[llvm] e836223 - [Object][AMDGPU] Support REL relocations (#143966)

[via llvm-commits]

Author: Scott Linder
Date: 2025-06-16T15:03:02-04:00
New Revision: e8362234f60612a250d832cc8d0f68fe7fa9ea17

URL: https://github.com/llvm/llvm-project/commit/e8362234f60612a250d832cc8d0f68fe7fa9ea17
DIFF: https://github.com/llvm/llvm-project/commit/e8362234f60612a250d832cc8d0f68fe7fa9ea17.diff

LOG: [Object][AMDGPU] Support REL relocations (#143966)

Shaders compiled with DXC/LLPC generate these relocations, and even if
that changes in the future we want to handle existing binaries. The
friction to support this and the maintenance cost long term both seem
incredibly low, considering other targets like ARM support both REL/RELA
static relocations behind the same interface.

Added: 
    llvm/test/DebugInfo/AMDGPU/dwarfdump-rel.yaml

Modified: 
    llvm/docs/AMDGPUUsage.rst
    llvm/lib/Object/RelocationResolver.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/docs/AMDGPUUsage.rst b/llvm/docs/AMDGPUUsage.rst
index 39f04f8e01b85..c052b076c21c3 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'
+...