[PATCH] D73399: [ELF][PPC32] Fix st_value of canonical PLT

[Fangrui Song via Phabricator via llvm-commits]

MaskRay created this revision.
MaskRay added a reviewer: Bdragon28.
Herald added subscribers: llvm-commits, jsji, kbarton, arichardson, nemanjai, emaste.
Herald added a reviewer: espindola.
Herald added a project: LLVM.

Unlikely other targets, ppc32 .glink (PltSection) has a footer
(PLTresolve), not a header. Setting pltHeaderSize to 0x40 can make
st_value of an canonical PLT entry off by 0x40.

  // Relocations.cpp
  replaceWithDefined(
      sym, in.plt,
      target->pltHeaderSize + target->pltEntrySize * sym.pltIndex, 0);

Add PltSection::footerSize to support ppc32.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D73399

Files:
  lld/ELF/Arch/PPC.cpp
  lld/ELF/SyntheticSections.cpp
  lld/ELF/SyntheticSections.h
  lld/test/ELF/ppc32-canonical-plt-pcrel.s


Index: lld/test/ELF/ppc32-canonical-plt-pcrel.s
===================================================================
--- /dev/null
+++ lld/test/ELF/ppc32-canonical-plt-pcrel.s
@@ -0,0 +1,32 @@
+# REQUIRES: ppc
+
+## Test that we create canonical PLT entries for -no-pie.
+
+# RUN: llvm-mc -filetype=obj -triple=powerpc %s -o %t.o
+# RUN: llvm-mc -filetype=obj -triple=powerpc %p/Inputs/canonical-plt-pcrel.s -o %t1.o
+# RUN: ld.lld %t1.o -o %t1.so -shared -soname=so
+
+# RUN: ld.lld %t.o %t1.so -o %t
+# RUN: llvm-readobj -r %t | FileCheck --check-prefix=REL %s
+# RUN: llvm-readelf -S --dyn-syms %t | FileCheck %s
+
+# REL:      Relocations [
+# REL-NEXT:   .rela.plt {
+# REL-NEXT:     R_PPC_JMP_SLOT func 0x0
+# REL-NEXT:     R_PPC_JMP_SLOT ifunc 0x0
+# REL-NEXT:   }
+# REL-NEXT: ]
+
+# CHECK: .glink PROGBITS 100101dc
+
+## The canonical PLT entry of func is at &.glink[0]
+## The canonical PLT entry of ifunc is at &.glink[1]
+# CHECK: 100101dc 0 FUNC GLOBAL DEFAULT UND func
+# CHECK: 100101e0 0 FUNC GLOBAL DEFAULT UND ifunc
+
+.globl _start
+_start:
+  lis 3, func at ha
+  la 3, func at l(3)
+  lis 4, ifunc at ha
+  la 4, ifunc at l(4)
Index: lld/ELF/SyntheticSections.h
===================================================================
--- lld/ELF/SyntheticSections.h
+++ lld/ELF/SyntheticSections.h
@@ -684,6 +684,7 @@
   size_t getNumEntries() const { return entries.size(); }
 
   size_t headerSize = 0;
+  size_t footerSize = 0;
 
 private:
   std::vector<const Symbol *> entries;
Index: lld/ELF/SyntheticSections.cpp
===================================================================
--- lld/ELF/SyntheticSections.cpp
+++ lld/ELF/SyntheticSections.cpp
@@ -2449,6 +2449,9 @@
   if (config->emachine == EM_PPC || config->emachine == EM_PPC64) {
     name = ".glink";
     alignment = 4;
+    // PLTresolve is at the bottom of .glink
+    if (config->emachine == EM_PPC)
+      footerSize = 64;
   }
 
   // On x86 when IBT is enabled, this section contains the second PLT (lazy
@@ -2486,7 +2489,7 @@
 }
 
 size_t PltSection::getSize() const {
-  return headerSize + entries.size() * target->pltEntrySize;
+  return headerSize + entries.size() * target->pltEntrySize + footerSize;
 }
 
 bool PltSection::isNeeded() const {
Index: lld/ELF/Arch/PPC.cpp
===================================================================
--- lld/ELF/Arch/PPC.cpp
+++ lld/ELF/Arch/PPC.cpp
@@ -92,7 +92,7 @@
   uint32_t glink = in.plt->getVA(); // VA of .glink
   const uint8_t *end = buf + 64;
   if (config->isPic) {
-    uint32_t afterBcl = in.plt->getSize() - target->pltHeaderSize + 12;
+    uint32_t afterBcl = in.plt->getSize() - 64 + 12; // 12 bytes from PLTresolve
     uint32_t gotBcl = got + 4 - (glink + afterBcl);
     write32(buf + 0, 0x3d6b0000 | ha(afterBcl));  // addis r11,r11,1f-glink at ha
     write32(buf + 4, 0x7c0802a6);                 // mflr r0
@@ -150,7 +150,7 @@
   gotBaseSymInGotPlt = false;
   gotHeaderEntriesNum = 3;
   gotPltHeaderEntriesNum = 0;
-  pltHeaderSize = 64; // size of PLTresolve in .glink
+  pltHeaderSize = 0; // PLTresolve is a footer in .glink
   pltEntrySize = 4;
   ipltEntrySize = 16;
 


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