forked from OSchip/llvm-project
[lld][ELF] Support for zero flag section groups
This change introduces support for zero flag ELF section groups to lld. lld already supports COMDAT sections, which in ELF are a special type of ELF section groups. These are generally useful to enable linker GC where you want a group of sections to always travel together, that is to be either retained or discarded as a whole, but without the COMDAT semantics. Other ELF linkers already support zero flag ELF section groups and this change helps us reach feature parity. Differential Revision: https://reviews.llvm.org/D96636
This commit is contained in:
Petr Hosek
parent
fbee4a0c79
commit
bfa4235e6e
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@ -609,27 +609,20 @@ void ObjFile<ELFT>::initializeSections(bool ignoreComdats) {
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StringRef signature = getShtGroupSignature(objSections, sec);
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this->sections[i] = &InputSection::discarded;
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ArrayRef<Elf_Word> entries =
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CHECK(obj.template getSectionContentsAsArray<Elf_Word>(sec), this);
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if (entries.empty())
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fatal(toString(this) + ": empty SHT_GROUP");
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// The first word of a SHT_GROUP section contains flags. Currently,
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// the standard defines only "GRP_COMDAT" flag for the COMDAT group.
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// An group with the empty flag doesn't define anything; such sections
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// are just skipped.
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if (entries[0] == 0)
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continue;
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if (entries[0] != GRP_COMDAT)
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Elf_Word flag = entries[0];
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if (flag && flag != GRP_COMDAT)
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fatal(toString(this) + ": unsupported SHT_GROUP format");
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bool isNew =
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ignoreComdats ||
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bool keepGroup =
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(flag & GRP_COMDAT) == 0 || ignoreComdats ||
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symtab->comdatGroups.try_emplace(CachedHashStringRef(signature), this)
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.second;
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if (isNew) {
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if (keepGroup) {
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if (config->relocatable)
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this->sections[i] = createInputSection(sec);
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selectedGroups.push_back(entries);
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@ -7,48 +7,99 @@
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# RUN: ld.lld --gc-sections %t.o -o %t.dead
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# RUN: llvm-readobj -S %t.dead | FileCheck %s --check-prefix=CHECK-DEAD
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## .mynote.bar is retained because it is not in a group.
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# CHECK-DEAD-NOT: Name: .myanote.foo
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# CHECK-DEAD-NOT: Name: .mytext.foo
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# CHECK-DEAD-NOT: Name: .mybss.foo
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# CHECK-DEAD-NOT: Name: .mynote.foo
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# CHECK-DEAD: Name: .mynote.bar
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## .mynote.ccc is retained because it is not in a group.
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# CHECK-DEAD-NOT: Name: .myanote.aaa
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# CHECK-DEAD-NOT: Name: .mytext.aaa
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# CHECK-DEAD-NOT: Name: .mybss.aaa
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# CHECK-DEAD-NOT: Name: .mynote.aaa
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# CHECK-DEAD-NOT: Name: .myanote.bbb
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# CHECK-DEAD-NOT: Name: .mytext.bbb
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# CHECK-DEAD-NOT: Name: .mybss.bbb
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# CHECK-DEAD-NOT: Name: .mynote.bbb
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# CHECK-DEAD: Name: .mynote.ccc
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# RUN: ld.lld --gc-sections %t.o -o %t -e anote_foo
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# RUN: llvm-readobj -S %t | FileCheck %s --check-prefix=CHECK-LIVE
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# RUN: ld.lld --gc-sections %t.o -o %t -e foo
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# RUN: llvm-readobj -S %t | FileCheck %s --check-prefix=CHECK-LIVE
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# RUN: ld.lld --gc-sections %t.o -o %t -e bss_foo
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# RUN: llvm-readobj -S %t | FileCheck %s --check-prefix=CHECK-LIVE
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# RUN: ld.lld --gc-sections %t.o -o %t -e anote_aaa
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# RUN: llvm-readobj -S %t | FileCheck %s --check-prefix=CHECK-LIVE-GROUP
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# RUN: ld.lld --gc-sections %t.o -o %t -e aaa
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# RUN: llvm-readobj -S %t | FileCheck %s --check-prefix=CHECK-LIVE-GROUP
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# RUN: ld.lld --gc-sections %t.o -o %t -e bss_aaa
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# RUN: llvm-readobj -S %t | FileCheck %s --check-prefix=CHECK-LIVE-GROUP
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## note_foo as the entry point does not make much sense because it is defined
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## note_zero as the entry point does not make much sense because it is defined
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## in a non-SHF_ALLOC section. This is just to demonstrate the behavior.
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# RUN: ld.lld --gc-sections %t.o -o %t -e note_foo
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# RUN: llvm-readobj -S %t | FileCheck %s --check-prefix=CHECK-LIVE
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# RUN: ld.lld --gc-sections %t.o -o %t -e note_aaa
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# RUN: llvm-readobj -S %t | FileCheck %s --check-prefix=CHECK-LIVE-GROUP
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# CHECK-LIVE: Name: .myanote.foo
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# CHECK-LIVE: Name: .mytext.foo
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# CHECK-LIVE: Name: .mybss.foo
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# CHECK-LIVE: Name: .mynote.foo
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# CHECK-LIVE: Name: .mynote.bar
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# CHECK-LIVE-GROUP: Name: .myanote.aaa
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# CHECK-LIVE-GROUP: Name: .mytext.aaa
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# CHECK-LIVE-GROUP: Name: .mybss.aaa
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# CHECK-LIVE-GROUP: Name: .mynote.aaa
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# CHECK-LIVE-GROUP-NOT: Name: .myanote.bbb
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# CHECK-LIVE-GROUP-NOT: Name: .mytext.bbb
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# CHECK-LIVE-GROUP-NOT: Name: .mybss.bbb
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# CHECK-LIVE-GROUP-NOT: Name: .mynote.bbb
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# CHECK-LIVE-GROUP: Name: .mynote.ccc
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.globl anote_foo, foo, bss_foo, note_foo
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# RUN: ld.lld --gc-sections %t.o -o %t -e anote_bbb
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# RUN: llvm-readobj -S %t | FileCheck %s --check-prefix=CHECK-LIVE-COMDAT
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# RUN: ld.lld --gc-sections %t.o -o %t -e bbb
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# RUN: llvm-readobj -S %t | FileCheck %s --check-prefix=CHECK-LIVE-COMDAT
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# RUN: ld.lld --gc-sections %t.o -o %t -e bss_bbb
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# RUN: llvm-readobj -S %t | FileCheck %s --check-prefix=CHECK-LIVE-COMDAT
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.section .myanote.foo,"aG",@note,foo,comdat
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anote_foo:
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## note_bbb as the entry point does not make much sense because it is defined
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## in a non-SHF_ALLOC section. This is just to demonstrate the behavior.
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# RUN: ld.lld --gc-sections %t.o -o %t -e note_bbb
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# RUN: llvm-readobj -S %t | FileCheck %s --check-prefix=CHECK-LIVE-COMDAT
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# CHECK-LIVE-COMDAT-NOT: Name: .myanote.aaa
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# CHECK-LIVE-COMDAT-NOT: Name: .mytext.aaa
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# CHECK-LIVE-COMDAT-NOT: Name: .mybss.aaa
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# CHECK-LIVE-COMDAT-NOT: Name: .mynote.aaa
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# CHECK-LIVE-COMDAT: Name: .myanote.bbb
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# CHECK-LIVE-COMDAT: Name: .mytext.bbb
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# CHECK-LIVE-COMDAT: Name: .mybss.bbb
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# CHECK-LIVE-COMDAT: Name: .mynote.bbb
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# CHECK-LIVE-COMDAT: Name: .mynote.ccc
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## These sections are in a zero flag group `aaa`.
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.globl anote_aaa, aaa, bss_aaa, note_aaa
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.section .myanote.aaa,"aG",@note,aaa
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anote_aaa:
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.byte 0
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.section .mytext.foo,"axG",@progbits,foo,comdat
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foo:
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.section .mytext.aaa,"axG",@progbits,aaa
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aaa:
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.byte 0
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.section .mybss.foo,"awG",@nobits,foo,comdat
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bss_foo:
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.section .mybss.aaa,"awG",@nobits,aaa
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bss_aaa:
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.byte 0
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.section .mynote.foo,"G",@note,foo,comdat
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note_foo:
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.section .mynote.aaa,"G",@note,aaa
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note_aaa:
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.byte 0
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.section .mynote.bar,"",@note
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## These sections are in a COMDAT group `bbb`.
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.globl anote_bbb, bbb, bss_bbb, note_bbb
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.section .myanote.bbb,"aG",@note,bbb,comdat
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anote_bbb:
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.byte 0
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.section .mytext.bbb,"axG",@progbits,bbb,comdat
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bbb:
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.byte 0
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.section .mybss.bbb,"awG",@nobits,bbb,comdat
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bss_bbb:
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.byte 0
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.section .mynote.bbb,"G",@note,bbb,comdat
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note_bbb:
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.byte 0
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## This section isn't in any group.
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.section .mynote.ccc,"",@note
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.byte 0
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