[lld] [lld] Reject --read-workers when lld is built without thread support (PR #163925)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-lld-macho

Author: David Spickett (DavidSpickett)

<details>
<summary>Changes</summary>

Also expand the #ifdef to remove unused code in this configuration. As suggested in https://github.com/llvm/llvm-project/pull/147134#issuecomment-3328612158.

I have also:
* Expanded the error message to explain why it's not allowed.
* Added a test for the error.
* Marked the original test as unsupported when threads are disabled.

Fixes issues we have had on Armv8 with threading disabled where this test would crash every so often.

This change will hopefully be superseded by #<!-- -->157917, but that has been in review a long time and I want to make the bot stable again.

I could just disable the test, but I'd like lld to function properly in general in the meantime too.

Co-authored-by: John Holdsworth <github@<!-- -->johnholdsworth.com>

---
Full diff: https://github.com/llvm/llvm-project/pull/163925.diff


6 Files Affected:

- (modified) lld/MachO/Driver.cpp (+9-2) 
- (modified) lld/test/CMakeLists.txt (+1) 
- (added) lld/test/MachO/read-workers-no-thread-support.s (+10) 
- (modified) lld/test/MachO/read-workers.s (+1-1) 
- (modified) lld/test/lit.cfg.py (+3) 
- (modified) lld/test/lit.site.cfg.py.in (+1) 


``````````diff
diff --git a/lld/MachO/Driver.cpp b/lld/MachO/Driver.cpp
index bfd35aef72b58..9b67db9fa55cf 100644
--- a/lld/MachO/Driver.cpp
+++ b/lld/MachO/Driver.cpp
@@ -291,6 +291,7 @@ struct DeferredFile {
 };
 using DeferredFiles = std::vector<DeferredFile>;
 
+#if LLVM_ENABLE_THREADS
 class SerialBackgroundQueue {
   std::deque<std::function<void()>> queue;
   std::thread *running;
@@ -359,7 +360,6 @@ void multiThreadedPageInBackground(DeferredFiles &deferred) {
       (void)t;
     }
   };
-#if LLVM_ENABLE_THREADS
   { // Create scope for waiting for the taskGroup
     std::atomic_size_t index = 0;
     llvm::parallel::TaskGroup taskGroup;
@@ -373,7 +373,6 @@ void multiThreadedPageInBackground(DeferredFiles &deferred) {
         }
       });
   }
-#endif
 #ifndef NDEBUG
   auto dt = high_resolution_clock::now() - t0;
   if (Process::GetEnv("LLD_MULTI_THREAD_PAGE"))
@@ -390,6 +389,7 @@ static void multiThreadedPageIn(const DeferredFiles &deferred) {
     multiThreadedPageInBackground(files);
   });
 }
+#endif
 
 static InputFile *processFile(std::optional<MemoryBufferRef> buffer,
                               DeferredFiles *archiveContents, StringRef path,
@@ -1430,6 +1430,7 @@ static void createFiles(const InputArgList &args) {
     }
   }
 
+#if LLVM_ENABLE_THREADS
   if (config->readWorkers) {
     multiThreadedPageIn(deferredFiles);
 
@@ -1447,6 +1448,7 @@ static void createFiles(const InputArgList &args) {
     for (auto *archive : archives)
       archive->addLazySymbols();
   }
+#endif
 }
 
 static void gatherInputSections() {
@@ -1834,6 +1836,7 @@ bool link(ArrayRef<const char *> argsArr, llvm::raw_ostream &stdoutOS,
   }
 
   if (auto *arg = args.getLastArg(OPT_read_workers)) {
+#if LLVM_ENABLE_THREADS
     StringRef v(arg->getValue());
     unsigned workers = 0;
     if (!llvm::to_integer(v, workers, 0))
@@ -1841,6 +1844,10 @@ bool link(ArrayRef<const char *> argsArr, llvm::raw_ostream &stdoutOS,
             ": expected a non-negative integer, but got '" + arg->getValue() +
             "'");
     config->readWorkers = workers;
+#else
+    error(arg->getSpelling() +
+          ": option unavailable because lld was not built with thread support");
+#endif
   }
   if (auto *arg = args.getLastArg(OPT_threads_eq)) {
     StringRef v(arg->getValue());
diff --git a/lld/test/CMakeLists.txt b/lld/test/CMakeLists.txt
index abc8ea75da180..1bd3ad7e1765b 100644
--- a/lld/test/CMakeLists.txt
+++ b/lld/test/CMakeLists.txt
@@ -1,5 +1,6 @@
 llvm_canonicalize_cmake_booleans(
   ENABLE_BACKTRACES
+  LLVM_ENABLE_THREADS
   LLVM_ENABLE_ZLIB
   LLVM_ENABLE_ZSTD
   LLVM_ENABLE_LIBXML2
diff --git a/lld/test/MachO/read-workers-no-thread-support.s b/lld/test/MachO/read-workers-no-thread-support.s
new file mode 100644
index 0000000000000..16256be42af73
--- /dev/null
+++ b/lld/test/MachO/read-workers-no-thread-support.s
@@ -0,0 +1,10 @@
+# REQUIRES: x86 && !thread_support
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t.o
+
+# RUN: not %lld --read-workers=1 %t.o -o /dev/null
+
+# CHECK: error: --read-workers=: option unavailable because lld was built without thread support
+
+.globl _main
+_main:
+  ret
diff --git a/lld/test/MachO/read-workers.s b/lld/test/MachO/read-workers.s
index 6f0ea4d894408..4d2f88c2a757c 100644
--- a/lld/test/MachO/read-workers.s
+++ b/lld/test/MachO/read-workers.s
@@ -1,4 +1,4 @@
-# REQUIRES: x86
+# REQUIRES: x86 && thread_support
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t.o
 
 ## A non-negative integer is allowed.
diff --git a/lld/test/lit.cfg.py b/lld/test/lit.cfg.py
index 336945729954e..906afc52a0d09 100644
--- a/lld/test/lit.cfg.py
+++ b/lld/test/lit.cfg.py
@@ -182,3 +182,6 @@
 # ELF tests expect the default target for ld.lld to be ELF.
 if config.ld_lld_default_mingw:
     config.excludes.append("ELF")
+
+if config.enable_threads:
+    config.available_features.add("thread_support")
\ No newline at end of file
diff --git a/lld/test/lit.site.cfg.py.in b/lld/test/lit.site.cfg.py.in
index bb99976005543..703d3b1fd5337 100644
--- a/lld/test/lit.site.cfg.py.in
+++ b/lld/test/lit.site.cfg.py.in
@@ -26,6 +26,7 @@ config.ld_lld_default_mingw = @LLD_DEFAULT_LD_LLD_IS_MINGW@
 config.build_examples = @LLVM_BUILD_EXAMPLES@
 config.has_plugins = @LLVM_ENABLE_PLUGINS@
 config.linked_bye_extension = @LLVM_BYE_LINK_INTO_TOOLS@
+config.enable_threads = @LLVM_ENABLE_THREADS@
 
 import lit.llvm
 lit.llvm.initialize(lit_config, config)

``````````

</details>


https://github.com/llvm/llvm-project/pull/163925