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llvm-project/lld/test/ELF/note-alignment.s

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[ELF] Place SHT_NOTE sections with the same alignment into one PT_NOTE Summary: While the generic ABI requires notes to be 8-byte aligned in ELF64, many vendor-specific notes (from Linux, NetBSD, Solaris, etc) use 4-byte alignment. In a PT_NOTE segment, if 4-byte aligned notes are followed by an 8-byte aligned note, the possible 4-byte padding may make consumers fail to parse the 8-byte aligned note. See PR41000 for a recent report about .note.gnu.property (NT_GNU_PROPERTY_TYPE_0). (Note, for NT_GNU_PROPERTY_TYPE_0, the consumers should probably migrate to PT_GNU_PROPERTY, but the alignment issue affects other notes as well.) To fix the issue, don't mix notes with different alignments in one PT_NOTE. If compilers emit 4-byte aligned notes before 8-byte aligned notes, we'll create at most 2 segments. sh_size%sh_addralign=0 is actually implied by the rule for linking unrecognized sections (in generic ABI), so we don't have to check that. Notes that match in name, type and attribute flags are concatenated into a single output section. The compilers have to ensure sh_size%sh_addralign=0 to make concatenated notes parsable. An alternative approach is to create a PT_NOTE for each SHT_NOTE, but we'll have to incur the sizeof(Elf64_Phdr)=56 overhead every time a new note section is introduced. Reviewers: ruiu, jakehehrlich, phosek, jhenderson, pcc, espindola Subscribers: emaste, arichardson, krytarowski, fedor.sergeev, llvm-commits Tags: #llvm Differential Revision: https://reviews.llvm.org/D61296 llvm-svn: 359853
2019-05-03 08:35:49 +08:00
# REQUIRES: x86
# RUN: llvm-mc -filetype=obj -triple=x86_64 %s -o %t.o
# RUN: ld.lld %t.o -o %t
# RUN: llvm-readelf -l %t | FileCheck %s
# Check that we don't mix 4-byte and 8-byte aligned notes in one PT_LOAD.
# The possible 4-byte padding before the 8-byte align note may make consumers
# fail to parse it.
# CHECK: NOTE {{0x[0-9a-f]+}} {{0x[0-9a-f]+}} {{0x[0-9a-f]+}} 0x000004 0x000004 R 0x4
# CHECK: NOTE {{0x[0-9a-f]+}} {{0x[0-9a-f]+}} {{0x[0-9a-f]+}} 0x000010 0x000010 R 0x8
# CHECK: NOTE {{0x[0-9a-f]+}} {{0x[0-9a-f]+}} {{0x[0-9a-f]+}} 0x000008 0x000008 R 0x4
# CHECK: 03 .note.a
# CHECK-NEXT: 04 .note.b .note.c
# CHECK-NEXT: 05 .note.d .note.e
.section .note.a, "a", @note
.align 4
.long 0
.section .note.b, "a", @note
.align 8
.quad 0
.section .note.c, "a", @note
.align 8
.quad 0
.section .note.d, "a", @note
.align 4
.long 0
.section .note.e, "a", @note
.align 4
.long 0