[PATCH] D44377: [ELF] - Drop SHF_LINK_ORDER flag from the output.

[George Rimar via Phabricator via llvm-commits]

grimar created this revision.
grimar added reviewers: ruiu, psmith, espindola.
Herald added subscribers: kristof.beyls, arichardson, emaste.

It should be useless to leave SHF_LINK_ORDER flag in the 
non-relocatable output because this flag is used only by the linker.
This patch removes it to make output cleaner.

I had to do an exception for SHT_ARM_EXIDX sections though
because otherwise, GNU strip tool reports a 
"sh_link not set for section `.ARM.exidx'" warning. 
This warning itself seems wrong/useless to me.


https://reviews.llvm.org/D44377

Files:
  ELF/Writer.cpp
  test/ELF/link-order-flag.s


Index: test/ELF/link-order-flag.s
===================================================================
--- test/ELF/link-order-flag.s
+++ test/ELF/link-order-flag.s
@@ -0,0 +1,31 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
+
+## Check we keep SHF_LINK_ORDER flag for -r
+# RUN: ld.lld -r %t.o -o %t
+# RUN: llvm-readobj -s %t | FileCheck %s --check-prefix=NODROP
+# NODROP:      Section {
+# NODROP:        Index:
+# NODROP:        Name: .bar
+# NODROP-NEXT:   Type: SHT_PROGBITS
+# NODROP-NEXT:   Flags [
+# NODROP-NEXT:     SHF_ALLOC
+# NODROP-NEXT:     SHF_LINK_ORDER
+# NODROP-NEXT:   ]
+
+## Check we drop SHF_LINK_ORDER flag for regular output.
+# RUN: ld.lld %t.o -o %t
+# RUN: llvm-readobj -s %t | FileCheck %s --check-prefix=DROP
+# DROP:      Section {
+# DROP:        Index:
+# DROP:        Name: .bar
+# DROP-NEXT:   Type: SHT_PROGBITS
+# DROP-NEXT:   Flags [
+# DROP-NEXT:     SHF_ALLOC
+# DROP-NEXT:   ]
+
+.section .foo,"a"
+.quad 0
+
+.section .bar,"ao", at progbits,.foo
+.quad 0
Index: ELF/Writer.cpp
===================================================================
--- ELF/Writer.cpp
+++ ELF/Writer.cpp
@@ -1351,6 +1351,13 @@
     for (BaseCommand *Base : Sec->SectionCommands)
       if (auto *ISD = dyn_cast<InputSectionDescription>(Base))
         llvm::erase_if(ISD->Sections, [](InputSection *IS) { return !IS; });
+
+    // In theory, there should not make sense to have this flag in the
+    // non-relocatable output because the flag is used by linker only.
+    // Binutils strip tool reports a warning when sh_link is not set for
+    // SHT_ARM_EXIDX though. So we have to keep it to workaround warning.
+    if (!Config->Relocatable && Sec->Type != SHT_ARM_EXIDX)
+      Sec->Flags &= ~SHF_LINK_ORDER;
   }
 }
 


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