bintools-wrapper: Init

Factor a bintools (i.e. binutils / cctools) wrapper out of cc-wrapper. While
only LD is wrapped, the setup hook defines environment variables on behalf of
other utilites.

pkgs/build-support/bintools-wrapper/add-hardening.sh

@@ -0,0 +1,53 @@
+hardeningFlags=(relro bindnow)
+# Intentionally word-split in case 'hardeningEnable' is defined in
+# Nix. Also, our bootstrap tools version of bash is old enough that
+# undefined arrays trip `set -u`.
+if [[ -v hardeningEnable[@] ]]; then
+  hardeningFlags+=(${hardeningEnable[@]})
+fi
+hardeningLDFlags=()
+
+declare -A hardeningDisableMap
+
+# Intentionally word-split in case 'hardeningDisable' is defined in Nix.
+for flag in ${hardeningDisable[@]:-IGNORED_KEY} @hardening_unsupported_flags@
+do
+  hardeningDisableMap[$flag]=1
+done
+
+if (( "${NIX_DEBUG:-0}" >= 1 )); then
+  printf 'HARDENING: disabled flags:' >&2
+  (( "${#hardeningDisableMap[@]}" )) && printf ' %q' "${!hardeningDisableMap[@]}" >&2
+  echo >&2
+fi
+
+if [[ -z "${hardeningDisableMap[all]:-}" ]]; then
+  if (( "${NIX_DEBUG:-0}" >= 1 )); then
+    echo 'HARDENING: Is active (not completely disabled with "all" flag)' >&2;
+  fi
+  for flag in "${hardeningFlags[@]}"
+  do
+    if [[ -z "${hardeningDisableMap[$flag]:-}" ]]; then
+      case $flag in
+        pie)
+          if [[ ! ("$*" =~ " -shared " || "$*" =~ " -static ") ]]; then
+            if (( "${NIX_DEBUG:-0}" >= 1 )); then echo HARDENING: enabling LDFlags -pie >&2; fi
+            hardeningLDFlags+=('-pie')
+          fi
+          ;;
+        relro)
+          if (( "${NIX_DEBUG:-0}" >= 1 )); then echo HARDENING: enabling relro >&2; fi
+          hardeningLDFlags+=('-z' 'relro')
+          ;;
+        bindnow)
+          if (( "${NIX_DEBUG:-0}" >= 1 )); then echo HARDENING: enabling bindnow >&2; fi
+          hardeningLDFlags+=('-z' 'now')
+          ;;
+        *)
+          # Ignore unsupported. Checked in Nix that at least *some*
+          # tool supports each flag.
+          ;;
+      esac
+    fi
+  done
+fi