From cf8c42f54605ad0d941751cd3b7d65b9a5463265 Mon Sep 17 00:00:00 2001
From: Simon Atanasyan <simon@atanasyan.com>
Date: Wed, 30 Mar 2016 22:43:14 +0000
Subject: [PATCH] [ELF][MIPS] Revert r264761 and add test case to demonstrate
 the problem

If we make R_MIPS_LO16 a relative relocation, linker:
- never creates R_MIPS_COPY relocation for it
- attempts to create R_MIPS_REL32 dynamic relocation if R_MIPS_LO16's
  target is a preemptible symbol

Differential Revision: http://reviews.llvm.org/D18607

llvm-svn: 264956
---
 lld/ELF/Target.cpp                    |  1 +
 lld/ELF/Writer.cpp                    |  9 +++++++++
 lld/test/ELF/mips-lo16-not-relative.s | 23 +++++++++++++++++++++++
 3 files changed, 33 insertions(+)
 create mode 100644 lld/test/ELF/mips-lo16-not-relative.s

diff --git a/lld/ELF/Target.cpp b/lld/ELF/Target.cpp
index c075c8d..09e3ee6 100644
--- a/lld/ELF/Target.cpp
+++ b/lld/ELF/Target.cpp
@@ -1844,6 +1844,7 @@ bool MipsTargetInfo<ELFT>::isRelRelative(uint32_t Type) const {
   case R_MIPS_32:
   case R_MIPS_64:
   case R_MIPS_HI16:
+  case R_MIPS_LO16:
   case R_MIPS_TLS_DTPREL_HI16:
   case R_MIPS_TLS_DTPREL_LO16:
   case R_MIPS_TLS_TPREL_HI16:
diff --git a/lld/ELF/Writer.cpp b/lld/ELF/Writer.cpp
index 2ab47f7..76cde10 100644
--- a/lld/ELF/Writer.cpp
+++ b/lld/ELF/Writer.cpp
@@ -434,6 +434,15 @@ void Writer<ELFT>::scanRelocs(InputSectionBase<ELFT> &C,
     }
 
     if (Config->EMachine == EM_MIPS) {
+      if (Type == R_MIPS_LO16)
+        // Ignore R_MIPS_LO16 relocation. If it is a pair for R_MIPS_GOT16 we
+        // already completed all required action (GOT entry allocation) when
+        // handle R_MIPS_GOT16. If it is a pair for R_MIPS_HI16 against
+        // _gp_disp it does not require dynamic relocation. If its a pair for
+        // R_MIPS_HI16 against a regular symbol it does not require dynamic
+        // relocation too because that case is possible for executable file
+        // linking only.
+        continue;
       if (&Body == Config->MipsGpDisp || &Body == Config->MipsLocalGp)
         // MIPS _gp_disp designates offset between start of function and 'gp'
         // pointer into GOT. __gnu_local_gp is equal to the current value of
diff --git a/lld/test/ELF/mips-lo16-not-relative.s b/lld/test/ELF/mips-lo16-not-relative.s
new file mode 100644
index 0000000..614e639
--- /dev/null
+++ b/lld/test/ELF/mips-lo16-not-relative.s
@@ -0,0 +1,23 @@
+# Check that R_MIPS_LO16 relocation is handled as non-relative,
+# and if a target symbol is a DSO data symbol, LLD create a copy
+# relocation.
+
+# RUN: llvm-mc -filetype=obj -triple=mips-unknown-linux \
+# RUN:         %S/Inputs/mips-dynamic.s -o %t.so.o
+# RUN: ld.lld %t.so.o -shared -o %t.so
+# RUN: llvm-mc -filetype=obj -triple=mips-unknown-linux %s -o %t.o
+# RUN: ld.lld %t.o %t.so -o %t.exe
+# RUN: llvm-readobj -r %t.exe | FileCheck %s
+
+# REQUIRES: mips
+
+# CHECK:      Relocations [
+# CHECK-NEXT:   Section (7) .rel.dyn {
+# CHECK-NEXT:     0x{{[0-9A-F]+}} R_MIPS_COPY data0 0x0
+# CHECK-NEXT:   }
+# CHECK-NEXT: ]
+
+  .text
+  .global __start
+__start:
+  addi   $t0, $t0, %lo(data0)
-- 
2.7.4