[PATCH] D47602: Correct aligment computation for shared object symbols

[Han Shen via Phabricator via llvm-commits]

shenhan updated this revision to Diff 149538.
shenhan added a comment.

@pcc thanks for the review. Updated the patch -

1. if getAlignment sees a ABS symbols, returns 0
2. initialize Ret to UINT64_MAX
3. in "addCopyRelSymbol", errors out if alignment is 0.
4. unit test case that tests for proper handling of ABS symbols.


Repository:
  rLLD LLVM Linker

https://reviews.llvm.org/D47602

Files:
  ELF/InputFiles.cpp
  ELF/Relocations.cpp
  test/ELF/Inputs/copy-relocation-zero-abs-addr.s
  test/ELF/copy-relocation-zero-abs-addr.s


Index: test/ELF/copy-relocation-zero-abs-addr.s
===================================================================
--- /dev/null
+++ 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: ]
Index: test/ELF/Inputs/copy-relocation-zero-abs-addr.s
===================================================================
--- /dev/null
+++ test/ELF/Inputs/copy-relocation-zero-abs-addr.s
@@ -0,0 +1,7 @@
+.globl ver1
+.globl ver2
+ ver1 = 0x0
+ ver2 = 0x0
+
+.type foo, at object
+.comm foo,16,16
Index: ELF/Relocations.cpp
===================================================================
--- ELF/Relocations.cpp
+++ ELF/Relocations.cpp
@@ -529,6 +529,9 @@
   uint64_t SymSize = SS.getSize();
   if (SymSize == 0)
     fatal("cannot create a copy relocation for symbol " + toString(SS));
+  if (SS.Alignment == 0)
+    fatal("cannot create a copy relocation for symbol "
+          "with absolute address " + toString(SS));
 
   // See if this symbol is in a read-only segment. If so, preserve the symbol's
   // memory protection by reserving space in the .bss.rel.ro section.
Index: ELF/InputFiles.cpp
===================================================================
--- ELF/InputFiles.cpp
+++ ELF/InputFiles.cpp
@@ -895,7 +895,12 @@
 template <class ELFT>
 uint32_t SharedFile<ELFT>::getAlignment(ArrayRef<Elf_Shdr> Sections,
                                         const Elf_Sym &Sym) {
-  uint64_t Ret = 1;
+  // If a sym has absolute address, no alignment information is
+  // needed (because it's final address is fixed), return 0.
+  if (Sym.st_shndx == SHN_ABS)
+    return 0;
+
+  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())


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D47602.149538.patch
Type: text/x-patch
Size: 3169 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20180601/4817f77d/attachment.bin>