Correct aligment computation for shared object symbols.

The original computation for shared object symbol alignment is wrong when
st_value equals 0. It is very unusual for dso symbols to have st_value equal 0.
But when it happens, it causes obscure run time bugs.

Differential Revision: https://reviews.llvm.org/D47602

llvm-svn: 334135

lld/ELF/InputFiles.cpp

@@ -900,16 +900,12 @@ std::vector<const typename ELFT::Verdef *> SharedFile<ELFT>::parseVerdefs() {
 template <class ELFT>
 uint32_t SharedFile<ELFT>::getAlignment(ArrayRef<Elf_Shdr> Sections,
                                         const Elf_Sym &Sym) {
-  uint64_t Ret = 1;
+  uint64_t Ret = UINT64_MAX;
   if (Sym.st_value)
     Ret = 1ULL << countTrailingZeros((uint64_t)Sym.st_value);
   if (0 < Sym.st_shndx && Sym.st_shndx < Sections.size())
     Ret = std::min<uint64_t>(Ret, Sections[Sym.st_shndx].sh_addralign);
-
-  if (Ret > UINT32_MAX)
-    error(toString(this) + ": alignment too large: " +
-          CHECK(Sym.getName(this->StringTable), this));
-  return Ret;
+  return (Ret > UINT32_MAX) ? 0 : Ret;
 }
 
 // Fully parse the shared object file. This must be called after parseSoName().

lld/ELF/Relocations.cpp

@@ -528,7 +528,7 @@ static void replaceWithDefined(Symbol &Sym, SectionBase *Sec, uint64_t Value,
 template <class ELFT> static void addCopyRelSymbol(SharedSymbol &SS) {
   // Copy relocation against zero-sized symbol doesn't make sense.
   uint64_t SymSize = SS.getSize();
-  if (SymSize == 0)
+  if (SymSize == 0 || SS.Alignment == 0)
     fatal("cannot create a copy relocation for symbol " + toString(SS));
 
   // See if this symbol is in a read-only segment. If so, preserve the symbol's

lld/test/ELF/Inputs/copy-relocation-zero-abs-addr.s

@@ -0,0 +1,7 @@
+.globl ver1
+.globl ver2
+ ver1 = 0x0
+ ver2 = 0x0
+
+.type foo,@object
+.comm foo,16,16

lld/test/ELF/Inputs/copy-relocation-zero-nonabs-addr.s

@@ -0,0 +1,7 @@
+.balign 1024
+.type foo,@object
+.globl foo
+goo:
+foo:
+  .long 0
+  .size foo,4

lld/test/ELF/Inputs/copy-relocation-zero-nonabs-addr.script

@@ -0,0 +1,3 @@
+SECTIONS {
+  goo = 0;
+};

lld/test/ELF/copy-relocation-zero-abs-addr.s

@@ -0,0 +1,44 @@
+// REQUIRES: x86
+// RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %p/Inputs/copy-relocation-zero-abs-addr.s -o %t.o
+// RUN: ld.lld -shared -o %t2.so %t.o
+// RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t3.o
+// RUN: ld.lld %t2.so %t3.o -o %t4
+// RUN: llvm-readobj -symbols %t2.so | FileCheck -check-prefix=ABSADDR %s
+// RUN: llvm-readobj -s -r --expand-relocs %t4 | FileCheck %s
+
+// This tests that symbols with absolute addresses are properly
+// handled. Normal DSO symbols are handled as usual.
+
+.text
+.globl _start
+_start:
+  movl $5, foo
+
+// ABSADDR:        Name: ver1
+// ABSADDR-NEXT:   Value: 0x0
+// ABSADDR-NEXT:   Size: 0
+// ABSADDR-NEXT:   Binding: Global
+// ABSADDR-NEXT:   Type: None
+// ABSADDR-NEXT:   Other: 0
+// ABSADDR-NEXT:   Section: Absolute (0xFFF1)
+// ABSADDR-NEXT: }
+// ABSADDR-NEXT: Symbol {
+// ABSADDR-NEXT:   Name: ver2
+// ABSADDR-NEXT:   Value: 0x0
+// ABSADDR-NEXT:   Size: 0
+// ABSADDR-NEXT:   Binding: Global
+// ABSADDR-NEXT:   Type: None
+// ABSADDR-NEXT:   Other: 0
+// ABSADDR-NEXT:   Section: Absolute (0xFFF1)
+// ABSADDR-NEXT: }
+
+// CHECK:      Relocations [
+// CHECK-NEXT:   Section (5) .rela.dyn {
+// CHECK-NEXT:     Relocation {
+// CHECK-NEXT:       Offset:
+// CHECK-NEXT:       Type: R_X86_64_COPY
+// CHECK-NEXT:       Symbol: foo
+// CHECK-NEXT:       Addend:
+// CHECK-NEXT:     }
+// CHECK-NEXT:   }
+// CHECK-NEXT: ]

lld/test/ELF/copy-relocation-zero-nonabs-addr.s

@@ -0,0 +1,29 @@
+// REQUIRES: x86
+// RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %p/Inputs/copy-relocation-zero-nonabs-addr.s -o %t1.o
+// RUN: ld.lld -Ttext=0 -o %t2.so --script=%p/Inputs/copy-relocation-zero-nonabs-addr.script %t1.o -shared
+// RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t3.o
+// RUN: ld.lld %t2.so %t3.o -o %t4
+// RUN: llvm-readobj --symbols %t2.so | FileCheck --check-prefix=CHECKSO %s
+// RUN: llvm-readobj --symbols %t4 | FileCheck %s
+
+.text
+.globl _start
+_start:
+  movl $5, foo
+
+// Make sure foo has st_value == 0.
+// CHECKSO:      Name: foo
+// CHECKSO-NEXT: Value: 0x0
+// CHECKSO-NEXT: Size: 4
+// CHECKSO-NEXT: Binding: Global
+// CHECKSO-NEXT: Type: Object
+// CHECKSO-NEXT: Other: 0
+// CHECKSO-NEXT: Section: .text
+
+// When foo has st_value == 0, it carries the section alignment.
+// In this case, section alignment is 2^10, 0x202400 meets the requirement.
+// CHECK:      Name: foo
+// CHECK-NEXT: Value: 0x202400
+// CHECK-NEXT: Size: 4
+// CHECK-NEXT: Binding: Global
+// CHECK-NEXT: Type: Object