Index: lit/Modules/ELF/many-sections.s
===================================================================
--- lit/Modules/ELF/many-sections.s
+++ lit/Modules/ELF/many-sections.s
@@ -7,7 +7,7 @@
 ## aaaaaaaa..dddddddd, plus a couple of standard ones (.strtab, etc.)
 ## Check the number is correct plus the names of a couple of chosen sections.
 
-# CHECK: Showing 65541 sections
+# CHECK: Showing 65540 sections
 # CHECK: Name: aaaaaaaa
 # CHECK: Name: bbbbbbbb
 # CHECK: Name: cccccccc
Index: lit/Modules/MachO/subsections.yaml
===================================================================
--- lit/Modules/MachO/subsections.yaml
+++ lit/Modules/MachO/subsections.yaml
@@ -3,6 +3,7 @@
 
 #CHECK:     Showing 2 sections
 #CHECK-NEXT:  Index: 0
+#CHECK-NEXT:  ID: 256
 #CHECK-NEXT:  Name: __PAGEZERO
 #CHECK-NEXT:  Type: container
 #CHECK-NEXT:  Permissions: ---
@@ -13,6 +14,7 @@
 #CHECK-NEXT:  There are no subsections
 #CHECK-EMPTY:
 #CHECK-NEXT:  Index: 1
+#CHECK-NEXT:  ID: 512
 #CHECK-NEXT:  Name: __TEXT
 #CHECK-NEXT:  Type: container
 #CHECK-NEXT:  Permissions: r-x
@@ -22,6 +24,7 @@
 #CHECK-NEXT:  File size: 4096
 #CHECK-NEXT:  Showing 3 subsections
 #CHECK-NEXT:    Index: 0
+#CHECK-NEXT:    ID: 1
 #CHECK-NEXT:    Name: __text
 #CHECK-NEXT:    Type: code
 #CHECK-NEXT:    Permissions: r-x
@@ -31,6 +34,7 @@
 #CHECK-NEXT:    File size: 22
 #CHECK-EMPTY:
 #CHECK-NEXT:    Index: 1
+#CHECK-NEXT:    ID: 2
 #CHECK-NEXT:    Name: __unwind_info
 #CHECK-NEXT:    Type: compact-unwind
 #CHECK-NEXT:    Permissions: r-x
@@ -40,6 +44,7 @@
 #CHECK-NEXT:    File size: 76
 #CHECK-EMPTY:
 #CHECK-NEXT:    Index: 2
+#CHECK-NEXT:    ID: 3
 #CHECK-NEXT:    Name: __eh_frame
 #CHECK-NEXT:    Type: eh-frame
 #CHECK-NEXT:    Permissions: r-x
Index: source/Plugins/ObjectFile/ELF/ObjectFileELF.h
===================================================================
--- source/Plugins/ObjectFile/ELF/ObjectFileELF.h
+++ source/Plugins/ObjectFile/ELF/ObjectFileELF.h
@@ -220,10 +220,10 @@
   /// The address class for each symbol in the elf file
   FileAddressToAddressClassMap m_address_class_map;
 
-  /// Returns a 1 based index of the given section header.
+  /// Returns the index of the given section header.
   size_t SectionIndex(const SectionHeaderCollIter &I);
 
-  /// Returns a 1 based index of the given section header.
+  /// Returns the index of the given section header.
   size_t SectionIndex(const SectionHeaderCollConstIter &I) const;
 
   // Parses the ELF program headers.
Index: source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp
===================================================================
--- source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp
+++ source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp
@@ -889,11 +889,11 @@
 }
 
 size_t ObjectFileELF::SectionIndex(const SectionHeaderCollIter &I) {
-  return std::distance(m_section_headers.begin(), I) + 1u;
+  return std::distance(m_section_headers.begin(), I);
 }
 
 size_t ObjectFileELF::SectionIndex(const SectionHeaderCollConstIter &I) const {
-  return std::distance(m_section_headers.begin(), I) + 1u;
+  return std::distance(m_section_headers.begin(), I);
 }
 
 bool ObjectFileELF::ParseHeader() {
@@ -1081,7 +1081,7 @@
     return 0;
   // sh_link: section header index of string table used by entries in the
   // section.
-  Section *dynstr = section_list->FindSectionByID(header->sh_link + 1).get();
+  Section *dynstr = section_list->FindSectionByID(header->sh_link).get();
   if (!dynstr)
     return 0;
 
@@ -1717,10 +1717,10 @@
 
 const ObjectFileELF::ELFSectionHeaderInfo *
 ObjectFileELF::GetSectionHeaderByIndex(lldb::user_id_t id) {
-  if (!id || !ParseSectionHeaders())
+  if (!ParseSectionHeaders())
     return NULL;
 
-  if (--id < m_section_headers.size())
+  if (id < m_section_headers.size())
     return &m_section_headers[id];
 
   return NULL;
@@ -1853,7 +1853,7 @@
     m_sections_ap.reset(new SectionList());
 
     VMAddressProvider address_provider(CalculateType());
-    for (SectionHeaderCollIter I = m_section_headers.begin();
+    for (SectionHeaderCollIter I = std::next(m_section_headers.begin());
          I != m_section_headers.end(); ++I) {
       const ELFSectionHeaderInfo &header = *I;
 
@@ -2000,7 +2000,7 @@
       symbol_type = eSymbolTypeUndefined;
       break;
     default:
-      symbol_section_sp = section_list->GetSectionAtIndex(section_idx);
+      symbol_section_sp = section_list->FindSectionByID(section_idx);
       break;
     }
 
@@ -2282,9 +2282,8 @@
   assert(symtab_hdr->sh_type == SHT_SYMTAB ||
          symtab_hdr->sh_type == SHT_DYNSYM);
 
-  // sh_link: section header index of associated string table. Section ID's are
-  // ones based.
-  user_id_t strtab_id = symtab_hdr->sh_link + 1;
+  // sh_link: section header index of associated string table.
+  user_id_t strtab_id = symtab_hdr->sh_link;
   Section *strtab = section_list->FindSectionByID(strtab_id).get();
 
   if (symtab && strtab) {
@@ -2494,10 +2493,6 @@
   if (!symtab_id || !plt_id)
     return 0;
 
-  // Section ID's are ones based;
-  symtab_id++;
-  plt_id++;
-
   const ELFSectionHeaderInfo *plt_hdr = GetSectionHeaderByIndex(plt_id);
   if (!plt_hdr)
     return 0;
@@ -2523,7 +2518,7 @@
     return 0;
 
   // sh_link points to associated string table.
-  Section *strtab = section_list->FindSectionByID(sym_hdr->sh_link + 1).get();
+  Section *strtab = section_list->FindSectionByID(sym_hdr->sh_link).get();
   if (!strtab)
     return 0;
 
@@ -2651,9 +2646,8 @@
   if (!section_list)
     return 0;
 
-  // Section ID's are ones based.
-  user_id_t symtab_id = rel_hdr->sh_link + 1;
-  user_id_t debug_id = rel_hdr->sh_info + 1;
+  user_id_t symtab_id = rel_hdr->sh_link;
+  user_id_t debug_id = rel_hdr->sh_info;
 
   const ELFSectionHeader *symtab_hdr = GetSectionHeaderByIndex(symtab_id);
   if (!symtab_hdr)
Index: tools/lldb-test/lldb-test.cpp
===================================================================
--- tools/lldb-test/lldb-test.cpp
+++ tools/lldb-test/lldb-test.cpp
@@ -732,6 +732,7 @@
     assert(S);
     AutoIndent Indent(Printer, 2);
     Printer.formatLine("Index: {0}", I);
+    Printer.formatLine("ID: {0}", S->GetID());
     Printer.formatLine("Name: {0}", S->GetName().GetStringRef());
     Printer.formatLine("Type: {0}", S->GetTypeAsCString());
     Printer.formatLine("Permissions: {0}", GetPermissionsAsCString(S->GetPermissions()));