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ELF: Write .eh_frame_hdr explicitly after writing .eh_frame.

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This lets us remove the special case from Writer::writeSections(), and also
fixes a bug where .eh_frame_hdr isn't necessarily written in the correct
order if a linker script moves .eh_frame and .eh_frame_hdr into the same
output section.

Differential Revision: https://reviews.llvm.org/D58795

llvm-svn: 355153
This commit is contained in:
Peter Collingbourne
2019-02-28 23:11:35 +00:00
parent 701593f1db
commit 7fb9eabda5
7 changed files with 57 additions and 40 deletions
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51
lld/ELF/Writer.cpp
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@@ -2407,16 +2407,14 @@ static uint8_t getAbiVersion() {
}
template <class ELFT> void Writer<ELFT>::writeHeader() {
uint8_t *Buf = Buffer->getBufferStart();
// For executable segments, the trap instructions are written before writing
// the header. Setting Elf header bytes to zero ensures that any unused bytes
// in header are zero-cleared, instead of having trap instructions.
memset(Buf, 0, sizeof(Elf_Ehdr));
memcpy(Buf, "\177ELF", 4);
memset(Out::BufferStart, 0, sizeof(Elf_Ehdr));
memcpy(Out::BufferStart, "\177ELF", 4);
// Write the ELF header.
auto *EHdr = reinterpret_cast<Elf_Ehdr *>(Buf);
auto *EHdr = reinterpret_cast<Elf_Ehdr *>(Out::BufferStart);
EHdr->e_ident[EI_CLASS] = Config->Is64 ? ELFCLASS64 : ELFCLASS32;
EHdr->e_ident[EI_DATA] = Config->IsLE ? ELFDATA2LSB : ELFDATA2MSB;
EHdr->e_ident[EI_VERSION] = EV_CURRENT;
@@ -2438,7 +2436,7 @@ template <class ELFT> void Writer<ELFT>::writeHeader() {
}
// Write the program header table.
auto *HBuf = reinterpret_cast<Elf_Phdr *>(Buf + EHdr->e_phoff);
auto *HBuf = reinterpret_cast<Elf_Phdr *>(Out::BufferStart + EHdr->e_phoff);
for (PhdrEntry *P : Phdrs) {
HBuf->p_type = P->p_type;
HBuf->p_flags = P->p_flags;
@@ -2460,7 +2458,7 @@ template <class ELFT> void Writer<ELFT>::writeHeader() {
// the value. The sentinel values and fields are:
// e_shnum = 0, SHdrs[0].sh_size = number of sections.
// e_shstrndx = SHN_XINDEX, SHdrs[0].sh_link = .shstrtab section index.
auto *SHdrs = reinterpret_cast<Elf_Shdr *>(Buf + EHdr->e_shoff);
auto *SHdrs = reinterpret_cast<Elf_Shdr *>(Out::BufferStart + EHdr->e_shoff);
size_t Num = OutputSections.size() + 1;
if (Num >= SHN_LORESERVE)
SHdrs->sh_size = Num;
@@ -2494,18 +2492,19 @@ template <class ELFT> void Writer<ELFT>::openFile() {
Expected<std::unique_ptr<FileOutputBuffer>> BufferOrErr =
FileOutputBuffer::create(Config->OutputFile, FileSize, Flags);
if (!BufferOrErr)
if (!BufferOrErr) {
error("failed to open " + Config->OutputFile + ": " +
llvm::toString(BufferOrErr.takeError()));
else
Buffer = std::move(*BufferOrErr);
return;
}
Buffer = std::move(*BufferOrErr);
Out::BufferStart = Buffer->getBufferStart();
}
template <class ELFT> void Writer<ELFT>::writeSectionsBinary() {
uint8_t *Buf = Buffer->getBufferStart();
for (OutputSection *Sec : OutputSections)
if (Sec->Flags & SHF_ALLOC)
Sec->writeTo<ELFT>(Buf + Sec->Offset);
Sec->writeTo<ELFT>(Out::BufferStart + Sec->Offset);
}
static void fillTrap(uint8_t *I, uint8_t *End) {
@@ -2524,11 +2523,12 @@ template <class ELFT> void Writer<ELFT>::writeTrapInstr() {
return;
// Fill the last page.
uint8_t *Buf = Buffer->getBufferStart();
for (PhdrEntry *P : Phdrs)
if (P->p_type == PT_LOAD && (P->p_flags & PF_X))
fillTrap(Buf + alignDown(P->p_offset + P->p_filesz, Target->PageSize),
Buf + alignTo(P->p_offset + P->p_filesz, Target->PageSize));
fillTrap(Out::BufferStart +
alignDown(P->p_offset + P->p_filesz, Target->PageSize),
Out::BufferStart +
alignTo(P->p_offset + P->p_filesz, Target->PageSize));
// Round up the file size of the last segment to the page boundary iff it is
// an executable segment to ensure that other tools don't accidentally
@@ -2544,27 +2544,16 @@ template <class ELFT> void Writer<ELFT>::writeTrapInstr() {
// Write section contents to a mmap'ed file.
template <class ELFT> void Writer<ELFT>::writeSections() {
uint8_t *Buf = Buffer->getBufferStart();
OutputSection *EhFrameHdr = nullptr;
if (In.EhFrameHdr && !In.EhFrameHdr->empty())
EhFrameHdr = In.EhFrameHdr->getParent();
// In -r or -emit-relocs mode, write the relocation sections first as in
// ELf_Rel targets we might find out that we need to modify the relocated
// section while doing it.
for (OutputSection *Sec : OutputSections)
if (Sec->Type == SHT_REL || Sec->Type == SHT_RELA)
Sec->writeTo<ELFT>(Buf + Sec->Offset);
Sec->writeTo<ELFT>(Out::BufferStart + Sec->Offset);
for (OutputSection *Sec : OutputSections)
if (Sec != EhFrameHdr && Sec->Type != SHT_REL && Sec->Type != SHT_RELA)
Sec->writeTo<ELFT>(Buf + Sec->Offset);
// The .eh_frame_hdr depends on .eh_frame section contents, therefore
// it should be written after .eh_frame is written.
if (EhFrameHdr)
EhFrameHdr->writeTo<ELFT>(Buf + EhFrameHdr->Offset);
if (Sec->Type != SHT_REL && Sec->Type != SHT_RELA)
Sec->writeTo<ELFT>(Out::BufferStart + Sec->Offset);
}
template <class ELFT> void Writer<ELFT>::writeBuildId() {
@@ -2572,9 +2561,7 @@ template <class ELFT> void Writer<ELFT>::writeBuildId() {
return;
// Compute a hash of all sections of the output file.
uint8_t *Start = Buffer->getBufferStart();
uint8_t *End = Start + FileSize;
In.BuildId->writeBuildId({Start, End});
In.BuildId->writeBuildId({Out::BufferStart, FileSize});
}
template void elf::writeResult<ELF32LE>();