[COFF] Correctly set the thumb bit in DLL export addresses

[mstorsjo]

Summary

The same adjustment is already done for the entry point in Writer.cpp and for relocations that point to executable code in Chunks.cpp.

[compnerd]

Does link actually set the ISA selection bit on the EAT entries? I don't remember that behaviour from it and I dont have it on hand to check.

COFF/DLL.cpp

331

Don't use +1. If the ISA selection bit is set, then you will have erased it.

[mstorsjo]

In D35767#818232, @compnerd wrote:

Does link actually set the ISA selection bit on the EAT entries? I don't remember that behaviour from it and I dont have it on hand to check.

Yes, I checked with MS link.exe and this matches what it does.

COFF/DLL.cpp

331

Ok, will change into | 1 instead.

[mstorsjo]

Updated to use | 1 instead of + 1 for setting the bit, renamed the variable from Offset to Bit accordingly.

[ruiu]

test/COFF/Inputs/export-armnt.yaml

1

Move the contents of this file to test/COFF/export-armnt.test to remove this file. Usually, when there's only one input file, you can write it in the test file itself.

[mstorsjo]

Merged the test input data into the test itself, as suggested by Rui.

[ruiu]

LGTM

COFF/DLL.cpp

 };
 
 class AddressTableChunk : public Chunk {
 public:
   explicit AddressTableChunk(size_t MaxOrdinal) : Size(MaxOrdinal + 1) {}
   size_t getSize() const override { return Size * 4; }
 
   void writeTo(uint8_t *Buf) const override {
+    uint32_t Bit = 0;
+    // Pointer to thumb code must have the LSB set, so adjust it.
+    if (Config->Machine == ARMNT)
+      Bit = 1;
     for (Export &E : Config->Exports) {
       uint8_t *P = Buf + OutputSectionOff + E.Ordinal * 4;
       if (E.ForwardChunk) {
-        write32le(P, E.ForwardChunk->getRVA());
+        write32le(P, E.ForwardChunk->getRVA() | Bit);
       } else {
-        write32le(P, cast<Defined>(E.Sym)->getRVA());
+        write32le(P, cast<Defined>(E.Sym)->getRVA() | Bit);
       }
     }
   }
 
 private:
   size_t Size;
 };
 

test/COFF/Inputs/export-armnt.yaml

+--- !COFF
+header:
+  Machine:         IMAGE_FILE_MACHINE_ARMNT
+  Characteristics: []
+sections:
+  - Name:            .text
+    Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+    Alignment:       4
+    SectionData:     704700bf704700bf704700bf
+  - Name:            .drectve
+    Characteristics: [ IMAGE_SCN_LNK_INFO, IMAGE_SCN_LNK_REMOVE ]
+    Alignment:       1
+    SectionData:     2f6578706f72743a6578706f7274666e3300  # /export:exportfn3
+symbols:
+  - Name:            .text
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    SectionDefinition:
+      Length:          12
+      NumberOfRelocations: 0
+      NumberOfLinenumbers: 0
+      CheckSum:        0
+      Number:          0
+  - Name:            _DllMainCRTStartup
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+  - Name:            exportfn1
+    Value:           4
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+  - Name:            exportfn2
+    Value:           8
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+  - Name:            exportfn3
+    Value:           8
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+  - Name:            '?mangled@@YAHXZ'
+    Value:           8
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+...

test/COFF/export-armnt.test

+# REQUIRES: arm
+
+# RUN: yaml2obj < %p/Inputs/export-armnt.yaml > %t.obj
+#
+# RUN: lld-link /out:%t.dll /dll %t.obj /export:exportfn1 /export:exportfn2
+# RUN: llvm-objdump -p %t.dll | FileCheck %s
+
+CHECK:      Export Table:
+CHECK:      DLL name: export-armnt.test.tmp.dll
+CHECK:      Ordinal      RVA  Name
+CHECK-NEXT:       0        0
+CHECK-NEXT:       1   0x1005  exportfn1
+CHECK-NEXT:       2   0x1009  exportfn2
+CHECK-NEXT:       3   0x1009  exportfn3