Index: llvm/lib/ObjectYAML/ELFEmitter.cpp
===================================================================
--- llvm/lib/ObjectYAML/ELFEmitter.cpp
+++ llvm/lib/ObjectYAML/ELFEmitter.cpp
@@ -399,9 +399,13 @@
   Header.e_shentsize =
       Doc.Header.SHEntSize ? (uint16_t)*Doc.Header.SHEntSize : sizeof(Elf_Shdr);
 
+  const bool NoShdrs = Doc.SectionHeaders &&
+                       Doc.SectionHeaders->Sections.empty() &&
+                       !Doc.SectionHeaders->Excluded;
+
   if (Doc.Header.SHOff)
     Header.e_shoff = *Doc.Header.SHOff;
-  else if (Doc.SectionHeaders && Doc.SectionHeaders->Sections.empty())
+  else if (NoShdrs)
     Header.e_shoff = 0;
   else
     Header.e_shoff = SHOff;
@@ -410,18 +414,17 @@
     Header.e_shnum = *Doc.Header.SHNum;
   else if (!Doc.SectionHeaders)
     Header.e_shnum = Doc.getSections().size();
-  else if (Doc.SectionHeaders->Sections.empty())
+  else if (NoShdrs)
     Header.e_shnum = 0;
   else
     Header.e_shnum = Doc.SectionHeaders->Sections.size() + /*Null section*/ 1;
 
   if (Doc.Header.SHStrNdx)
     Header.e_shstrndx = *Doc.Header.SHStrNdx;
-  else if ((!Doc.SectionHeaders || !Doc.SectionHeaders->Sections.empty()) &&
-           !ExcludedSectionHeaders.count(".shstrtab"))
-    Header.e_shstrndx = SN2I.get(".shstrtab");
-  else
+  else if (NoShdrs || ExcludedSectionHeaders.count(".shstrtab"))
     Header.e_shstrndx = 0;
+  else
+    Header.e_shstrndx = SN2I.get(".shstrtab");
 
   OS.write((const char *)&Header, sizeof(Header));
 }
@@ -1651,7 +1654,8 @@
 
 template <class ELFT>
 DenseMap<StringRef, size_t> ELFState<ELFT>::buildSectionHeaderReorderMap() {
-  if (!Doc.SectionHeaders || Doc.SectionHeaders->Sections.empty())
+  if (!Doc.SectionHeaders ||
+      (Doc.SectionHeaders->Sections.empty() && !Doc.SectionHeaders->Excluded))
     return DenseMap<StringRef, size_t>();
 
   DenseMap<StringRef, size_t> Ret;
Index: llvm/test/tools/yaml2obj/ELF/section-headers-exclude.yaml
===================================================================
--- llvm/test/tools/yaml2obj/ELF/section-headers-exclude.yaml
+++ llvm/test/tools/yaml2obj/ELF/section-headers-exclude.yaml
@@ -90,9 +90,7 @@
   Machine: EM_X86_64
 SectionHeaderTable:
   Sections: []
-  Excluded:
-    - Name: .strtab
-
+ 
 ## Check how we handle cases when a section is excluded, but its section index is needed.
 ## The general rule is: when a section is explicitly linked with another section, which is
 ## excluded, then we report an error. In the case when it is linked implicitly with an excluded
@@ -476,3 +474,44 @@
     - Name: .strtab
   Excluded:
     - Name: .shstrtab
+
+## Check that we keep the null SHF_UNDEF section when the "Sections" key is empty,
+## but the "Excluded" key is not
+# RUN: yaml2obj --docnum=18 %s -o %t10
+# RUN: llvm-readelf --sections %t10 | FileCheck %s --check-prefix=KEEP-NULL
+
+# KEEP-NULL:      There are 1 section headers, starting at offset 0x48:
+# KEEP-NULL:      [Nr] Name         Type Address          Off    Size   ES Flg Lk Inf Al
+# KEEP-NULL-NEXT: [ 0] <no-strings> NULL 0000000000000000 000000 000000 00     0   0  0
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_REL
+  Machine: EM_X86_64
+SectionHeaderTable:
+  Sections: []
+  Excluded:
+    - Name: .strtab
+    - Name: .shstrtab
+
+## Check we are able to report all possible errors mentioned above even when the "Sections" key is empty.
+# RUN: not yaml2obj %s --docnum=19 -o /dev/null 2>&1 | FileCheck %s --check-prefix=INVALID-EXCLUDED
+
+# INVALID-EXCLUDED: error: repeated section name: '.strtab' in the section header description
+# INVALID-EXCLUDED: error: section '.shstrtab' should be present in the 'Sections' or 'Excluded' lists
+# INVALID-EXCLUDED: error: section header contains undefined section '.unknown'
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_REL
+  Machine: EM_X86_64
+SectionHeaderTable:
+  Sections: []
+  Excluded:
+    - Name: .strtab
+    - Name: .strtab
+    - Name: .unknown