[elfabi] Add support for reading DT_NEEDED from binaries

This patch gives elfabi the ability to read DT_NEEDED entries from ELF binaries
to populate NeededLibs in TextAPI's ELFStub.

Differential Revision: https://reviews.llvm.org/D55852

llvm-svn: 351592

llvm/test/tools/llvm-elfabi/binary-read-neededlibs-bad-offset.test

+# RUN: yaml2obj %s > %t
+# RUN: not llvm-elfabi --elf %t --emit-tbe=%t.tbe 2>&1 | FileCheck %s
+
+!ELF
+FileHeader:
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  Type:            ET_DYN
+  Machine:         EM_X86_64
+Sections:
+  - Name:            .dynstr
+    Type:            SHT_STRTAB
+    Flags:           [ SHF_ALLOC ]
+    Address:         0x1000
+    #                "\0libfoo.so\0libbar.so\0somelib.so\0foo\0"
+    Content:         "006c6962666f6f2e736f006c69626261722e736f00736f6d656c69622e736f00666f6f00"
+  - Name:            .dynamic
+    Type:            SHT_DYNAMIC
+    Flags:           [ SHF_ALLOC ]
+    Address:         0x1024
+    Content:         "010000000000000001000000000000000e0000000000000015000000000000000100000000000000ffff0000000000000a0000000000000024000000000000000500000000000000001000000000000000000000000000000000000000000000"
+      # DT_NEEDED     1 (0x01)
+      # DT_SONAME     21 (0x15)
+      # Bad DT_NEEDED entry (offset outside string table):
+      # DT_NEEDED     65535 (0xffff)
+      # DT_STRSZ      36 (0x24)
+      # DT_STRTAB     0x1000
+      # DT_NULL       0x0
+    Size:            96
+ProgramHeaders:
+  - Type: PT_LOAD
+    Flags: [ PF_R ]
+    VAddr: 0x1000
+    PAddr: 0x1000
+    Align: 8
+    Sections:
+      - Section: .dynstr
+      - Section: .dynamic
+  - Type: PT_DYNAMIC
+    Flags: [ PF_X, PF_R ]
+    VAddr: 0x1024
+    PAddr: 0x1024
+    Sections:
+
+# CHECK: DT_NEEDED string offset (0x000000000000ffff) outside of dynamic string table

llvm/test/tools/llvm-elfabi/binary-read-neededlibs.test

+# RUN: yaml2obj %s -o %t
+# RUN: llvm-elfabi --elf %t --emit-tbe=- | FileCheck %s
+
+!ELF
+FileHeader:
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  Type:            ET_DYN
+  Machine:         EM_X86_64
+Sections:
+  - Name:            .dynstr
+    Type:            SHT_STRTAB
+    Flags:           [ SHF_ALLOC ]
+    Address:         0x1000
+    #                "\0libfoo.so\0libbar.so\0somelib.so\0foo\0"
+    Content:         "006c6962666f6f2e736f006c69626261722e736f00736f6d656c69622e736f00666f6f00"
+  - Name:            .dynamic
+    Type:            SHT_DYNAMIC
+    Flags:           [ SHF_ALLOC ]
+    Address:         0x1024
+    Content:         "010000000000000001000000000000000e00000000000000150000000000000001000000000000000b000000000000000a0000000000000024000000000000000500000000000000001000000000000000000000000000000000000000000000"
+      # DT_NEEDED     1 (0x01)
+      # DT_SONAME     21 (0x15)
+      # DT_NEEDED     11 (0x0b)
+      # DT_STRSZ      36 (0x24)
+      # DT_STRTAB     0x1000
+      # DT_NULL       0x0
+    Size:            96
+ProgramHeaders:
+  - Type: PT_LOAD
+    Flags: [ PF_R ]
+    VAddr: 0x1000
+    PAddr: 0x1000
+    Align: 8
+    Sections:
+      - Section: .dynstr
+      - Section: .dynamic
+  - Type: PT_DYNAMIC
+    Flags: [ PF_X, PF_R ]
+    VAddr: 0x1024
+    PAddr: 0x1024
+    Sections:
+
+# CHECK:      NeededLibs:
+# CHECK-NEXT:   - libfoo.so{{$}}
+# CHECK-NEXT:   - libbar.so{{$}}
+# CHECK-NEXT: Symbols: {}

llvm/tools/llvm-elfabi/ELFObjHandler.cpp

@@ -31,6 +31,7 @@ struct DynamicEntries {
   uint64_t StrTabAddr = 0;
   uint64_t StrSize = 0;
   Optional<uint64_t> SONameOffset;
+  std::vector<uint64_t> NeededLibNames;
 };
 
 /// This function behaves similarly to StringRef::substr(), but attempts to
@@ -94,6 +95,9 @@ static Error populateDynamic(DynamicEntries &Dyn,
       Dyn.StrSize = Entry.d_un.d_val;
       FoundDynStrSz = true;
       break;
+    case DT_NEEDED:
+      Dyn.NeededLibNames.push_back(Entry.d_un.d_val);
+      break;
     }
   }
 
@@ -111,6 +115,14 @@ static Error populateDynamic(DynamicEntries &Dyn,
         "DT_SONAME string offset (0x%016x) outside of dynamic string table",
         *Dyn.SONameOffset);
   }
+  for (uint64_t Offset : Dyn.NeededLibNames) {
+    if (Offset >= Dyn.StrSize) {
+      return createStringError(
+          object_error::parse_failed,
+          "DT_NEEDED string offset (0x%016x) outside of dynamic string table",
+          Offset);
+    }
+  }
 
   return Error::success();
 }
@@ -164,7 +176,16 @@ buildStub(const ELFObjectFile<ELFT> &ElfObj) {
     DestStub->SoName = *NameOrErr;
   }
 
-  // TODO: Populate NeededLibs from .dynamic entries and linked string table.
+  // Populate NeededLibs from .dynamic entries and dynamic string table.
+  for (uint64_t NeededStrOffset : DynEnt.NeededLibNames) {
+    Expected<StringRef> LibNameOrErr =
+        terminatedSubstr(DynStr, NeededStrOffset);
+    if (!LibNameOrErr) {
+      return appendToError(LibNameOrErr.takeError(), "when reading DT_NEEDED");
+    }
+    DestStub->NeededLibs.push_back(*LibNameOrErr);
+  }
+
   // TODO: Populate Symbols from .dynsym table and linked string table.
 
   return std::move(DestStub);