[ELF] Rename .bss.rel.ro to .data.rel.ro.bss for some Linker Scripts.

[peter.smith]

Summary

This is patch 3 of 3 spun out from D40029 covering: Name change when linker scripts are used.

LLD uses .bss.rel.ro for read-only copy relocations whereas the ld.bfd and gold linkers use .data.rel.ro. In some linker scripts including ld.bfd's internal linker script, the relro sections are placed sequentially assuming .data.rel.ro is used. LLD's use of .bss.rel.ro means that the copy relocations get matched into the .bss section causing the relro sections to be non-contiguous.

This change checks for a .data.rel.ro OutputSection when a linker script with the SECTIONS command is used. The section will match in the .data.rel.ro output section and will maintain contiguous relro.

[ruiu]

LGTM

ELF/Writer.cpp

292 ↗

(On Diff #123972)

nit: add a blank line before a comment.

295 ↗

(On Diff #123972)

nit: It feels a bit too long. I'd name HasDataRelRo or something like that.

[grimar]

test/ELF/relro-script.s

19 ↗

(On Diff #123972)

nit: Can you put REQURES at first line of test ?

[peter.smith]

Thanks for the comments, I've applied those prior to commit.

lld/trunk/ELF/Writer.cpp

template <class ELFT> void Writer<ELFT>::createSyntheticSections() {
 
   if (Config->BuildId != BuildIdKind::None) {
     InX::BuildId = make<BuildIdSection>();
     Add(InX::BuildId);
   }
 
   InX::Bss = make<BssSection>(".bss", 0, 1);
   Add(InX::Bss);
-  InX::BssRelRo = make<BssSection>(".bss.rel.ro", 0, 1);
+
+  // If there is a SECTIONS command and a .data.rel.ro section name use name
+  // .data.rel.ro.bss so that we match in the .data.rel.ro output section.
+  // This makes sure our relro is contiguous.
+  bool HasDataRelRo =
+      Script->HasSectionsCommand && findSection(".data.rel.ro");
+  InX::BssRelRo = make<BssSection>(
+      HasDataRelRo ? ".data.rel.ro.bss" : ".bss.rel.ro", 0, 1);
   Add(InX::BssRelRo);
 
   // Add MIPS-specific sections.
   if (Config->EMachine == EM_MIPS) {
     if (!Config->Shared && Config->HasDynSymTab) {
       InX::MipsRldMap = make<MipsRldMapSection>();
       Add(InX::MipsRldMap);
     }

lld/trunk/test/ELF/relro-script.s

+// REQUIRES: x86
+// RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %p/Inputs/shared.s -o %t.o
+// RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %p/Inputs/copy-in-shared.s -o %t2.o
+// RUN: ld.lld -shared %t.o %t2.o -o %t.so
+
+// ld.bfd and gold use .data.rel.ro rather than .bss.rel.ro. When a linker
+// script, such as ld.bfd's internal linker script has a .data.rel.ro
+// OutputSection we rename .bss.rel.ro to .data.rel.ro.bss in order to match in
+// .data.rel.ro. This keeps the relro sections contiguous.
+
+// Use the same sections and ordering as the ld.bfd internal linker script.
+// RUN: echo "SECTIONS { \
+// RUN: .data.rel.ro : { *(.data.rel.ro .data.rel.ro.*) } \
+// RUN: .dynamic : { *(.dynamic) } \
+// RUN: .got : { *(.got) } \
+// RUN: .got.plt : { *(.got.plt) } \
+// RUN: } " > %t.script
+// RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t3.o
+// RUN: ld.lld %t3.o %t.so -o %t --script=%t.script --print-map | FileCheck %s
+
+// CHECK: .data.rel.ro
+// CHECK-NEXT: <internal>:(.bss.rel.ro)
+        .section .text, "ax", @progbits
+        .global _start
+        .global bar
+        .global foo
+_start:
+        .quad bar
+        .quad foo