[PATCH] D78072: [lld][WebAssembly] Do not require --shared-memory with --relocatable

[Thomas Lively via Phabricator via llvm-commits]

tlively created this revision.
tlively added a reviewer: sbc100.
Herald added subscribers: llvm-commits, jfb, sunfish, aheejin, jgravelle-google, dschuff.
Herald added a project: LLVM.

wasm-ld requires --shared-memory to be passed when the atomics feature
is enabled because historically atomic operations were only valid with
shared memories. This change relaxes that requirement for when
building relocatable objects because their memories are not
meaningful. This technically maintains the validity of object files
because the threads spec now allows atomic operations with unshared
memories, although we don't support that elsewhere in the tools yet.

This fixes and Emscripten build issue reported at
https://bugs.chromium.org/p/webp/issues/detail?id=463.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D78072

Files:
  lld/test/wasm/shared-memory.yaml
  lld/wasm/Writer.cpp


Index: lld/wasm/Writer.cpp
===================================================================
--- lld/wasm/Writer.cpp
+++ lld/wasm/Writer.cpp
@@ -421,7 +421,8 @@
     for (const auto &key : used.keys())
       allowed.insert(std::string(key));
 
-  if (allowed.count("atomics") && !config->sharedMemory) {
+  if (allowed.count("atomics") && !config->sharedMemory &&
+      !config->relocatable) {
     if (inferFeatures)
       error(Twine("'atomics' feature is used by ") + used["atomics"] +
             ", so --shared-memory must be used");
Index: lld/test/wasm/shared-memory.yaml
===================================================================
--- lld/test/wasm/shared-memory.yaml
+++ lld/test/wasm/shared-memory.yaml
@@ -10,6 +10,8 @@
 
 # RUN: not wasm-ld --no-entry --features=atomics %t1.o -o - 2>&1 | FileCheck %s --check-prefix ATOMICS-NO-SHARED
 
+# RUN: wasm-ld --relocatable --features=atomics %t1.o -o - | obj2yaml | FileCheck %s --check-prefix ATOMICS-RELOCATABLE
+
 # RUN: wasm-ld --no-entry --shared-memory --max-memory=131072 --features=atomics,bulk-memory %t1.o -o - | obj2yaml | FileCheck %s --check-prefix SHARED
 
 --- !WASM
@@ -65,6 +67,11 @@
 
 # ATOMICS-NO-SHARED: 'atomics' feature is used, so --shared-memory must be used{{$}}
 
+# ATOMICS-RELOCATABLE:        - Type:            MEMORY
+# ATOMICS-RELOCATABLE-NEXT:     Memories:
+# ATOMICS-RELOCATABLE-NEXT:         Initial:         0x00000001
+# ATOMICS-RELOCATABLE-NEXT:   - Type:
+
 # SHARED:        - Type:            MEMORY
 # SHARED-NEXT:     Memories:
 # SHARED-NEXT:       - Flags:           [ HAS_MAX, IS_SHARED ]


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