From 2903a8a11f9ef0782867fc7efff07b705ea75838 Mon Sep 17 00:00:00 2001
From: Simon Atanasyan <simon@atanasyan.com>
Date: Mon, 12 Dec 2016 21:34:11 +0000
Subject: [PATCH] [ELF][MIPS] Calculate default _gp value relative to the GPREL
 section with the lowest address

llvm-svn: 289471
---
 lld/ELF/Writer.cpp            | 12 ++++++++++--
 lld/test/ELF/mips-gp-lowest.s | 44 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 54 insertions(+), 2 deletions(-)
 create mode 100644 lld/test/ELF/mips-gp-lowest.s

diff --git a/lld/ELF/Writer.cpp b/lld/ELF/Writer.cpp
index c63b883..d1c1ecd 100644
--- a/lld/ELF/Writer.cpp
+++ b/lld/ELF/Writer.cpp
@@ -1490,8 +1490,16 @@ template <class ELFT> void Writer<ELFT>::fixAbsoluteSymbols() {
   // Setup MIPS _gp_disp/__gnu_local_gp symbols which should
   // be equal to the _gp symbol's value.
   if (Config->EMachine == EM_MIPS) {
-    if (!ElfSym<ELFT>::MipsGp->Value)
-      ElfSym<ELFT>::MipsGp->Value = In<ELFT>::MipsGot->getVA() + 0x7ff0;
+    if (!ElfSym<ELFT>::MipsGp->Value) {
+      // Find GP-relative section with the lowest address
+      // and use this address to calculate default _gp value.
+      uintX_t Gp = -1;
+      for (const OutputSectionBase * OS : OutputSections)
+        if ((OS->Flags & SHF_MIPS_GPREL) && OS->Addr < Gp)
+          Gp = OS->Addr;
+      if (Gp != (uintX_t)-1)
+        ElfSym<ELFT>::MipsGp->Value = Gp + 0x7ff0;
+    }
     if (ElfSym<ELFT>::MipsGpDisp)
       ElfSym<ELFT>::MipsGpDisp->Value = ElfSym<ELFT>::MipsGp->Value;
     if (ElfSym<ELFT>::MipsLocalGp)
diff --git a/lld/test/ELF/mips-gp-lowest.s b/lld/test/ELF/mips-gp-lowest.s
new file mode 100644
index 0000000..b3d30aa
--- /dev/null
+++ b/lld/test/ELF/mips-gp-lowest.s
@@ -0,0 +1,44 @@
+# Check that default _gp value is calculated relative
+# to the GP-relative section with the lowest address.
+
+# RUN: llvm-mc -filetype=obj -triple=mips-unknown-linux %s -o %t.o
+# RUN: echo "SECTIONS { \
+# RUN:          .sdata : { *(.sdata) } \
+# RUN:          .got  : { *(.got) } }" > %t.rel.script
+# RUN: ld.lld %t.o --script %t.rel.script -shared -o %t.so
+# RUN: llvm-readobj -s -t %t.so | FileCheck %s
+
+# REQUIRES: mips
+
+  .text
+  .global foo
+foo:
+  lui  $gp, %call16(foo)
+
+  .sdata
+  .word 0
+
+# CHECK:      Section {
+# CHECK:        Name: .sdata
+# CHECK-NEXT:   Type: SHT_PROGBITS
+# CHECK-NEXT:   Flags [
+# CHECK-NEXT:     SHF_ALLOC
+# CHECK-NEXT:     SHF_MIPS_GPREL
+# CHECK-NEXT:     SHF_WRITE
+# CHECK-NEXT:   ]
+# CHECK-NEXT:   Address: 0xDD
+# CHECK:      }
+# CHECK:      Section {
+# CHECK:        Name: .got
+# CHECK-NEXT:   Type: SHT_PROGBITS
+# CHECK-NEXT:   Flags [
+# CHECK-NEXT:     SHF_ALLOC
+# CHECK-NEXT:     SHF_MIPS_GPREL
+# CHECK-NEXT:     SHF_WRITE
+# CHECK-NEXT:   ]
+# CHECK-NEXT:   Address: 0xE4
+# CHECK:      }
+
+# CHECK:      Name: _gp (5)
+# CHECK-NEXT: Value: 0x80CD
+#                    ^-- 0xDD + 0x7ff0
-- 
2.7.4