[PATCH] D53993: [ELF] Set sh_link to 0 in static link to make GNU strip happy

[Fangrui Song via Phabricator via llvm-commits]

MaskRay updated this revision to Diff 172212.
MaskRay edited the summary of this revision.
MaskRay removed a subscriber: javed.absar.
MaskRay added a comment.

A simple reproduce command. I forgot to add --verbatim in my arc diff command :)


Repository:
  rLLD LLVM Linker

https://reviews.llvm.org/D53993

Files:
  ELF/SyntheticSections.cpp
  test/ELF/aarch64-gnu-ifunc.s
  test/ELF/gnu-ifunc-i386.s
  test/ELF/gnu-ifunc.s


Index: test/ELF/gnu-ifunc.s
===================================================================
--- test/ELF/gnu-ifunc.s
+++ 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
Index: test/ELF/gnu-ifunc-i386.s
===================================================================
--- test/ELF/gnu-ifunc-i386.s
+++ 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
Index: test/ELF/aarch64-gnu-ifunc.s
===================================================================
--- test/ELF/aarch64-gnu-ifunc.s
+++ 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
Index: ELF/SyntheticSections.cpp
===================================================================
--- ELF/SyntheticSections.cpp
+++ ELF/SyntheticSections.cpp
@@ -1491,15 +1491,15 @@
 }
 
 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, .rela?.plt contains R_*_IRELATIVE
+  // relocations due to IFUNC (e.g. strcpy). Just set sh_link to 0 as there is
+  // no .dynsym. We cannot set it to .symtab as otherwise GNU strip (as of
+  // 2018-10) will change the address of .rela.plt (and rename it to
+  // .rela.got.plt) and break __rela_iplt_{start,end} used in
+  // glibc/csu/libc-start.c:apply_irel. Note, GNU readelf will warn "Link field
+  // (0) should index a symtab section", but we can live with that.
+  getParent()->Link =
+      In.DynSymTab ? In.DynSymTab->getParent()->SectionIndex : 0;
 
   if (In.RelaIplt == this || In.RelaPlt == this)
     getParent()->Info = In.GotPlt->getParent()->SectionIndex;


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