diff --git a/lld/ELF/Config.h b/lld/ELF/Config.h
--- a/lld/ELF/Config.h
+++ b/lld/ELF/Config.h
@@ -127,6 +127,7 @@
   llvm::StringRef sysroot;
   llvm::StringRef thinLTOCacheDir;
   llvm::StringRef thinLTOIndexOnlyArg;
+  llvm::StringRef whyExtract;
   llvm::StringRef ltoBasicBlockSections;
   std::pair<llvm::StringRef, llvm::StringRef> thinLTOObjectSuffixReplace;
   std::pair<llvm::StringRef, llvm::StringRef> thinLTOPrefixReplace;
diff --git a/lld/ELF/Driver.cpp b/lld/ELF/Driver.cpp
--- a/lld/ELF/Driver.cpp
+++ b/lld/ELF/Driver.cpp
@@ -94,6 +94,7 @@
     objectFiles.clear();
     sharedFiles.clear();
     backwardReferences.clear();
+    whyExtract.clear();
 
     tar = nullptr;
     memset(&in, 0, sizeof(in));
@@ -1171,6 +1172,7 @@
   config->warnCommon = args.hasFlag(OPT_warn_common, OPT_no_warn_common, false);
   config->warnSymbolOrdering =
       args.hasFlag(OPT_warn_symbol_ordering, OPT_no_warn_symbol_ordering, true);
+  config->whyExtract = args.getLastArgValue(OPT_why_extract);
   config->zCombreloc = getZFlag(args, "combreloc", "nocombreloc", true);
   config->zCopyreloc = getZFlag(args, "copyreloc", "nocopyreloc", true);
   config->zForceBti = hasZOption(args, "force-bti");
@@ -1694,13 +1696,16 @@
 }
 
 // Force Sym to be entered in the output.
-static void handleUndefined(Symbol *sym) {
+static void handleUndefined(Symbol *sym, const char *option) {
   // Since a symbol may not be used inside the program, LTO may
   // eliminate it. Mark the symbol as "used" to prevent it.
   sym->isUsedInRegularObj = true;
 
-  if (sym->isLazy())
-    sym->fetch();
+  if (!sym->isLazy())
+    return;
+  sym->fetch();
+  if (!config->whyExtract.empty())
+    whyExtract.emplace_back(option, sym->file, *sym);
 }
 
 // As an extension to GNU linkers, lld supports a variant of `-u`
@@ -1723,7 +1728,7 @@
   }
 
   for (Symbol *sym : syms)
-    handleUndefined(sym);
+    handleUndefined(sym, "--undefined-glob");
 }
 
 static void handleLibcall(StringRef name) {
@@ -2244,7 +2249,7 @@
 
   // If an entry symbol is in a static archive, pull out that file now.
   if (Symbol *sym = symtab->find(config->entry))
-    handleUndefined(sym);
+    handleUndefined(sym, "--entry");
 
   // Handle the `--undefined-glob <pattern>` options.
   for (StringRef pat : args::getStrings(args, OPT_undefined_glob))
diff --git a/lld/ELF/MapFile.h b/lld/ELF/MapFile.h
--- a/lld/ELF/MapFile.h
+++ b/lld/ELF/MapFile.h
@@ -12,6 +12,7 @@
 namespace lld {
 namespace elf {
 void writeMapFile();
+void writeWhyExtract();
 void writeCrossReferenceTable();
 void writeArchiveStats();
 } // namespace elf
diff --git a/lld/ELF/MapFile.cpp b/lld/ELF/MapFile.cpp
--- a/lld/ELF/MapFile.cpp
+++ b/lld/ELF/MapFile.cpp
@@ -215,6 +215,25 @@
   }
 }
 
+void elf::writeWhyExtract() {
+  if (config->whyExtract.empty())
+    return;
+
+  std::error_code ec;
+  raw_fd_ostream os(config->whyExtract, ec, sys::fs::OF_None);
+  if (ec) {
+    error("--why-extract=: cannot open " + config->whyExtract + ": " +
+          ec.message());
+    return;
+  }
+
+  os << "reference\textracted\tsymbol\n";
+  for (auto &entry : whyExtract) {
+    os << std::get<0>(entry) << '\t' << toString(std::get<1>(entry)) << '\t'
+       << toString(std::get<2>(entry)) << '\n';
+  }
+}
+
 static void print(StringRef a, StringRef b) {
   lld::outs() << left_justify(a, 49) << " " << b << "\n";
 }
diff --git a/lld/ELF/Options.td b/lld/ELF/Options.td
--- a/lld/ELF/Options.td
+++ b/lld/ELF/Options.td
@@ -492,6 +492,8 @@
     "Force load of all members in a static library",
     "Do not force load of all members in a static library (default)">;
 
+def why_extract: JJ<"why-extract=">, HelpText<"Print to a file about why archive members are extracted">;
+
 defm wrap : Eq<"wrap", "Redirect symbol references to __wrap_symbol and "
                        "__real_symbol references to symbol">,
             MetaVarName<"<symbol>">;
diff --git a/lld/ELF/Symbols.h b/lld/ELF/Symbols.h
--- a/lld/ELF/Symbols.h
+++ b/lld/ELF/Symbols.h
@@ -20,6 +20,7 @@
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/Object/Archive.h"
 #include "llvm/Object/ELF.h"
+#include <tuple>
 
 namespace lld {
 // Returns a string representation for a symbol for diagnostics.
@@ -582,6 +583,11 @@
                       std::pair<const InputFile *, const InputFile *>>
     backwardReferences;
 
+// A tuple of (reference, extractedFile, sym). Used by --why-extract=.
+extern SmallVector<std::tuple<std::string, const InputFile *, const Symbol &>,
+                   0>
+    whyExtract;
+
 } // namespace elf
 } // namespace lld
 
diff --git a/lld/ELF/Symbols.cpp b/lld/ELF/Symbols.cpp
--- a/lld/ELF/Symbols.cpp
+++ b/lld/ELF/Symbols.cpp
@@ -64,6 +64,8 @@
 Defined *ElfSym::tlsModuleBase;
 DenseMap<const Symbol *, std::pair<const InputFile *, const InputFile *>>
     elf::backwardReferences;
+SmallVector<std::tuple<std::string, const InputFile *, const Symbol &>, 0>
+    elf::whyExtract;
 
 static uint64_t getSymVA(const Symbol &sym, int64_t &addend) {
   switch (sym.kind()) {
@@ -321,6 +323,11 @@
   message(toString(sym->file) + s + sym->getName());
 }
 
+static void printWhyExtract(const InputFile *reference,
+                            const InputFile &extracted, const Symbol &sym) {
+  whyExtract.emplace_back(toString(reference), &extracted, sym);
+}
+
 void elf::maybeWarnUnorderableSymbol(const Symbol *sym) {
   if (!config->warnSymbolOrdering)
     return;
@@ -533,6 +540,9 @@
                    file->groupId < other.file->groupId;
     fetch();
 
+    if (!config->whyExtract.empty())
+      printWhyExtract(other.file, *file, *this);
+
     // We don't report backward references to weak symbols as they can be
     // overridden later.
     //
@@ -742,7 +752,10 @@
     return;
   }
 
+  const InputFile *oldFile = file;
   other.fetch();
+  if (!config->whyExtract.empty())
+    printWhyExtract(oldFile, *file, *this);
 }
 
 void Symbol::resolveShared(const SharedSymbol &other) {
diff --git a/lld/ELF/Writer.cpp b/lld/ELF/Writer.cpp
--- a/lld/ELF/Writer.cpp
+++ b/lld/ELF/Writer.cpp
@@ -622,11 +622,12 @@
     for (OutputSection *sec : outputSections)
       sec->addr = 0;
 
-  // Handle --print-map(-M)/--Map, --cref and --print-archive-stats=. Dump them
-  // before checkSections() because the files may be useful in case
-  // checkSections() or openFile() fails, for example, due to an erroneous file
-  // size.
+  // Handle --print-map(-M)/--Map, --why-extract=, --cref and
+  // --print-archive-stats=. Dump them before checkSections() because the files
+  // may be useful in case checkSections() or openFile() fails, for example, due
+  // to an erroneous file size.
   writeMapFile();
+  writeWhyExtract();
   writeCrossReferenceTable();
   writeArchiveStats();
 
diff --git a/lld/docs/ld.lld.1 b/lld/docs/ld.lld.1
--- a/lld/docs/ld.lld.1
+++ b/lld/docs/ld.lld.1
@@ -658,6 +658,8 @@
 Report unresolved symbols as warnings.
 .It Fl -whole-archive
 Force load of all members in a static library.
+.It Fl -why-extract Ns = Ns Ar file
+Print to a file about why archive members are extracted.
 .It Fl -wrap Ns = Ns Ar symbol
 Redirect
 .Ar symbol
diff --git a/lld/test/ELF/why-extract.s b/lld/test/ELF/why-extract.s
new file mode 100644
--- /dev/null
+++ b/lld/test/ELF/why-extract.s
@@ -0,0 +1,71 @@
+# REQUIRES: x86
+
+# RUN: rm -rf %t && split-file %s %t
+# RUN: llvm-mc -filetype=obj -triple=x86_64 %t/main.s -o %t/main.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64 %t/a.s -o %t/a.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64 %t/a_b.s -o %t/a_b.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64 %t/b.s -o %t/b.o
+# RUN: llvm-ar rc %t/a.a %t/a.o
+# RUN: llvm-ar rc %t/a_b.a %t/a_b.o
+# RUN: llvm-ar rc %t/b.a %t/b.o
+# RUN: cd %t
+
+# RUN: ld.lld main.o a_b.a b.a -o /dev/null --why-extract=why.txt
+# RUN: FileCheck %s --match-full-lines --strict-whitespace < why.txt
+
+#      CHECK:reference	extracted	symbol
+# CHECK-NEXT:main.o	a_b.a(a_b.o)	a
+# CHECK-NEXT:a_b.a(a_b.o)	b.a(b.o)	b()
+
+## - means stdout.
+# RUN: ld.lld main.o a_b.a b.a -o /dev/null --no-demangle --why-extract=- | FileCheck %s --check-prefix=MANGLED
+
+# MANGLED: a_b.a(a_b.o)	b.a(b.o)	_Z1bv
+
+# RUN: ld.lld main.o a.a b.a -o /dev/null -u _Z1bv --why-extract=- | FileCheck %s --check-prefix=UNDEFINED
+
+## We insert -u symbol before processing other files, so its name is <internal>.
+## This is not ideal.
+# UNDEFINED: <internal>	b.a(b.o)	b()
+
+# RUN: ld.lld main.o a.a b.a -o /dev/null --undefined-glob '_Z1b*' --why-extract=- | FileCheck %s --check-prefix=UNDEFINED_GLOB
+
+# UNDEFINED_GLOB: --undefined-glob	b.a(b.o)	b()
+
+# RUN: ld.lld main.o a.a b.a -o /dev/null -e _Z1bv --why-extract=- | FileCheck %s --check-prefix=ENTRY
+
+# ENTRY: --entry	b.a(b.o)	b()
+
+# RUN: ld.lld main.o b.a -o /dev/null -T a.lds --why-extract=- | FileCheck %s --check-prefix=SCRIPT
+
+# SCRIPT: <internal>	b.a(b.o)	b()
+
+# RUN: ld.lld main.o --start-lib a_b.o b.o --end-lib -o /dev/null --why-extract=- | FileCheck %s --check-prefix=LAZY
+
+# LAZY: main.o	a_b.o	a
+# LAZY: a_b.o	b.o	b()
+
+# RUN: not ld.lld -shared main.o -o /dev/null --why-extract=/ 2>&1 | FileCheck %s --check-prefix=ERR
+
+# ERR: error: --why-extract=: cannot open /: {{.*}}
+
+#--- main.s
+.globl _start
+_start:
+  call a
+
+#--- a.s
+.globl a
+a:
+
+#--- a_b.s
+.globl a
+a:
+  call _Z1bv
+
+#--- b.s
+.globl _Z1bv
+_Z1bv:
+
+#--- a.lds
+a = _Z1bv;