[PATCH] D37520: [ELF] - Fix removing of unused synthetic sections.

[George Rimar via Phabricator via llvm-commits]

grimar updated this revision to Diff 114561.
grimar added a comment.

- Addressed review comments.
- Changed inplementation to use `Live` flag for removing output section.


https://reviews.llvm.org/D37520

Files:
  ELF/LinkerScript.cpp
  ELF/Writer.cpp
  test/ELF/linkerscript/unused-synthetic.s


Index: test/ELF/linkerscript/unused-synthetic.s
===================================================================
--- test/ELF/linkerscript/unused-synthetic.s
+++ test/ELF/linkerscript/unused-synthetic.s
@@ -1,7 +1,7 @@
 # REQUIRES: x86
 # RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o
 # RUN: echo "SECTIONS { \
-# RUN:    .got  : { *(.got) } \
+# RUN:    .got  : { *(.got) *(.got) } \
 # RUN:    .plt  : { *(.plt) } \
 # RUN:    .text : { *(.text) } \
 # RUN:  }" > %t.script
Index: ELF/Writer.cpp
===================================================================
--- ELF/Writer.cpp
+++ ELF/Writer.cpp
@@ -1071,8 +1071,7 @@
 }
 
 template <class ELFT> void Writer<ELFT>::sortSections() {
-  if (Script->Opt.HasSections)
-    Script->adjustSectionsBeforeSorting();
+  Script->adjustSectionsBeforeSorting();
 
   // Don't sort if using -r. It is not necessary and we want to preserve the
   // relative order for SHF_LINK_ORDER sections.
@@ -1200,24 +1199,25 @@
     if ((SS == InX::Got || SS == InX::MipsGot) && ElfSym::GlobalOffsetTable)
       continue;
 
-    std::vector<BaseCommand *>::iterator Empty = OS->Commands.end();
-    for (auto I = OS->Commands.begin(), E = OS->Commands.end(); I != E; ++I) {
-      BaseCommand *B = *I;
+    // SS is an unused synthetic section. Remove it from output section command.
+    for (BaseCommand *B : OS->Commands) {
       if (auto *ISD = dyn_cast<InputSectionDescription>(B)) {
-        llvm::erase_if(ISD->Sections,
-                       [=](InputSection *IS) { return IS == SS; });
-        if (ISD->Sections.empty())
-          Empty = I;
+        auto It = llvm::find(ISD->Sections, SS);
+        if (It == ISD->Sections.end())
+          continue;
+        ISD->Sections.erase(It);
+        break;
       }
     }
-    if (Empty != OS->Commands.end())
-      OS->Commands.erase(Empty);
 
-    // If there are no other sections in the output section, remove it from the
-    // output.
-    if (OS->Commands.empty())
-      llvm::erase_if(Script->Opt.Commands,
-                     [&](BaseCommand *Cmd) { return Cmd == OS; });
+    // If output section now contains no any other input sections
+    // and no other commands, mark is as dead.
+    bool IsEmpty = llvm::all_of(OS->Commands, [](BaseCommand *B) {
+      auto *ISD = dyn_cast<InputSectionDescription>(B);
+      return ISD && ISD->Sections.empty();
+    });
+    if (IsEmpty)
+      OS->Live = false;
   }
 }
 
@@ -1326,6 +1326,7 @@
   removeUnusedSyntheticSections();
 
   sortSections();
+  Script->removeEmptyCommands();
 
   // Now that we have the final list, create a list of all the
   // OutputSections for convenience.
Index: ELF/LinkerScript.cpp
===================================================================
--- ELF/LinkerScript.cpp
+++ ELF/LinkerScript.cpp
@@ -686,6 +686,8 @@
   // Try and find an appropriate memory region to assign offsets in.
   for (BaseCommand *Base : Opt.Commands) {
     if (auto *Sec = dyn_cast<OutputSection>(Base)) {
+      if (!Sec->Live)
+        continue;
       Sec->MemRegion = findMemoryRegion(Sec);
       // Handle align (e.g. ".foo : ALIGN(16) { ... }").
       if (Sec->AlignExpr)
@@ -722,8 +724,6 @@
       DefPhdrs = Sec->Phdrs;
     }
   }
-
-  removeEmptyCommands();
 }
 
 static OutputSection *findFirstSection(PhdrEntry *Load) {


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