From a6298fb160633578f5c4c1e739044274ba8fe520 Mon Sep 17 00:00:00 2001
From: Keith Smiley <keithbsmiley@gmail.com>
Date: Fri, 28 Jan 2022 18:46:51 -0800
Subject: [PATCH] [lld-macho] Add support for -add_empty_section

This is a ld64 option equivalent to `-sectcreate seg sect /dev/null`
that's useful for creating sections like the RESTRICT section.

Differential Revision: https://reviews.llvm.org/D117749
---
 lld/MachO/Driver.cpp        |  6 ++++++
 lld/MachO/Options.td        |  4 ++++
 lld/test/MachO/sectcreate.s | 18 ++++++++++++++++++
 3 files changed, 28 insertions(+)

diff --git a/lld/MachO/Driver.cpp b/lld/MachO/Driver.cpp
index e4c9f4d..f0cddab 100644
--- a/lld/MachO/Driver.cpp
+++ b/lld/MachO/Driver.cpp
@@ -1484,6 +1484,12 @@ bool macho::link(ArrayRef<const char *> argsArr, llvm::raw_ostream &stdoutOS,
         inputFiles.insert(make<OpaqueFile>(*buffer, segName, sectName));
     }
 
+    for (const Arg *arg : args.filtered(OPT_add_empty_section)) {
+      StringRef segName = arg->getValue(0);
+      StringRef sectName = arg->getValue(1);
+      inputFiles.insert(make<OpaqueFile>(MemoryBufferRef(), segName, sectName));
+    }
+
     gatherInputSections();
     if (config->callGraphProfileSort)
       extractCallGraphProfile();
diff --git a/lld/MachO/Options.td b/lld/MachO/Options.td
index 3d1d976..ab79aa7 100644
--- a/lld/MachO/Options.td
+++ b/lld/MachO/Options.td
@@ -252,6 +252,10 @@ def segcreate : MultiArg<["-"], "segcreate", 3>,
     Alias<sectcreate>,
     HelpText<"Alias for -sectcreate">,
     Group<grp_content>;
+def add_empty_section : MultiArg<["-"], "add_empty_section", 2>,
+    MetaVarName<"<segment> <section>">,
+    HelpText<"Create an empty <section> in <segment>">,
+    Group<grp_content>;
 def filelist : Separate<["-"], "filelist">,
     MetaVarName<"<file>">,
     HelpText<"Read names of files to link from <file>">,
diff --git a/lld/test/MachO/sectcreate.s b/lld/test/MachO/sectcreate.s
index 03847e1..919c553 100644
--- a/lld/test/MachO/sectcreate.s
+++ b/lld/test/MachO/sectcreate.s
@@ -7,6 +7,7 @@
 # RUN:     -sectcreate SEG SEC1 %t1 \
 # RUN:     -segcreate SEG SEC2 %t3 \
 # RUN:     -sectcreate SEG SEC1 %t2 \
+# RUN:     -add_empty_section __DATA __data \
 # RUN:     -o %t %t.o
 # RUN: llvm-objdump -s %t | FileCheck %s
 
@@ -16,10 +17,17 @@
 # RUN:     -sectcreate SEG SEC1 %t1 \
 # RUN:     -segcreate SEG SEC2 %t3 \
 # RUN:     -sectcreate SEG SEC1 %t2 \
+# RUN:     -add_empty_section SEG SEC1 \
 # RUN:     -o %t %t.o
 # RUN: llvm-objdump -s %t | FileCheck --check-prefix=STRIPPED %s
 # RUN: llvm-readobj --sections %t | FileCheck --check-prefix=STRIPPEDSEC %s
 
+# RUN: %lld -add_empty_section foo bar -o %t %t.o
+# RUN: llvm-readobj --sections %t | FileCheck --check-prefix=EMPTYSECTION %s
+
+# RUN: %lld -sectcreate SEG SEC1 %t1 -add_empty_section SEG SEC1 -o %t %t.o
+# RUN: llvm-readobj --sections %t | FileCheck --check-prefix=CREATEDANDEMPTY %s
+
 # CHECK: Contents of section __TEXT,__text:
 # CHECK: Contents of section __DATA,__data:
 # CHECK: my string!.
@@ -40,6 +48,16 @@
 
 # STRIPPEDSEC-NOT: NoDeadStrip
 
+# EMPTYSECTION: Name: bar
+# EMPTYSECTION: Segment: foo
+# EMPTYSECTION: Size: 0x0
+# EMPTYSECTION-NOT: Name:
+
+# CREATEDANDEMPTY: Name: SEC1
+# CREATEDANDEMPTY: Segment: SEG
+# CREATEDANDEMPTY: Size: 0x10
+# CREATEDANDEMPTY-NOT: Name:
+
 .text
 .global _main
 _main:
-- 
2.7.4