Emit PT_GNU_PROPERTY program header if .note.gnu.property is present

It looks like Linux kernel reads this program header to enable BTI on ARM64.

src/arch-arm32.cc

@@ -722,7 +722,11 @@ u64 get_eflags(Context<E> &ctx) {
 void fixup_arm_exidx_section(Context<E> &ctx) {
   Timer t(ctx, "fixup_arm_exidx_section");
 
-  OutputSection<E> *osec = find_section(ctx, SHT_ARM_EXIDX);
+  Chunk<E> *chunk = find_chunk(ctx, SHT_ARM_EXIDX);
+  if (!chunk)
+    return;
+
+  OutputSection<E> *osec = chunk->to_osec();
   if (!osec)
     return;
 
@@ -780,7 +784,7 @@ void fixup_arm_exidx_section(Context<E> &ctx) {
   // .ARM.exidx's sh_link should be set to the .text section index.
   // Runtime doesn't care about it, but the binutils's strip command does.
   if (ctx.shdr) {
-    if (Chunk<E> *text = find_section(ctx, ".text")) {
+    if (Chunk<E> *text = find_chunk(ctx, ".text")) {
       osec->shdr.sh_link = text->shndx;
       ctx.shdr->copy_buf(ctx);
     }

src/elf.h

@@ -191,6 +191,7 @@ enum : u32 {
   PT_GNU_EH_FRAME = 0x6474e550,
   PT_GNU_STACK = 0x6474e551,
   PT_GNU_RELRO = 0x6474e552,
+  PT_GNU_PROPERTY = 0x6474e553,
   PT_OPENBSD_RANDOMIZE = 0x65a3dbe6,
   PT_ARM_EXIDX = 0x70000001,
   PT_RISCV_ATTRIBUTES = 0x70000003,

src/mold.h

@@ -341,10 +341,10 @@ template <typename E> u64 get_dtp_addr(const ElfPhdr<E> &);
 //
 
 template <typename E>
-OutputSection<E> *find_section(Context<E> &ctx, u32 sh_type);
+Chunk<E> *find_chunk(Context<E> &ctx, u32 sh_type);
 
 template <typename E>
-OutputSection<E> *find_section(Context<E> &ctx, std::string_view name);
+Chunk<E> *find_chunk(Context<E> &ctx, std::string_view name);
 
 template <typename E>
 u64 get_eflags(Context<E> &ctx) {

src/output-chunks.cc

@@ -25,20 +25,18 @@ static u32 elf_hash(std::string_view name) {
 }
 
 template <typename E>
-OutputSection<E> *find_section(Context<E> &ctx, u32 sh_type) {
+Chunk<E> *find_chunk(Context<E> &ctx, u32 sh_type) {
   for (Chunk<E> *chunk : ctx.chunks)
-    if (OutputSection<E> *osec = chunk->to_osec())
-      if (osec->shdr.sh_type == sh_type)
-        return osec;
+    if (chunk->shdr.sh_type == sh_type)
+      return chunk;
   return nullptr;
 }
 
 template <typename E>
-OutputSection<E> *find_section(Context<E> &ctx, std::string_view name) {
+Chunk<E> *find_chunk(Context<E> &ctx, std::string_view name) {
   for (Chunk<E> *chunk : ctx.chunks)
-    if (OutputSection<E> *osec = chunk->to_osec())
-      if (osec->name == name)
-        return osec;
+    if (chunk->name == name)
+      return chunk;
   return nullptr;
 }
 
@@ -267,6 +265,10 @@ static std::vector<ElfPhdr<E>> create_phdr(Context<E> &ctx) {
   if (ctx.eh_frame_hdr)
     define(PT_GNU_EH_FRAME, PF_R, ctx.eh_frame_hdr);
 
+  // Add PT_GNU_PROPERTY
+  if (Chunk<E> *chunk = find_chunk(ctx, ".note.gnu.property"))
+    define(PT_GNU_PROPERTY, PF_R, chunk);
+
   // Add PT_GNU_STACK, which is a marker segment that doesn't really
   // contain any segments. It controls executable bit of stack area.
   {
@@ -293,8 +295,8 @@ static std::vector<ElfPhdr<E>> create_phdr(Context<E> &ctx) {
 
   // Create a PT_ARM_EDXIDX
   if constexpr (is_arm32<E>)
-    if (OutputSection<E> *osec = find_section(ctx, SHT_ARM_EXIDX))
-      define(PT_ARM_EXIDX, PF_R, osec);
+    if (Chunk<E> *chunk = find_chunk(ctx, SHT_ARM_EXIDX))
+      define(PT_ARM_EXIDX, PF_R, chunk);
 
   // Create a PT_RISCV_ATTRIBUTES
   if constexpr (is_riscv<E>)
@@ -734,19 +736,19 @@ static std::vector<Word<E>> create_dynamic_section(Context<E> &ctx) {
     define(DT_STRSZ, ctx.dynstr->shdr.sh_size);
   }
 
-  if (find_section(ctx, SHT_INIT_ARRAY)) {
+  if (find_chunk(ctx, SHT_INIT_ARRAY)) {
     define(DT_INIT_ARRAY, ctx.__init_array_start->value);
     define(DT_INIT_ARRAYSZ,
            ctx.__init_array_end->value - ctx.__init_array_start->value);
   }
 
-  if (find_section(ctx, SHT_PREINIT_ARRAY)) {
+  if (find_chunk(ctx, SHT_PREINIT_ARRAY)) {
     define(DT_PREINIT_ARRAY, ctx.__preinit_array_start->value);
     define(DT_PREINIT_ARRAYSZ,
            ctx.__preinit_array_end->value - ctx.__preinit_array_start->value);
   }
 
-  if (find_section(ctx, SHT_FINI_ARRAY)) {
+  if (find_chunk(ctx, SHT_FINI_ARRAY)) {
     define(DT_FINI_ARRAY, ctx.__fini_array_start->value);
     define(DT_FINI_ARRAYSZ,
            ctx.__fini_array_end->value - ctx.__fini_array_start->value);
@@ -2949,8 +2951,8 @@ template class RelocSection<E>;
 template class ComdatGroupSection<E>;
 template class GnuDebuglinkSection<E>;
 
-template OutputSection<E> *find_section(Context<E> &, u32);
-template OutputSection<E> *find_section(Context<E> &, std::string_view);
+template Chunk<E> *find_chunk(Context<E> &, u32);
+template Chunk<E> *find_chunk(Context<E> &, std::string_view);
 template i64 to_phdr_flags(Context<E> &ctx, Chunk<E> *chunk);
 template ElfSym<E> to_output_esym(Context<E> &, Symbol<E> &, u32, U32<E> *);
 

src/passes.cc

@@ -1271,10 +1271,13 @@ void fixup_ctors_in_init_array(Context<E> &ctx) {
     }
   };
 
-  if (OutputSection<E> *osec = find_section(ctx, ".init_array"))
-    fixup(*osec);
-  if (OutputSection<E> *osec = find_section(ctx, ".fini_array"))
-    fixup(*osec);
+  if (Chunk<E> *chunk = find_chunk(ctx, ".init_array"))
+    if (OutputSection<E> *osec = chunk->to_osec())
+      fixup(*osec);
+
+  if (Chunk<E> *chunk = find_chunk(ctx, ".fini_array"))
+    if (OutputSection<E> *osec = chunk->to_osec())
+      fixup(*osec);
 }
 
 template <typename T>

test/gnu-property.sh

@@ -0,0 +1,10 @@
+#!/bin/bash
+. $(dirname $0)/common.inc
+
+cat <<EOF | $CC -o $t/a.o -c -xc -
+int main() {}
+EOF
+
+$CC -B. -o $t/exe $t/a.o -no-pie
+readelf -W --sections $t/exe | grep -Fqw .note.gnu.property || skip
+readelf -W --segments $t/exe | grep -qw GNU_PROPERTY