[llvm] 79030a2 - [llvm-objdump] Fix dumping dynamic relative relocations for SHT_REL

[Alex Richardson via llvm-commits]

Author: Alex Richardson
Date: 2021-04-28T12:23:00+01:00
New Revision: 79030a22cc0fce072ec411b167baf154ffee4e0e

URL: https://github.com/llvm/llvm-project/commit/79030a22cc0fce072ec411b167baf154ffee4e0e
DIFF: https://github.com/llvm/llvm-project/commit/79030a22cc0fce072ec411b167baf154ffee4e0e.diff

LOG: [llvm-objdump] Fix dumping dynamic relative relocations for SHT_REL

Previously printing R_386_RELATIVE relocations would trigger
`error: can't read an entry at 0x40: it goes past the end of the section (0x40)`
I found this while writing a test case for LLD (D100490).
This also includes some minor cleanup in the elf-dynamic-relcos.test
llvm-objdump test based on the newly added test.

Reviewed By: jhenderson, MaskRay

Differential Revision: https://reviews.llvm.org/D100489

Added: 
    llvm/test/tools/llvm-objdump/X86/elf-dynamic-relocs-rel.test

Modified: 
    llvm/test/tools/llvm-objdump/X86/elf-dynamic-relocs.test
    llvm/tools/llvm-objdump/ELFDump.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/test/tools/llvm-objdump/X86/elf-dynamic-relocs-rel.test b/llvm/test/tools/llvm-objdump/X86/elf-dynamic-relocs-rel.test
new file mode 100644
index 0000000000000..f62f5e38f9711
--- /dev/null
+++ b/llvm/test/tools/llvm-objdump/X86/elf-dynamic-relocs-rel.test
@@ -0,0 +1,62 @@
+## Show that llvm-objdump can dump dynamic relocations for Elf_Rel relocations
+## where the relocation references a symbol and where it does not.
+
+# RUN: yaml2obj %s -o %t
+# RUN: llvm-objdump --dynamic-reloc %t | FileCheck %s
+# RUN: llvm-objdump -R %t | FileCheck %s
+
+# CHECK:      DYNAMIC RELOCATION RECORDS
+# CHECK-NEXT: 00000030 R_386_RELATIVE *ABS*
+# CHECK-NEXT: 00000010 R_386_NONE foo
+# CHECK-EMPTY:
+
+--- !ELF
+FileHeader:
+  Class:           ELFCLASS32
+  Data:            ELFDATA2LSB
+  Type:            ET_DYN
+  Machine:         EM_386
+ProgramHeaders:
+  - Type:     PT_LOAD
+    FirstSec: .rel.dyn
+    LastSec:  .data
+  - Type:     PT_DYNAMIC
+    VAddr:    0x10
+    FirstSec: .dynamic
+    LastSec:  .dynamic
+Sections:
+  - Name:            .rel.dyn
+    Type:            SHT_REL
+    Link:            .dynsym
+    Flags:           [ SHF_ALLOC ]
+    AddressAlign:    0x4
+    Relocations:
+      - Offset:          0x30
+        Type:            R_386_RELATIVE
+      - Offset:          0x10
+        Symbol:          foo
+        Type:            R_386_NONE
+  - Name:            .dynamic
+    Type:            SHT_DYNAMIC
+    Flags:           [ SHF_ALLOC ]
+    Link:            .dynstr
+    AddressAlign:    0x4
+    Entries:
+      - Tag:             DT_REL
+        Value:           0x0
+      - Tag:             DT_RELSZ
+        Value:           0x10
+      - Tag:             DT_RELENT
+        Value:           0x8
+      - Tag:             DT_RELCOUNT
+        Value:           0x1
+      - Tag:             DT_NULL
+        Value:           0x0
+  - Name:            .data
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_WRITE, SHF_ALLOC ]
+    AddressAlign:    0x4
+    Content:         '80110000'
+DynamicSymbols:
+  - Name:    foo
+    Section: .data

diff  --git a/llvm/test/tools/llvm-objdump/X86/elf-dynamic-relocs.test b/llvm/test/tools/llvm-objdump/X86/elf-dynamic-relocs.test
index 37ed0555437ba..6fae5b3328841 100644
--- a/llvm/test/tools/llvm-objdump/X86/elf-dynamic-relocs.test
+++ b/llvm/test/tools/llvm-objdump/X86/elf-dynamic-relocs.test
@@ -3,14 +3,14 @@
 ## properly identify relocation tables.
 
 # RUN: yaml2obj %s -o %t
-# RUN: llvm-objdump --dynamic-reloc %t | FileCheck --implicit-check-not=R_X86 %s
-# RUN: llvm-objdump -R %t | FileCheck --implicit-check-not=R_X86 %s
+# RUN: llvm-objdump --dynamic-reloc %t | FileCheck %s
+# RUN: llvm-objdump -R %t | FileCheck %s
 
-# CHECK:      file format elf64-x86-64
 # CHECK:      DYNAMIC RELOCATION RECORDS
 # CHECK-NEXT: 0000000000000000 R_X86_64_RELATIVE *ABS*
 # CHECK-NEXT: 0000000000000000 R_X86_64_JUMP_SLOT bar
 # CHECK-NEXT: 0000000000000008 R_X86_64_NONE foo
+# CHECK-EMPTY:
 
 --- !ELF
 FileHeader:
@@ -50,7 +50,7 @@ Sections:
     Flags:        [SHF_ALLOC]
     Relocations:
       - Offset: 0
-        Symbol: 2 # bar
+        Symbol: bar
         Type:   R_X86_64_JUMP_SLOT
   - Name:         .rel.dyn
     Type:         SHT_REL
@@ -61,7 +61,7 @@ Sections:
     Flags:        [SHF_ALLOC]
     Relocations:
       - Offset: 8
-        Symbol: 1 # foo
+        Symbol: foo
         Type:   R_X86_64_NONE
   - Name:         .dynamic
     Type:         SHT_DYNAMIC

diff  --git a/llvm/tools/llvm-objdump/ELFDump.cpp b/llvm/tools/llvm-objdump/ELFDump.cpp
index 1c4d59179cc72..31af0cda5e327 100644
--- a/llvm/tools/llvm-objdump/ELFDump.cpp
+++ b/llvm/tools/llvm-objdump/ELFDump.cpp
@@ -74,7 +74,10 @@ static Error getRelocationValueString(const ELFObjectFile<ELFT> *Obj,
     const typename ELFT::Rela *ERela = Obj->getRela(Rel);
     Addend = ERela->r_addend;
     Undef = ERela->getSymbol(false) == 0;
-  } else if ((*SecOrErr)->sh_type != ELF::SHT_REL) {
+  } else if ((*SecOrErr)->sh_type == ELF::SHT_REL) {
+    const typename ELFT::Rel *ERel = Obj->getRel(Rel);
+    Undef = ERel->getSymbol(false) == 0;
+  } else {
     return make_error<BinaryError>();
   }