[ObjectYAML][ELF] Take alignment into account when generating notes #118157
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The [System V ABI](https://www.sco.com/developers/gabi/latest/ch5.pheader.html#note_section) states that the note entries and their descriptor fields must be aligned to 4 or 8 bytes for 32-bit and 64-bit objects respectively. In practice, 64-bit systems can use both alignments, with the actual format being distinguished by the alignment of the segment. For example, the [Linux gABI extension](https://github.com/hjl-tools/linux-abi/wiki/linux-abi-draft.pdf) contains a special note on this, see 2.1.7 "Alignment of Note Sections". This patch adjusts the format of the generated notes to the specified section alignment. Since `llvm-readobj` was fixed in a similar way in [D150022](https://reviews.llvm.org/D150022], `[Object] Fix handling of Elf_Nhdr with sh_addralign=8`, the generated notes can now be parsed successfully by the tool.
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@llvm/pr-subscribers-objectyaml Author: Igor Kudrin (igorkudrin) ChangesThe System V ABI states that the note entries and their descriptor fields must be aligned to 4 or 8 bytes for 32-bit and 64-bit objects respectively. In practice, 64-bit systems can use both alignments, with the actual format being distinguished by the alignment of the segment. For example, the Linux gABI extension contains a special note on this, see 2.1.7 "Alignment of Note Sections". This patch adjusts the format of the generated notes to the specified section alignment. Since Full diff: https://github.com/llvm/llvm-project/pull/118157.diff 2 Files Affected:
diff --git a/llvm/lib/ObjectYAML/ELFEmitter.cpp b/llvm/lib/ObjectYAML/ELFEmitter.cpp
index 476334024151a9..8603f2f73b858d 100644
--- a/llvm/lib/ObjectYAML/ELFEmitter.cpp
+++ b/llvm/lib/ObjectYAML/ELFEmitter.cpp
@@ -1799,6 +1799,20 @@ void ELFState<ELFT>::writeSectionContent(Elf_Shdr &SHeader,
if (!Section.Notes)
return;
+ unsigned Align;
+ switch (SHeader.sh_addralign) {
+ case 0:
+ case 4:
+ Align = 4;
+ break;
+ case 8:
+ Align = 8;
+ break;
+ default:
+ reportError(Section.Name + ": invalid alignment for a note section: 0x" +
+ Twine::utohexstr(SHeader.sh_addralign));
+ }
+
uint64_t Offset = CBA.tell();
for (const ELFYAML::NoteEntry &NE : *Section.Notes) {
// Write name size.
@@ -1820,13 +1834,13 @@ void ELFState<ELFT>::writeSectionContent(Elf_Shdr &SHeader,
if (!NE.Name.empty()) {
CBA.write(NE.Name.data(), NE.Name.size());
CBA.write('\0');
- CBA.padToAlignment(4);
+ CBA.padToAlignment(Align);
}
// Write description and padding.
if (NE.Desc.binary_size() != 0) {
CBA.writeAsBinary(NE.Desc);
- CBA.padToAlignment(4);
+ CBA.padToAlignment(Align);
}
}
diff --git a/llvm/test/tools/yaml2obj/ELF/note-section.yaml b/llvm/test/tools/yaml2obj/ELF/note-section.yaml
index 80359c4ec01833..067690f8f25b00 100644
--- a/llvm/test/tools/yaml2obj/ELF/note-section.yaml
+++ b/llvm/test/tools/yaml2obj/ELF/note-section.yaml
@@ -333,3 +333,74 @@ Sections:
- Name: ABC
Desc: '123456'
Type: NT_VERSION
+
+## Check that an incorrect alignment is reported
+
+# RUN: not yaml2obj --docnum=16 %s 2>&1 | FileCheck %s --check-prefix=ERR_ALIGN1
+# ERR_ALIGN1: error: .note.foo: invalid alignment for a note section: 0x1
+
+--- !ELF
+FileHeader:
+ Class: ELFCLASS64
+ Data: ELFDATA2LSB
+ Type: ET_EXEC
+Sections:
+ - Name: .note.foo
+ Type: SHT_NOTE
+ AddressAlign: 1
+ Notes:
+ - Type: 0x1
+
+## Check that note entries and their `Desc` fields are aligned according to the
+## specified section alignment
+
+# RUN: yaml2obj --docnum=17 %s -o - | \
+# RUN: llvm-readobj --sections --section-data - | \
+# RUN: FileCheck %s --check-prefix=TEST17
+
+# TEST17: Name: .note.foo4
+# TEST17: SectionData (
+# TEST17-NEXT: 0000: 05000000 02000000 01000000 41424344 |............ABCD|
+# TEST17-NEXT: 0010: 00000000 01020000 03000000 03000000 |................|
+# TEST17-NEXT: 0020: 02000000 41420000 03040500 03000000 |....AB..........|
+# TEST17-NEXT: 0030: 00000000 03000000 41420000 |........AB..|
+# TEST17-NEXT: )
+# TEST17: Name: .note.foo8
+# TEST17: SectionData (
+# TEST17-NEXT: 0000: 05000000 02000000 01000000 41424344 |............ABCD|
+# TEST17-NEXT: 0010: 00000000 00000000 01020000 00000000 |................|
+# TEST17-NEXT: 0020: 03000000 03000000 02000000 41420000 |............AB..|
+# TEST17-NEXT: 0030: 03040500 00000000 03000000 00000000 |................|
+# TEST17-NEXT: 0040: 03000000 41420000 |....AB..|
+# TEST17-NEXT: )
+
+--- !ELF
+FileHeader:
+ Class: ELFCLASS64
+ Data: ELFDATA2LSB
+ Type: ET_EXEC
+Sections:
+ - Name: .note.foo4
+ Type: SHT_NOTE
+ AddressAlign: 4
+ Notes:
+ - Name: ABCD
+ Desc: 0102
+ Type: NT_VERSION
+ - Name: AB
+ Desc: 030405
+ Type: NT_ARCH
+ - Name: AB
+ Type: NT_GNU_BUILD_ID
+ - Name: .note.foo8
+ Type: SHT_NOTE
+ AddressAlign: 8
+ Notes:
+ - Name: ABCD
+ Desc: 0102
+ Type: NT_VERSION
+ - Name: AB
+ Desc: 030405
+ Type: NT_ARCH
+ - Name: AB
+ Type: NT_GNU_BUILD_ID
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MaskRay
approved these changes
Nov 30, 2024
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LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/162/builds/11692 Here is the relevant piece of the build log for the reference |
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LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/140/builds/12139 Here is the relevant piece of the build log for the reference |
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LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/56/builds/13522 Here is the relevant piece of the build log for the reference |
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LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/60/builds/14147 Here is the relevant piece of the build log for the reference |
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LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/16/builds/9941 Here is the relevant piece of the build log for the reference |
igorkudrin
added a commit
to igorkudrin/llvm-project
that referenced
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Dec 3, 2024
… notes" This relands llvm#118157 with a fix for the use of an uninitialised variable. The [System V ABI](https://www.sco.com/developers/gabi/latest/ch5.pheader.html#note_section) states that the note entries and their descriptor fields must be aligned to 4 or 8 bytes for 32-bit or 64-bit objects respectively. In practice, 64-bit systems can use both alignments, with the actual format being determined by the alignment of the segment. For example, the [Linux gABI extension](https://github.com/hjl-tools/linux-abi/wiki/linux-abi-draft.pdf) contains a special note on this, see 2.1.7 "Alignment of Note Sections". This patch adjusts the format of the generated notes to the specified section alignment. Since `llvm-readobj` was fixed in a similar way in [D150022](https://reviews.llvm.org/D150022), "[Object] Fix handling of Elf_Nhdr with sh_addralign=8", the generated notes can now be parsed successfully by the tool.
igorkudrin
added a commit
that referenced
this pull request
Dec 5, 2024
… notes" (#118434) This relands #118157 with a fix for the use of an uninitialized variable and additional tests. The System V ABI (https://www.sco.com/developers/gabi/latest/ch5.pheader.html#note_section) states that the note entries and their descriptor fields must be aligned to 4 or 8 bytes for 32-bit or 64-bit objects respectively. In practice, 64-bit systems can use both alignments, with the actual format being determined by the alignment of the segment. For example, the Linux gABI extension (https://github.com/hjl-tools/linux-abi/wiki/linux-abi-draft.pdf) contains a special note on this, see 2.1.7 "Alignment of Note Sections". This patch adjusts the format of the generated notes to the specified section alignment. Since `llvm-readobj` was fixed in a similar way in https://reviews.llvm.org/D150022, "[Object] Fix handling of Elf_Nhdr with sh_addralign=8", the generated notes can now be parsed successfully by the tool.
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The System V ABI states that the note entries and their descriptor fields must be aligned to 4 or 8 bytes for 32-bit or 64-bit objects respectively. In practice, 64-bit systems can use both alignments, with the actual format being determined by the alignment of the segment. For example, the Linux gABI extension contains a special note on this, see 2.1.7 "Alignment of Note Sections".
This patch adjusts the format of the generated notes to the specified section alignment. Since
llvm-readobjwas fixed in a similar way in D150022, "[Object] Fix handling of Elf_Nhdr with sh_addralign=8", the generated notes can now be parsed successfully by the tool.