Support CREL as input section

Author: rui314

.github/workflows/ci.yml

@@ -70,6 +70,7 @@ jobs:
         - gentoo/stage3
         - opensuse/tumbleweed
         - ubuntu:22.04
+        - ubuntu:25.04
     runs-on: ubuntu-latest
     container: ${{ matrix.distro }}
     steps:

install-build-deps.sh

@@ -10,8 +10,7 @@ set -x
 case "$ID" in
 ubuntu | pop | linuxmint | debian | raspbian | neon)
   apt-get update
-  apt-get install -y cmake gcc g++
-  if [ "$ID-$VERSION_ID" = ubuntu-20.04 ]; then apt-get install -y g++-10; fi
+  apt-get install -y cmake gcc g++ clang gdb
   ;;
 fedora | amzn | rhel | centos)
   dnf install -y gcc-g++ cmake glibc-static libstdc++-static diffutils util-linux tar

lib/common.h

@@ -490,6 +490,23 @@ inline u64 read_uleb(u8 *buf) {
   return read_uleb(&tmp);
 }
 
+inline i64 read_sleb(u8 **buf) {
+  u64 val = 0;
+  u8 shift = 0;
+  u8 byte;
+  do {
+    byte = *(*buf)++;
+    val |= (byte & 0x7f) << shift;
+    shift += 7;
+  } while (byte & 0x80);
+  return sign_extend(val, shift);
+}
+
+inline i64 read_sleb(u8 *buf) {
+  u8 *tmp = buf;
+  return read_sleb(&tmp);
+}
+
 inline u64 read_uleb(std::string_view *str) {
   u8 *start = (u8 *)str->data();
   u8 *ptr = start;

src/elf.h

@@ -78,6 +78,7 @@ enum : u32 {
   SHT_GROUP = 17,
   SHT_SYMTAB_SHNDX = 18,
   SHT_RELR = 19,
+  SHT_CREL = 0x40000014,
   SHT_LOOS = 0x60000000,
   SHT_LLVM_ADDRSIG = 0x6fff4c03,
   SHT_GNU_HASH = 0x6ffffff6,

src/input-files.cc

@@ -236,6 +236,37 @@ static bool is_known_section_type(const ElfShdr<E> &shdr) {
   return false;
 }
 
+template <typename E>
+std::vector<ElfRel<E>> decode_crel(Context<E> &ctx, std::string_view contents) {
+  u8 *p = (u8 *)contents.data();
+  u64 hdr = read_uleb(&p);
+  i64 nrels = hdr >> 3;
+  i64 nflags = (hdr & 0b100) ? 3 : 2;
+  i64 scale = hdr & 0b11;
+
+  i64 offset = 0;
+  i64 addend = 0;
+  i64 symidx = 0;
+  i64 type = 0;
+
+  std::vector<ElfRel<E>> vec;
+  vec.reserve(nrels);
+
+  while (vec.size() < nrels) {
+    u64 val = read_uleb(&p);
+    offset += (val >> nflags) << scale;
+
+    if (val & 1)
+      symidx += read_sleb(&p);
+    if (val & 2)
+      type += read_sleb(&p);
+    if (nflags == 3 && (val & 4))
+      addend += read_sleb(&p);
+    vec.emplace_back(offset, type, symidx, addend);
+  }
+  return vec;
+}
+
 template <typename E>
 void ObjectFile<E>::initialize_sections(Context<E> &ctx) {
   // Read sections
@@ -300,6 +331,10 @@ void ObjectFile<E>::initialize_sections(Context<E> &ctx) {
       comdat_groups.push_back({group, (i32)i, entries.subspan(1)});
       break;
     }
+    case SHT_CREL:
+      decoded_crel.resize(i + 1);
+      decoded_crel[i] = decode_crel(ctx, this->get_string(ctx, shdr));
+      break;
     case SHT_REL:
     case SHT_RELA:
     case SHT_SYMTAB:
@@ -436,16 +471,12 @@ void ObjectFile<E>::initialize_sections(Context<E> &ctx) {
   // Attach relocation sections to their target sections.
   for (i64 i = 0; i < this->elf_sections.size(); i++) {
     const ElfShdr<E> &shdr = this->elf_sections[i];
-    if (shdr.sh_type != (E::is_rela ? SHT_RELA : SHT_REL))
-      continue;
-
-    if (shdr.sh_info >= sections.size())
-      Fatal(ctx) << *this << ": invalid relocated section index: "
-                 << (u32)shdr.sh_info;
-
-    if (std::unique_ptr<InputSection<E>> &target = sections[shdr.sh_info]) {
-      assert(target->relsec_idx == -1);
-      target->relsec_idx = i;
+    if (shdr.sh_type == (E::is_rela ? SHT_RELA : SHT_REL) ||
+        shdr.sh_type == SHT_CREL) {
+      if (std::unique_ptr<InputSection<E>> &target = sections[shdr.sh_info]) {
+        assert(target->relsec_idx == -1);
+        target->relsec_idx = i;
+      }
     }
   }
 

src/mold.h

@@ -1418,6 +1418,7 @@ class ObjectFile : public InputFile<E> {
   std::vector<bool> has_symver;
   std::vector<ComdatGroupRef<E>> comdat_groups;
   std::vector<InputSection<E> *> eh_frame_sections;
+  std::vector<std::vector<ElfRel<E>>> decoded_crel;
   bool exclude_libs = false;
   std::map<u32, u32> gnu_properties;
   bool needs_executable_stack = false;
@@ -2573,7 +2574,11 @@ template <typename E>
 inline std::span<ElfRel<E>> InputSection<E>::get_rels(Context<E> &ctx) const {
   if (relsec_idx == -1)
     return {};
-  return file.template get_data<ElfRel<E>>(ctx, file.elf_sections[relsec_idx]);
+
+  ElfShdr<E> &shdr = file.elf_sections[relsec_idx];
+  if (shdr.sh_type == SHT_CREL)
+    return file.decoded_crel[relsec_idx];
+  return file.template get_data<ElfRel<E>>(ctx, shdr);
 }
 
 template <typename E>