[libc] Add dlfcn.h placeholder

libc/config/linux/aarch64/entrypoints.txt

@@ -17,6 +17,12 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.ctype.tolower
     libc.src.ctype.toupper
 
+    # dlfcn.h entrypoints
+    libc.src.dlfcn.dlclose
+    libc.src.dlfcn.dlerror
+    libc.src.dlfcn.dlopen
+    libc.src.dlfcn.dlsym
+
     # errno.h entrypoints
     libc.src.errno.errno
 

libc/config/linux/x86_64/entrypoints.txt

@@ -17,6 +17,12 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.ctype.tolower
     libc.src.ctype.toupper
 
+    # dlfcn.h entrypoints
+    libc.src.dlfcn.dlclose
+    libc.src.dlfcn.dlerror
+    libc.src.dlfcn.dlopen
+    libc.src.dlfcn.dlsym
+
     # errno.h entrypoints
     libc.src.errno.errno
 

libc/docs/dev/undefined_behavior.rst

@@ -89,3 +89,7 @@ The C23 standard states that if the value of the ``rnd`` argument of the
 the value of a math rounding direction macro, the direction of rounding is
 unspecified. LLVM's libc chooses to use the ``FP_INT_TONEAREST`` rounding
 direction in this case.
+
+Non-const Constant Return Values
+--------------------------------
+Some libc functions, like ``dlerror()``, return ``char *`` instead of ``const char *`` and then tell the caller they promise not to to modify this value. Any modification of this value is undefined behavior.

libc/spec/posix.td

@@ -222,6 +222,40 @@ def POSIX : StandardSpec<"POSIX"> {
       []  // Functions
   >;
 
+  HeaderSpec DlFcn = HeaderSpec<
+    "dlfcn.h",
+    [
+      Macro<"RTLD_LAZY">,
+      Macro<"RTLD_NOW">,
+      Macro<"RTLD_GLOBAL">,
+      Macro<"RTLD_LOCAL">,
+    ],
+    [],  // Types
+    [], // Enumerations
+    [
+      FunctionSpec<
+          "dlclose",
+          RetValSpec<IntType>,
+          [ArgSpec<VoidPtr>]
+      >,
+      FunctionSpec<
+          "dlerror",
+          RetValSpec<CharPtr>,
+          []
+      >,
+      FunctionSpec<
+          "dlopen",
+          RetValSpec<VoidPtr>,
+          [ArgSpec<ConstCharPtr>, ArgSpec<IntType>]
+      >,
+      FunctionSpec<
+          "dlsym",
+          RetValSpec<VoidPtr>,
+          [ArgSpec<VoidRestrictedPtr>, ArgSpec<ConstCharRestrictedPtr>]
+      >,
+    ]
+  >;
+
   HeaderSpec FCntl = HeaderSpec<
     "fcntl.h",
     [], // Macros
@@ -1690,6 +1724,7 @@ def POSIX : StandardSpec<"POSIX"> {
     ArpaInet,
     CType,
     Dirent,
+    DlFcn,
     Errno,
     FCntl,
     PThread,

libc/src/CMakeLists.txt

@@ -1,6 +1,7 @@
 add_subdirectory(__support)
 
 add_subdirectory(ctype)
+add_subdirectory(dlfcn)
 add_subdirectory(errno)
 add_subdirectory(fenv)
 add_subdirectory(inttypes)

libc/src/dlfcn/CMakeLists.txt

@@ -0,0 +1,40 @@
+add_entrypoint_object(
+  dlclose
+  SRCS
+    dlclose.cpp
+  HDRS
+    dlclose.h
+)
+
+add_entrypoint_object(
+  dlerror
+  SRCS
+    dlerror.cpp
+  HDRS
+    dlerror.h
+  DEPENDS
+    libc.include.dlfcn
+    libc.src.errno.errno
+)
+
+add_entrypoint_object(
+  dlopen
+  SRCS
+    dlopen.cpp
+  HDRS
+    dlopen.h
+  DEPENDS
+    libc.include.dlfcn
+    libc.src.errno.errno
+)
+
+add_entrypoint_object(
+  dlsym
+  SRCS
+    dlsym.cpp
+  HDRS
+    dlsym.h
+  DEPENDS
+    libc.include.dlfcn
+    libc.src.errno.errno
+)

libc/src/dlfcn/dlclose.cpp

@@ -0,0 +1,18 @@
+//===-- Implementation of dlclose -----------------------------------------===//
+//
+// 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 "dlclose.h"
+
+#include "src/__support/common.h"
+
+namespace LIBC_NAMESPACE {
+
+// TODO(@izaakschroeder): https://github.com/llvm/llvm-project/issues/97917
+LLVM_LIBC_FUNCTION(int, dlclose, (void *)) { return -1; }
+
+} // namespace LIBC_NAMESPACE

libc/src/dlfcn/dlclose.h

@@ -0,0 +1,18 @@
+//===-- Implementation header of dlclose ------------------------*- 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_DLCLOSE_H
+#define LLVM_LIBC_SRC_DLFCN_DLCLOSE_H
+
+namespace LIBC_NAMESPACE {
+
+int dlclose(void *);
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_DLFCN_DLCLOSE_H

libc/src/dlfcn/dlerror.cpp

@@ -0,0 +1,20 @@
+//===-- Implementation of delerror ----------------------------------------===//
+//
+// 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 "dlerror.h"
+
+#include "src/__support/common.h"
+
+namespace LIBC_NAMESPACE {
+
+// TODO(@izaakschroeder): https://github.com/llvm/llvm-project/issues/97918
+LLVM_LIBC_FUNCTION(char *, dlerror, ()) {
+  return const_cast<char *>("unsupported");
+}
+
+} // namespace LIBC_NAMESPACE

libc/src/dlfcn/dlerror.h

@@ -0,0 +1,18 @@
+//===-- Implementation header of dlerror ------------------------*- 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_DLERROR_H
+#define LLVM_LIBC_SRC_DLFCN_DLERROR_H
+
+namespace LIBC_NAMESPACE {
+
+char *dlerror();
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_DLFCN_DLERROR_H

libc/src/dlfcn/dlopen.cpp

@@ -0,0 +1,18 @@
+//===-- Implementation of dlopen -----------------------------------------===//
+//
+// 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 "dlopen.h"
+
+#include "src/__support/common.h"
+
+namespace LIBC_NAMESPACE {
+
+// TODO(@izaakschroeder): https://github.com/llvm/llvm-project/issues/97919
+LLVM_LIBC_FUNCTION(void *, dlopen, (const char *, int)) { return nullptr; }
+
+} // namespace LIBC_NAMESPACE

libc/src/dlfcn/dlopen.h

@@ -0,0 +1,18 @@
+//===-- Implementation header of dlopen -------------------------*- 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_DLOPEN_H
+#define LLVM_LIBC_SRC_DLFCN_DLOPEN_H
+
+namespace LIBC_NAMESPACE {
+
+void *dlopen(const char *, int);
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_DLFCN_DLOPEN_H

libc/src/dlfcn/dlsym.cpp

@@ -0,0 +1,18 @@
+//===-- Implementation of dlsym ------------------------------------------===//
+//
+// 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 "dlsym.h"
+
+#include "src/__support/common.h"
+
+namespace LIBC_NAMESPACE {
+
+// TODO(@izaakschroeder): https://github.com/llvm/llvm-project/issues/97920
+LLVM_LIBC_FUNCTION(void *, dlsym, (void *, const char *)) { return nullptr; }
+
+} // namespace LIBC_NAMESPACE

libc/src/dlfcn/dlsym.h

@@ -0,0 +1,18 @@
+//===-- Implementation header of dlsym --------------------------*- 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_DLSYM_H
+#define LLVM_LIBC_SRC_DLFCN_DLSYM_H
+
+namespace LIBC_NAMESPACE {
+
+void *dlsym(void *, const char *);
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_DLFCN_DLSYM_H