[lld] r318940 - [ELF] Rename .bss.rel.ro to .data.rel.ro.bss for some Linker Scripts.

[Peter Smith via llvm-commits]

Author: psmith
Date: Fri Nov 24 00:48:29 2017
New Revision: 318940

URL: http://llvm.org/viewvc/llvm-project?rev=318940&view=rev
Log:
[ELF] Rename .bss.rel.ro to .data.rel.ro.bss for some Linker Scripts.

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.

Differential Revision: https://reviews.llvm.org/D40365

Fixes PR35265


Added:
    lld/trunk/test/ELF/relro-script.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=318940&r1=318939&r2=318940&view=diff
==============================================================================
--- lld/trunk/ELF/Writer.cpp (original)
+++ lld/trunk/ELF/Writer.cpp Fri Nov 24 00:48:29 2017
@@ -289,7 +289,14 @@ template <class ELFT> void Writer<ELFT>:
 
   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.

Added: lld/trunk/test/ELF/relro-script.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/relro-script.s?rev=318940&view=auto
==============================================================================
--- lld/trunk/test/ELF/relro-script.s (added)
+++ lld/trunk/test/ELF/relro-script.s Fri Nov 24 00:48:29 2017
@@ -0,0 +1,29 @@
+// 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