Fix linker feature detection being performed on wrong linker

Bazel forces use of `lld` and `ld.gold` if found, but performed feature detection on the default linker instead.

Fixes bazelbuild#20834

Closes bazelbuild#20833.

PiperOrigin-RevId: 598565598
Change-Id: I4890f278c5cc33d4e6a6ebb10d796fb1c22f9ba6

tools/cpp/unix_cc_configure.bzl

@@ -161,10 +161,9 @@ def _is_compiler_option_supported(repository_ctx, cc, option):
  ])
  return result.stderr.find(option) == -1
 
-def _is_linker_option_supported(repository_ctx, cc, option, pattern):
+def _is_linker_option_supported(repository_ctx, cc, force_linker_flags, option, pattern):
  """Checks that `option` is supported by the C linker. Doesn't %-escape the option."""
- result = repository_ctx.execute([
- cc,
+ result = repository_ctx.execute([cc] + force_linker_flags + [
  option,
  "-o",
  "/dev/null",
@@ -213,9 +212,9 @@ def _add_compiler_option_if_supported(repository_ctx, cc, option):
  """Returns `[option]` if supported, `[]` otherwise. Doesn't %-escape the option."""
  return [option] if _is_compiler_option_supported(repository_ctx, cc, option) else []
 
-def _add_linker_option_if_supported(repository_ctx, cc, option, pattern):
+def _add_linker_option_if_supported(repository_ctx, cc, force_linker_flags, option, pattern):
  """Returns `[option]` if supported, `[]` otherwise. Doesn't %-escape the option."""
- return [option] if _is_linker_option_supported(repository_ctx, cc, option, pattern) else []
+ return [option] if _is_linker_option_supported(repository_ctx, cc, force_linker_flags, option, pattern) else []
 
 def _get_no_canonical_prefixes_opt(repository_ctx, cc):
  # If the compiler sometimes rewrites paths in the .d files without symlinks
@@ -420,16 +419,40 @@ def configure_unix_toolchain(repository_ctx, cpu_value, overriden_tools):
  False,
  ), ":")
 
+ gold_or_lld_linker_path = (
+ _find_linker_path(repository_ctx, cc, "lld", is_clang) or
+ _find_linker_path(repository_ctx, cc, "gold", is_clang)
+ )
+ cc_path = repository_ctx.path(cc)
+ if not str(cc_path).startswith(str(repository_ctx.path(".")) + "/"):
+ # cc is outside the repository, set -B
+ bin_search_flags = ["-B" + escape_string(str(cc_path.dirname))]
+ else:
+ # cc is inside the repository, don't set -B.
+ bin_search_flags = []
+ if not gold_or_lld_linker_path:
+ ld_path = repository_ctx.path(tool_paths["ld"])
+ if ld_path.dirname != cc_path.dirname:
+ bin_search_flags.append("-B" + str(ld_path.dirname))
+ force_linker_flags = []
+ if gold_or_lld_linker_path:
+ force_linker_flags.append("-fuse-ld=" + gold_or_lld_linker_path)
+
+ # TODO: It's unclear why these flags aren't added on macOS.
+ if bin_search_flags and not darwin:
+ force_linker_flags.extend(bin_search_flags)
  use_libcpp = darwin or bsd
  is_as_needed_supported = _is_linker_option_supported(
  repository_ctx,
  cc,
+ force_linker_flags,
  "-Wl,-no-as-needed",
  "-no-as-needed",
  )
  is_push_state_supported = _is_linker_option_supported(
  repository_ctx,
  cc,
+ force_linker_flags,
  "-Wl,--push-state",
  "--push-state",
  )
@@ -463,21 +486,6 @@ def configure_unix_toolchain(repository_ctx, cpu_value, overriden_tools):
  bazel_linklibs,
  False,
  ), ":")
- gold_or_lld_linker_path = (
- _find_linker_path(repository_ctx, cc, "lld", is_clang) or
- _find_linker_path(repository_ctx, cc, "gold", is_clang)
- )
- cc_path = repository_ctx.path(cc)
- if not str(cc_path).startswith(str(repository_ctx.path(".")) + "/"):
- # cc is outside the repository, set -B
- bin_search_flags = ["-B" + escape_string(str(cc_path.dirname))]
- else:
- # cc is inside the repository, don't set -B.
- bin_search_flags = []
- if not gold_or_lld_linker_path:
- ld_path = repository_ctx.path(tool_paths["ld"])
- if ld_path.dirname != cc_path.dirname:
- bin_search_flags.append("-B" + str(ld_path.dirname))
  coverage_compile_flags, coverage_link_flags = _coverage_flags(repository_ctx, darwin)
  print_resource_dir_supported = _is_compiler_option_supported(
  repository_ctx,
@@ -610,19 +618,18 @@ def configure_unix_toolchain(repository_ctx, cpu_value, overriden_tools):
  ),
  "%{cxx_flags}": get_starlark_list(cxx_opts + _escaped_cplus_include_paths(repository_ctx)),
  "%{conly_flags}": get_starlark_list(conly_opts),
- "%{link_flags}": get_starlark_list((
- ["-fuse-ld=" + gold_or_lld_linker_path] if gold_or_lld_linker_path else []
- ) + (
+ "%{link_flags}": get_starlark_list(force_linker_flags + (
  ["-Wl,-no-as-needed"] if is_as_needed_supported else []
  ) + _add_linker_option_if_supported(
  repository_ctx,
  cc,
+ force_linker_flags,
  "-Wl,-z,relro,-z,now",
  "-z",
  ) + (
  [
  "-headerpad_max_install_names",
- ] if darwin else bin_search_flags + [
+ ] if darwin else [
  # Gold linker only? Can we enable this by default?
  # "-Wl,--warn-execstack",
  # "-Wl,--detect-odr-violations"
@@ -664,6 +671,7 @@ def configure_unix_toolchain(repository_ctx, cpu_value, overriden_tools):
  ["-Wl,-dead_strip"] if darwin else _add_linker_option_if_supported(
  repository_ctx,
  cc,
+ force_linker_flags,
  "-Wl,--gc-sections",
  "-gc-sections",
  ),