[PATCH] D54782: [ELF] Take IPLT header size in account when -z retpolineplt is specified

[Fangrui Song via Phabricator via llvm-commits]

MaskRay created this revision.
Herald added subscribers: llvm-commits, krytarowski, arichardson, emaste.
Herald added a reviewer: espindola.

This fixes PR39711: -z now -z retpolineplt has broken IPLT

Statically linked executable does not have PLT, but may have IPLT with zero header size. When -z retpolineplt is specified, however, the repoline header size should be taken into account.

I've checked that this fixes the FreeBSD reproduce in PR39711 and a Linux program linked against glibc.


Repository:
  rLLD LLVM Linker

https://reviews.llvm.org/D54782

Files:
  ELF/Symbols.cpp
  ELF/SyntheticSections.cpp


Index: ELF/SyntheticSections.cpp
===================================================================
--- ELF/SyntheticSections.cpp
+++ ELF/SyntheticSections.cpp
@@ -2280,7 +2280,8 @@
 PltSection::PltSection(bool IsIplt)
     : SyntheticSection(SHF_ALLOC | SHF_EXECINSTR, SHT_PROGBITS, 16,
                        Config->EMachine == EM_PPC64 ? ".glink" : ".plt"),
-      HeaderSize(IsIplt ? 0 : Target->PltHeaderSize), IsIplt(IsIplt) {
+      HeaderSize(IsIplt && !Config->ZRetpolineplt ? 0 : Target->PltHeaderSize),
+      IsIplt(IsIplt) {
   // The PLT needs to be writable on SPARC as the dynamic linker will
   // modify the instructions in the PLT entries.
   if (Config->EMachine == EM_SPARCV9)
@@ -2290,7 +2291,7 @@
 void PltSection::writeTo(uint8_t *Buf) {
   // At beginning of PLT but not the IPLT, we have code to call the dynamic
   // linker to resolve dynsyms at runtime. Write such code.
-  if (!IsIplt)
+  if (!IsIplt || Config->ZRetpolineplt)
     Target->writePltHeader(Buf);
   size_t Off = HeaderSize;
   // The IPlt is immediately after the Plt, account for this in RelOff
Index: ELF/Symbols.cpp
===================================================================
--- ELF/Symbols.cpp
+++ ELF/Symbols.cpp
@@ -144,8 +144,11 @@
 }
 
 uint64_t Symbol::getPltVA() const {
-  if (this->IsInIplt)
+  if (this->IsInIplt) {
+    if (Config->ZRetpolineplt)
+      return In.Plt->getVA() + Target->getPltEntryOffset(PltIndex);
     return In.Iplt->getVA() + PltIndex * Target->PltEntrySize;
+  }
   return In.Plt->getVA() + Target->getPltEntryOffset(PltIndex);
 }
 


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