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Reland "[ObjectYAML][ELF] Take alignment into account when generating 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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2 files changed

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‎llvm/lib/ObjectYAML/ELFEmitter.cpp‎

Lines changed: 18 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -1799,6 +1799,21 @@ void ELFState<ELFT>::writeSectionContent(Elf_Shdr &SHeader,
17991799
if (!Section.Notes)
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return;
18011801

1802+
unsigned Align;
1803+
switch (Section.AddressAlign) {
1804+
case 0:
1805+
case 4:
1806+
Align = 4;
1807+
break;
1808+
case 8:
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Align = 8;
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break;
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default:
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reportError(Section.Name + ": invalid alignment for a note section: 0x" +
1813+
Twine::utohexstr(Section.AddressAlign));
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return;
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}
1816+
18021817
uint64_t Offset = CBA.tell();
18031818
for (const ELFYAML::NoteEntry &NE : *Section.Notes) {
18041819
// Write name size.
@@ -1820,14 +1835,15 @@ void ELFState<ELFT>::writeSectionContent(Elf_Shdr &SHeader,
18201835
if (!NE.Name.empty()) {
18211836
CBA.write(NE.Name.data(), NE.Name.size());
18221837
CBA.write('\0');
1823-
CBA.padToAlignment(4);
18241838
}
18251839

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// Write description and padding.
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if (NE.Desc.binary_size() != 0) {
1842+
CBA.padToAlignment(Align);
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CBA.writeAsBinary(NE.Desc);
1829-
CBA.padToAlignment(4);
18301844
}
1845+
1846+
CBA.padToAlignment(Align);
18311847
}
18321848

18331849
SHeader.sh_size = CBA.tell() - Offset;

‎llvm/test/tools/yaml2obj/ELF/note-section.yaml‎

Lines changed: 181 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -333,3 +333,184 @@ Sections:
333333
- Name: ABC
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Desc: '123456'
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Type: NT_VERSION
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## Check that an incorrect alignment is reported.
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# RUN: not yaml2obj --docnum=16 %s 2>&1 | FileCheck %s --check-prefix=ERR_ALIGN1
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# ERR_ALIGN1: error: .note.foo: invalid alignment for a note section: 0x1
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--- !ELF
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FileHeader:
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Class: ELFCLASS64
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Data: ELFDATA2LSB
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Type: ET_EXEC
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Sections:
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- Name: .note.foo
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Type: SHT_NOTE
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AddressAlign: 1
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Notes:
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- Type: 0x1
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## Check that note entries and their "Desc" fields are aligned according to the
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## specified section alignment.
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# RUN: yaml2obj --docnum=17 -D ELFCLASS=64 %s -o - | \
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# RUN: llvm-readobj --sections --section-data --notes - | \
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# RUN: FileCheck %s --check-prefix=TEST17
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# RUN: yaml2obj --docnum=17 -D ELFCLASS=32 %s -o - | \
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# RUN: llvm-readobj --sections --section-data --notes - | \
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# RUN: FileCheck %s --check-prefix=TEST17
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# TEST17: Name: .note.foo4
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# TEST17: SectionData (
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# TEST17-NEXT: 0000: 05000000 02000000 01000000 41424344 |............ABCD|
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# TEST17-NEXT: 0010: 00000000 01020000 00000000 03000000 |................|
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# TEST17-NEXT: 0020: 02000000 03040500 04000000 00000000 |................|
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# TEST17-NEXT: 0030: 03000000 474E5500 |....GNU.|
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# TEST17-NEXT: )
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# TEST17: Name: .note.foo8
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# TEST17: SectionData (
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# TEST17-NEXT: 0000: 05000000 02000000 01000000 41424344 |............ABCD|
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# TEST17-NEXT: 0010: 00000000 00000000 01020000 00000000 |................|
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# TEST17-NEXT: 0020: 00000000 03000000 02000000 00000000 |................|
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# TEST17-NEXT: 0030: 03040500 00000000 04000000 00000000 |................|
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# TEST17-NEXT: 0040: 03000000 474E5500 |....GNU.|
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# TEST17-NEXT: )
380+
# TEST17: NoteSections [
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# TEST17-NEXT: NoteSection {
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# TEST17-NEXT: Name: .note.foo4
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# TEST17-NEXT: Offset:
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# TEST17-NEXT: Size:
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# TEST17-NEXT: Notes [
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# TEST17-NEXT: {
387+
# TEST17-NEXT: Owner: ABCD
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# TEST17-NEXT: Data size: 0x2
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# TEST17-NEXT: Type: NT_VERSION (version)
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# TEST17-NEXT: Description data (
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# TEST17-NEXT: 0000: 0102 |..|
392+
# TEST17-NEXT: )
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# TEST17-NEXT: }
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# TEST17-NEXT: {
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# TEST17-NEXT: Owner:
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# TEST17-NEXT: Data size: 0x3
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# TEST17-NEXT: Type: NT_ARCH (architecture)
398+
# TEST17-NEXT: Description data (
399+
# TEST17-NEXT: 0000: 030405 |...|
400+
# TEST17-NEXT: )
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# TEST17-NEXT: }
402+
# TEST17-NEXT: {
403+
# TEST17-NEXT: Owner: GNU
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# TEST17-NEXT: Data size: 0x0
405+
# TEST17-NEXT: Type: NT_GNU_BUILD_ID (unique build ID bitstring)
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# TEST17-NEXT: Build ID:
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# TEST17-NEXT: }
408+
# TEST17-NEXT: ]
409+
# TEST17-NEXT: }
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# TEST17-NEXT: NoteSection {
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# TEST17-NEXT: Name: .note.foo8
412+
# TEST17-NEXT: Offset:
413+
# TEST17-NEXT: Size:
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# TEST17-NEXT: Notes [
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# TEST17-NEXT: {
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# TEST17-NEXT: Owner: ABCD
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# TEST17-NEXT: Data size: 0x2
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# TEST17-NEXT: Type: NT_VERSION (version)
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# TEST17-NEXT: Description data (
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# TEST17-NEXT: 0000: 0102 |..|
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# TEST17-NEXT: )
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# TEST17-NEXT: }
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# TEST17-NEXT: {
424+
# TEST17-NEXT: Owner:
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# TEST17-NEXT: Data size: 0x3
426+
# TEST17-NEXT: Type: NT_ARCH (architecture)
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# TEST17-NEXT: Description data (
428+
# TEST17-NEXT: 0000: 030405 |...|
429+
# TEST17-NEXT: )
430+
# TEST17-NEXT: }
431+
# TEST17-NEXT: {
432+
# TEST17-NEXT: Owner: GNU
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# TEST17-NEXT: Data size: 0x0
434+
# TEST17-NEXT: Type: NT_GNU_BUILD_ID (unique build ID bitstring)
435+
# TEST17-NEXT: Build ID:
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# TEST17-NEXT: }
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# TEST17-NEXT: ]
438+
# TEST17-NEXT: }
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# TEST17-NEXT: ]
440+
441+
--- !ELF
442+
FileHeader:
443+
Class: ELFCLASS[[ELFCLASS]]
444+
Data: ELFDATA2LSB
445+
Type: ET_EXEC
446+
Sections:
447+
- Name: .note.foo4
448+
Type: SHT_NOTE
449+
AddressAlign: 4
450+
Notes:
451+
- Name: ABCD
452+
Type: NT_VERSION
453+
Desc: 0102
454+
- Type: NT_ARCH
455+
Desc: 030405
456+
- Name: GNU
457+
Type: NT_GNU_BUILD_ID
458+
- Name: .note.foo8
459+
Type: SHT_NOTE
460+
AddressAlign: 8
461+
Notes:
462+
- Name: ABCD
463+
Type: NT_VERSION
464+
Desc: 0102
465+
- Type: NT_ARCH
466+
Desc: 030405
467+
- Name: GNU
468+
Type: NT_GNU_BUILD_ID
469+
470+
## Check that the alignment for note entries is taken from the "AddressAlign"
471+
## field even if "ShAddrAlign" is also specified; an unexpected value in the
472+
## "ShAddrAlign" property does not trigger an incorrect alignment error.
473+
474+
# RUN: yaml2obj --docnum=18 -D ADDRALIGN=0 -D SHADDRALIGN=8 %s -o - | \
475+
# RUN: llvm-readobj --sections --section-data --notes - | \
476+
# RUN: FileCheck %s --check-prefixes=TEST18,TEST18_4
477+
478+
# RUN: yaml2obj --docnum=18 -D ADDRALIGN=4 -D SHADDRALIGN=3 %s -o - | \
479+
# RUN: llvm-readobj --sections --section-data --notes - | \
480+
# RUN: FileCheck %s --check-prefixes=TEST18,TEST18_4
481+
482+
# RUN: yaml2obj --docnum=18 -D ADDRALIGN=8 -D SHADDRALIGN=4 %s -o - | \
483+
# RUN: llvm-readobj --sections --section-data --notes - | \
484+
# RUN: FileCheck %s --check-prefixes=TEST18,TEST18_8
485+
486+
# TEST18: Name: .note
487+
# TEST18: SectionData (
488+
# TEST18_4-NEXT: 0000: 05000000 02000000 01000000 41424344 |............ABCD|
489+
# TEST18_4-NEXT: 0010: 00000000 01020000 00000000 03000000 |................|
490+
# TEST18_4-NEXT: 0020: 02000000 03040500 04000000 00000000 |................|
491+
# TEST18_4-NEXT: 0030: 03000000 474E5500 |....GNU.|
492+
# TEST18_8-NEXT: 0000: 05000000 02000000 01000000 41424344 |............ABCD|
493+
# TEST18_8-NEXT: 0010: 00000000 00000000 01020000 00000000 |................|
494+
# TEST18_8-NEXT: 0020: 00000000 03000000 02000000 00000000 |................|
495+
# TEST18_8-NEXT: 0030: 03040500 00000000 04000000 00000000 |................|
496+
# TEST18_8-NEXT: 0040: 03000000 474E5500 |....GNU.|
497+
# TEST18-NEXT: )
498+
499+
--- !ELF
500+
FileHeader:
501+
Class: ELFCLASS64
502+
Data: ELFDATA2LSB
503+
Type: ET_EXEC
504+
Sections:
505+
- Name: .note
506+
Type: SHT_NOTE
507+
AddressAlign: [[ADDRALIGN]]
508+
ShAddrAlign: [[SHADDRALIGN]]
509+
Notes:
510+
- Name: ABCD
511+
Type: NT_VERSION
512+
Desc: 0102
513+
- Type: NT_ARCH
514+
Desc: 030405
515+
- Name: GNU
516+
Type: NT_GNU_BUILD_ID

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