From 27d036e9952387dff6eafe009f1769b575148454 Mon Sep 17 00:00:00 2001
From: Fangrui Song <maskray@google.com>
Date: Thu, 1 Nov 2018 22:28:58 +0000
Subject: [PATCH] [ELF] Change sh_link of .rel{,a}.plt to make GNU strip happy

Summary:
D52830 sets sh_link to .symtab in static link, which breaks executable stripped by GNU strip.
It may also be odd that .rela.plt (SHF_ALLOC) points to .symtab (non-SHF_ALLOC).

Change the logic on pcc's suggestion.

Before:

% clang -fuse-ld=lld -static -xc =(printf 'int main(){}') # or gcc
% strip a.out; ./a.out
unexpected reloc type in static binary[1]    61634 segmentation fault  ./a.out

Reviewers: ruiu, grimar, emaste, espindola

Reviewed By: ruiu

Subscribers: pcc, arichardson, llvm-commits

Differential Revision: https://reviews.llvm.org/D53993

llvm-svn: 345899
---
 lld/ELF/SyntheticSections.cpp    | 14 +++++---------
 lld/test/ELF/aarch64-gnu-ifunc.s |  2 +-
 lld/test/ELF/gnu-ifunc-i386.s    |  2 +-
 lld/test/ELF/gnu-ifunc.s         |  5 +----
 4 files changed, 8 insertions(+), 15 deletions(-)

diff --git a/lld/ELF/SyntheticSections.cpp b/lld/ELF/SyntheticSections.cpp
index 2cca1fe..9d2e0a7 100644
--- a/lld/ELF/SyntheticSections.cpp
+++ b/lld/ELF/SyntheticSections.cpp
@@ -1491,15 +1491,11 @@ void RelocationBaseSection::addReloc(const DynamicReloc &Reloc) {
 }
 
 void RelocationBaseSection::finalizeContents() {
-  // If all relocations are R_*_{,I}RELATIVE they don't refer to any dynamic
-  // symbol and we don't need a dynamic symbol table. If that is the case, use
-  // the index of the regular symbol table section (if exists) or 0.
-  if (In.DynSymTab)
-    getParent()->Link = In.DynSymTab->getParent()->SectionIndex;
-  else if (In.SymTab)
-    getParent()->Link = In.SymTab->getParent()->SectionIndex;
-  else
-    getParent()->Link = 0;
+  // When linking glibc statically, .rel{,a}.plt contains R_*_IRELATIVE
+  // relocations due to IFUNC (e.g. strcpy). sh_link will be set to 0 in that
+  // case.
+  InputSection *SymTab = Config->Relocatable ? In.SymTab : In.DynSymTab;
+  getParent()->Link = SymTab ? SymTab->getParent()->SectionIndex : 0;
 
   if (In.RelaIplt == this || In.RelaPlt == this)
     getParent()->Info = In.GotPlt->getParent()->SectionIndex;
diff --git a/lld/test/ELF/aarch64-gnu-ifunc.s b/lld/test/ELF/aarch64-gnu-ifunc.s
index 0a38fba..9a15f13 100644
--- a/lld/test/ELF/aarch64-gnu-ifunc.s
+++ b/lld/test/ELF/aarch64-gnu-ifunc.s
@@ -15,7 +15,7 @@
 // CHECK-NEXT:  Address: [[RELA:.*]]
 // CHECK-NEXT:  Offset: 0x158
 // CHECK-NEXT:  Size: 48
-// CHECK-NEXT:  Link: 6
+// CHECK-NEXT:  Link: 0
 // CHECK-NEXT:  Info: 4
 // CHECK-NEXT:  AddressAlignment: 8
 // CHECK-NEXT:  EntrySize: 24
diff --git a/lld/test/ELF/gnu-ifunc-i386.s b/lld/test/ELF/gnu-ifunc-i386.s
index 2ddf80c..bfc1587 100644
--- a/lld/test/ELF/gnu-ifunc-i386.s
+++ b/lld/test/ELF/gnu-ifunc-i386.s
@@ -15,7 +15,7 @@
 // CHECK-NEXT:  Address: [[RELA:.*]]
 // CHECK-NEXT:  Offset: 0xD4
 // CHECK-NEXT:  Size: 16
-// CHECK-NEXT:  Link: 6
+// CHECK-NEXT:  Link: 0
 // CHECK-NEXT:  Info: 4
 // CHECK-NEXT:  AddressAlignment: 4
 // CHECK-NEXT:  EntrySize: 8
diff --git a/lld/test/ELF/gnu-ifunc.s b/lld/test/ELF/gnu-ifunc.s
index 5aa5b0a..25c71b0 100644
--- a/lld/test/ELF/gnu-ifunc.s
+++ b/lld/test/ELF/gnu-ifunc.s
@@ -15,16 +15,13 @@
 // CHECK-NEXT:  Address: [[RELA:.*]]
 // CHECK-NEXT:  Offset: 0x158
 // CHECK-NEXT:  Size: 48
-// CHECK-NEXT:  Link: [[SYMTAB:.*]]
+// CHECK-NEXT:  Link: 0
 // CHECK-NEXT:  Info: [[GOTPLT:.*]]
 // CHECK-NEXT:  AddressAlignment: 8
 // CHECK-NEXT:  EntrySize: 24
 // CHECK-NEXT: }
 // CHECK:      Index: [[GOTPLT]]
 // CHECK-NEXT: Name: .got.plt
-// CHECK:      Index: [[SYMTAB]]
-// CHECK-NEXT: Name: .symtab
-// CHECK-NEXT: Type: SHT_SYMTAB
 // CHECK:      Relocations [
 // CHECK-NEXT:   Section ({{.*}}) .rela.plt {
 // CHECK-NEXT:     0x202000 R_X86_64_IRELATIVE
-- 
2.7.4