RuntimeDyldELF: Don't abort on R_AARCH64_NONE relocation

[yota9]

Summary

Do nothing on R_AARCH64_NONE relocation. The relocation is used by BOLT when re-linking the final binary. It is used as a dummy relocation hack in order to stop the RuntimeDyld to skip the allocation of the section.

[MaskRay]

How does BOLT use the relocation type?

(BOLT is in the monorepo now) If you give instructions, reviewers may have a better idea.
While I do not know how ExecutionEngine handles the situation, in other ELF components I review/contribute we really need a test for every relocation type.
This is important to not regress while refactoring code.

[yota9]

Hello @MaskRay . It is used in DwarfLineTable::emitCU as a dummy relocation hack in order to stop the RuntimeDyld to skip the allocation of the section. Also I would like to point that all the other targets have the proper R_*_NONE handling :)

[yota9]

Add test

[lhames]

LGTM.

[MaskRay]

llvm/test/ExecutionEngine/RuntimeDyld/AArch64/ELF_ARM64_none.yaml

4

. after a complete sentence.

In other ELF components we prefer ## for non-RUN non-CHECK comments. I haven't checked whether test/ExecutionEngine wants to follow this convention.

24

remove

R_AARCH64_NONE doesn't need a symbol

[MaskRay]

I'd suggest AARCH64_NONE instead of ARM64_none

[yota9]

@MaskRay I don't mind to rename it, I've named it with ARM64 because most of the tests in this directory are named with arm64.

[MaskRay]

OK. I don't mind that much. Just noticed that the directory name is AArch64/. In ELF, various AArch64/ARM64 related constants are called AARCH64 instead of ARM64.

[yota9]

Done

llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldELF.cpp

LLVM_DEBUG(dbgs() << "resolveAArch64Relocation, LocalAddress: 0x"
                     << " Value: 0x" << format("%llx", Value) << " Type: 0x"
                     << format("%x", Type) << " Addend: 0x"
                     << format("%llx", Addend) << "\n");
 
   switch (Type) {
   default:
     report_fatal_error("Relocation type not implemented yet!");
     break;
+  case ELF::R_AARCH64_NONE:
+    break;
   case ELF::R_AARCH64_ABS16: {
     uint64_t Result = Value + Addend;
     assert(static_cast<int64_t>(Result) >= INT16_MIN && Result < UINT16_MAX);
     write(isBE, TargetPtr, static_cast<uint16_t>(Result & 0xffffU));
     break;
   }
   case ELF::R_AARCH64_ABS32: {
     uint64_t Result = Value + Addend;

llvm/test/ExecutionEngine/RuntimeDyld/AArch64/ELF_ARM64_none.yaml

+# RUN: yaml2obj %s -o %t.o
+# RUN: llvm-rtdyld -triple=arm64-none-linux-gnu %t.o -printline
+
+# Verify rtdyld doesn't abort in presence of R_AARCH64_NONE
+
+!ELF
+FileHeader:
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  OSABI:           ELFOSABI_FREEBSD
+  Type:            ET_REL
+  Machine:         EM_AARCH64
+Sections:
+  - Name:            .text
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC ]
+  - Name:            .rela.text
+    Type:            SHT_RELA
+    Link:            .symtab
+    Info:            .text
+    Relocations:
+      - Offset:          0x0000000000000000
+        Type:            R_AARCH64_NONE
+Symbols:
+  - Name: _main
+    Section: .text
+    Binding: STB_GLOBAL
+    Value: 0
+    Size: 4