diff --git a/llvm/docs/CommandGuide/llvm-objcopy.rst b/llvm/docs/CommandGuide/llvm-objcopy.rst
--- a/llvm/docs/CommandGuide/llvm-objcopy.rst
+++ b/llvm/docs/CommandGuide/llvm-objcopy.rst
@@ -217,6 +217,12 @@
  Remove from the output all local or undefined symbols that are not required by
  relocations. Also remove all debug sections.
 
+.. option:: --update-section <name>=<file>
+
+ Replace the contents of the section ``<name>`` with contents from the file
+ ``<file>``. If the section ``<name>`` is part of a segment, the new contents
+ cannot be larger than the existing section.
+
 .. option:: --version, -V
 
  Display the version of the :program:`llvm-objcopy` executable.
diff --git a/llvm/tools/llvm-objcopy/ObjcopyOpts.td b/llvm/tools/llvm-objcopy/ObjcopyOpts.td
--- a/llvm/tools/llvm-objcopy/ObjcopyOpts.td
+++ b/llvm/tools/llvm-objcopy/ObjcopyOpts.td
@@ -222,5 +222,5 @@
       MetaVarName<"name=[section:]value[,flags]">;
 
 defm update_section
-    : Eq<"update-section", "Add section <name> with contents from a file <file>.">,
+    : Eq<"update-section", "Replace the contents of section <name> with contents from a file <file>.">,
       MetaVarName<"name=file">;