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8057a16e18
N_FUNC_COLD is a new MachO symbol attribute. It's a hint to the linker
to order a symbol towards the end of its section, to improve locality.
Example:
```
void a1() {}
__attribute__((cold)) void a2() {}
void a3() {}
int main() {
a1();
a2();
a3();
return 0;
}
```
A linker that supports N_FUNC_COLD will order _a2 to the end of the text
section. From `nm -njU` output, we see:
```
_a1
_a3
_main
_a2
```
Differential Revision: https://reviews.llvm.org/D57190
llvm-svn: 352227
141 lines
4.2 KiB
C++
141 lines
4.2 KiB
C++
//===- MCSymbolMachO.h - ---------------------------------------*- C++ -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_MC_MCSYMBOLMACHO_H
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#define LLVM_MC_MCSYMBOLMACHO_H
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#include "llvm/ADT/Twine.h"
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#include "llvm/MC/MCSymbol.h"
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namespace llvm {
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class MCSymbolMachO : public MCSymbol {
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/// We store the value for the 'desc' symbol field in the
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/// lowest 16 bits of the implementation defined flags.
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enum MachOSymbolFlags : uint16_t { // See <mach-o/nlist.h>.
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SF_DescFlagsMask = 0xFFFF,
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// Reference type flags.
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SF_ReferenceTypeMask = 0x0007,
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SF_ReferenceTypeUndefinedNonLazy = 0x0000,
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SF_ReferenceTypeUndefinedLazy = 0x0001,
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SF_ReferenceTypeDefined = 0x0002,
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SF_ReferenceTypePrivateDefined = 0x0003,
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SF_ReferenceTypePrivateUndefinedNonLazy = 0x0004,
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SF_ReferenceTypePrivateUndefinedLazy = 0x0005,
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// Other 'desc' flags.
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SF_ThumbFunc = 0x0008,
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SF_NoDeadStrip = 0x0020,
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SF_WeakReference = 0x0040,
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SF_WeakDefinition = 0x0080,
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SF_SymbolResolver = 0x0100,
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SF_AltEntry = 0x0200,
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SF_Cold = 0x0400,
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// Common alignment
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SF_CommonAlignmentMask = 0xF0FF,
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SF_CommonAlignmentShift = 8
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};
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public:
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MCSymbolMachO(const StringMapEntry<bool> *Name, bool isTemporary)
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: MCSymbol(SymbolKindMachO, Name, isTemporary) {}
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// Reference type methods.
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void clearReferenceType() const {
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modifyFlags(0, SF_ReferenceTypeMask);
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}
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void setReferenceTypeUndefinedLazy(bool Value) const {
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modifyFlags(Value ? SF_ReferenceTypeUndefinedLazy : 0,
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SF_ReferenceTypeUndefinedLazy);
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}
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// Other 'desc' methods.
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void setThumbFunc() const {
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modifyFlags(SF_ThumbFunc, SF_ThumbFunc);
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}
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bool isNoDeadStrip() const {
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return getFlags() & SF_NoDeadStrip;
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}
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void setNoDeadStrip() const {
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modifyFlags(SF_NoDeadStrip, SF_NoDeadStrip);
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}
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bool isWeakReference() const {
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return getFlags() & SF_WeakReference;
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}
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void setWeakReference() const {
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modifyFlags(SF_WeakReference, SF_WeakReference);
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}
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bool isWeakDefinition() const {
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return getFlags() & SF_WeakDefinition;
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}
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void setWeakDefinition() const {
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modifyFlags(SF_WeakDefinition, SF_WeakDefinition);
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}
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bool isSymbolResolver() const {
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return getFlags() & SF_SymbolResolver;
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}
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void setSymbolResolver() const {
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modifyFlags(SF_SymbolResolver, SF_SymbolResolver);
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}
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void setAltEntry() const {
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modifyFlags(SF_AltEntry, SF_AltEntry);
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}
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bool isAltEntry() const {
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return getFlags() & SF_AltEntry;
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}
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void setCold() const { modifyFlags(SF_Cold, SF_Cold); }
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bool isCold() const { return getFlags() & SF_Cold; }
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void setDesc(unsigned Value) const {
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assert(Value == (Value & SF_DescFlagsMask) &&
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"Invalid .desc value!");
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setFlags(Value & SF_DescFlagsMask);
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}
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/// Get the encoded value of the flags as they will be emitted in to
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/// the MachO binary
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uint16_t getEncodedFlags(bool EncodeAsAltEntry) const {
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uint16_t Flags = getFlags();
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// Common alignment is packed into the 'desc' bits.
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if (isCommon()) {
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if (unsigned Align = getCommonAlignment()) {
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unsigned Log2Size = Log2_32(Align);
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assert((1U << Log2Size) == Align && "Invalid 'common' alignment!");
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if (Log2Size > 15)
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report_fatal_error("invalid 'common' alignment '" +
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Twine(Align) + "' for '" + getName() + "'",
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false);
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Flags = (Flags & SF_CommonAlignmentMask) |
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(Log2Size << SF_CommonAlignmentShift);
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}
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}
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if (EncodeAsAltEntry)
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Flags |= SF_AltEntry;
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return Flags;
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}
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static bool classof(const MCSymbol *S) { return S->isMachO(); }
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};
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}
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#endif
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