Do not allow delay-importing data symbols.

[ruiu]

Summary

If you pass /delayload:<dllname> to the COFF linker, it creates thunks
so that DLLs are loaded when they are used for the first time instead of
load-time.

This mechanism do not work for data symbols as there's no way to trap
acccesses to data imported from DLLs. (Technically, I think if we make
dllimport table read-only, we could actually trap accesses and delay-load
data symbols, but that's not what Windows usually do.)

This patch is to report an error when you try to delay-load data symbols.

Fixes https://bugs.llvm.org/show_bug.cgi?id=33106

[pcc]

LGTM

I think if we make dllimport table read-only, we could actually trap accesses

If you wanted to trap a read, it wouldn't work to make it read-only, right?

[ruiu]

I was trying to say is to not map pages so that we can trap memory accesses.

[pcc]

In D33557#764664, @ruiu wrote:

I was trying to say is to not map pages so that we can trap memory accesses.

Yeah, that's what I thought you meant.

lld/trunk/COFF/Writer.cpp

void Writer::createImportTables() {
   for (ImportFile *File : Symtab->ImportFiles) {
     if (!File->Live)
       continue;
 
     if (DefinedImportThunk *Thunk = File->ThunkSym)
       Text->addChunk(Thunk->getChunk());
 
     if (Config->DelayLoads.count(StringRef(File->DLLName).lower())) {
+      if (!File->ThunkSym)
+        fatal("cannot delay-load " + toString(File) +
+              " due to import of data: " + toString(*File->ImpSym));
       DelayIdata.add(File->ImpSym);
     } else {
       Idata.add(File->ImpSym);
     }
   }
 
   if (!Idata.empty()) {
     OutputSection *Sec = createSection(".idata");

lld/trunk/test/COFF/Inputs/delayimports-error.yaml

+--- !COFF
+header:
+  Machine:         IMAGE_FILE_MACHINE_AMD64
+  Characteristics: []
+sections:
+  - Name:            .data
+    Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_MEM_READ, IMAGE_SCN_MEM_WRITE ]
+    Alignment:       4
+    SectionData:     0000000000000000
+symbols:
+  - Name:            .data
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    SectionDefinition:
+      Length:          8
+      NumberOfRelocations: 0
+      NumberOfLinenumbers: 0
+      CheckSum:        0
+      Number:          0
+  - Name:            datasym
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+...

lld/trunk/test/COFF/delayimports-error.test

+# RUN: mkdir -p %t.dir
+# RUN: yaml2obj < %p/Inputs/delayimports-error.yaml > %t1.obj
+# RUN: lld-link /out:%t.dir/foo.dll /dll %t1.obj /export:datasym,DATA /noentry
+
+# RUN: yaml2obj < %s > %t2.obj
+# RUN: not lld-link /out:%t.exe /entry:main %t2.obj %t.dir/foo.lib /delayload:foo.dll \
+# RUN:   /alternatename:__delayLoadHelper2=main /opt:noref >& %t.log
+# RUN: FileCheck %s < %t.log
+
+# CHECK: cannot delay-load foo.dll due to import of data: __imp_datasym
+
+--- !COFF
+header:
+  Machine:         IMAGE_FILE_MACHINE_AMD64
+  Characteristics: []
+sections:
+  - Name:            .text
+    Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+    Alignment:       16
+    SectionData:     0000000000000000
+symbols:
+  - Name:            .text
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    SectionDefinition:
+      Length:          8
+      NumberOfRelocations: 0
+      NumberOfLinenumbers: 0
+      CheckSum:        0
+      Number:          0
+  - Name:            main
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_FUNCTION
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+  - Name:            __imp_datasym
+    Value:           0
+    SectionNumber:   0
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+...