[Mach-O] Create GOT entries for external references

macho/input-sections.cc

@@ -43,8 +43,11 @@ static Relocation read_reloc(Context &ctx, ObjectFile &file,
   else
     unreachable();
 
+  bool is_gotref = (r.type == X86_64_RELOC_GOT_LOAD || r.type == X86_64_RELOC_GOT);
+
   if (r.is_extern)
-    return {r.offset, (bool)r.is_pcrel, addend, file.syms[r.idx], nullptr};
+    return {r.offset, (bool)r.is_pcrel, is_gotref, addend, file.syms[r.idx],
+            nullptr};
 
   u32 addr;
   if (r.is_pcrel) {
@@ -58,7 +61,9 @@ static Relocation read_reloc(Context &ctx, ObjectFile &file,
   Subsection *target = file.sections[r.idx - 1]->find_subsection(ctx, addr);
   if (!target)
     Fatal(ctx) << file << ": bad relocation: " << r.offset;
-  return {r.offset, (bool)r.is_pcrel, addr - target->input_addr, nullptr, target};
+
+  return {r.offset, (bool)r.is_pcrel, is_gotref, addr - target->input_addr,
+          nullptr, target};
 }
 
 void InputSection::parse_relocations(Context &ctx) {
@@ -88,8 +93,12 @@ void InputSection::parse_relocations(Context &ctx) {
 void InputSection::scan_relocations(Context &ctx) {
   for (Relocation &rel : rels) {
     Symbol *sym = rel.sym;
-    if (sym && sym->file && sym->file->is_dylib)
-      sym->needs_stub = true;
+    if (sym && sym->file && sym->file->is_dylib) {
+      if (rel.is_gotref)
+        sym->flags |= NEEDS_GOT;
+      else
+        sym->flags |= NEEDS_STUB;
+    }
   }
 }
 
@@ -97,15 +106,23 @@ void Subsection::apply_reloc(Context &ctx, u8 *buf) {
   for (const Relocation &rel : std::span(isec.rels).subspan(rel_offset, nrels)) {
     u32 *loc = (u32 *)(buf + rel.offset);
 
-    if (rel.sym) {
-      *loc = rel.sym->get_addr(ctx) + rel.addend;
-    } else {
-      *loc = rel.subsec->isec.osec->hdr.addr + rel.subsec->output_offset +
-             rel.addend;
-    }
+#define S (rel.sym ? rel.sym->get_addr(ctx) : \
+           rel.subsec->isec.osec->hdr.addr + rel.subsec->output_offset)
+#define A rel.addend
+#define P (isec.osec->hdr.addr + output_offset + rel.offset)
+#define G rel.sym->get_got_addr(ctx)
 
-    if (rel.is_pcrel)
-      *loc = *loc - isec.osec->hdr.addr - output_offset - rel.offset - 4;
+    if (rel.is_gotref)
+      *loc = G - P - 4;
+    else if (rel.is_pcrel)
+      *loc = S + A - P - 4;
+    else
+      *loc = S + A;
+
+#undef S
+#undef A
+#undef P
+#undef G
   }
 }
 

macho/main.cc

@@ -90,10 +90,15 @@ static void create_synthetic_chunks(Context &ctx) {
 static void export_symbols(Context &ctx) {
   ctx.got.add(ctx, intern(ctx, "dyld_stub_binder"));
 
-  for (DylibFile *dylib : ctx.dylibs)
-    for (Symbol *sym : dylib->syms)
-      if (sym->file == dylib && sym->needs_stub)
-        ctx.stubs.add(ctx, sym);
+  for (DylibFile *dylib : ctx.dylibs) {
+    for (Symbol *sym : dylib->syms) {
+      if (sym->file == dylib)
+        if (sym->flags & NEEDS_STUB)
+          ctx.stubs.add(ctx, sym);
+      if (sym->flags & NEEDS_GOT)
+        ctx.got.add(ctx, sym);
+    }
+  }
 }
 
 static i64 assign_offsets(Context &ctx) {

macho/mold.h

@@ -29,6 +29,7 @@ struct Symbol;
 struct Relocation {
   u32 offset = 0;
   bool is_pcrel = false;
+  bool is_gotref = false;
   i64 addend = 0;
   Symbol *sym = nullptr;
   Subsection *subsec = nullptr;
@@ -141,6 +142,11 @@ public:
 // Symbol
 //
 
+enum {
+  NEEDS_GOT  = 1 << 0,
+  NEEDS_STUB = 1 << 1,
+};
+
 struct Symbol {
   Symbol() = default;
   Symbol(std::string_view name) : name(name) {}
@@ -154,7 +160,7 @@ struct Symbol {
   i32 stub_idx = -1;
   i32 got_idx = -1;
   tbb::spin_mutex mu;
-  std::atomic_bool needs_stub = false;
+  std::atomic_uint8_t flags = 0;
   u8 is_extern : 1 = false;
   u8 referenced_dynamically : 1 = false;
 

test/macho/hello3.sh

@@ -0,0 +1,21 @@
+#!/bin/bash
+set -e
+cd $(dirname $0)
+mold=`pwd`/../../ld64.mold
+echo -n "Testing $(basename -s .sh $0) ... "
+t=$(pwd)/../../out/test/macho/$(basename -s .sh $0)
+mkdir -p $t
+
+cat <<EOF | cc -o $t/a.o -c -xc -
+#include <stdio.h>
+
+int main() {
+  printf("Hello");
+  fprintf(stdout, " world\n");
+}
+EOF
+
+clang -fuse-ld=$mold -o $t/exe $t/a.o
+$t/exe | grep -q 'Hello world'
+
+echo OK

test/macho/hello4.sh

@@ -0,0 +1,23 @@
+#!/bin/bash
+set -e
+cd $(dirname $0)
+mold=`pwd`/../../ld64.mold
+echo -n "Testing $(basename -s .sh $0) ... "
+t=$(pwd)/../../out/test/macho/$(basename -s .sh $0)
+mkdir -p $t
+
+cat <<EOF | cc -o $t/a.o -c -xc -
+#include <stdio.h>
+
+int main() {
+  printf("Hello");
+  fprintf(stdout, " world\n");
+  fprintf(stderr, "Hello stderr\n");
+}
+EOF
+
+clang -fuse-ld=$mold -o $t/exe $t/a.o
+$t/exe 2> /dev/null | grep -q 'Hello world'
+$t/exe 2>&1 > /dev/null | grep -q 'Hello stderr'
+
+echo OK