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[llvm-objcopy][MachO] Make --remove-section clean up dead symbols

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Make --remove-section clean up dead symbols, return an Error if it can't be safely done.

Test plan: make check-all

Differential revision: https://reviews.llvm.org/D78474
This commit is contained in:
Alexander Shaposhnikov
2020-04-22 14:26:28 -07:00
parent 1a78b0bd38
commit f34fdbcf99
6 changed files with 315 additions and 25 deletions
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128
llvm/test/tools/llvm-objcopy/MachO/remove-section-dead-symbols.test Normal file
View File

@@ -0,0 +1,128 @@
# RUN: yaml2obj %s -o %t
# RUN: llvm-objcopy --remove-section __DATA,C %t %t.copy
# RUN: llvm-readobj --symbols %t.copy | FileCheck %s
# CHECK: Symbols [
# CHECK-NEXT: Symbol {
# CHECK-NEXT: Name: _A (1)
# CHECK-NEXT: Extern
# CHECK-NEXT: Type: Section (0xE)
# CHECK-NEXT: Section: __data (0x2)
# CHECK-NEXT: RefType: UndefinedNonLazy (0x0)
# CHECK-NEXT: Flags [ (0x0)
# CHECK-NEXT: ]
# CHECK-NEXT: Value: 0x0
# CHECK-NEXT: }
# CHECK-NEXT: ]
--- !mach-o
FileHeader:
magic: 0xFEEDFACF
cputype: 0x01000007
cpusubtype: 0x00000003
filetype: 0x00000001
ncmds: 4
sizeofcmds: 432
flags: 0x00002000
reserved: 0x00000000
LoadCommands:
- cmd: LC_SEGMENT_64
cmdsize: 312
segname: ''
vmaddr: 0
vmsize: 8
fileoff: 464
filesize: 8
maxprot: 7
initprot: 7
nsects: 3
flags: 0
Sections:
- sectname: __text
segname: __TEXT
addr: 0x0000000000000000
size: 0
offset: 0x000001D0
align: 0
reloff: 0x00000000
nreloc: 0
flags: 0x80000000
reserved1: 0x00000000
reserved2: 0x00000000
reserved3: 0x00000000
content: ''
- sectname: __data
segname: __DATA
addr: 0x0000000000000000
size: 4
offset: 0x000001D0
align: 2
reloff: 0x00000000
nreloc: 0
flags: 0x00000000
reserved1: 0x00000000
reserved2: 0x00000000
reserved3: 0x00000000
content: '01000000'
- sectname: C
segname: __DATA
addr: 0x0000000000000004
size: 4
offset: 0x000001D4
align: 2
reloff: 0x00000000
nreloc: 0
flags: 0x00000000
reserved1: 0x00000000
reserved2: 0x00000000
reserved3: 0x00000000
content: '02000000'
- cmd: LC_VERSION_MIN_MACOSX
cmdsize: 16
version: 658944
sdk: 0
- cmd: LC_SYMTAB
cmdsize: 24
symoff: 472
nsyms: 2
stroff: 504
strsize: 8
- cmd: LC_DYSYMTAB
cmdsize: 80
ilocalsym: 0
nlocalsym: 0
iextdefsym: 0
nextdefsym: 2
iundefsym: 2
nundefsym: 0
tocoff: 0
ntoc: 0
modtaboff: 0
nmodtab: 0
extrefsymoff: 0
nextrefsyms: 0
indirectsymoff: 0
nindirectsyms: 0
extreloff: 0
nextrel: 0
locreloff: 0
nlocrel: 0
LinkEditData:
NameList:
- n_strx: 4
n_type: 0x0F
n_sect: 2
n_desc: 0
n_value: 0
- n_strx: 1
n_type: 0x0F
n_sect: 3
n_desc: 0
n_value: 4
StringTable:
- ''
- _B
- _A
- ''
...

120
llvm/test/tools/llvm-objcopy/MachO/remove-section-error.test Normal file
View File

@@ -0,0 +1,120 @@
# RUN: yaml2obj %s -o %t
# RUN: not llvm-objcopy --remove-section __DATA,C %t /dev/null 2>&1 | FileCheck %s
# CHECK: symbol '_a' defined in section with index '2' cannot be removed because it is referenced by a relocation in section '__TEXT,__text'
## The binary used in this test was built as follows:
## main.c:
## __attribute__((section("__DATA,C"))) int a = 2;
## int f() { return a; }
## build command:
## clang -fno-exceptions -fno-unwind-tables -c main.c -o main.o
--- !mach-o
FileHeader:
magic: 0xFEEDFACF
cputype: 0x01000007
cpusubtype: 0x00000003
filetype: 0x00000001
ncmds: 4
sizeofcmds: 360
flags: 0x00002000
reserved: 0x00000000
LoadCommands:
- cmd: LC_SEGMENT_64
cmdsize: 232
segname: ''
vmaddr: 0
vmsize: 16
fileoff: 392
filesize: 16
maxprot: 7
initprot: 7
nsects: 2
flags: 0
Sections:
- sectname: __text
segname: __TEXT
addr: 0x0000000000000000
size: 12
offset: 0x00000188
align: 4
reloff: 0x00000198
nreloc: 1
flags: 0x80000400
reserved1: 0x00000000
reserved2: 0x00000000
reserved3: 0x00000000
content: 554889E58B05000000005DC3
relocations:
- address: 0x00000006
symbolnum: 0
pcrel: true
length: 2
extern: true
type: 1
scattered: false
value: 0
- sectname: C
segname: __DATA
addr: 0x000000000000000C
size: 4
offset: 0x00000194
align: 2
reloff: 0x00000000
nreloc: 0
flags: 0x00000000
reserved1: 0x00000000
reserved2: 0x00000000
reserved3: 0x00000000
content: '02000000'
- cmd: LC_BUILD_VERSION
cmdsize: 24
platform: 1
minos: 658944
sdk: 658944
ntools: 0
- cmd: LC_SYMTAB
cmdsize: 24
symoff: 416
nsyms: 2
stroff: 448
strsize: 8
- cmd: LC_DYSYMTAB
cmdsize: 80
ilocalsym: 0
nlocalsym: 0
iextdefsym: 0
nextdefsym: 2
iundefsym: 2
nundefsym: 0
tocoff: 0
ntoc: 0
modtaboff: 0
nmodtab: 0
extrefsymoff: 0
nextrefsyms: 0
indirectsymoff: 0
nindirectsyms: 0
extreloff: 0
nextrel: 0
locreloff: 0
nlocrel: 0
LinkEditData:
NameList:
- n_strx: 4
n_type: 0x0F
n_sect: 2
n_desc: 0
n_value: 12
- n_strx: 1
n_type: 0x0F
n_sect: 1
n_desc: 0
n_value: 0
StringTable:
- ''
- _f
- _a
- ''
...

6
llvm/tools/llvm-objcopy/MachO/MachOObjcopy.cpp
View File

@@ -20,7 +20,7 @@ namespace macho {
using namespace object;
using SectionPred = std::function<bool(const std::unique_ptr<Section> &Sec)>;
static void removeSections(const CopyConfig &Config, Object &Obj) {
static Error removeSections(const CopyConfig &Config, Object &Obj) {
SectionPred RemovePred = [](const std::unique_ptr<Section> &) { return false; };
if (!Config.ToRemove.empty()) {
@@ -180,7 +180,9 @@ static Error handleArgs(const CopyConfig &Config, Object &Obj) {
return createStringError(llvm::errc::invalid_argument,
"option not supported by llvm-objcopy for MachO");
}
removeSections(Config, Obj);
if (Error E = removeSections(Config, Obj))
return E;
// Mark symbols to determine which symbols are still needed.
if (Config.StripAll)

34
llvm/tools/llvm-objcopy/MachO/MachOReader.cpp
View File

@@ -28,10 +28,11 @@ void MachOReader::readHeader(Object &O) const {
}
template <typename SectionType>
Section constructSectionCommon(SectionType Sec) {
Section constructSectionCommon(SectionType Sec, uint32_t Index) {
StringRef SegName(Sec.segname, strnlen(Sec.segname, sizeof(Sec.segname)));
StringRef SectName(Sec.sectname, strnlen(Sec.sectname, sizeof(Sec.sectname)));
Section S(SegName, SectName);
S.Index = Index;
S.Addr = Sec.addr;
S.Size = Sec.size;
S.Offset = Sec.offset;
@@ -45,14 +46,15 @@ Section constructSectionCommon(SectionType Sec) {
return S;
}
template <typename SectionType> Section constructSection(SectionType Sec);
template <typename SectionType>
Section constructSection(SectionType Sec, uint32_t Index);
template <> Section constructSection(MachO::section Sec) {
return constructSectionCommon(Sec);
template <> Section constructSection(MachO::section Sec, uint32_t Index) {
return constructSectionCommon(Sec, Index);
}
template <> Section constructSection(MachO::section_64 Sec) {
Section S = constructSectionCommon(Sec);
template <> Section constructSection(MachO::section_64 Sec, uint32_t Index) {
Section S = constructSectionCommon(Sec, Index);
S.Reserved3 = Sec.reserved3;
return S;
}
@@ -62,7 +64,7 @@ template <typename SectionType, typename SegmentType>
std::vector<std::unique_ptr<Section>>
extractSections(const object::MachOObjectFile::LoadCommandInfo &LoadCmd,
const object::MachOObjectFile &MachOObj,
size_t &NextSectionIndex) {
uint32_t &NextSectionIndex) {
auto End = LoadCmd.Ptr + LoadCmd.C.cmdsize;
const SectionType *Curr =
reinterpret_cast<const SectionType *>(LoadCmd.Ptr + sizeof(SegmentType));
@@ -72,9 +74,11 @@ extractSections(const object::MachOObjectFile::LoadCommandInfo &LoadCmd,
SectionType Sec;
memcpy((void *)&Sec, Curr, sizeof(SectionType));
MachO::swapStruct(Sec);
Sections.push_back(std::make_unique<Section>(constructSection(Sec)));
Sections.push_back(
std::make_unique<Section>(constructSection(Sec, NextSectionIndex)));
} else {
Sections.push_back(std::make_unique<Section>(constructSection(*Curr)));
Sections.push_back(
std::make_unique<Section>(constructSection(*Curr, NextSectionIndex)));
}
Section &S = *Sections.back();
@@ -110,7 +114,7 @@ extractSections(const object::MachOObjectFile::LoadCommandInfo &LoadCmd,
void MachOReader::readLoadCommands(Object &O) const {
// For MachO sections indices start from 1.
size_t NextSectionIndex = 1;
uint32_t NextSectionIndex = 1;
for (auto LoadCmd : MachOObj.load_commands()) {
LoadCommand LC;
switch (LoadCmd.C.cmd) {
@@ -189,12 +193,10 @@ void MachOReader::readSymbolTable(Object &O) const {
for (auto Symbol : MachOObj.symbols()) {
SymbolEntry SE =
(MachOObj.is64Bit()
? constructSymbolEntry(
StrTable,
MachOObj.getSymbol64TableEntry(Symbol.getRawDataRefImpl()))
: constructSymbolEntry(
StrTable,
MachOObj.getSymbolTableEntry(Symbol.getRawDataRefImpl())));
? constructSymbolEntry(StrTable, MachOObj.getSymbol64TableEntry(
Symbol.getRawDataRefImpl()))
: constructSymbolEntry(StrTable, MachOObj.getSymbolTableEntry(
Symbol.getRawDataRefImpl())));
O.SymTable.Symbols.push_back(std::make_unique<SymbolEntry>(SE));
}

42
llvm/tools/llvm-objcopy/MachO/Object.cpp
View File

@@ -1,5 +1,7 @@
#include "Object.h"
#include "../llvm-objcopy.h"
#include "llvm/ADT/SmallPtrSet.h"
#include <unordered_set>
namespace llvm {
namespace objcopy {
@@ -22,11 +24,41 @@ void SymbolTable::removeSymbols(
std::end(Symbols));
}
void Object::removeSections(function_ref<bool(const std::unique_ptr<Section> &)> ToRemove) {
for (LoadCommand &LC : LoadCommands)
LC.Sections.erase(std::remove_if(std::begin(LC.Sections),
std::end(LC.Sections), ToRemove),
std::end(LC.Sections));
Error Object::removeSections(
function_ref<bool(const std::unique_ptr<Section> &)> ToRemove) {
std::unordered_set<uint32_t> RemovedSectionsIndices;
for (LoadCommand &LC : LoadCommands) {
auto It = std::stable_partition(
std::begin(LC.Sections), std::end(LC.Sections),
[&](const std::unique_ptr<Section> &Sec) { return !ToRemove(Sec); });
for (auto I = It, End = LC.Sections.end(); I != End; ++I)
RemovedSectionsIndices.insert((*I)->Index);
LC.Sections.erase(It, LC.Sections.end());
}
auto IsDead = [&](const std::unique_ptr<SymbolEntry> &S) -> bool {
Optional<uint32_t> Section = S->section();
return (Section && RemovedSectionsIndices.count(*Section));
};
SmallPtrSet<const SymbolEntry *, 2> DeadSymbols;
for (const std::unique_ptr<SymbolEntry> &Sym : SymTable.Symbols)
if (IsDead(Sym))
DeadSymbols.insert(Sym.get());
for (const LoadCommand &LC : LoadCommands)
for (const std::unique_ptr<Section> &Sec : LC.Sections)
for (const RelocationInfo &R : Sec->Relocations)
if (R.Symbol && DeadSymbols.count(R.Symbol))
return createStringError(std::errc::invalid_argument,
"symbol '%s' defined in section with index "
"'%u' cannot be removed because it is "
"referenced by a relocation in section '%s'",
R.Symbol->Name.c_str(),
*(R.Symbol->section()),
Sec->CanonicalName.c_str());
SymTable.removeSymbols(IsDead);
return Error::success();
}
void Object::addLoadCommand(LoadCommand LC) {

10
llvm/tools/llvm-objcopy/MachO/Object.h
View File

@@ -37,6 +37,7 @@ struct MachHeader {
struct RelocationInfo;
struct Section {
uint32_t Index;
std::string Segname;
std::string Sectname;
// CanonicalName is a string formatted as “<Segname>,<Sectname>".
@@ -83,7 +84,7 @@ struct LoadCommand {
// The raw content of the payload of the load command (located right after the
// corresponding struct). In some cases it is either empty or can be
// copied-over without digging into its structure.
std::vector<uint8_t> Payload;
std::vector<uint8_t> Payload;
// Some load commands can contain (inside the payload) an array of sections,
// though the contents of the sections are stored separately. The struct
@@ -115,6 +116,10 @@ struct SymbolEntry {
bool isUndefinedSymbol() const {
return (n_type & MachO::N_TYPE) == MachO::N_UNDF;
}
Optional<uint32_t> section() const {
return n_sect == MachO::NO_SECT ? None : Optional<uint32_t>(n_sect);
}
};
/// The location of the symbol table inside the binary is described by LC_SYMTAB
@@ -306,7 +311,8 @@ struct Object {
Object() : NewSectionsContents(Alloc) {}
void removeSections(function_ref<bool(const std::unique_ptr<Section> &)> ToRemove);
Error
removeSections(function_ref<bool(const std::unique_ptr<Section> &)> ToRemove);
void addLoadCommand(LoadCommand LC);
/// Creates a new segment load command in the object and returns a reference