[PATCH] D29636: [ELF] - Added partial support for --emit-relocs (no --gc-section case) #2
Rafael Avila de Espindola via llvm-commits
llvm-commits at lists.llvm.org
Tue Feb 7 07:46:30 PST 2017
I still think we should leave the DISCARD and gc case for a followup
patch. Without it this is a trivial patch.
Cheers,
Rafael
George Rimar via Phabricator <reviews at reviews.llvm.org> writes:
> grimar created this revision.
>
> It is close to https://reviews.llvm.org/D29273, but has different implementation of filtering out
> .rel[a] sections if target section was discarded.
>
> Also testcase was simplified.
>
>
> https://reviews.llvm.org/D29636
>
> Files:
> ELF/Config.h
> ELF/Driver.cpp
> ELF/InputFiles.cpp
> ELF/InputSection.cpp
> ELF/LinkerScript.cpp
> ELF/Options.td
> ELF/OutputSections.cpp
> ELF/Writer.cpp
> test/ELF/Inputs/emit-relocs.s
> test/ELF/emit-relocs-gc.s
> test/ELF/emit-relocs.s
> test/ELF/linkerscript/emit-reloc-discard.s
>
> Index: test/ELF/linkerscript/emit-reloc-discard.s
> ===================================================================
> --- test/ELF/linkerscript/emit-reloc-discard.s
> +++ test/ELF/linkerscript/emit-reloc-discard.s
> @@ -0,0 +1,14 @@
> +# REQUIRES: x86
> +# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o
> +# RUN: echo "SECTIONS { /DISCARD/ : { *(.bbb) } }" > %t.script
> +# RUN: ld.lld --emit-relocs --script %t.script %t.o -o %t1
> +# RUN: llvm-readobj -r %t1 | FileCheck %s
> +
> +# CHECK: Relocations [
> +# CHECK-NEXT: ]
> +
> +.section .aaa,"", at progbits
> +.Lfoo:
> +
> +.section .bbb,"", at progbits
> +.long .Lfoo
> Index: test/ELF/emit-relocs.s
> ===================================================================
> --- test/ELF/emit-relocs.s
> +++ test/ELF/emit-relocs.s
> @@ -0,0 +1,98 @@
> +# REQUIRES: x86
> +# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t1.o
> +# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %p/Inputs/emit-relocs.s -o %t2.o
> +# RUN: ld.lld --emit-relocs %t1.o %t2.o -o %t
> +# RUN: llvm-readobj -t -r %t | FileCheck %s
> +
> +## Check single dash form.
> +# RUN: ld.lld -emit-relocs %t1.o %t2.o -o %t1
> +# RUN: llvm-readobj -t -r %t1 | FileCheck %s
> +
> +## Check alias.
> +# RUN: ld.lld -q %t1.o %t2.o -o %t2
> +# RUN: llvm-readobj -t -r %t2 | FileCheck %s
> +
> +# CHECK: Relocations [
> +# CHECK-NEXT: Section ({{.*}}) .rela.text {
> +# CHECK-NEXT: 0x201002 R_X86_64_32 .text 0x1
> +# CHECK-NEXT: 0x201007 R_X86_64_PLT32 fn 0xFFFFFFFFFFFFFFFC
> +# CHECK-NEXT: 0x20100E R_X86_64_32 .text 0x1
> +# CHECK-NEXT: 0x201013 R_X86_64_PLT32 fn2 0xFFFFFFFFFFFFFFFC
> +# CHECK-NEXT: }
> +# CHECK-NEXT: ]
> +# CHECK-NEXT: Symbols [
> +# CHECK-NEXT: Symbol {
> +# CHECK-NEXT: Name:
> +# CHECK-NEXT: Value: 0x0
> +# CHECK-NEXT: Size: 0
> +# CHECK-NEXT: Binding: Local
> +# CHECK-NEXT: Type: None
> +# CHECK-NEXT: Other: 0
> +# CHECK-NEXT: Section: Undefined
> +# CHECK-NEXT: }
> +# CHECK-NEXT: Symbol {
> +# CHECK-NEXT: Name: bar
> +# CHECK-NEXT: Value: 0x201001
> +# CHECK-NEXT: Size: 0
> +# CHECK-NEXT: Binding: Local
> +# CHECK-NEXT: Type: None
> +# CHECK-NEXT: Other: 0
> +# CHECK-NEXT: Section: .text
> +# CHECK-NEXT: }
> +# CHECK-NEXT: Symbol {
> +# CHECK-NEXT: Name:
> +# CHECK-NEXT: Value: 0x201000
> +# CHECK-NEXT: Size: 0
> +# CHECK-NEXT: Binding: Local
> +# CHECK-NEXT: Type: Section
> +# CHECK-NEXT: Other: 0
> +# CHECK-NEXT: Section: .text
> +# CHECK-NEXT: }
> +# CHECK-NEXT: Symbol {
> +# CHECK-NEXT: Name: foo
> +# CHECK-NEXT: Value: 0x20100D
> +# CHECK-NEXT: Size: 0
> +# CHECK-NEXT: Binding: Local
> +# CHECK-NEXT: Type: None
> +# CHECK-NEXT: Other: 0
> +# CHECK-NEXT: Section: .text
> +# CHECK-NEXT: }
> +# CHECK-NEXT: Symbol {
> +# CHECK-NEXT: Name:
> +# CHECK-NEXT: Value: 0x20100C
> +# CHECK-NEXT: Size: 0
> +# CHECK-NEXT: Binding: Local
> +# CHECK-NEXT: Type: Section
> +# CHECK-NEXT: Other: 0
> +# CHECK-NEXT: Section: .text
> +# CHECK-NEXT: }
> +# CHECK-NEXT: Symbol {
> +# CHECK-NEXT: Name: fn
> +# CHECK-NEXT: Value: 0x201000
> +# CHECK-NEXT: Size: 0
> +# CHECK-NEXT: Binding: Global
> +# CHECK-NEXT: Type: Function
> +# CHECK-NEXT: Other: 0
> +# CHECK-NEXT: Section: .text
> +# CHECK-NEXT: }
> +# CHECK-NEXT: Symbol {
> +# CHECK-NEXT: Name: fn2
> +# CHECK-NEXT: Value: 0x20100C
> +# CHECK-NEXT: Size: 0
> +# CHECK-NEXT: Binding: Global
> +# CHECK-NEXT: Type: Function
> +# CHECK-NEXT: Other: 0
> +# CHECK-NEXT: Section: .text
> +# CHECK-NEXT: }
> +# CHECK-NEXT: ]
> +
> +.section .text
> +.globl fn
> +.type fn, at function
> +fn:
> + nop
> +
> +bar:
> + movl $bar, %edx
> + callq fn at PLT
> + nop
> Index: test/ELF/emit-relocs-gc.s
> ===================================================================
> --- test/ELF/emit-relocs-gc.s
> +++ test/ELF/emit-relocs-gc.s
> @@ -0,0 +1,5 @@
> +# REQUIRES: x86
> +# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t1.o
> +# RUN: not ld.lld --gc-sections --emit-relocs %t1.o -o %t 2>&1 \
> +# RUN: | FileCheck -check-prefix=ERR %s
> +# ERR: --emit-relocs and --gc-sections may not be used together
> Index: test/ELF/Inputs/emit-relocs.s
> ===================================================================
> --- test/ELF/Inputs/emit-relocs.s
> +++ test/ELF/Inputs/emit-relocs.s
> @@ -0,0 +1,10 @@
> +.section .text
> +.globl fn2
> +.type fn2, at function
> +fn2:
> + nop
> +
> +foo:
> + movl $foo, %edx
> + callq fn2 at PLT
> + nop
> Index: ELF/Writer.cpp
> ===================================================================
> --- ELF/Writer.cpp
> +++ ELF/Writer.cpp
> @@ -449,9 +449,9 @@
> if (B.isFile())
> return false;
>
> - // We keep sections in symtab for relocatable output.
> + // We keep sections in symtab for relocatable output and --emit-reloc.
> if (B.isSection())
> - return Config->Relocatable;
> + return Config->Relocatable || Config->EmitRelocs;
>
> // If sym references a section in a discarded group, don't keep it.
> if (Sec == &InputSection<ELFT>::Discarded)
> Index: ELF/OutputSections.cpp
> ===================================================================
> --- ELF/OutputSections.cpp
> +++ ELF/OutputSections.cpp
> @@ -116,7 +116,8 @@
> }
>
> uint32_t Type = this->Type;
> - if (!Config->Relocatable || (Type != SHT_RELA && Type != SHT_REL))
> + if ((!Config->Relocatable && !Config->EmitRelocs) ||
> + (Type != SHT_RELA && Type != SHT_REL))
> return;
>
> this->Link = In<ELFT>::SymTab->OutSec->SectionIndex;
> Index: ELF/Options.td
> ===================================================================
> --- ELF/Options.td
> +++ ELF/Options.td
> @@ -70,6 +70,8 @@
> def eh_frame_hdr: F<"eh-frame-hdr">,
> HelpText<"Request creation of .eh_frame_hdr section and PT_GNU_EH_FRAME segment header">;
>
> +def emit_relocs: F<"emit-relocs">, HelpText<"Generate relocations in output">;
> +
> def enable_new_dtags: F<"enable-new-dtags">,
> HelpText<"Enable new dynamic tags">;
>
> @@ -283,6 +285,7 @@
> def alias_discard_all_x: Flag<["-"], "x">, Alias<discard_all>;
> def alias_discard_locals_X: Flag<["-"], "X">, Alias<discard_locals>;
> def alias_dynamic_list: J<"dynamic-list=">, Alias<dynamic_list>;
> +def alias_emit_relocs: Flag<["-"], "q">, Alias<emit_relocs>;
> def alias_entry_e: JoinedOrSeparate<["-"], "e">, Alias<entry>;
> def alias_entry_entry: J<"entry=">, Alias<entry>;
> def alias_error_limit: J<"error-limit=">, Alias<error_limit>;
> Index: ELF/LinkerScript.cpp
> ===================================================================
> --- ELF/LinkerScript.cpp
> +++ ELF/LinkerScript.cpp
> @@ -288,6 +288,20 @@
> return Ret;
> }
>
> +template <class ELFT> static void scanRelocationSections() {
> + for (InputSectionBase<ELFT> *S : Symtab<ELFT>::X->Sections) {
> + if (S->Type != SHT_REL && S->Type != SHT_RELA)
> + continue;
> + InputSection<ELFT> *IS = cast<InputSection<ELFT>>(S);
> + if (!IS->getFile())
> + continue;
> + ArrayRef<InputSectionBase<ELFT> *> Sections = IS->getFile()->getSections();
> + InputSectionBase<ELFT> *Target = Sections[IS->Info];
> + if (Target == &InputSection<ELFT>::Discarded || !Target->Live)
> + S->Live = false;
> + }
> +}
> +
> template <class ELFT>
> void LinkerScript<ELFT>::addSection(OutputSectionFactory<ELFT> &Factory,
> InputSectionBase<ELFT> *Sec,
> @@ -366,6 +380,12 @@
> addSection(Factory, S, Cmd->Name);
> }
> }
> +
> + // When --emit-relocs is used, we leave .rel[a]* sections in the output.
> + // If target section was discarded from script, we should not emit the
> + // relocation section for it. scanRelocationSections() handles that case.
> + if (Config->EmitRelocs)
> + scanRelocationSections<ELFT>();
> }
>
> // Add sections that didn't match any sections command.
> Index: ELF/InputSection.cpp
> ===================================================================
> --- ELF/InputSection.cpp
> +++ ELF/InputSection.cpp
> @@ -214,9 +214,9 @@
> return Sections[this->Info];
> }
>
> -// This is used for -r. We can't use memcpy to copy relocations because we need
> -// to update symbol table offset and section index for each relocation. So we
> -// copy relocations one by one.
> +// This is used for -r and --emit-relocs. We can't use memcpy to copy
> +// relocations because we need to update symbol table offset and section index
> +// for each relocation. So we copy relocations one by one.
> template <class ELFT>
> template <class RelTy>
> void InputSection<ELFT>::copyRelocations(uint8_t *Buf, ArrayRef<RelTy> Rels) {
> @@ -235,7 +235,11 @@
>
> if (Config->Rela)
> P->r_addend = getAddend<ELFT>(Rel);
> - P->r_offset = RelocatedSection->getOffset(Rel.r_offset);
> +
> + // Output section VA is zero for -r, so r_offset is an offset within the
> + // section, but for --emit-relocs it is an absolute address.
> + P->r_offset = RelocatedSection->OutSec->Addr +
> + RelocatedSection->getOffset(Rel.r_offset);
> P->setSymbolAndType(In<ELFT>::SymTab->getSymbolIndex(&Body), Type,
> Config->Mips64EL);
> }
> @@ -514,7 +518,8 @@
> return;
> }
>
> - // If -r is given, then an InputSection may be a relocation section.
> + // If -r or --emit-relocs is given, then an InputSection
> + // may be a relocation section.
> if (this->Type == SHT_RELA) {
> copyRelocations(Buf + OutSecOff, this->template getDataAs<Elf_Rela>());
> return;
> Index: ELF/InputFiles.cpp
> ===================================================================
> --- ELF/InputFiles.cpp
> +++ ELF/InputFiles.cpp
> @@ -399,6 +399,18 @@
> }
> assert(isUInt<31>(NumRelocations));
> Target->NumRelocations = NumRelocations;
> +
> + // Relocation sections processed by the linker are usually removed
> + // from the output, so returning `nullptr` for the normal case.
> + // However, if -emit-relocs is given, we need to leave them in the output.
> + // (Some post link analysis tools need this information.)
> + if (Config->EmitRelocs) {
> + if (!isa<InputSection<ELFT>>(Target))
> + fatal(toString(this) + ": --emit-relocs for relocations sections "
> + "pointing to .eh_frame is not supported due to "
> + "an implementation limitation");
> + return make<InputSection<ELFT>>(this, &Sec, Name);
> + }
> return nullptr;
> }
> }
> Index: ELF/Driver.cpp
> ===================================================================
> --- ELF/Driver.cpp
> +++ ELF/Driver.cpp
> @@ -234,6 +234,11 @@
> if (Config->Pie)
> error("-r and -pie may not be used together");
> }
> +
> + // -emit-relocs and -gc-sections don't conflict in theory, but LLD currently
> + // does not support the combination due to an implementation limitation.
> + if (Config->EmitRelocs && Config->GcSections)
> + error("--emit-relocs and --gc-sections may not be used together");
> }
>
> static StringRef getString(opt::InputArgList &Args, unsigned Key,
> @@ -519,6 +524,7 @@
> Config->BsymbolicFunctions = Args.hasArg(OPT_Bsymbolic_functions);
> Config->Demangle = getArg(Args, OPT_demangle, OPT_no_demangle, true);
> Config->DisableVerify = Args.hasArg(OPT_disable_verify);
> + Config->EmitRelocs = Args.hasArg(OPT_emit_relocs);
> Config->EhFrameHdr = Args.hasArg(OPT_eh_frame_hdr);
> Config->EnableNewDtags = !Args.hasArg(OPT_disable_new_dtags);
> Config->ExportDynamic =
> Index: ELF/Config.h
> ===================================================================
> --- ELF/Config.h
> +++ ELF/Config.h
> @@ -102,6 +102,7 @@
> bool Demangle = true;
> bool DisableVerify;
> bool EhFrameHdr;
> + bool EmitRelocs;
> bool EnableNewDtags;
> bool ExportDynamic;
> bool FatalWarnings;
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