[llvm] [ObjectYAML][ELF] Report incorrect offset to generate notes (PR #118741)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-objectyaml

Author: Igor Kudrin (igorkudrin)

<details>
<summary>Changes</summary>

All notes in the note section must be correctly aligned, including the first. The tool should refuse to generate notes if the section offset is incorrect in this respect.

---
Full diff: https://github.com/llvm/llvm-project/pull/118741.diff


2 Files Affected:

- (modified) llvm/lib/ObjectYAML/ELFEmitter.cpp (+8-1) 
- (modified) llvm/test/tools/yaml2obj/ELF/note-section.yaml (+55) 


``````````diff
diff --git a/llvm/lib/ObjectYAML/ELFEmitter.cpp b/llvm/lib/ObjectYAML/ELFEmitter.cpp
index 5daf6c32ec936a..cc41bbe6bbde24 100644
--- a/llvm/lib/ObjectYAML/ELFEmitter.cpp
+++ b/llvm/lib/ObjectYAML/ELFEmitter.cpp
@@ -1796,7 +1796,7 @@ template <class ELFT>
 void ELFState<ELFT>::writeSectionContent(Elf_Shdr &SHeader,
                                          const ELFYAML::NoteSection &Section,
                                          ContiguousBlobAccumulator &CBA) {
-  if (!Section.Notes)
+  if (!Section.Notes || Section.Notes->empty())
     return;
 
   unsigned Align;
@@ -1814,6 +1814,13 @@ void ELFState<ELFT>::writeSectionContent(Elf_Shdr &SHeader,
     return;
   }
 
+  if (CBA.getOffset() != alignTo(CBA.getOffset(), Align)) {
+    reportError(Section.Name + ": invalid offset of a note section: 0x" +
+                Twine::utohexstr(CBA.getOffset()) + ", should be aligned to " +
+                Twine(Align));
+    return;
+  }
+
   uint64_t Offset = CBA.tell();
   for (const ELFYAML::NoteEntry &NE : *Section.Notes) {
     // Write name size.
diff --git a/llvm/test/tools/yaml2obj/ELF/note-section.yaml b/llvm/test/tools/yaml2obj/ELF/note-section.yaml
index 10fd36fefeabfd..e48c323f594da6 100644
--- a/llvm/test/tools/yaml2obj/ELF/note-section.yaml
+++ b/llvm/test/tools/yaml2obj/ELF/note-section.yaml
@@ -514,3 +514,58 @@ Sections:
         Desc: 030405
       - Name: GNU
         Type: NT_GNU_BUILD_ID
+
+## Check that an incorrect offset for generating notes is reported.
+
+# RUN: not yaml2obj --docnum=19 %s 2>&1 | FileCheck %s --check-prefix=ERR_OFFSET
+# ERR_OFFSET: error: .note: invalid offset of a note section: 0x{{.*}}, should be aligned to 4
+
+--- !ELF
+FileHeader:
+  Class: ELFCLASS32
+  Data:  ELFDATA2LSB
+  Type:  ET_EXEC
+Sections:
+  - Name: .dummy
+    Type: SHT_PROGBITS
+    Size: 1
+  - Name: .note
+    Type: SHT_NOTE
+    Notes:
+      - Type: 0x1
+
+## Do not issue an error if the notes array is empty
+
+# RUN: yaml2obj --docnum=20 %s -o - | \
+# RUN:   llvm-readobj --sections --section-data - | \
+# RUN:   FileCheck %s --check-prefix=TEST20
+
+# TEST20:      Section {
+# TEST20:      Name: .note
+# TEST20-NEXT:   Type: SHT_NOTE
+# TEST20-NEXT:   Flags [ (0x0)
+# TEST20-NEXT:   ]
+# TEST20-NEXT:   Address:
+# TEST20-NEXT:   Offset:
+# TEST20-NEXT:   Size: 0
+# TEST20-NEXT:   Link:
+# TEST20-NEXT:   Info:
+# TEST20-NEXT:   AddressAlignment: 5
+# TEST20-NEXT:   EntrySize:
+# TEST20-NEXT:   SectionData (
+# TEST20-NEXT:   )
+# TEST20-NEXT: }
+
+--- !ELF
+FileHeader:
+  Class: ELFCLASS32
+  Data:  ELFDATA2LSB
+  Type:  ET_EXEC
+Sections:
+  - Name: .dummy
+    Type: SHT_PROGBITS
+    Size: 1
+  - Name: .note
+    Type: SHT_NOTE
+    AddressAlign: 5
+    Notes: []

``````````

</details>


https://github.com/llvm/llvm-project/pull/118741