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Reland D61583 [ELF] Error on relocations to STT_SECTION symbols if the sections were discarded 

This is implemented by creating Undefined (instead of Defined) for such
local STT_SECTION symbols. It allows us to catch errors when there are
relocations to such discarded sections (e.g. in PR41693, ld.bfd and gold
error but we don't). Updated comdat-discarded-error.s checks we emit
friendly error message.

For relocatable-eh-frame.s, ld.lld -r a.o a.o will now error
"STT_SECTION symbol should be defined" because the section .eh_frame
refers to is now an Undefined instead of a Defined.
So I have to change `error()` to `warn()` to retain the output.

rLLD361144 inadvertently enabled the error for --gdb-index
(in LLDDwarfObj<ELFT>::findAux()).

Relocations from .debug_info (not in comdat) to .text.* (in comdat) for
DW_AT_low_pc are common. If an .text.* was discarded, rLLD361144 would error,
which was unexpected. (Note, if we don't error as this patch does,
InputSection::relocateNonAlloc() will resolve such relocations).

llvm-svn: 361830
This commit is contained in:
Fangrui Song 2019-05-28 14:34:28 +00:00
parent 49e432d030
commit 5d3b3188f7
10 changed files with 100 additions and 12 deletions
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5
lld/ELF/DWARF.cpp
View File

@ -93,8 +93,11 @@ LLDDwarfObj<ELFT>::findAux(const InputSectionBase &Sec, uint64_t Pos,
uint32_t SecIndex = File->getSectionIndex(Sym);
// Broken debug info can point to a non-Defined symbol.
auto *DR = dyn_cast<Defined>(&File->getRelocTargetSym(Rel));
Symbol &S = File->getRelocTargetSym(Rel);
auto *DR = dyn_cast<Defined>(&S);
if (!DR) {
if (S.isSection())
return None;
RelType Type = Rel.getType(Config->IsMips64EL);
if (Type != Target->NoneRel)
error(toString(File) + ": relocation " + lld::toString(Type) + " at 0x" +

3
lld/ELF/InputFiles.cpp
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@ -997,6 +997,9 @@ template <class ELFT> void ObjFile<ELFT>::initializeSymbols() {
if (ESym.st_shndx == SHN_UNDEF)
this->Symbols[I] = make<Undefined>(this, Name, Binding, StOther, Type);
else if (Sec == &InputSection::Discarded)
this->Symbols[I] = make<Undefined>(this, Name, Binding, StOther, Type,
/*DiscardedSecIdx=*/SecIdx);
else
this->Symbols[I] =
make<Defined>(this, Name, Binding, StOther, Type, Value, Size, Sec);

3
lld/ELF/InputSection.cpp
View File

@ -438,7 +438,8 @@ void InputSection::copyRelocations(uint8_t *Buf, ArrayRef<RelTy> Rels) {
// hopefully creates a frame that is ignored at runtime.
auto *D = dyn_cast<Defined>(&Sym);
if (!D) {
error("STT_SECTION symbol should be defined");
warn("STT_SECTION symbol should be defined");
P->setSymbolAndType(0, 0, false);
continue;
}
SectionBase *Section = D->Section->Repl;

14
lld/ELF/Relocations.cpp
View File

@ -681,9 +681,17 @@ static std::string maybeReportDiscarded(Undefined &Sym, InputSectionBase &Sec,
return "";
ArrayRef<Elf_Shdr_Impl<ELFT>> ObjSections =
CHECK(File->getObj().sections(), File);
std::string Msg =
"relocation refers to a symbol in a discarded section: " + toString(Sym) +
"\n>>> defined in " + toString(File);
std::string Msg;
if (Sym.Type == ELF::STT_SECTION) {
Msg = "relocation refers to a discarded section: ";
Msg += CHECK(
File->getObj().getSectionName(&ObjSections[Sym.DiscardedSecIdx]), File);
} else {
Msg = "relocation refers to a symbol in a discarded section: " +
toString(Sym);
}
Msg += "\n>>> defined in " + toString(File);
Elf_Shdr_Impl<ELFT> ELFSec = ObjSections[Sym.DiscardedSecIdx - 1];
if (ELFSec.sh_type != SHT_GROUP)

12
lld/test/ELF/comdat-discarded-error.s
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@ -5,7 +5,7 @@
# RUN: echo '.section .text.foo,"axG",@progbits,foo,comdat; .globl bar; bar:' | \
# RUN: llvm-mc -filetype=obj -triple=x86_64 - -o %t3.o
# RUN: not ld.lld %t1.o %t2.o %t3.o -o /dev/null 2>&1 | FileCheck %s
# RUN: not ld.lld %t2.o %t3.o %t1.o -o /dev/null 2>&1 | FileCheck %s
# CHECK: error: relocation refers to a symbol in a discarded section: bar
# CHECK-NEXT: >>> defined in {{.*}}3.o
@ -13,6 +13,16 @@
# CHECK-NEXT: >>> prevailing definition is in {{.*}}2.o
# CHECK-NEXT: >>> referenced by {{.*}}1.o:(.text+0x1)
# CHECK: error: relocation refers to a discarded section: .text.foo
# CHECK-NEXT: >>> defined in {{.*}}1.o
# CHECK-NEXT: >>> section group signature: foo
# CHECK-NEXT: >>> prevailing definition is in {{.*}}2.o
# CHECK-NEXT: >>> referenced by {{.*}}1.o:(.data+0x0)
.globl _start
_start:
jmp bar
.section .text.foo,"axG",@progbits,foo,comdat
.data
.quad .text.foo

63
lld/test/ELF/comdat-discarded-gdb-index.s Normal file
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@ -0,0 +1,63 @@
# REQUIRES: x86
# RUN: llvm-mc -filetype=obj -triple=x86_64 %s -o %t.o
# RUN: ld.lld --gdb-index %t.o %t.o -o %t
## .debug_info has a relocation to .text.foo . The second %t.o is discarded.
## Check we don't error on the relocation.
# CHECK: .rela.debug_info {
# CHECK-NEXT: 0xC R_X86_64_64 .text.foo 0x0
.section .text.foo,"axG",@progbits,foo,comdat
.globl foo
.Lfunc_begin0:
foo:
ret
.Lfunc_end0:
.section .debug_abbrev,"",@progbits
.byte 1 # Abbreviation Code
.byte 17 # DW_TAG_compile_unit
.byte 1 # DW_CHILDREN_yes
.byte 17 # DW_AT_low_pc
.byte 1 # DW_FORM_addr
.byte 18 # DW_AT_high_pc
.byte 6 # DW_FORM_data4
.ascii "\264B" # DW_AT_GNU_pubnames
.byte 25 # DW_FORM_flag_present
.byte 0 # EOM(1)
.byte 0 # EOM(2)
.byte 2 # Abbreviation Code
.byte 46 # DW_TAG_subprogram
.byte 0 # DW_CHILDREN_no
.byte 3 # DW_AT_name
.byte 8 # DW_FORM_string
.byte 0 # EOM(1)
.byte 0 # EOM(2)
.byte 0
.section .debug_info,"",@progbits
.Lcu_begin0:
.long .Lcu_end0 - .Lcu_begin0 - 4
.short 4 # DWARF version number
.long 0 # Offset Into Abbrev. Section
.byte 4 # Address Size
.Ldie0:
.byte 1 # Abbrev [1] DW_TAG_compile_unit
.quad .Lfunc_begin0 # DW_AT_low_pc
.long .Lfunc_end0 - .Lfunc_begin0 # DW_AT_high_pc
.byte 2 # Abbrev [2] DW_TAG_subprogram
.asciz "foo" # DW_AT_name
.byte 0
.Lcu_end0:
.section .debug_gnu_pubnames,"",@progbits
.long .LpubNames_end0 - .LpubNames_begin0
.LpubNames_begin0:
.short 2 # Version
.long .Lcu_begin0 # CU Offset
.long .Lcu_end0 - .Lcu_begin0
.long .Ldie0 - .Lcu_begin0
.byte 48 # Attributes: FUNCTION, EXTERNAL
.asciz "foo" # External Name
.long 0
.LpubNames_end0:

2
lld/test/ELF/comdat-discarded-reloc.s
View File

@ -1,7 +1,7 @@
# REQUIRES: x86
# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %p/Inputs/comdat-discarded-reloc.s -o %t2.o
# RUN: ld.lld -gc-sections %t.o %t2.o -o %t
# RUN: ld.lld -gc-sections --noinhibit-exec %t.o %t2.o -o /dev/null
## ELF spec doesn't allow a relocation to point to a deduplicated
## COMDAT section. Unfortunately this happens in practice (e.g. .eh_frame)

4
lld/test/ELF/comdat.s
View File

@ -1,7 +1,7 @@
// REQUIRES: x86
// RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
// RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %p/Inputs/comdat.s -o %t2.o
// RUN: ld.lld -shared %t.o %t.o %t2.o -o %t
// RUN: ld.lld -shared %t.o %t2.o -o %t
// RUN: llvm-objdump -d %t | FileCheck %s
// RUN: llvm-readobj -S --symbols %t | FileCheck --check-prefix=READ %s
@ -31,9 +31,7 @@ foo:
// CHECK-EMPTY:
// CHECK-NEXT: bar:
// 0x1000 - 0x1001 - 5 = -6
// 0 - 0x1006 - 5 = -4107
// CHECK-NEXT: 1001: {{.*}} callq -6
// CHECK-NEXT: 1006: {{.*}} callq -4107
.section .text3,"axG",@progbits,zed,comdat,unique,0

2
lld/test/ELF/invalid-undef-section-symbol.test
View File

@ -1,5 +1,5 @@
# RUN: yaml2obj %s -o %t.o
# RUN: not ld.lld -r %t.o -o /dev/null 2>&1 | FileCheck %s
# RUN: not ld.lld -r --fatal-warnings %t.o -o /dev/null 2>&1 | FileCheck %s
# We used to crash at this.
# CHECK: STT_SECTION symbol should be defined

4
lld/test/ELF/relocatable-eh-frame.s
View File

@ -1,10 +1,12 @@
# REQUIRES: x86
# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
# RUN: ld.lld -r %t.o %t.o -o %t
# RUN: ld.lld -r %t.o %t.o -o %t 2>&1 | FileCheck --check-prefix=WARN %s
# RUN: llvm-readobj -r %t | FileCheck %s
# RUN: ld.lld %t -o %t.so -shared
# RUN: llvm-objdump -h %t.so | FileCheck --check-prefix=DSO %s
# WARN: STT_SECTION symbol should be defined
# DSO: .eh_frame 00000034
# CHECK: Relocations [