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[BOLT] Change .debug_line emission for non-simple functions 

Summary:
We use a special routine to emit line info for functions that we do not
overwrite. The resulting DWARF was not quite efficient as we were
advancing addresses using a larger than needed opcodes. Since there were
only a few functions that we didn't emit/overwrite, it was not a big
issue.

However, in lite mode the majority of functions are not overwritten and
as a result, the inefficiency in debug line encoding got exposed and
binaries were getting larger than expected .debug_line sections.

Fix it by using more conventional line table opcodes for address
advancing.

(cherry picked from FBD21423074)
This commit is contained in:
Maksim Panchenko 2020-05-05 23:56:50 -07:00
parent 96c4168ddc
commit 689447bf10
2 changed files with 97 additions and 39 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

134
bolt/llvm.patch
View File

@ -942,7 +942,7 @@ index c99f2521f8f..e6b4a88f469 100644
MCSection *getCompactUnwindSection() const { return CompactUnwindSection; }
MCSection *getDwarfAbbrevSection() const { return DwarfAbbrevSection; }
diff --git a/include/llvm/MC/MCObjectStreamer.h b/include/llvm/MC/MCObjectStreamer.h
index 8e9b4ac5632..d2c569e3399 100644
index 8e9b4ac5632..50b8c9e305b 100644
--- a/include/llvm/MC/MCObjectStreamer.h
+++ b/include/llvm/MC/MCObjectStreamer.h
@@ -121,6 +121,8 @@ public:
@ -954,6 +954,16 @@ index 8e9b4ac5632..d2c569e3399 100644
void emitValueToOffset(const MCExpr *Offset, unsigned char Value,
SMLoc Loc) override;
void
@@ -134,6 +136,9 @@ public:
void EmitDwarfAdvanceLineAddr(int64_t LineDelta, const MCSymbol *LastLabel,
const MCSymbol *Label,
unsigned PointerSize);
+ void EmitDwarfAdvanceLineAddr(int64_t LineDelta, uint64_t Address,
+ uint64_t AddressDelta,
+ unsigned PointerSize);
void EmitDwarfAdvanceFrameAddr(const MCSymbol *LastLabel,
const MCSymbol *Label);
void EmitCVLocDirective(unsigned FunctionId, unsigned FileNo, unsigned Line,
diff --git a/include/llvm/MC/MCStreamer.h b/include/llvm/MC/MCStreamer.h
index 582a836023b..f1e341bd624 100644
--- a/include/llvm/MC/MCStreamer.h
@ -2595,16 +2605,16 @@ index a0f9a857e3c..01a34eb13a7 100644
RelaxedFrag =
relaxCVInlineLineTable(Layout, *cast<MCCVInlineLineTableFragment>(I));
diff --git a/lib/MC/MCDwarf.cpp b/lib/MC/MCDwarf.cpp
index 0e0ea965d14..49885269d06 100644
index 0e0ea965d14..a2a0ea6006e 100644
--- a/lib/MC/MCDwarf.cpp
+++ b/lib/MC/MCDwarf.cpp
@@ -156,12 +156,36 @@ EmitDwarfLineTable(MCObjectStreamer *MCOS, MCSection *Section,
@@ -156,12 +156,27 @@ EmitDwarfLineTable(MCObjectStreamer *MCOS, MCSection *Section,
unsigned Flags = DWARF2_LINE_DEFAULT_IS_STMT ? DWARF2_FLAG_IS_STMT : 0;
unsigned Isa = 0;
unsigned Discriminator = 0;
+ uint64_t LastAddress = -1ULL;
+ (void)LastAddress;
MCSymbol *LastLabel = nullptr;
+ const MCAsmInfo *AsmInfo = MCOS->getContext().getAsmInfo();
// Loop through each MCDwarfLineEntry and encode the dwarf line number table.
- for (const MCDwarfLineEntry &LineEntry : LineEntries) {
@ -2614,29 +2624,20 @@ index 0e0ea965d14..49885269d06 100644
+ const MCDwarfLineEntry &LineEntry = *it;
int64_t LineDelta = static_cast<int64_t>(LineEntry.getLine()) - LastLine;
+ uint64_t Address = LineEntry.getAbsoluteAddr();
+ if (Address != -1ULL) {
+ auto nit = it;
+ if (++nit == ie) {
+ // We are using a hacky way to update debug info for functions that we
+ // didn't rewrite. We don't have a code section context, and should
+ // emit end_sequence at the address indicated by the last entry.
+ MCOS->EmitIntValue(dwarf::DW_LNS_extended_op, 1);
+ MCOS->EmitIntValue(8 + 1, 1);
+ MCOS->EmitIntValue(dwarf::DW_LNE_set_address, 1);
+ MCOS->EmitIntValue(Address, 8);
+ MCDwarfLineAddr::Emit(MCOS,
+ MCOS->getAssembler().getDWARFLinetableParams(),
+ INT64_MAX,
+ 0);
+ return;
+ }
+ const uint64_t Address = LineEntry.getAbsoluteAddr();
+ if (Address != -1ULL && std::next(it) == ie) {
+ // If emitting absolute addresses, the last entry only carries address
+ // info for the DW_LNE_end_sequence. This entry compensates for the lack
+ // of the section context used to emit the end of section label.
+ MCOS->EmitDwarfAdvanceLineAddr(INT64_MAX, -1ULL, Address - LastAddress,
+ AsmInfo->getCodePointerSize());
+ return;
+ }
+
if (FileNum != LineEntry.getFileNum()) {
FileNum = LineEntry.getFileNum();
MCOS->EmitIntValue(dwarf::DW_LNS_set_file, 1);
@@ -197,18 +221,33 @@ EmitDwarfLineTable(MCObjectStreamer *MCOS, MCSection *Section,
@@ -197,18 +212,34 @@ EmitDwarfLineTable(MCObjectStreamer *MCOS, MCSection *Section,
if (LineEntry.getFlags() & DWARF2_FLAG_EPILOGUE_BEGIN)
MCOS->EmitIntValue(dwarf::DW_LNS_set_epilogue_begin, 1);
@ -2656,20 +2657,21 @@ index 0e0ea965d14..49885269d06 100644
+ // At this point we want to emit/create the sequence to encode the delta in
+ // line numbers and the increment of the address from the previous Label
+ // and the current Label.
+ const MCAsmInfo *asmInfo = MCOS->getContext().getAsmInfo();
+ MCOS->EmitDwarfAdvanceLineAddr(LineDelta, LastLabel, Label,
+ asmInfo->getCodePointerSize());
+ AsmInfo->getCodePointerSize());
+ LastLabel = Label;
+ LastAddress = -1ULL;
+ } else {
+ MCOS->EmitIntValue(dwarf::DW_LNS_extended_op, 1);
+ // DW_LNE_set_address length: pointer size (8) + 1
+ MCOS->EmitIntValue(8 + 1, 1);
+ MCOS->EmitIntValue(dwarf::DW_LNE_set_address, 1);
+ MCOS->EmitIntValue(Address, 8);
+ MCOS->EmitIntValue(dwarf::DW_LNS_advance_line, 1);
+ MCOS->EmitSLEB128IntValue(LineDelta);
+ MCOS->EmitIntValue(dwarf::DW_LNS_copy, 1);
+ if (LastAddress == -1ULL) {
+ MCOS->EmitDwarfAdvanceLineAddr(LineDelta, Address, 0,
+ AsmInfo->getCodePointerSize());
+ } else {
+ MCOS->EmitDwarfAdvanceLineAddr(LineDelta, -1ULL,
+ Address - LastAddress,
+ AsmInfo->getCodePointerSize());
+ }
+ LastAddress = Address;
+ LastLabel = nullptr;
+ }
Discriminator = 0;
@ -2678,7 +2680,15 @@ index 0e0ea965d14..49885269d06 100644
}
// Emit a DW_LNE_end_sequence for the end of the section.
@@ -250,7 +289,7 @@ void MCDwarfLineTable::Emit(MCObjectStreamer *MCOS,
@@ -222,7 +253,6 @@ EmitDwarfLineTable(MCObjectStreamer *MCOS, MCSection *Section,
MCContext &Ctx = MCOS->getContext();
MCOS->SwitchSection(Ctx.getObjectFileInfo()->getDwarfLineSection());
- const MCAsmInfo *AsmInfo = Ctx.getAsmInfo();
MCOS->EmitDwarfAdvanceLineAddr(INT64_MAX, LastLabel, SectionEnd,
AsmInfo->getCodePointerSize());
}
@@ -250,7 +280,7 @@ void MCDwarfLineTable::Emit(MCObjectStreamer *MCOS,
MCOS->SwitchSection(context.getObjectFileInfo()->getDwarfLineSection());
// Handle the rest of the Compile Units.
@ -2687,7 +2697,7 @@ index 0e0ea965d14..49885269d06 100644
CUIDTablePair.second.EmitCU(MCOS, Params, LineStr);
if (LineStr)
@@ -514,8 +553,12 @@ MCDwarfLineTableHeader::Emit(MCStreamer *MCOS, MCDwarfLineTableParams Params,
@@ -514,8 +544,12 @@ MCDwarfLineTableHeader::Emit(MCStreamer *MCOS, MCDwarfLineTableParams Params,
void MCDwarfLineTable::EmitCU(MCObjectStreamer *MCOS,
MCDwarfLineTableParams Params,
@ -2702,7 +2712,7 @@ index 0e0ea965d14..49885269d06 100644
// Put out the line tables.
for (const auto &LineSec : MCLineSections.getMCLineEntries())
@@ -1253,12 +1296,217 @@ public:
@@ -1253,12 +1287,217 @@ public:
void EmitCFIInstruction(const MCCFIInstruction &Instr);
};
@ -2920,7 +2930,7 @@ index 0e0ea965d14..49885269d06 100644
void FrameEmitterImpl::EmitCFIInstruction(const MCCFIInstruction &Instr) {
int dataAlignmentFactor = getDataAlignmentFactor(Streamer);
auto *MRI = Streamer.getContext().getRegisterInfo();
@@ -1373,7 +1621,28 @@ void FrameEmitterImpl::EmitCFIInstruction(const MCCFIInstruction &Instr) {
@@ -1373,7 +1612,28 @@ void FrameEmitterImpl::EmitCFIInstruction(const MCCFIInstruction &Instr) {
Streamer.EmitIntValue(dwarf::DW_CFA_GNU_args_size, 1);
Streamer.EmitULEB128IntValue(Instr.getOffset());
return;
@ -3065,7 +3075,7 @@ index 83da8ac1bae..820aa688e5f 100644
Ctx->getELFSection(".tdata", ELF::SHT_PROGBITS,
ELF::SHF_ALLOC | ELF::SHF_TLS | ELF::SHF_WRITE);
diff --git a/lib/MC/MCObjectStreamer.cpp b/lib/MC/MCObjectStreamer.cpp
index 0a684588110..87dea6bfc28 100644
index 0a684588110..b3aa9e9cea8 100644
--- a/lib/MC/MCObjectStreamer.cpp
+++ b/lib/MC/MCObjectStreamer.cpp
@@ -273,9 +273,9 @@ bool MCObjectStreamer::mayHaveInstructions(MCSection &Sec) const {
@ -3080,7 +3090,55 @@ index 0a684588110..87dea6bfc28 100644
}
void MCObjectStreamer::EmitInstructionImpl(const MCInst &Inst,
@@ -494,6 +494,13 @@ void MCObjectStreamer::EmitCodeAlignment(unsigned ByteAlignment,
@@ -377,12 +377,17 @@ static const MCExpr *buildSymbolDiff(MCObjectStreamer &OS, const MCSymbol *A,
static void emitDwarfSetLineAddr(MCObjectStreamer &OS,
MCDwarfLineTableParams Params,
int64_t LineDelta, const MCSymbol *Label,
+ uint64_t Address,
int PointerSize) {
// emit the sequence to set the address
OS.EmitIntValue(dwarf::DW_LNS_extended_op, 1);
OS.EmitULEB128IntValue(PointerSize + 1);
OS.EmitIntValue(dwarf::DW_LNE_set_address, 1);
- OS.EmitSymbolValue(Label, PointerSize);
+ if (Label) {
+ OS.EmitSymbolValue(Label, PointerSize);
+ } else {
+ OS.EmitIntValue(Address, PointerSize);
+ }
// emit the sequence for the LineDelta (from 1) and a zero address delta.
MCDwarfLineAddr::Emit(&OS, Params, LineDelta, 0);
@@ -394,7 +399,7 @@ void MCObjectStreamer::EmitDwarfAdvanceLineAddr(int64_t LineDelta,
unsigned PointerSize) {
if (!LastLabel) {
emitDwarfSetLineAddr(*this, Assembler->getDWARFLinetableParams(), LineDelta,
- Label, PointerSize);
+ Label, 0, PointerSize);
return;
}
const MCExpr *AddrDelta = buildSymbolDiff(*this, Label, LastLabel);
@@ -407,6 +412,19 @@ void MCObjectStreamer::EmitDwarfAdvanceLineAddr(int64_t LineDelta,
insert(new MCDwarfLineAddrFragment(LineDelta, *AddrDelta));
}
+void MCObjectStreamer::EmitDwarfAdvanceLineAddr(int64_t LineDelta,
+ uint64_t Address,
+ uint64_t AddressDelta,
+ unsigned PointerSize) {
+ if (Address != -1ULL) {
+ emitDwarfSetLineAddr(*this, Assembler->getDWARFLinetableParams(), LineDelta,
+ nullptr, Address, PointerSize);
+ return;
+ }
+ MCDwarfLineAddr::Emit(this, Assembler->getDWARFLinetableParams(), LineDelta,
+ AddressDelta);
+}
+
void MCObjectStreamer::EmitDwarfAdvanceFrameAddr(const MCSymbol *LastLabel,
const MCSymbol *Label) {
const MCExpr *AddrDelta = buildSymbolDiff(*this, Label, LastLabel);
@@ -494,6 +512,13 @@ void MCObjectStreamer::EmitCodeAlignment(unsigned ByteAlignment,
cast<MCAlignFragment>(getCurrentFragment())->setEmitNops(true);
}

2
bolt/src/BinaryEmitter.cpp
View File

@ -946,7 +946,7 @@ void BinaryEmitter::emitDebugLineInfoForNonSimpleFunctions() {
// Add an empty entry past the end of the function
// for end_sequence mark.
BC.Ctx->setCurrentDwarfLoc(0, 0, 0, 0, 0, 0,
Address + Function.getMaxSize());
Address + Function.getMaxSize());
auto Loc = BC.Ctx->getCurrentDwarfLoc();
BC.Ctx->clearDwarfLocSeen();
OutputLineTable.addLineEntry(MCDwarfLineEntry{nullptr, Loc},