[Mips] Set default base address for MIPS executables to 0x400000. Assign

the lowest segment address to the MIPS_BASE_ADDRESS dynamic tag.

llvm-svn: 199234

lld/lib/ReaderWriter/ELF/Mips/MipsLinkingContext.cpp

@@ -34,6 +34,18 @@ bool MipsLinkingContext::isLittleEndian() const {
   return Mips32ElELFType::TargetEndianness == llvm::support::little;
 }
 
+uint64_t MipsLinkingContext::getBaseAddress() const {
+  if (_baseAddress == 0 && getOutputELFType() == llvm::ELF::ET_EXEC)
+    return 0x400000;
+  return _baseAddress;
+}
+
+StringRef MipsLinkingContext::entrySymbolName() const {
+  if (_outputELFType == elf::ET_EXEC && _entrySymbolName.empty())
+    return "__start";
+  return _entrySymbolName;
+}
+
 void MipsLinkingContext::addPasses(PassManager &pm) {
   auto pass = createMipsRelocationPass(*this);
   if (pass)

lld/lib/ReaderWriter/ELF/Mips/MipsLinkingContext.h

@@ -35,6 +35,8 @@ public:
 
   // ELFLinkingContext
   virtual bool isLittleEndian() const;
+  virtual uint64_t getBaseAddress() const;
+  virtual StringRef entrySymbolName() const;
   virtual void addPasses(PassManager &pm);
 };
 

lld/lib/ReaderWriter/ELF/Mips/MipsTargetHandler.cpp

@@ -64,7 +64,7 @@ public:
     // The base address of the segment.
     dyn.d_un.d_ptr = 0;
     dyn.d_tag = DT_MIPS_BASE_ADDRESS;
-    addEntry(dyn);
+    _dt_baseaddr = addEntry(dyn);
 
     // Number of local global offset table entries.
     dyn.d_un.d_val = 0;
@@ -91,6 +91,13 @@ public:
   virtual void updateDynamicTable() {
     DynamicTable<Mips32ElELFType>::updateDynamicTable();
 
+    // Assign the minimum segment address to the DT_MIPS_BASE_ADDRESS tag.
+    auto baseAddr = std::numeric_limits<uint64_t>::max();
+    for (auto si : _layout.segments())
+      if (si->segmentType() != llvm::ELF::PT_NULL)
+        baseAddr = std::min(baseAddr, si->virtualAddr());
+    _entries[_dt_baseaddr].d_un.d_val = baseAddr;
+
     auto &got = _layout.getGOTSection();
 
     _entries[_dt_symtabno].d_un.d_val = getSymbolTable()->size();
@@ -108,6 +115,7 @@ private:
   std::size_t _dt_localgot;
   std::size_t _dt_gotsym;
   std::size_t _dt_pltgot;
+  std::size_t _dt_baseaddr;
 };
 }
 

lld/test/elf/Mips/base-address.test

@@ -0,0 +1,65 @@
+# Check executable base address configuration. Base address should be
+# equal to 0x400000 and the MIPS_BASE_ADDRESS dynamic tag's value should
+# be the same.
+# RUN: llvm-mc -triple=mipsel -filetype=obj -o=%t1 %s
+# RUN: lld -flavor gnu -target mipsel --noinhibit-exec -o %t2 %t1
+# RUN: llvm-readobj -dynamic-table -program-headers %t2 | FileCheck %s
+
+# CHECK: DynamicSection [ (15 entries)
+# CHECK:   Tag        Type                 Name/Value
+# CHECK:   0x00000004 HASH                 0x400110
+# CHECK:   0x00000005 STRTAB               0x400130
+# CHECK:   0x00000006 SYMTAB               0x400120
+# CHECK:   0x0000000A STRSZ                1 (bytes)
+# CHECK:   0x0000000B SYMENT               16 (bytes)
+# CHECK:   0x0000001A FINI_ARRAY           0x0
+# CHECK:   0x0000001C FINI_ARRAYSZ         0 (bytes)
+# CHECK:   0x70000001 MIPS_RLD_VERSION     1
+# CHECK:   0x70000005 MIPS_FLAGS           0x2
+# CHECK:   0x70000006 MIPS_BASE_ADDRESS    0x400000
+# CHECK:   0x7000000A MIPS_LOCAL_GOTNO     2
+# CHECK:   0x70000011 MIPS_SYMTABNO        1
+# CHECK:   0x70000013 MIPS_GOTSYM          0x1
+# CHECK:   0x00000003 PLTGOT               0x401000
+# CHECK:   0x00000000 NULL                 0x0
+# CHECK: ]
+
+# CHECK: ProgramHeaders [
+# CHECK:   ProgramHeader {
+# CHECK:     Type: PT_PHDR (0x6)
+# CHECK:     Offset: 0x34
+# CHECK:     VirtualAddress: 0x400034
+# CHECK:   }
+# CHECK:   ProgramHeader {
+# CHECK:     Type: PT_INTERP (0x3)
+# CHECK:     Offset: 0xF4
+# CHECK:     VirtualAddress: 0x4000F4
+# CHECK:   }
+# CHECK:   ProgramHeader {
+# CHECK:     Type: PT_LOAD (0x1)
+# CHECK:     Offset: 0x0
+# CHECK:     VirtualAddress: 0x400000
+# CHECK:   }
+# CHECK:   ProgramHeader {
+# CHECK:     Type: PT_LOAD (0x1)
+# CHECK:     Offset: 0x1000
+# CHECK:     VirtualAddress: 0x401000
+# CHECK:   }
+# CHECK:   ProgramHeader {
+# CHECK:     Type: PT_LOAD (0x1)
+# CHECK:     Offset: 0x2000
+# CHECK:     VirtualAddress: 0x402000
+# CHECK:   }
+# CHECK:   ProgramHeader {
+# CHECK:     Type: PT_DYNAMIC (0x2)
+# CHECK:     Offset: 0x138
+# CHECK:     VirtualAddress: 0x400138
+# CHECK:   }
+# CHECK: ]
+
+    .global main
+    .ent    main
+main:
+    nop
+    .end    main
+