[lld] r307037 - [ELF] Remove unused synthetic sections from script commands

[Petr Hosek via llvm-commits]

Author: phosek
Date: Mon Jul  3 08:49:25 2017
New Revision: 307037

URL: http://llvm.org/viewvc/llvm-project?rev=307037&view=rev
Log:
[ELF] Remove unused synthetic sections from script commands

Script commands are processed before unused synthetic sections are
removed. Therefore, if a linker script matches one of these sections
it'll get emitted as an empty output section because the logic for
removing unused synthetic sections ignores script commands which
could have already matched and captured one of these sections. This
patch fixes that by also removing the unused synthetic sections from
the script commands.

Differential Revision: https://reviews.llvm.org/D34800

Added:
    lld/trunk/test/ELF/linkerscript/unused-synthetic.s
Modified:
    lld/trunk/ELF/Writer.cpp

Modified: lld/trunk/ELF/Writer.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Writer.cpp?rev=307037&r1=307036&r2=307037&view=diff
==============================================================================
--- lld/trunk/ELF/Writer.cpp (original)
+++ lld/trunk/ELF/Writer.cpp Mon Jul  3 08:49:25 2017
@@ -1149,8 +1149,17 @@ static void removeUnusedSyntheticSection
     SS->Live = false;
     // If there are no other sections in the output section, remove it from the
     // output.
-    if (OS->Sections.empty())
+    if (OS->Sections.empty()) {
       V.erase(std::find(V.begin(), V.end(), OS));
+      // Also remove script commands matching the output section.
+      auto &Cmds = Script->Opt.Commands;
+      auto I = std::remove_if(Cmds.begin(), Cmds.end(), [&](BaseCommand *Cmd) {
+        if (auto *OSCmd = dyn_cast<OutputSectionCommand>(Cmd))
+          return OSCmd->Sec == OS;
+        return false;
+      });
+      Cmds.erase(I, Cmds.end());
+    }
   }
 }
 

Added: lld/trunk/test/ELF/linkerscript/unused-synthetic.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/linkerscript/unused-synthetic.s?rev=307037&view=auto
==============================================================================
--- lld/trunk/test/ELF/linkerscript/unused-synthetic.s (added)
+++ lld/trunk/test/ELF/linkerscript/unused-synthetic.s Mon Jul  3 08:49:25 2017
@@ -0,0 +1,18 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o
+# RUN: echo "SECTIONS { \
+# RUN:    .got  : { *(.got) } \
+# RUN:    .plt  : { *(.plt) } \
+# RUN:    .text : { *(.text) } \
+# RUN:  }" > %t.script
+# RUN: ld.lld -shared -o %t.so --script %t.script %t.o
+
+# RUN: llvm-objdump -section-headers %t.so | FileCheck %s
+# CHECK-NOT:  .got
+# CHECK-NOT:  .plt
+# CHECK:      .text
+# CHECK-NEXT: .dynsym
+
+.global _start
+_start:
+  nop