aboutsummaryrefslogtreecommitdiffstats
diff options
context:
space:
mode:
Diffstat
-rw-r--r--include/llvm/MC/MCAssembler.h10
-rw-r--r--include/llvm/MC/MCStreamer.h14
-rw-r--r--lib/MC/MCAsmStreamer.cpp9
-rw-r--r--lib/MC/MCAssembler.cpp23
-rw-r--r--lib/MC/MCMachOStreamer.cpp17
-rw-r--r--lib/MC/MCNullStreamer.cpp3
6 files changed, 73 insertions, 3 deletions
diff --git a/include/llvm/MC/MCAssembler.h b/include/llvm/MC/MCAssembler.h
index 4527f3c..882929f 100644
--- a/include/llvm/MC/MCAssembler.h
+++ b/include/llvm/MC/MCAssembler.h
@@ -195,12 +195,16 @@ class MCAlignFragment : public MCFragment {
/// cannot be satisfied in this width then this fragment is ignored.
unsigned MaxBytesToEmit;
+ /// EmitNops - true when aligning code and optimal nops to be used for filling
+ bool EmitNops;
+
public:
MCAlignFragment(unsigned _Alignment, int64_t _Value, unsigned _ValueSize,
- unsigned _MaxBytesToEmit, MCSectionData *SD = 0)
+ unsigned _MaxBytesToEmit, bool _EmitNops,
+ MCSectionData *SD = 0)
: MCFragment(FT_Align, SD), Alignment(_Alignment),
Value(_Value),ValueSize(_ValueSize),
- MaxBytesToEmit(_MaxBytesToEmit) {}
+ MaxBytesToEmit(_MaxBytesToEmit), EmitNops(_EmitNops) {}
/// @name Accessors
/// @{
@@ -217,6 +221,8 @@ public:
unsigned getMaxBytesToEmit() const { return MaxBytesToEmit; }
+ unsigned getEmitNops() const { return EmitNops; }
+
/// @}
static bool classof(const MCFragment *F) {
diff --git a/include/llvm/MC/MCStreamer.h b/include/llvm/MC/MCStreamer.h
index b104b9a..696d024 100644
--- a/include/llvm/MC/MCStreamer.h
+++ b/include/llvm/MC/MCStreamer.h
@@ -232,6 +232,20 @@ namespace llvm {
unsigned ValueSize = 1,
unsigned MaxBytesToEmit = 0) = 0;
+ /// EmitCodeAlignment - Emit nops until the byte alignment @p ByteAlignment
+ /// is reached.
+ ///
+ /// This used to align code where the alignment bytes may be executed. This
+ /// can emit different bytes for different sizes to optimize execution.
+ ///
+ /// @param ByteAlignment - The alignment to reach. This must be a power of
+ /// two on some targets.
+ /// @param MaxBytesToEmit - The maximum numbers of bytes to emit, or 0. If
+ /// the alignment cannot be reached in this many bytes, no bytes are
+ /// emitted.
+ virtual void EmitCodeAlignment(unsigned ByteAlignment,
+ unsigned MaxBytesToEmit = 0) = 0;
+
/// EmitValueToOffset - Emit some number of copies of @p Value until the
/// byte offset @p Offset is reached.
///
diff --git a/lib/MC/MCAsmStreamer.cpp b/lib/MC/MCAsmStreamer.cpp
index 6add1b4..07a9553 100644
--- a/lib/MC/MCAsmStreamer.cpp
+++ b/lib/MC/MCAsmStreamer.cpp
@@ -134,6 +134,9 @@ public:
unsigned ValueSize = 1,
unsigned MaxBytesToEmit = 0);
+ virtual void EmitCodeAlignment(unsigned ByteAlignment,
+ unsigned MaxBytesToEmit = 0);
+
virtual void EmitValueToOffset(const MCExpr *Offset,
unsigned char Value = 0);
@@ -513,6 +516,12 @@ void MCAsmStreamer::EmitValueToAlignment(unsigned ByteAlignment, int64_t Value,
EmitEOL();
}
+void MCAsmStreamer::EmitCodeAlignment(unsigned ByteAlignment,
+ unsigned MaxBytesToEmit) {
+ // FIXME: a hack for now to only work for x86 using the 0x90 nop opcode.
+ EmitValueToAlignment(ByteAlignment, 0x90, 1, MaxBytesToEmit);
+}
+
void MCAsmStreamer::EmitValueToOffset(const MCExpr *Offset,
unsigned char Value) {
// FIXME: Verify that Offset is associated with the current section.
diff --git a/lib/MC/MCAssembler.cpp b/lib/MC/MCAssembler.cpp
index 528c5c0..2c698e7 100644
--- a/lib/MC/MCAssembler.cpp
+++ b/lib/MC/MCAssembler.cpp
@@ -42,6 +42,8 @@ STATISTIC(EmittedFragments, "Number of emitted assembler fragments");
static void WriteFileData(raw_ostream &OS, const MCSectionData &SD,
MachObjectWriter &MOW);
+static uint64_t WriteNopData(uint64_t Count, MachObjectWriter &MOW);
+
/// isVirtualSection - Check if this is a section which does not actually exist
/// in the object file.
static bool isVirtualSection(const MCSection &Section) {
@@ -1058,6 +1060,19 @@ void MCAssembler::LayoutSection(MCSectionData &SD) {
SD.setFileSize(Address - SD.getAddress());
}
+/// WriteNopData - Write optimal nops to the output file for the \arg Count
+/// bytes. This returns the number of bytes written. It may return 0 if
+/// the \arg Count is more than the maximum optimal nops.
+///
+/// FIXME this is X86 32-bit specific and should move to a better place.
+static uint64_t WriteNopData(uint64_t Count, MachObjectWriter &MOW) {
+ // FIXME for now just use the 0x90 nop opcode byte.
+ for (uint64_t i = 0; i < Count; i++)
+ MOW.Write8 (uint8_t(0x90));
+
+ return Count;
+}
+
/// WriteFileData - Write the \arg F data to the output file.
static void WriteFileData(raw_ostream &OS, const MCFragment &F,
MachObjectWriter &MOW) {
@@ -1081,6 +1096,14 @@ static void WriteFileData(raw_ostream &OS, const MCFragment &F,
"' is not a divisor of padding size '" +
Twine(AF.getFileSize()) + "'");
+ // See if we are aligning with nops, and if so do that first to try to fill
+ // the Count bytes. Then if that did not fill any bytes or there are any
+ // bytes left to fill use the the Value and ValueSize to fill the rest.
+ if (AF.getEmitNops()) {
+ uint64_t NopByteCount = WriteNopData(Count, MOW);
+ Count -= NopByteCount;
+ }
+
for (uint64_t i = 0; i != Count; ++i) {
switch (AF.getValueSize()) {
default:
diff --git a/lib/MC/MCMachOStreamer.cpp b/lib/MC/MCMachOStreamer.cpp
index 797be86..a7a8a5d 100644
--- a/lib/MC/MCMachOStreamer.cpp
+++ b/lib/MC/MCMachOStreamer.cpp
@@ -137,6 +137,8 @@ public:
virtual void EmitValueToAlignment(unsigned ByteAlignment, int64_t Value = 0,
unsigned ValueSize = 1,
unsigned MaxBytesToEmit = 0);
+ virtual void EmitCodeAlignment(unsigned ByteAlignment,
+ unsigned MaxBytesToEmit = 0);
virtual void EmitValueToOffset(const MCExpr *Offset,
unsigned char Value = 0);
@@ -357,7 +359,20 @@ void MCMachOStreamer::EmitValueToAlignment(unsigned ByteAlignment,
if (MaxBytesToEmit == 0)
MaxBytesToEmit = ByteAlignment;
new MCAlignFragment(ByteAlignment, Value, ValueSize, MaxBytesToEmit,
- CurSectionData);
+ false /* EmitNops */, CurSectionData);
+
+ // Update the maximum alignment on the current section if necessary.
+ if (ByteAlignment > CurSectionData->getAlignment())
+ CurSectionData->setAlignment(ByteAlignment);
+}
+
+void MCMachOStreamer::EmitCodeAlignment(unsigned ByteAlignment,
+ unsigned MaxBytesToEmit) {
+ if (MaxBytesToEmit == 0)
+ MaxBytesToEmit = ByteAlignment;
+ // FIXME the 0x90 is the default x86 1 byte nop opcode.
+ new MCAlignFragment(ByteAlignment, 0x90, 1, MaxBytesToEmit,
+ true /* EmitNops */, CurSectionData);
// Update the maximum alignment on the current section if necessary.
if (ByteAlignment > CurSectionData->getAlignment())
diff --git a/lib/MC/MCNullStreamer.cpp b/lib/MC/MCNullStreamer.cpp
index 46e9ebf..ab61799 100644
--- a/lib/MC/MCNullStreamer.cpp
+++ b/lib/MC/MCNullStreamer.cpp
@@ -55,6 +55,9 @@ namespace {
unsigned ValueSize = 1,
unsigned MaxBytesToEmit = 0) {}
+ virtual void EmitCodeAlignment(unsigned ByteAlignment,
+ unsigned MaxBytesToEmit = 0) {}
+
virtual void EmitValueToOffset(const MCExpr *Offset,
unsigned char Value = 0) {}
generated by cgit v1.1 at 2024-09-12 01:08:11 +0000