, and its PT_TLS; and it
+  // could report the vDSO.
+  (void)callback, (void)arg;
+  return 0;
+}
+
+} // namespace LIBC_NAMESPACE_DECL

libc/src/link/dl_iterate_phdr.cpp

@@ -0,0 +1,22 @@
+//===-- Implementation header of dl_iterate_phdr ---------------*- C++ -*-===//
+//
+// 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_SRC_DLFCN_DL_ITERATE_PHDR_H
+#define LLVM_LIBC_SRC_DLFCN_DL_ITERATE_PHDR_H
+
+#include "hdr/types/struct_dl_phdr_info.h"
+#include "include/llvm-libc-types/__dl_iterate_phdr_callback_t.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+int dl_iterate_phdr(__dl_iterate_phdr_callback_t, void *);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_DLFCN_DL_ITERATE_PHDR_H

libc/src/link/dl_iterate_phdr.h

@@ -44,6 +44,7 @@
     "gnu": "GNU",
     "linux": "Linux",
     "uefi": "UEFI",
+    "svid": "SVID",
 }
 
 HEADER_TEMPLATE = """\