[PATCH] D54495: [LLD] [COFF] Remove empty sections before calculating the size of section headers

[Martin Storsjö via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rLLD347704: [COFF] Remove empty sections before calculating the size of section headers (authored by mstorsjo, committed by ).

Repository:
  rLLD LLVM Linker

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D54495/new/

https://reviews.llvm.org/D54495

Files:
  COFF/Writer.cpp
  test/COFF/header-size.s


Index: test/COFF/header-size.s
===================================================================
--- test/COFF/header-size.s
+++ test/COFF/header-size.s
@@ -0,0 +1,12 @@
+// REQUIRES: x86
+// RUN: llvm-mc -filetype=obj -triple=x86_64-windows %s -o %t.obj
+// RUN: lld-link -entry:main -subsystem:console %t.obj -out:%t.exe
+// RUN: llvm-readobj -sections %t.exe | FileCheck %s
+    .globl main
+main:
+    ret
+
+// Check that the first section data comes at 512 bytes in the file.
+// If the size allocated for headers would include size for section
+// headers which aren't written, PointerToRawData would be 0x400 instead.
+// CHECK: PointerToRawData: 0x200
Index: COFF/Writer.cpp
===================================================================
--- COFF/Writer.cpp
+++ COFF/Writer.cpp
@@ -173,6 +173,7 @@
   void createExportTable();
   void mergeSections();
   void readRelocTargets();
+  void removeUnusedSections();
   void assignAddresses();
   void finalizeAddresses();
   void removeEmptySections();
@@ -500,6 +501,7 @@
   createExportTable();
   mergeSections();
   readRelocTargets();
+  removeUnusedSections();
   finalizeAddresses();
   removeEmptySections();
   setSectionPermissions();
@@ -882,6 +884,21 @@
     EdataSec->addChunk(C);
 }
 
+void Writer::removeUnusedSections() {
+  // Remove sections that we can be sure won't get content, to avoid
+  // allocating space for their section headers.
+  auto IsUnused = [this](OutputSection *S) {
+    if (S == RelocSec)
+      return false; // This section is populated later.
+    // MergeChunks have zero size at this point, as their size is finalized
+    // later. Only remove sections that have no Chunks at all.
+    return S->Chunks.empty();
+  };
+  OutputSections.erase(
+      std::remove_if(OutputSections.begin(), OutputSections.end(), IsUnused),
+      OutputSections.end());
+}
+
 // The Windows loader doesn't seem to like empty sections,
 // so we remove them if any.
 void Writer::removeEmptySections() {


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D54495.175559.patch
Type: text/x-patch
Size: 1992 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20181127/70ab315c/attachment.bin>