[llvm] r357475 - [llvm-objcopy]Allow llvm-objcopy to be used on an ELF file with no section headers
James Henderson via llvm-commits
llvm-commits at lists.llvm.org
Tue Apr 2 07:11:13 PDT 2019
Author: jhenderson
Date: Tue Apr 2 07:11:13 2019
New Revision: 357475
URL: http://llvm.org/viewvc/llvm-project?rev=357475&view=rev
Log:
[llvm-objcopy]Allow llvm-objcopy to be used on an ELF file with no section headers
This patch fixes https://bugs.llvm.org/show_bug.cgi?id=41293 and
https://bugs.llvm.org/show_bug.cgi?id=41045. llvm-objcopy assumed that
it could always read a section header string table. This isn't the case
when the sections were previously all stripped, and the e_shstrndx field
was set to 0. This patch fixes this. It also fixes a double space in an
error message relating to this issue, and prevents llvm-objcopy from
adding extra space for non-existent section headers, meaning that
--strip-sections on the output of a previous --strip-sections run
produces identical output, simplifying the test.
Reviewed by: rupprecht, grimar
Differential Revision: https://reviews.llvm.org/D59989
Added:
llvm/trunk/test/tools/llvm-objcopy/ELF/copy-after-strip-sections.test
Modified:
llvm/trunk/tools/llvm-objcopy/ELF/Object.cpp
llvm/trunk/tools/llvm-objcopy/ELF/Object.h
Added: llvm/trunk/test/tools/llvm-objcopy/ELF/copy-after-strip-sections.test
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/tools/llvm-objcopy/ELF/copy-after-strip-sections.test?rev=357475&view=auto
==============================================================================
--- llvm/trunk/test/tools/llvm-objcopy/ELF/copy-after-strip-sections.test (added)
+++ llvm/trunk/test/tools/llvm-objcopy/ELF/copy-after-strip-sections.test Tue Apr 2 07:11:13 2019
@@ -0,0 +1,26 @@
+# llvm-objcopy's --strip-sections removes the section headers. It should be
+# possible to run the tool on the output after this operation. Performing any
+# subsequent stripping operation, or copying the object, should produce
+# identical output.
+
+# RUN: yaml2obj %s -o %t.in
+# RUN: llvm-objcopy %t.in %t.stripped --strip-sections
+# RUN: llvm-objcopy %t.stripped %t.stripped2 --strip-sections
+# RUN: llvm-objcopy %t.stripped2 %t.out
+# RUN: cmp %t.stripped %t.stripped2
+# RUN: cmp %t.stripped %t.out
+
+--- !ELF
+FileHeader:
+ Class: ELFCLASS64
+ Data: ELFDATA2LSB
+ Type: ET_EXEC
+ Machine: EM_X86_64
+Sections:
+ - Name: .text
+ Type: SHT_PROGBITS
+ Content: 'facefeed'
+ProgramHeaders:
+ - Type: PT_LOAD
+ Sections:
+ - Section: .text
Modified: llvm/trunk/tools/llvm-objcopy/ELF/Object.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/tools/llvm-objcopy/ELF/Object.cpp?rev=357475&r1=357474&r2=357475&view=diff
==============================================================================
--- llvm/trunk/tools/llvm-objcopy/ELF/Object.cpp (original)
+++ llvm/trunk/tools/llvm-objcopy/ELF/Object.cpp Tue Apr 2 07:11:13 2019
@@ -1212,13 +1212,16 @@ template <class ELFT> void ELFBuilder<EL
if (ShstrIndex == SHN_XINDEX)
ShstrIndex = unwrapOrError(ElfFile.getSection(0))->sh_link;
- Obj.SectionNames =
- Obj.sections().template getSectionOfType<StringTableSection>(
- ShstrIndex,
- "e_shstrndx field value " + Twine(Ehdr.e_shstrndx) +
- " in elf header " + " is invalid",
- "e_shstrndx field value " + Twine(Ehdr.e_shstrndx) +
- " in elf header " + " is not a string table");
+ if (ShstrIndex == SHN_UNDEF)
+ Obj.HadShdrs = false;
+ else
+ Obj.SectionNames =
+ Obj.sections().template getSectionOfType<StringTableSection>(
+ ShstrIndex,
+ "e_shstrndx field value " + Twine(Ehdr.e_shstrndx) +
+ " in elf header is invalid",
+ "e_shstrndx field value " + Twine(Ehdr.e_shstrndx) +
+ " in elf header is not a string table");
}
Writer::~Writer() {}
@@ -1372,6 +1375,10 @@ template <class ELFT> void ELFWriter<ELF
}
}
+template <class ELFT>
+ELFWriter<ELFT>::ELFWriter(Object &Obj, Buffer &Buf, bool WSH)
+ : Writer(Obj, Buf), WriteSectionHeaders(WSH && Obj.HadShdrs) {}
+
Error Object::removeSections(
std::function<bool(const SectionBase &)> ToRemove) {
@@ -1558,9 +1565,10 @@ template <class ELFT> void ELFWriter<ELF
template <class ELFT> size_t ELFWriter<ELFT>::totalSize() const {
// We already have the section header offset so we can calculate the total
// size by just adding up the size of each section header.
- auto NullSectionSize = WriteSectionHeaders ? sizeof(Elf_Shdr) : 0;
- return Obj.SHOffset + Obj.sections().size() * sizeof(Elf_Shdr) +
- NullSectionSize;
+ if (!WriteSectionHeaders)
+ return Obj.SHOffset;
+ size_t ShdrCount = Obj.sections().size() + 1; // Includes null shdr.
+ return Obj.SHOffset + ShdrCount * sizeof(Elf_Shdr);
}
template <class ELFT> Error ELFWriter<ELFT>::write() {
Modified: llvm/trunk/tools/llvm-objcopy/ELF/Object.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/tools/llvm-objcopy/ELF/Object.h?rev=357475&r1=357474&r2=357475&view=diff
==============================================================================
--- llvm/trunk/tools/llvm-objcopy/ELF/Object.h (original)
+++ llvm/trunk/tools/llvm-objcopy/ELF/Object.h Tue Apr 2 07:11:13 2019
@@ -226,12 +226,11 @@ private:
public:
virtual ~ELFWriter() {}
- bool WriteSectionHeaders = true;
+ bool WriteSectionHeaders;
Error finalize() override;
Error write() override;
- ELFWriter(Object &Obj, Buffer &Buf, bool WSH)
- : Writer(Obj, Buf), WriteSectionHeaders(WSH) {}
+ ELFWriter(Object &Obj, Buffer &Buf, bool WSH);
};
class BinaryWriter : public Writer {
@@ -810,6 +809,7 @@ public:
uint32_t Version;
uint32_t Flags;
+ bool HadShdrs = true;
StringTableSection *SectionNames = nullptr;
SymbolTableSection *SymbolTable = nullptr;
SectionIndexSection *SectionIndexTable = nullptr;
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