[ARM] Fix RELA relocations for 32bit ARM.

RELA relocations for 32 bit ARM ignored the addend. Some tools generate
them instead of REL type relocations. This fixes PR50473.

    Reviewed By: MaskRay, peter.smith

    Differential Revision: https://reviews.llvm.org/D105214

Author: Wolfgang Pieb

llvm/lib/Object/RelocationResolver.cpp

@@ -312,12 +312,17 @@ static bool supportsARM(uint64_t Type) {
 }
 
 static uint64_t resolveARM(uint64_t Type, uint64_t Offset, uint64_t S,
-                           uint64_t LocData, int64_t /*Addend*/) {
+                           uint64_t LocData, int64_t Addend) {
+  // Support both RELA and REL relocations. The caller is responsible
+  // for supplying the correct values for LocData and Addend, i.e.
+  // Addend == 0 for REL and LocData == 0 for RELA.
+  assert((LocData == 0 || Addend == 0) &&
+         "one of LocData and Addend must be 0");
   switch (Type) {
   case ELF::R_ARM_ABS32:
-    return (S + LocData) & 0xFFFFFFFF;
+    return (S + LocData + Addend) & 0xFFFFFFFF;
   case ELF::R_ARM_REL32:
-    return (S + LocData - Offset) & 0xFFFFFFFF;
+    return (S + LocData + Addend - Offset) & 0xFFFFFFFF;
   }
   llvm_unreachable("Invalid relocation type");
 }
@@ -744,8 +749,13 @@ uint64_t resolveRelocation(RelocationResolver Resolver, const RelocationRef &R,
         return Elf64BEObj->getRelSection(R.getRawDataRefImpl())->sh_type;
       };
 
-      if (GetRelSectionType() == ELF::SHT_RELA)
+      if (GetRelSectionType() == ELF::SHT_RELA) {
         Addend = getELFAddend(R);
+        // RISCV relocations use both LocData and Addend.
+        if (Obj->getArch() != Triple::riscv32 &&
+            Obj->getArch() != Triple::riscv64)
+          LocData = 0;
+      }
     }
 
     return Resolver(R.getType(), R.getOffset(), S, LocData, Addend);

llvm/test/DebugInfo/ARM/dwarfdump-rela.yaml

@@ -0,0 +1,87 @@
+# Test if we are handling RELA relocations for ARM correctly using llvm-dwarfdump.
+#
+# RUN: yaml2obj %s -o %t
+# RUN: llvm-dwarfdump -i %t | FileCheck %s
+
+# CHECK:      DW_TAG_compile_unit
+# CHECK-NEXT: DW_AT_name {{.*}}("correct")
+# CHECK-NEXT: DW_AT_type ([[TYPEDIE:0x[0-9A-Fa-f]+]] "correct")
+# CHECK:      [[TYPEDIE]]: DW_TAG_base_type
+# CHECK-NEXT: DW_AT_name {{.*}}("correct")
+
+--- !ELF
+FileHeader:
+  Class:           ELFCLASS32
+  Data:            ELFDATA2LSB
+  Type:            ET_REL
+  Machine:         EM_ARM
+  Flags:           [ EF_ARM_EABI_VER5 ]
+Sections:
+  # A rudimentary v5 compile unit with an AT_name and an AT_type referencing
+  # a rudimentary DW_TAG_base_type DIE with an AT_name attribute.
+  - Name:            .debug_info
+    Type:            SHT_PROGBITS
+    Content:         17000000050001040000000001A000000000000000020000000000
+  - Name:            .debug_abbrev
+    Type:            SHT_PROGBITS
+    Content:         011101030E49130000022400030E0000
+  - Name:            .debug_str
+    Type:            SHT_PROGBITS
+  - Name:            .rela.debug_info
+    Type:            SHT_RELA
+    Link:            .symtab
+    AddressAlign:    0x4
+    Offset:          0x929
+    Info:            .debug_info
+    Relocations:
+      - Offset:          0x8
+        Symbol:          .debug_abbrev
+        Type:            R_ARM_ABS32
+      # The compile unit name is found via a R_ARM_ABS32 relocation.
+      - Offset:          0xD
+        Symbol:          .debug_str
+        Type:            R_ARM_ABS32
+        Addend:          6
+      # The DW_TAG_base_type is found via a R_ARM_REL32 relocation.
+      # This is completely artificial and unlikely to be ever generated
+      # by a compiler or other tool. We make sure that the relocation is
+      # resolved by (Symbol - Offset + Addend).
+      - Offset:          0x11
+        Symbol:          .debug_info
+        Type:            R_ARM_REL32
+        Addend:          0x26
+      - Offset:          0x16
+        Symbol:          .debug_str
+        Type:            R_ARM_ABS32
+        Addend:          6
+  - Type:            SectionHeaderTable
+    Sections:
+      - Name:            .symtab
+      - Name:            .strtab
+      - Name:            .shstrtab
+      - Name:            .debug_info
+      - Name:            .debug_abbrev
+      - Name:            .debug_str
+      - Name:            .rela.debug_info
+Symbols:
+  - Name:            test.cpp
+    Type:            STT_FILE
+    Index:           SHN_ABS
+  - Name:            .debug_info
+    Type:            STT_SECTION
+    Section:         .debug_info
+  - Name:            .debug_abbrev
+    Type:            STT_SECTION
+    Section:         .debug_abbrev
+  - Name:            .debug_str
+    Type:            STT_SECTION
+    Section:         .debug_str
+  - Name:            .debug_info_cudie
+    Type:            STT_OBJECT
+    Section:         .debug_info
+    Value:           0xC
+DWARF:
+  debug_str:
+    - 'wrong'
+    - 'correct'
+...