From 61d7ef343828ce338ac901d86bfbd951592ff8d8 Mon Sep 17 00:00:00 2001
From: Fangrui Song <maskray@google.com>
Date: Fri, 7 Jun 2019 03:47:22 +0000
Subject: [PATCH] [MC][ELF] Don't create relocations with section symbols for
 STB_LOCAL ifunc

We should keep the symbol type (STT_GNU_IFUNC) for a local ifunc because
it may result in an IRELATIVE reloc that the dynamic loader will use to
resolve the address at startup time.

There is another problem that is not fixed by this patch: a PC relative
relocation should also create a relocation with the ifunc symbol.

llvm-svn: 362767
---
 lib/MC/ELFObjectWriter.cpp |  6 ++++++
 test/MC/ELF/ifunc-reloc.s  | 39 +++++++++++++++++++++++++-------------
 2 files changed, 32 insertions(+), 13 deletions(-)

diff --git a/lib/MC/ELFObjectWriter.cpp b/lib/MC/ELFObjectWriter.cpp
index 95b0e274526..99cab4e8c5d 100644
--- a/lib/MC/ELFObjectWriter.cpp
+++ b/lib/MC/ELFObjectWriter.cpp
@@ -1373,6 +1373,12 @@ bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
     return true;
   }
 
+  // Keep symbol type for a local ifunc because it may result in an IRELATIVE
+  // reloc that the dynamic loader will use to resolve the address at startup
+  // time.
+  if (Sym->getType() == ELF::STT_GNU_IFUNC)
+    return true;
+
   // If a relocation points to a mergeable section, we have to be careful.
   // If the offset is zero, a relocation with the section will encode the
   // same information. With a non-zero offset, the situation is different.
diff --git a/test/MC/ELF/ifunc-reloc.s b/test/MC/ELF/ifunc-reloc.s
index b4917371b0f..101e6b83f84 100644
--- a/test/MC/ELF/ifunc-reloc.s
+++ b/test/MC/ELF/ifunc-reloc.s
@@ -1,16 +1,29 @@
-// RUN: llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu %s -o - | llvm-readobj -r | FileCheck %s
-        .global sym
-        .type sym, @gnu_indirect_function
-alias: 
-        .global alias
-        .type alias, @function
-        .set sym, alias
+# RUN: llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu %s -o - | llvm-readobj -r | FileCheck %s
+.global alias
+.type alias, @function
+alias:
+  callq global
 
+.global global
+.type global, @gnu_indirect_function
+.set global, alias
 
-        callq sym
+.type local, @gnu_indirect_function
+.set local, alias
 
-// CHECK: Relocations [
-// CHECK-NEXT:   Section {{.*}} .rela.text {
-// CHECK-NEXT:     0x1 R_X86_64_PLT32 sym 0xFFFFFFFFFFFFFFFC
-// CHECK-NEXT:   }
-// CHECK-NEXT: ]
+## Check we don't create the relocations with a section symbol for both global
+## They may result in IRELATIVE relocs that the dynamic loader will use to
+## resolve addresses at startup time.
+.data
+.quad global
+.quad local
+
+# CHECK:      Relocations [
+# CHECK-NEXT:   Section {{.*}} .rela.text {
+# CHECK-NEXT:     0x1 R_X86_64_PLT32 global 0xFFFFFFFFFFFFFFFC
+# CHECK-NEXT:   }
+# CHECK-NEXT:   Section {{.*}} .rela.data {
+# CHECK-NEXT:     0x0 R_X86_64_64 global 0x0
+# CHECK-NEXT:     0x8 R_X86_64_64 local 0x0
+# CHECK-NEXT:   }
+# CHECK-NEXT: ]