[lld][WebAssembly] Fix crash with -pie without --allow-undefined

`shouldImport` was not returning true in PIC mode even though out assumption elsewhere (in Relocations.cpp:scanRelocations) is that we don't report undefined symbols in PIC mode today. This was resulting functions that were undefined and but also not imported which hits an assert later on that all functions have valid indexes. Differential Revision: https://reviews.llvm.org/D101716
llvm · May 4, 2021 · 808fcdd · 808fcdd
1 parent 24ce194
commit 808fcdd
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Showing 3 changed files with 19 additions and 15 deletions.
diff --git a/lld/test/wasm/pie.ll b/lld/test/wasm/pie.ll
@@ -1,5 +1,5 @@
 ; RUN: llc -relocation-model=pic -mattr=+mutable-globals -filetype=obj %s -o %t.o
-; RUN: wasm-ld --no-gc-sections --allow-undefined --experimental-pic -pie -o %t.wasm %t.o
+; RUN: wasm-ld --no-gc-sections --experimental-pic -pie -o %t.wasm %t.o
 
 target triple = "wasm32-unknown-emscripten"
 
@@ -26,9 +26,12 @@ entry:
 }
 
 define void @_start() {
+  call void @external_func()
   ret void
 }
 
+declare void @external_func()
+
 ;      CHECK: Sections:
 ; CHECK-NEXT:   - Type:            CUSTOM
 ; CHECK-NEXT:     Name:            dylink
@@ -88,27 +91,29 @@ define void @_start() {
 ; RUN: obj2yaml %t.shmem.wasm | FileCheck %s --check-prefix=SHMEM
 
 ; SHMEM:         - Type:            CODE
-; SHMEM:           - Index:           5
+; SHMEM:           - Index:           6
 ; SHMEM-NEXT:        Locals:          []
-; SHMEM-NEXT:        Body:            100210040B
+; SHMEM-NEXT:        Body:            100310050B
 
 ; SHMEM:         FunctionNames:
 ; SHMEM-NEXT:      - Index:           0
-; SHMEM-NEXT:        Name:            __wasm_call_ctors
+; SHMEM-NEXT:        Name:            external_func
 ; SHMEM-NEXT:      - Index:           1
-; SHMEM-NEXT:        Name:            __wasm_init_tls
+; SHMEM-NEXT:        Name:            __wasm_call_ctors
 ; SHMEM-NEXT:      - Index:           2
-; SHMEM-NEXT:        Name:            __wasm_init_memory
+; SHMEM-NEXT:        Name:            __wasm_init_tls
 ; SHMEM-NEXT:      - Index:           3
-; SHMEM-NEXT:        Name:            __wasm_apply_data_relocs
+; SHMEM-NEXT:        Name:            __wasm_init_memory
 ; SHMEM-NEXT:      - Index:           4
-; SHMEM-NEXT:        Name:            __wasm_apply_global_relocs
+; SHMEM-NEXT:        Name:            __wasm_apply_data_relocs
 ; SHMEM-NEXT:      - Index:           5
-; SHMEM-NEXT:        Name:            __wasm_start
+; SHMEM-NEXT:        Name:            __wasm_apply_global_relocs
 ; SHMEM-NEXT:      - Index:           6
-; SHMEM-NEXT:        Name:            foo
+; SHMEM-NEXT:        Name:            __wasm_start
 ; SHMEM-NEXT:      - Index:           7
-; SHMEM-NEXT:        Name:            get_data_address
+; SHMEM-NEXT:        Name:            foo
 ; SHMEM-NEXT:      - Index:           8
+; SHMEM-NEXT:        Name:            get_data_address
+; SHMEM-NEXT:      - Index:           9
 ; SHMEM-NEXT:        Name:            _start
 
diff --git a/lld/wasm/Relocations.cpp b/lld/wasm/Relocations.cpp
@@ -150,10 +150,9 @@ void scanRelocations(InputChunk *chunk) {
           addGOTEntry(sym);
         break;
       }
-    } else {
+    } else if (sym->isUndefined() && !config->relocatable && !sym->isWeak()) {
       // Report undefined symbols
-      if (sym->isUndefined() && !config->relocatable && !sym->isWeak())
-        reportUndefined(sym);
+      reportUndefined(sym);
     }
   }
 }

diff --git a/lld/wasm/Writer.cpp b/lld/wasm/Writer.cpp
@@ -560,7 +560,7 @@ static bool shouldImport(Symbol *sym) {
   if (isa<DataSymbol>(sym))
     return false;
 
-  if (config->relocatable ||
+  if ((config->isPic || config->relocatable) ||
       config->unresolvedSymbols == UnresolvedPolicy::ImportFuncs)
     return true;
   if (config->allowUndefinedSymbols.count(sym->getName()) != 0)