[PATCH] D42681: [ELF] - Remove unused synthetic sections correctly.

[George Rimar via Phabricator via llvm-commits]

grimar updated this revision to Diff 132114.
grimar added a comment.

- Addressed review comment.


https://reviews.llvm.org/D42681

Files:
  ELF/Writer.cpp
  test/ELF/linkerscript/unused-synthetic.s
  test/ELF/linkerscript/unused-synthetic2.s


Index: test/ELF/linkerscript/unused-synthetic2.s
===================================================================
--- test/ELF/linkerscript/unused-synthetic2.s
+++ test/ELF/linkerscript/unused-synthetic2.s
@@ -0,0 +1,9 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=armv7-unknown-linux-gnueabi %s -o %t.o
+# RUN: echo "SECTIONS { .trap : { *(.ARM.exidx) *(.dummy) } }" > %t.script
+
+## We incorrectly removed unused synthetic sections and crashed before.
+## Check we do not crash and do not produce .trap output section.
+# RUN: ld.lld -shared -o %t.so --script %t.script %t.o
+# RUN: llvm-objdump -section-headers %t.so | FileCheck %s
+# CHECK-NOT: .trap
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
@@ -1342,23 +1342,21 @@
     if (!OS || !SS->empty())
       continue;
 
-    std::vector<BaseCommand *>::iterator Empty = OS->SectionCommands.end();
-    for (auto I = OS->SectionCommands.begin(), E = OS->SectionCommands.end();
-         I != E; ++I) {
-      BaseCommand *B = *I;
-      if (auto *ISD = dyn_cast<InputSectionDescription>(B)) {
+    // If we reach here, then SS is an unused synthetic section and we want to
+    // remove it from corresponding input section description of output section.
+    for (BaseCommand *B : OS->SectionCommands)
+      if (auto *ISD = dyn_cast<InputSectionDescription>(B))
         llvm::erase_if(ISD->Sections,
                        [=](InputSection *IS) { return IS == SS; });
-        if (ISD->Sections.empty())
-          Empty = I;
-      }
-    }
-    if (Empty != OS->SectionCommands.end())
-      OS->SectionCommands.erase(Empty);
 
-    // If there are no other sections in the output section, remove it from the
-    // output.
-    if (OS->SectionCommands.empty())
+    // If there are no other alive sections or commands left in the output
+    // section description, we remove it from the output.
+    bool IsEmpty = llvm::all_of(OS->SectionCommands, [](BaseCommand *B) {
+      if (auto *ISD = dyn_cast<InputSectionDescription>(B))
+        return ISD->Sections.empty();
+      return false;
+    });
+    if (IsEmpty)
       OS->Live = false;
   }
 }


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