[PATCH] D95341: [yaml2obj] - Allow empty SectionHeaderTable definitions.

[George Rimar via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
grimar marked an inline comment as done.
Closed by commit rG68195b15a36c: [yaml2obj] - Allow empty SectionHeaderTable definitions. (authored by grimar).

Changed prior to commit:
  https://reviews.llvm.org/D95341?vs=318945&id=319773#toc

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D95341/new/

https://reviews.llvm.org/D95341

Files:
  llvm/include/llvm/ObjectYAML/ELFYAML.h
  llvm/lib/ObjectYAML/ELFEmitter.cpp
  llvm/lib/ObjectYAML/ELFYAML.cpp
  llvm/test/tools/yaml2obj/ELF/section-headers.yaml


Index: llvm/test/tools/yaml2obj/ELF/section-headers.yaml
===================================================================
--- llvm/test/tools/yaml2obj/ELF/section-headers.yaml
+++ llvm/test/tools/yaml2obj/ELF/section-headers.yaml
@@ -151,10 +151,18 @@
     Sections:  []
     NoHeaders: [[NOHEADERS]]
 
-## Check that we do not allow an empty SectionHeaderTable tag and suggest to use an explicit syntax instead.
-# RUN: not yaml2obj %s --docnum=5 -o /dev/null 2>&1 | FileCheck %s --check-prefix=NO-VALUE
+## Check that we allow using an empty SectionHeaderTable definition.
+## It can be used to emit the default section header table at an arbitrary position.
 
-# NO-VALUE: SectionHeaderTable can't be empty. Use 'NoHeaders' key to drop the section header table
+# RUN: yaml2obj %s --docnum=5 -o %t5.novalues
+# RUN: llvm-readelf --sections %t5.novalues | \
+# RUN:   FileCheck %s --check-prefix=NO-VALUES
+
+## Check we placed the section header table before the .foo section.
+
+# NO-VALUES: There are 4 section headers, starting at offset 0x40:
+# NO-VALUES: [Nr] Name Type     Address          Off    Size
+# NO-VALUES: [ 1] .foo PROGBITS 0000000000000000 000140 000000
 
 --- !ELF
 FileHeader:
@@ -162,9 +170,9 @@
   Data:  ELFDATA2LSB
   Type:  ET_REL
 Sections:
+  - Type: SectionHeaderTable
   - Name: .foo
     Type: SHT_PROGBITS
-  - Type: SectionHeaderTable
 
 ## Test that we are still able to override e_shoff, e_shnum and e_shstrndx
 ## fields even when we do not produce section headers.
Index: llvm/lib/ObjectYAML/ELFYAML.cpp
===================================================================
--- llvm/lib/ObjectYAML/ELFYAML.cpp
+++ llvm/lib/ObjectYAML/ELFYAML.cpp
@@ -1474,9 +1474,6 @@
   if (const auto *SHT = dyn_cast<ELFYAML::SectionHeaderTable>(C.get())) {
     if (SHT->NoHeaders && (SHT->Sections || SHT->Excluded || SHT->Offset))
       return "NoHeaders can't be used together with Offset/Sections/Excluded";
-    if (!SHT->NoHeaders && !SHT->Sections && !SHT->Excluded)
-      return "SectionHeaderTable can't be empty. Use 'NoHeaders' key to drop "
-             "the section header table";
     return "";
   }
 
Index: llvm/lib/ObjectYAML/ELFEmitter.cpp
===================================================================
--- llvm/lib/ObjectYAML/ELFEmitter.cpp
+++ llvm/lib/ObjectYAML/ELFEmitter.cpp
@@ -555,7 +555,8 @@
   const ELFYAML::SectionHeaderTable &SectionHeaders =
       Doc.getSectionHeaderTable();
   if (SectionHeaders.IsImplicit ||
-      (SectionHeaders.NoHeaders && !SectionHeaders.NoHeaders.getValue()))
+      (SectionHeaders.NoHeaders && !SectionHeaders.NoHeaders.getValue()) ||
+      SectionHeaders.isDefault())
     return Index;
 
   assert(!SectionHeaders.NoHeaders.getValueOr(false) ||
@@ -1744,7 +1745,8 @@
 DenseMap<StringRef, size_t> ELFState<ELFT>::buildSectionHeaderReorderMap() {
   const ELFYAML::SectionHeaderTable &SectionHeaders =
       Doc.getSectionHeaderTable();
-  if (SectionHeaders.IsImplicit || SectionHeaders.NoHeaders)
+  if (SectionHeaders.IsImplicit || SectionHeaders.NoHeaders ||
+      SectionHeaders.isDefault())
     return DenseMap<StringRef, size_t>();
 
   DenseMap<StringRef, size_t> Ret;
Index: llvm/include/llvm/ObjectYAML/ELFYAML.h
===================================================================
--- llvm/include/llvm/ObjectYAML/ELFYAML.h
+++ llvm/include/llvm/ObjectYAML/ELFYAML.h
@@ -296,13 +296,15 @@
   Optional<bool> NoHeaders;
 
   size_t getNumHeaders(size_t SectionsNum) const {
-    if (IsImplicit)
+    if (IsImplicit || isDefault())
       return SectionsNum;
     if (NoHeaders)
       return (*NoHeaders) ? 0 : SectionsNum;
     return (Sections ? Sections->size() : 0) + /*Null section*/ 1;
   }
 
+  bool isDefault() const { return !Sections && !Excluded && !NoHeaders; }
+
   static constexpr StringRef TypeStr = "SectionHeaderTable";
 };
 


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