[llvm] [Object][AMDGPU] Support REL relocations (PR #143966)

[Scott Linder via llvm-commits]

https://github.com/slinder1 created https://github.com/llvm/llvm-project/pull/143966

None

>From e003eabafbcc415479fbfa0b0f405f05f6e53e48 Mon Sep 17 00:00:00 2001
From: Scott Linder <Scott.Linder at amd.com>
Date: Thu, 12 Jun 2025 19:35:06 +0000
Subject: [PATCH] [Object][AMDGPU] Support REL relocations

---
 llvm/docs/AMDGPUUsage.rst                     |  3 +-
 llvm/lib/Object/RelocationResolver.cpp        |  6 +-
 llvm/test/DebugInfo/AMDGPU/dwarfdump-rel.yaml | 86 +++++++++++++++++++
 3 files changed, 92 insertions(+), 3 deletions(-)
 create mode 100644 llvm/test/DebugInfo/AMDGPU/dwarfdump-rel.yaml

diff --git a/llvm/docs/AMDGPUUsage.rst b/llvm/docs/AMDGPUUsage.rst
index 174a497c51b26..4aea702a702ab 100644
--- a/llvm/docs/AMDGPUUsage.rst
+++ b/llvm/docs/AMDGPUUsage.rst
@@ -2709,7 +2709,8 @@ The following relocation types are supported:
 the ``mesa3d`` OS, which does not support ``R_AMDGPU_ABS64``.
 
 There is no current OS loader support for 32-bit programs and so
-``R_AMDGPU_ABS32`` is not used.
+``R_AMDGPU_ABS32`` is only generated for static relocations, for example to
+implement some DWARF32 forms.
 
 .. _amdgpu-loaded-code-object-path-uniform-resource-identifier:
 
diff --git a/llvm/lib/Object/RelocationResolver.cpp b/llvm/lib/Object/RelocationResolver.cpp
index 8cf748aa5681c..b6318bbe3ab74 100644
--- a/llvm/lib/Object/RelocationResolver.cpp
+++ b/llvm/lib/Object/RelocationResolver.cpp
@@ -274,11 +274,13 @@ static bool supportsAmdgpu(uint64_t Type) {
 }
 
 static uint64_t resolveAmdgpu(uint64_t Type, uint64_t Offset, uint64_t S,
-                              uint64_t /*LocData*/, int64_t Addend) {
+                              uint64_t LocData, int64_t Addend) {
+  assert((LocData == 0 || Addend == 0) &&
+         "one of LocData and Addend must be 0");
   switch (Type) {
   case ELF::R_AMDGPU_ABS32:
   case ELF::R_AMDGPU_ABS64:
-    return S + Addend;
+    return S + LocData + Addend;
   default:
     llvm_unreachable("Invalid relocation type");
   }
diff --git a/llvm/test/DebugInfo/AMDGPU/dwarfdump-rel.yaml b/llvm/test/DebugInfo/AMDGPU/dwarfdump-rel.yaml
new file mode 100644
index 0000000000000..23b7f087e9570
--- /dev/null
+++ b/llvm/test/DebugInfo/AMDGPU/dwarfdump-rel.yaml
@@ -0,0 +1,86 @@
+# RUN: yaml2obj %s -o %t
+# RUN: llvm-dwarfdump -i %t | FileCheck %s
+
+# Test REL relocation handling for AMDGPU
+
+# CHECK: DW_TAG_compile_unit
+# CHECK: DW_AT_producer ("dxc")
+# CHECK: DW_AT_name (".\\example.hlsl")
+# CHECK: DW_AT_str_offsets_base (0x00000008)
+
+--- !ELF
+FileHeader:
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  OSABI:           ELFOSABI_AMDGPU_PAL
+  Type:            ET_REL
+  Machine:         EM_AMDGPU
+  Flags:           [ EF_AMDGPU_MACH_AMDGCN_GFX1201 ]
+  SectionHeaderStringTable: .strtab
+Sections:
+  - Name:            .debug_abbrev
+    Type:            SHT_PROGBITS
+    AddressAlign:    0x1
+    Content:         01110125251305032572171017110B120673178C0117000000
+  - Name:            .debug_info
+    Type:            SHT_PROGBITS
+    AddressAlign:    0x1
+    Content:         23000000050001080000000001000400010800000000000000005C000000080000000C00000000
+  - Name:            .debug_str_offsets
+    Type:            SHT_PROGBITS
+    AddressAlign:    0x1
+    Content:         0C000000050000000000000004000000
+  - Name:            .rel.debug_info
+    Type:            SHT_REL
+    Flags:           [ SHF_INFO_LINK ]
+    Link:            .symtab
+    AddressAlign:    0x8
+    Info:            .debug_info
+    Relocations:
+      - Offset:          0x8
+        Symbol:          .debug_abbrev
+        Type:            R_AMDGPU_ABS32
+      - Offset:          0x11
+        Symbol:          .debug_str_offsets
+        Type:            R_AMDGPU_ABS32
+  - Name:            .rel.debug_str_offsets
+    Type:            SHT_REL
+    Flags:           [ SHF_INFO_LINK ]
+    Link:            .symtab
+    AddressAlign:    0x8
+    Info:            .debug_str_offsets
+    Relocations:
+      - Offset:          0x8
+        Symbol:          .debug_str
+        Type:            R_AMDGPU_ABS32
+      - Offset:          0xC
+        Symbol:          .debug_str
+        Type:            R_AMDGPU_ABS32
+  - Type:            SectionHeaderTable
+    Sections:
+      - Name:            .strtab
+      - Name:            .debug_abbrev
+      - Name:            .debug_info
+      - Name:            .rel.debug_info
+      - Name:            .debug_str_offsets
+      - Name:            .rel.debug_str_offsets
+      - Name:            .debug_str
+      - Name:            .symtab
+Symbols:
+  - Name:            .debug_abbrev
+    Type:            STT_SECTION
+    Section:         .debug_abbrev
+  - Name:            .debug_info
+    Type:            STT_SECTION
+    Section:         .debug_info
+  - Name:            .debug_str_offsets
+    Type:            STT_SECTION
+    Section:         .debug_str_offsets
+  - Name:            .debug_str
+    Type:            STT_SECTION
+    Section:         .debug_str
+DWARF:
+  debug_str:
+    - 'dxc'
+    - '.\example.hlsl'
+...