Add support for SHT_RELA in vkgc

Currently LLVM generates relocations in an ELF SHT_REL section. To allow for changing the compiler to use SHT_RELA instead, this patch updates vkgcElfReader and vkgcPipelineDumper to support both section types.
GPUOpen-Drivers · Nov 29, 2023 · 631d2e2 · 631d2e2
1 parent bbef90e
commit 631d2e2
Show file tree

Hide file tree

Showing 3 changed files with 57 additions and 13 deletions.
diff --git a/tool/dumper/vkgcPipelineDumper.cpp b/tool/dumper/vkgcPipelineDumper.cpp
@@ -2065,7 +2065,7 @@ OStream &operator<<(OStream &out, ElfReader<Elf> &reader) {
         offset += noteHeaderSize + noteNameSize + alignTo(node->descSize, sizeof(unsigned));
         assert(offset <= section->secHead.sh_size);
       }
-    } else if (strcmp(section->name, RelocName) == 0) {
+    } else if (strcmp(section->name, RelocName) == 0 || strcmp(section->name, RelocAName) == 0) {
       // Output .reloc section
       out << section->name << " (size = " << section->secHead.sh_size << " bytes)\n";
       const unsigned relocCount = reader.getRelocationCount();
@@ -2075,7 +2075,10 @@ OStream &operator<<(OStream &out, ElfReader<Elf> &reader) {
         ElfSymbol elfSym = {};
         reader.getSymbol(reloc.symIdx, &elfSym);
         snprintf(formatBuf, sizeof(formatBuf), "    %-35s", elfSym.pSymName);
-        out << "#" << i << "    " << formatBuf << "    offset = " << reloc.offset << "\n";
+        out << "#" << i << "    " << formatBuf << "    offset = " << reloc.offset;
+        if (reloc.useExplicitAddend)
+          out << ", addend = " << reloc.addend;
+        out << "\n";
       }
     } else if (strncmp(section->name, AmdGpuConfigName, sizeof(AmdGpuConfigName) - 1) == 0) {
       // Output .AMDGPU.config section

diff --git a/util/vkgcElfReader.cpp b/util/vkgcElfReader.cpp
@@ -137,6 +137,8 @@ template <class Elf> Result ElfReader<Elf>::ReadFromBuffer(const void *buffer, s
   // Get section index
   m_symSecIdx = GetSectionIndex(SymTabName);
   m_relocSecIdx = GetSectionIndex(RelocName);
+  if (m_relocSecIdx < 0)
+    m_relocSecIdx = GetSectionIndex(RelocAName);
   m_strtabSecIdx = GetSectionIndex(StrTabName);
   m_textSecIdx = GetSectionIndex(TextName);
 
@@ -210,14 +212,24 @@ template <class Elf> unsigned ElfReader<Elf>::getRelocationCount() const {
 // @param idx : Relocation index
 // @param [out] reloc : Info of the relocation
 template <class Elf> void ElfReader<Elf>::getRelocation(unsigned idx, ElfReloc *reloc) const {
-  auto &section = m_sections[m_relocSecIdx];
-
-  auto relocs = reinterpret_cast<const typename Elf::Reloc *>(section->data);
-  reloc->offset = relocs[idx].r_offset;
-  reloc->symIdx = relocs[idx].r_symbol;
-  reloc->type = relocs[idx].r_type;
-  reloc->addend = 0;
-  reloc->useExplicitAddend = false;
+  auto *section = m_sections[m_relocSecIdx];
+
+  if (section->secHead.sh_type == SHT_REL) {
+    auto relocs = reinterpret_cast<const typename Elf::Reloc *>(section->data);
+    reloc->offset = relocs[idx].r_offset;
+    reloc->symIdx = relocs[idx].r_symbol;
+    reloc->type = relocs[idx].r_type;
+    reloc->addend = 0;
+    reloc->useExplicitAddend = false;
+  } else {
+    assert(section->secHead.sh_type == SHT_RELA);
+    auto relocs = reinterpret_cast<const typename Elf::RelocA *>(section->data);
+    reloc->offset = relocs[idx].r_offset;
+    reloc->symIdx = relocs[idx].r_symbol;
+    reloc->type = relocs[idx].r_type;
+    reloc->addend = relocs[idx].r_addend;
+    reloc->useExplicitAddend = true;
+  }
 }
 
 // =====================================================================================================================

diff --git a/util/vkgcElfReader.h b/util/vkgcElfReader.h
@@ -129,6 +129,8 @@ enum ElfSectionHeaderTypes : uint32_t {
   SHT_HASH = 5,     // Symbol hash table
   SHT_DYNAMIC = 6,  // Information for dynamic linking
   SHT_NOTE = 7,     // Information about the file
+  SHT_NOBITS = 8,   // Data occupies no space in the file
+  SHT_REL = 9,      // Relocation entries; no explicit addends
 };
 
 // Enumerates ELF Section flags.
@@ -150,7 +152,8 @@ static const char ShStrTabName[] = ".shstrtab"; // Name of ".shstrtab" section
 static const char StrTabName[] = ".strtab";     // Name of ".strtab" section
 static const char SymTabName[] = ".symtab";     // Name of ".symtab" section
 static const char NoteName[] = ".note";         // Name of ".note" section
-static const char RelocName[] = ".rel.text";    // Name of ".reloc" section
+static const char RelocName[] = ".rel.text";    // Name of SHT_REL section
+static const char RelocAName[] = ".rela.text";  // Name of SHT_RELA section
 static const char CommentName[] = ".comment";   // Name of ".comment" section
 
 static const uint32_t NT_AMD_AMDGPU_ISA = 11; // Note type of AMDGPU ISA version
@@ -221,7 +224,7 @@ struct Elf32 {
     uint16_t st_shndx; // Which section (header table index) it's defined in
   };
 
-  // ELF relocation entry (without explicit append)
+  // ELF relocation entry (without explicit addend)
   struct Reloc {
     uint32_t r_offset; // Location (file byte offset, or program virtual address)
     union {
@@ -233,6 +236,19 @@ struct Elf32 {
     };
   };
 
+  // ELF relocation entry with explicit addend
+  struct RelocA {
+    uint32_t r_offset; // Location (file byte offset, or program virtual address)
+    union {
+      uint32_t r_info; // Symbol table index and type of relocation to apply
+      struct {
+        uint32_t r_type : 8;    // Type of relocation
+        uint32_t r_symbol : 24; // Index of the symbol in the symbol table
+      };
+    };
+    uint32_t r_addend; // Compute value for relocatable field by adding this
+  };
+
   // ELF program header
   struct Phdr {
     uint32_t p_type;   // Type of segment
@@ -301,7 +317,7 @@ struct Elf64 {
     uint64_t st_size;  // Size of the symbol
   };
 
-  // ELF relocation entry
+  // ELF relocation entry (without explicit addend)
   struct Reloc {
     uint64_t r_offset; // Location (file byte offset, or program virtual address)
     union {
@@ -313,6 +329,19 @@ struct Elf64 {
     };
   };
 
+  // ELF relocation entry with explicit addend
+  struct RelocA {
+    uint64_t r_offset; // Location (file byte offset, or program virtual address)
+    union {
+      uint64_t r_info; // Symbol table index and type of relocation to apply
+      struct {
+        uint32_t r_type;   // Type of relocation
+        uint32_t r_symbol; // Index of the symbol in the symbol table
+      };
+    };
+    uint64_t r_addend; // Compute value for relocatable field by adding this
+  };
+
   // ELF program header
   struct Phdr {
     uint32_t p_type;   // Type of segment