[ELF] Add -z ibt

Fixes #229

elf/cmdline.cc

@@ -658,6 +658,9 @@ void parse_nonpositional_args(Context<E> &ctx,
       ctx.arg.z_initfirst = true;
     } else if (read_z_flag(args, "interpose")) {
       ctx.arg.z_interpose = true;
+    } else if (read_z_flag(args, "ibt")) {
+      ctx.arg.z_ibt = true;
+      ctx.arg.z_ibtplt = true;
     } else if (read_z_flag(args, "ibtplt")) {
       ctx.arg.z_ibtplt = true;
     } else if (read_z_flag(args, "muldefs")) {

elf/mold.h

@@ -1270,6 +1270,7 @@ struct Context {
     bool z_dlopen = true;
     bool z_dump = true;
     bool z_execstack = false;
+    bool z_ibt = false;
     bool z_ibtplt = false;
     bool z_initfirst = false;
     bool z_interpose = false;

elf/output-chunks.cc

@@ -1768,6 +1768,8 @@ void NotePropertySection<E>::update_shdr(Context<E> &ctx) {
   for (ObjectFile<E> *file : ctx.objs)
     features &= file->features;
 
+  if (ctx.arg.z_ibt)
+    features |= GNU_PROPERTY_X86_FEATURE_1_IBT;
   if (ctx.arg.z_shstk)
     features |= GNU_PROPERTY_X86_FEATURE_1_SHSTK;
 

test/elf/z-ibt.sh

@@ -0,0 +1,27 @@
+#!/bin/bash
+export LANG=
+set -e
+CC="${CC:-cc}"
+CXX="${CXX:-c++}"
+testname=$(basename -s .sh "$0")
+echo -n "Testing $testname ... "
+cd "$(dirname "$0")"/../..
+mold="$(pwd)/mold"
+t=out/test/elf/$testname
+mkdir -p $t
+
+cat <<EOF | $CC -o $t/a.o -c -x assembler -
+.globl main
+main:
+  call _exit@PLT
+EOF
+
+$CC -B. -o $t/exe $t/a.o
+readelf --notes $t/exe > $t/log
+! grep -qw SHSTK $t/log
+
+$CC -B. -o $t/exe $t/a.o -Wl,-z,ibt
+readelf --notes $t/exe | grep -qw IBT
+objdump -d  -j .plt $t/exe | grep -q 'bnd jmp'
+
+echo OK