[llvm] 69b312c - [llvm-objdump] Create fake sections for a ELF core file
James Henderson via llvm-commits
llvm-commits at lists.llvm.org
Thu Jul 14 05:40:13 PDT 2022
Author: Namhyung Kim
Date: 2022-07-14T13:39:59+01:00
New Revision: 69b312cde428056186928a3c1b6ad84e45de0353
URL: https://github.com/llvm/llvm-project/commit/69b312cde428056186928a3c1b6ad84e45de0353
DIFF: https://github.com/llvm/llvm-project/commit/69b312cde428056186928a3c1b6ad84e45de0353.diff
LOG: [llvm-objdump] Create fake sections for a ELF core file
The linux perf tools use /proc/kcore for disassembly kernel functions.
Actually it copies the relevant parts to a temp file and then pass it to
objdump. But it doesn't have section headers so llvm-objdump cannot
handle it.
Let's create fake section headers for the program headers. It'd have a
single section for each segment to cover the entire range. And for this
purpose we can consider only executable code segments.
With this change, I can see the following command shows proper outputs.
perf annotate --stdio --objdump=/path/to/llvm-objdump
Differential Revision: https://reviews.llvm.org/D128705
Added:
llvm/test/tools/llvm-objdump/X86/disassemble-no-section.test
Modified:
llvm/include/llvm/Object/ELF.h
llvm/include/llvm/Object/ELFObjectFile.h
llvm/test/Object/objdump-no-sectionheaders.test
llvm/tools/llvm-objdump/llvm-objdump.cpp
llvm/tools/llvm-objdump/llvm-objdump.h
Removed:
################################################################################
diff --git a/llvm/include/llvm/Object/ELF.h b/llvm/include/llvm/Object/ELF.h
index 1a59ba94098f3..794d29fd99133 100644
--- a/llvm/include/llvm/Object/ELF.h
+++ b/llvm/include/llvm/Object/ELF.h
@@ -181,6 +181,7 @@ class ELFFile {
private:
StringRef Buf;
+ std::vector<Elf_Shdr> FakeSections;
ELFFile(StringRef Object);
@@ -389,6 +390,8 @@ class ELFFile {
Expected<ArrayRef<uint8_t>> getSectionContents(const Elf_Shdr &Sec) const;
Expected<ArrayRef<uint8_t>> getSegmentContents(const Elf_Phdr &Phdr) const;
Expected<std::vector<BBAddrMap>> decodeBBAddrMap(const Elf_Shdr &Sec) const;
+
+ void createFakeSections();
};
using ELF32LEFile = ELFFile<ELF32LE>;
@@ -757,11 +760,37 @@ Expected<ELFFile<ELFT>> ELFFile<ELFT>::create(StringRef Object) {
return ELFFile(Object);
}
+/// Used by llvm-objdump -d (which needs sections for disassembly) to
+/// disassemble objects without a section header table (e.g. ET_CORE objects
+/// analyzed by linux perf or ET_EXEC with llvm-strip --strip-sections).
+template <class ELFT> void ELFFile<ELFT>::createFakeSections() {
+ if (!FakeSections.empty())
+ return;
+ auto PhdrsOrErr = program_headers();
+ if (!PhdrsOrErr)
+ return;
+
+ for (auto Phdr : *PhdrsOrErr) {
+ if (!(Phdr.p_type & ELF::PT_LOAD) || !(Phdr.p_flags & ELF::PF_X))
+ continue;
+ Elf_Shdr FakeShdr = {};
+ FakeShdr.sh_type = ELF::SHT_PROGBITS;
+ FakeShdr.sh_flags = ELF::SHF_ALLOC | ELF::SHF_EXECINSTR;
+ FakeShdr.sh_addr = Phdr.p_vaddr;
+ FakeShdr.sh_size = Phdr.p_memsz;
+ FakeShdr.sh_offset = Phdr.p_offset;
+ FakeSections.push_back(FakeShdr);
+ }
+}
+
template <class ELFT>
Expected<typename ELFT::ShdrRange> ELFFile<ELFT>::sections() const {
const uintX_t SectionTableOffset = getHeader().e_shoff;
- if (SectionTableOffset == 0)
+ if (SectionTableOffset == 0) {
+ if (!FakeSections.empty())
+ return makeArrayRef(FakeSections.data(), FakeSections.size());
return ArrayRef<Elf_Shdr>();
+ }
if (getHeader().e_shentsize != sizeof(Elf_Shdr))
return createError("invalid e_shentsize in ELF header: " +
diff --git a/llvm/include/llvm/Object/ELFObjectFile.h b/llvm/include/llvm/Object/ELFObjectFile.h
index c449a3dafc0ce..ed2f70b0da251 100644
--- a/llvm/include/llvm/Object/ELFObjectFile.h
+++ b/llvm/include/llvm/Object/ELFObjectFile.h
@@ -457,6 +457,8 @@ template <class ELFT> class ELFObjectFile : public ELFObjectFileBase {
elf_symbol_iterator_range getDynamicSymbolIterators() const override;
bool isRelocatableObject() const override;
+
+ void createFakeSections() { EF.createFakeSections(); }
};
using ELF32LEObjectFile = ELFObjectFile<ELF32LE>;
diff --git a/llvm/test/Object/objdump-no-sectionheaders.test b/llvm/test/Object/objdump-no-sectionheaders.test
index ebefa760bf14d..b6f09355395d1 100644
--- a/llvm/test/Object/objdump-no-sectionheaders.test
+++ b/llvm/test/Object/objdump-no-sectionheaders.test
@@ -1,6 +1,8 @@
; RUN: llvm-objdump -h %p/Inputs/no-sections.elf-x86-64 \
; RUN: | FileCheck %s
-; CHECK: Sections:
-; CHECK: Idx Name Size VMA Type
-; CHECK-NOT: {{.}}
+; CHECK: Sections:
+; CHECK-NEXT: Idx Name Size VMA Type
+; CHECK-NEXT: 0 000006ec 0000000000400000 TEXT
+; CHECK-NEXT: 1 00000000 0000000000000000 TEXT
+; CHECK-NOT: {{.}}
diff --git a/llvm/test/tools/llvm-objdump/X86/disassemble-no-section.test b/llvm/test/tools/llvm-objdump/X86/disassemble-no-section.test
new file mode 100644
index 0000000000000..b1811b3626ddf
--- /dev/null
+++ b/llvm/test/tools/llvm-objdump/X86/disassemble-no-section.test
@@ -0,0 +1,51 @@
+## This test checks -d disassembles an ELF file without section headers.
+## Such files include kcore files extracted by linux perf tools, or
+## executables with section headers stripped by e.g.
+## llvm-strip --strip-sections.
+
+# RUN: yaml2obj %s -o %t
+# RUN: llvm-objdump -d %t | FileCheck %s
+
+# CHECK: Disassembly of section :
+# CHECK-EMPTY:
+# CHECK-NEXT: <>:
+# CHECK-NEXT: 55 pushq %rbp
+# CHECK-NEXT: 48 89 e5 movq %rsp, %rbp
+# CHECK-NEXT: 0f 1f 40 00 nopl (%rax)
+# CHECK-NEXT: 5d popq %rbp
+# CHECK-NEXT: c3 retq
+
+## Check disassembly with an address range.
+# RUN: llvm-objdump -d --start-address=0xffffffff00000000 \
+# RUN: --stop-address=0xffffffff00000004 %t 2>&1 | \
+# RUN: FileCheck %s --check-prefix RANGE
+
+# RANGE: no section overlaps the range
+# RANGE-EMPTY:
+# RANGE-NEXT: Disassembly of section :
+# RANGE-EMPTY:
+# RANGE-NEXT: <>:
+# RANGE-NEXT: 55 pushq %rbp
+# RANGE-NEXT: 48 89 e5 movq %rsp, %rbp
+# RANGE-EMPTY:
+
+!ELF
+FileHeader:
+ Class: ELFCLASS64
+ Data: ELFDATA2LSB
+ Type: ET_CORE
+ Machine: EM_X86_64
+Sections:
+ - Type: SectionHeaderTable
+ NoHeaders: true
+ - Type: Fill
+ Name: code
+ Pattern: "554889E50F1F40005DC3"
+ Size: 10
+ Offset: 0x1000
+ProgramHeaders:
+ - Type: PT_LOAD
+ Flags: [ PF_X ]
+ VAddr: 0xFFFFFFFF00000000
+ FirstSec: code
+ LastSec: code
diff --git a/llvm/tools/llvm-objdump/llvm-objdump.cpp b/llvm/tools/llvm-objdump/llvm-objdump.cpp
index 1245f9e182069..39962240fdf7a 100644
--- a/llvm/tools/llvm-objdump/llvm-objdump.cpp
+++ b/llvm/tools/llvm-objdump/llvm-objdump.cpp
@@ -1131,7 +1131,21 @@ static void emitPostInstructionInfo(formatted_raw_ostream &FOS,
FOS.flush();
}
-static void disassembleObject(const Target *TheTarget, const ObjectFile &Obj,
+static void createFakeELFSections(ObjectFile &Obj) {
+ assert(Obj.isELF());
+ if (auto *Elf32LEObj = dyn_cast<ELF32LEObjectFile>(&Obj))
+ Elf32LEObj->createFakeSections();
+ else if (auto *Elf64LEObj = dyn_cast<ELF64LEObjectFile>(&Obj))
+ Elf64LEObj->createFakeSections();
+ else if (auto *Elf32BEObj = dyn_cast<ELF32BEObjectFile>(&Obj))
+ Elf32BEObj->createFakeSections();
+ else if (auto *Elf64BEObj = cast<ELF64BEObjectFile>(&Obj))
+ Elf64BEObj->createFakeSections();
+ else
+ llvm_unreachable("Unsupported binary format");
+}
+
+static void disassembleObject(const Target *TheTarget, ObjectFile &Obj,
MCContext &Ctx, MCDisassembler *PrimaryDisAsm,
MCDisassembler *SecondaryDisAsm,
const MCInstrAnalysis *MIA, MCInstPrinter *IP,
@@ -1198,6 +1212,9 @@ static void disassembleObject(const Target *TheTarget, const ObjectFile &Obj,
if (Obj.isWasm())
addMissingWasmCodeSymbols(cast<WasmObjectFile>(Obj), AllSymbols);
+ if (Obj.isELF() && Obj.sections().empty())
+ createFakeELFSections(Obj);
+
BumpPtrAllocator A;
StringSaver Saver(A);
addPltEntries(Obj, AllSymbols, Saver);
@@ -1688,7 +1705,7 @@ static void disassembleObject(const Target *TheTarget, const ObjectFile &Obj,
reportWarning("failed to disassemble missing symbol " + Sym, FileName);
}
-static void disassembleObject(const ObjectFile *Obj, bool InlineRelocs) {
+static void disassembleObject(ObjectFile *Obj, bool InlineRelocs) {
const Target *TheTarget = getTarget(Obj);
// Package up features to be passed to target/subtarget
@@ -1890,7 +1907,7 @@ static size_t getMaxSectionNameWidth(const ObjectFile &Obj) {
return MaxWidth;
}
-void objdump::printSectionHeaders(const ObjectFile &Obj) {
+void objdump::printSectionHeaders(ObjectFile &Obj) {
size_t NameWidth = getMaxSectionNameWidth(Obj);
size_t AddressWidth = 2 * Obj.getBytesInAddress();
bool HasLMAColumn = shouldDisplayLMA(Obj);
@@ -1903,6 +1920,9 @@ void objdump::printSectionHeaders(const ObjectFile &Obj) {
outs() << "Idx " << left_justify("Name", NameWidth) << " Size "
<< left_justify("VMA", AddressWidth) << " Type\n";
+ if (Obj.isELF() && Obj.sections().empty())
+ createFakeELFSections(Obj);
+
uint64_t Idx;
for (const SectionRef &Section : ToolSectionFilter(Obj, &Idx)) {
StringRef Name = unwrapOrError(Section.getName(), Obj.getFileName());
diff --git a/llvm/tools/llvm-objdump/llvm-objdump.h b/llvm/tools/llvm-objdump/llvm-objdump.h
index dd9f58aa33087..c64c042d513e7 100644
--- a/llvm/tools/llvm-objdump/llvm-objdump.h
+++ b/llvm/tools/llvm-objdump/llvm-objdump.h
@@ -124,7 +124,7 @@ SectionFilter ToolSectionFilter(llvm::object::ObjectFile const &O,
bool isRelocAddressLess(object::RelocationRef A, object::RelocationRef B);
void printRelocations(const object::ObjectFile *O);
void printDynamicRelocations(const object::ObjectFile *O);
-void printSectionHeaders(const object::ObjectFile &O);
+void printSectionHeaders(object::ObjectFile &O);
void printSectionContents(const object::ObjectFile *O);
void printSymbolTable(const object::ObjectFile &O, StringRef ArchiveName,
StringRef ArchitectureName = StringRef(),
More information about the llvm-commits
mailing list