void SVMELFProgramWriter::rwCompress(MCAssembler &Asm, const MCAsmLayout &Layout, SVMMemoryLayout &ML)
{
/*
* Look for all segments with initialized data for RAM, flatten them, and
* compress the resulting data. Create a new segment with the compressed
* RWDATA. This segment will always be included in the binary. The originals
* are considered debug-only sections, since they are no longer needed
* at runtime.
*/
// Flattened binary contents of RAM
std::vector<uint8_t> plaintext;
// Iterate over SPS_RW sections
for (MCAssembler::const_iterator IS = Asm.begin(), ES = Asm.end(); IS != ES; ++IS) {
const MCSectionData *SD = &*IS;
if (ML.getSectionKind(SD) != SPS_RW_PLAIN)
continue;
int offset = ML.getSectionMemAddress(SD) - SVMTargetMachine::getRAMBase();
int limit = SVMTargetMachine::getRAMSize();
// Iterate over fragments, pasting them into 'plaintext'
for (MCSectionData::const_iterator IF = SD->begin(), EF = SD->end(); IF != EF; ++IF) {
const MCFragment *F = &*IF;
if (F->getKind() == MCFragment::FT_Data) {
const MCDataFragment *DF = cast<MCDataFragment>(F);
int fragmentOffset = Layout.getFragmentOffset(F);
for (unsigned i = 0; i < DF->getContents().size(); i++) {
int totalOffset = fragmentOffset + offset + i;
if (totalOffset < limit) {
while (totalOffset >= int(plaintext.size()))
plaintext.push_back(0);
plaintext[totalOffset] = DF->getContents()[i];
}
}
}
}
}
// FastLZ requires a minimum of 16 bytes to compress. Pad our section data.
while (plaintext.size() < 16)
plaintext.push_back(0);
// Compress using FastLZ level 1
std::vector<uint8_t> compressed(plaintext.size() * 2);
compressed.resize(fastlz_compress_level(1, &plaintext[0], plaintext.size(), &compressed[0]));
// Create the new section
const MCSectionELF *LZSection =
Asm.getContext().getELFSection(".rwdata.lz", ELF::SHT_NOTE,
0, SectionKind::getDataNoRel());
MCSectionData &LZSectionSD = Asm.getOrCreateSectionData(*LZSection);
LZSectionSD.setAlignment(1);
// Force it to be interpreted as SPS_RW, and set the decompressed size
ML.setSectionKind(&LZSectionSD, SPS_RW_Z);
ML.setSectionMemSize(&LZSectionSD, plaintext.size());
// Add compressed data
MCDataFragment *F = new MCDataFragment(&LZSectionSD);
F->getContents().append(compressed.begin(), compressed.end());
}
