From a55fc7161481ec4410a55c2e1b82d7c6d68949d6 Mon Sep 17 00:00:00 2001
From: Martin Storsjo <martin@martin.st>
Date: Fri, 20 Jul 2018 05:44:34 +0000
Subject: [PATCH] [COFF] Write the debug directory and build id to a separate
 section for MinGW

For dwarf debug info, an executable normally either contains the debug
info, or it is stripped out. To reduce the storage needed (slightly)
for the debug info kept separately from the released, stripped binaries,
one can choose to only copy the debug data from the original executable
(essentially the reverse of the strip operation), producing a file with
only debug info.

When copying the debug data from an executable with GNU objcopy,
the build id and debug directory need to reside in a separate section,
as this will be kept while the rest of the .rdata section is removed.

Differential Revision: https://reviews.llvm.org/D49352

llvm-svn: 337526
---
 lld/COFF/Writer.cpp         |  8 ++++++--
 lld/test/COFF/debug-reloc.s | 16 ++++++++++++++++
 2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/lld/COFF/Writer.cpp b/lld/COFF/Writer.cpp
index d17cc7b71dec..607a1d1c8ee4 100644
--- a/lld/COFF/Writer.cpp
+++ b/lld/COFF/Writer.cpp
@@ -201,6 +201,7 @@ private:
 
   OutputSection *TextSec;
   OutputSection *RdataSec;
+  OutputSection *BuildidSec;
   OutputSection *DataSec;
   OutputSection *PdataSec;
   OutputSection *IdataSec;
@@ -420,6 +421,7 @@ void Writer::createSections() {
   TextSec = CreateSection(".text", CODE | R | X);
   CreateSection(".bss", BSS | R | W);
   RdataSec = CreateSection(".rdata", DATA | R);
+  BuildidSec = CreateSection(".buildid", DATA | R);
   DataSec = CreateSection(".data", DATA | R | W);
   PdataSec = CreateSection(".pdata", DATA | R);
   IdataSec = CreateSection(".idata", DATA | R);
@@ -503,6 +505,8 @@ void Writer::createMiscChunks() {
   if (Config->Debug) {
     DebugDirectory = make<DebugDirectoryChunk>(DebugRecords);
 
+    OutputSection *DebugInfoSec = Config->MinGW ? BuildidSec : RdataSec;
+
     // Make a CVDebugRecordChunk even when /DEBUG:CV is not specified.  We
     // output a PDB no matter what, and this chunk provides the only means of
     // allowing a debugger to match a PDB and an executable.  So we need it even
@@ -511,9 +515,9 @@ void Writer::createMiscChunks() {
     BuildId = CVChunk;
     DebugRecords.push_back(CVChunk);
 
-    RdataSec->addChunk(DebugDirectory);
+    DebugInfoSec->addChunk(DebugDirectory);
     for (Chunk *C : DebugRecords)
-      RdataSec->addChunk(C);
+      DebugInfoSec->addChunk(C);
   }
 
   // Create SEH table. x86-only.
diff --git a/lld/test/COFF/debug-reloc.s b/lld/test/COFF/debug-reloc.s
index 43b511112a80..57ab9bf9cdbc 100644
--- a/lld/test/COFF/debug-reloc.s
+++ b/lld/test/COFF/debug-reloc.s
@@ -5,7 +5,13 @@
 # RUN: lld-link -lldmingw -debug:dwarf -out:%t.exe -entry:mainfunc -subsystem:console %t.obj
 # RUN: llvm-readobj -sections %t.exe | FileCheck %s -check-prefix SECTIONS
 # RUN: llvm-readobj -coff-basereloc %t.exe | FileCheck %s -check-prefix RELOCS
+# RUN: llvm-readobj -file-headers %t.exe | FileCheck %s -check-prefix HEADERS
+# RUN: llvm-readobj -coff-debug-directory %t.exe | FileCheck %s -check-prefix DEBUG
 
+# SECTIONS:         Number: 2
+# SECTIONS-NEXT:    Name: .buildid (2E 62 75 69 6C 64 69 64)
+# SECTIONS-NEXT:    VirtualSize: 0x35
+# SECTIONS-NEXT:    VirtualAddress: 0x2000
 # SECTIONS:         Number: 3
 # SECTIONS-NEXT:    Name: .data (2E 64 61 74 61 00 00 00)
 # SECTIONS-NEXT:    VirtualSize: 0x8
@@ -22,6 +28,16 @@
 # RELOCS-NEXT:   }
 # RELOCS-NEXT: ]
 
+# HEADERS:     DebugRVA: 0x2000
+# HEADERS:     DebugSize: 0x1C
+
+# DEBUG: DebugDirectory [
+# DEBUG:   DebugEntry {
+# DEBUG:     Type: CodeView (0x2)
+# DEBUG:     SizeOfData: 0x19
+# DEBUG:     AddressOfRawData: 0x201C
+# DEBUG:     PointerToRawData: 0x61C
+
 	.text
 	.def	 mainfunc;
 	.scl	2;