[elfabi] Add support for reading DT_SONAME from binaries

This change gives the llvm-elfabi tool the ability to read DT_SONAME from a binary ELF file into an ELFStub.

Added:

 - DynamicEntries struct for storing dynamic entries that are relevant to elfabi.
 - terminatedSubstr() retrieves a null-terminated substring from a StringRef.
 - appendToError() appends a string to an error, allowing more specific error messages.

Differential Revision: https://reviews.llvm.org/D55629

llvm-svn: 351361
diff --git a/llvm/test/tools/llvm-elfabi/binary-read-no-dt-strtab.test b/llvm/test/tools/llvm-elfabi/binary-read-no-dt-strtab.test
new file mode 100644
index 0000000..25fcbdc
--- /dev/null
+++ b/llvm/test/tools/llvm-elfabi/binary-read-no-dt-strtab.test
@@ -0,0 +1,42 @@
+# 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:         0x0000
+    Content:         "00"
+  - Name:            .dynamic
+    Type:            SHT_DYNAMIC
+    Flags:           [ SHF_ALLOC ]
+    Address:         0x0008
+    AddressAlign:    8
+    Content:         "0a00000000000000010000000000000000000000000000000000000000000000"
+      # DT_STRSZ      1 (0x1)
+      # DT_NULL       0x0
+    Size:            32
+    Link:            .dynstr
+ProgramHeaders:
+  - Type: PT_LOAD
+    Flags: [ PF_R ]
+    VAddr: 0x0000
+    PAddr: 0x0000
+    Align: 8
+    Sections:
+      - Section: .dynstr
+      - Section: .dynamic
+  - Type: PT_DYNAMIC
+    Flags: [ PF_X, PF_R ]
+    VAddr: 0x0008
+    PAddr: 0x0008
+    Sections:
+      - Section: .dynamic
+
+# CHECK: Couldn't locate dynamic string table (no DT_STRTAB entry)