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[BOLT] Abort on out-of-section symbols in GOT (#100801)

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This patch aborts BOLT execution if it finds out-of-section (section
end) symbol in GOT table. In order to handle such situations properly in
future, we would need to have an arch-dependent way to analyze
relocations or its sequences, e.g., for ARM it would probably be ADRP +
LDR analysis in order to get GOT entry address. Currently, it is also
challenging because GOT-related relocation symbols are replaced to
__BOLT_got_zero. Anyway, it seems to be quite a rare case, which seems
to be only? related to static binaries. For the most part, it seems that
it should be handled on the linker stage, since static binary should not
have GOT table at all. LLD linker with relaxations enabled would replace
instruction addresses from GOT directly to target symbols, which
eliminates the problem.

Anyway, in order to achieve detection of such cases, this patch fixes a
few things in BOLT:
1. For the end symbols, we're now using the section provided by ELF
binary. Previously it would be tied with a wrong section found by symbol
address.
2. The end symbols would have limited registration we would only
add them in name->data GlobalSymbols map, since using address->data
BinaryDataMap map would likely be impossible due to address duality of
such symbols.
3. The outdated BD->getSection (currently returning refence, not
pointer) check in postProcessSymbolTable is replaced by getSize check in
order to allow zero-sized top-level symbols if they are located in
zero-sized sections. For the most part, such things could only be found
in tests, but I don't see a reason not to handle such cases.
4. Updated section-end-sym test and removed x86_64 requirement since
there is no reason for this (tested on aarch64 linux)

The test was provided by peterwaller-arm (thank you) in #100096 and
slightly modified by me.
This commit is contained in:
Vladislav Khmelevsky
2024-08-07 16:26:12 +04:00
committed by GitHub
parent 097ddd3565
commit a4900f0d93
6 changed files with 98 additions and 16 deletions
Download Patch File Download Diff File Expand all files Collapse all files

3
bolt/include/bolt/Core/BinaryContext.h
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@@ -911,7 +911,8 @@ public:
/// of \p Flags.
MCSymbol *registerNameAtAddress(StringRef Name, uint64_t Address,
uint64_t Size, uint16_t Alignment,
unsigned Flags = 0);
unsigned Flags = 0,
BinarySection *Section = NULL);
/// Return BinaryData registered at a given \p Address or nullptr if no
/// global symbol was registered at the location.

22
bolt/lib/Core/BinaryContext.cpp
View File

@@ -1056,18 +1056,28 @@ void BinaryContext::adjustCodePadding() {
MCSymbol *BinaryContext::registerNameAtAddress(StringRef Name, uint64_t Address,
uint64_t Size,
uint16_t Alignment,
unsigned Flags) {
unsigned Flags,
BinarySection *Section) {
// Register the name with MCContext.
MCSymbol *Symbol = Ctx->getOrCreateSymbol(Name);
BinaryData *BD;
// Register out of section symbols only in GlobalSymbols map
if (Section && Section->getEndAddress() == Address) {
BD = new BinaryData(*Symbol, Address, Size, Alignment ? Alignment : 1,
*Section, Flags);
GlobalSymbols[Name] = BD;
return Symbol;
}
auto GAI = BinaryDataMap.find(Address);
BinaryData *BD;
if (GAI == BinaryDataMap.end()) {
ErrorOr<BinarySection &> SectionOrErr = getSectionForAddress(Address);
BinarySection &Section =
SectionOrErr ? SectionOrErr.get() : absoluteSection();
BinarySection &SectionRef = Section ? *Section
: SectionOrErr ? SectionOrErr.get()
: absoluteSection();
BD = new BinaryData(*Symbol, Address, Size, Alignment ? Alignment : 1,
Section, Flags);
SectionRef, Flags);
GAI = BinaryDataMap.emplace(Address, BD).first;
GlobalSymbols[Name] = BD;
updateObjectNesting(GAI);
@@ -1402,7 +1412,7 @@ void BinaryContext::postProcessSymbolTable() {
if ((BD->getName().starts_with("SYMBOLat") ||
BD->getName().starts_with("DATAat")) &&
!BD->getParent() && !BD->getSize() && !BD->isAbsolute() &&
BD->getSection()) {
BD->getSection().getSize()) {
this->errs() << "BOLT-WARNING: zero-sized top level symbol: " << *BD
<< "\n";
Valid = false;

51
bolt/lib/Rewrite/RewriteInstance.cpp
View File

@@ -955,13 +955,13 @@ void RewriteInstance::discoverFileObjects() {
uint64_t SymbolSize = ELFSymbolRef(Symbol).getSize();
uint64_t SymbolAlignment = Symbol.getAlignment();
auto registerName = [&](uint64_t FinalSize) {
auto registerName = [&](uint64_t FinalSize, BinarySection *Section = NULL) {
// Register names even if it's not a function, e.g. for an entry point.
BC->registerNameAtAddress(UniqueName, SymbolAddress, FinalSize,
SymbolAlignment, SymbolFlags);
SymbolAlignment, SymbolFlags, Section);
if (!AlternativeName.empty())
BC->registerNameAtAddress(AlternativeName, SymbolAddress, FinalSize,
SymbolAlignment, SymbolFlags);
SymbolAlignment, SymbolFlags, Section);
};
section_iterator Section =
@@ -986,12 +986,25 @@ void RewriteInstance::discoverFileObjects() {
<< " for function\n");
if (SymbolAddress == Section->getAddress() + Section->getSize()) {
ErrorOr<BinarySection &> SectionOrError =
BC->getSectionForAddress(Section->getAddress());
// Skip symbols from invalid sections
if (!SectionOrError) {
BC->errs() << "BOLT-WARNING: " << UniqueName << " (0x"
<< Twine::utohexstr(SymbolAddress)
<< ") does not have any section\n";
continue;
}
assert(SymbolSize == 0 &&
"unexpect non-zero sized symbol at end of section");
LLVM_DEBUG(
dbgs()
<< "BOLT-DEBUG: rejecting as symbol points to end of its section\n");
registerName(SymbolSize);
LLVM_DEBUG({
dbgs() << "BOLT-DEBUG: rejecting as symbol " << UniqueName
<< " points to end of " << SectionOrError->getName()
<< " section\n";
});
registerName(SymbolSize, &SectionOrError.get());
continue;
}
@@ -2623,6 +2636,30 @@ void RewriteInstance::handleRelocation(const SectionRef &RelocatedSection,
}
}
if (Relocation::isGOT(RType) && !Relocation::isTLS(RType)) {
auto exitOnGotEndSymol = [&](StringRef Name) {
BC->errs() << "BOLT-ERROR: GOT table contains currently unsupported "
"section end symbol "
<< Name << "\n";
exit(1);
};
if (SymbolIter != InputFile->symbol_end() && ReferencedSection) {
if (cantFail(SymbolIter->getAddress()) ==
ReferencedSection->getEndAddress())
exitOnGotEndSymol(cantFail(SymbolIter->getName()));
} else {
// If no section and symbol are provided by relocation, try to find the
// symbol by its name, including the possibility that the symbol is local.
BinaryData *BD = BC->getBinaryDataByName(SymbolName);
if (!BD && NR.getUniquifiedNameCount(SymbolName) == 1)
BD = BC->getBinaryDataByName(NR.getUniqueName(SymbolName, 1));
if ((BD && BD->getAddress() == BD->getSection().getEndAddress()))
exitOnGotEndSymol(BD->getName());
}
}
if (!ReferencedSection)
ReferencedSection = BC->getSectionForAddress(SymbolAddress);

6
bolt/test/AArch64/Inputs/got_end_of_section_symbol.lld_script Normal file
View File

@@ -0,0 +1,6 @@
SECTIONS {
PROVIDE (__executable_start = SEGMENT_START("text-segment", 0x400000)); . = SEGMENT_START("text-segment", 0x400000) + SIZEOF_HEADERS;
.data : { *(.data) *(.array) }
.text : { *(.text) }
.got : { *(.got) *(.igot) }
}

28
bolt/test/AArch64/got_end_of_section_symbol.s Normal file
View File

@@ -0,0 +1,28 @@
# RUN: llvm-mc -filetype=obj -triple aarch64-unknown-unknown \
# RUN: %s -o %t.o
# RUN: %clang %cflags -nostartfiles -nodefaultlibs -static -Wl,--no-relax \
# RUN: -Wl,-q -Wl,-T %S/Inputs/got_end_of_section_symbol.lld_script \
# RUN: %t.o -o %t.exe
# RUN: not llvm-bolt %t.exe -o %t.bolt 2>&1 | FileCheck %s
# CHECK: BOLT-ERROR: GOT table contains currently unsupported section end
# CHECK-SAME: symbol array_end
.section .array, "a", @progbits
.globl array_start
.globl array_end
array_start:
.word 0
array_end:
.section .text
.globl _start
.type _start, %function
_start:
adrp x1, #:got:array_start
ldr x1, [x1, #:got_lo12:array_start]
adrp x0, #:got:array_end
ldr x0, [x0, #:got_lo12:array_end]
adrp x2, #:got:_start
ldr x2, [x2, #:got_lo12:_start]
ret

4
bolt/test/X86/section-end-sym.s
View File

@@ -1,7 +1,7 @@
## Check that BOLT doesn't consider end-of-section symbols (e.g., _etext) as
## functions.
# REQUIRES: x86_64-linux, asserts
# REQUIRES: system-linux, asserts
# RUN: llvm-mc -filetype=obj -triple x86_64-unknown-linux %s -o %t.o
# RUN: ld.lld %t.o -o %t.exe -q
@@ -9,7 +9,7 @@
# RUN: | FileCheck %s
# CHECK: considering symbol etext for function
# CHECK-NEXT: rejecting as symbol points to end of its section
# CHECK-NEXT: rejecting as symbol etext points to end of .text section
# CHECK-NOT: Binary Function "etext{{.*}}" after building cfg