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llvm-mirror/lib/MC/MCAsmBackend.cpp
Derek Schuff 28f861215e Support dwarf fission for wasm object files
Initial support for dwarf fission sections (-gsplit-dwarf) on wasm.
The most interesting change is support for writing 2 files (.o and .dwo) in the
wasm object writer. My approach moves object-writing logic into its own function
and calls it twice, swapping out the endian::Writer (W) in between calls.
It also splits the import-preparation step into its own function (and skips it when writing a dwo).

Differential Revision: https://reviews.llvm.org/D85685
2020-09-17 14:42:41 -07:00

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4.2 KiB
C++

//===- MCAsmBackend.cpp - Target MC Assembly Backend ----------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "llvm/MC/MCAsmBackend.h"
#include "llvm/ADT/None.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/MC/MCELFObjectWriter.h"
#include "llvm/MC/MCFixupKindInfo.h"
#include "llvm/MC/MCMachObjectWriter.h"
#include "llvm/MC/MCObjectWriter.h"
#include "llvm/MC/MCWasmObjectWriter.h"
#include "llvm/MC/MCWinCOFFObjectWriter.h"
#include "llvm/MC/MCXCOFFObjectWriter.h"
#include <cassert>
#include <cstddef>
#include <cstdint>
using namespace llvm;
MCAsmBackend::MCAsmBackend(support::endianness Endian) : Endian(Endian) {}
MCAsmBackend::~MCAsmBackend() = default;
std::unique_ptr<MCObjectWriter>
MCAsmBackend::createObjectWriter(raw_pwrite_stream &OS) const {
auto TW = createObjectTargetWriter();
switch (TW->getFormat()) {
case Triple::ELF:
return createELFObjectWriter(cast<MCELFObjectTargetWriter>(std::move(TW)), OS,
Endian == support::little);
case Triple::MachO:
return createMachObjectWriter(cast<MCMachObjectTargetWriter>(std::move(TW)),
OS, Endian == support::little);
case Triple::COFF:
return createWinCOFFObjectWriter(
cast<MCWinCOFFObjectTargetWriter>(std::move(TW)), OS);
case Triple::Wasm:
return createWasmObjectWriter(cast<MCWasmObjectTargetWriter>(std::move(TW)),
OS);
case Triple::XCOFF:
return createXCOFFObjectWriter(
cast<MCXCOFFObjectTargetWriter>(std::move(TW)), OS);
default:
llvm_unreachable("unexpected object format");
}
}
std::unique_ptr<MCObjectWriter>
MCAsmBackend::createDwoObjectWriter(raw_pwrite_stream &OS,
raw_pwrite_stream &DwoOS) const {
auto TW = createObjectTargetWriter();
switch (TW->getFormat()) {
case Triple::ELF:
return createELFDwoObjectWriter(
cast<MCELFObjectTargetWriter>(std::move(TW)), OS, DwoOS,
Endian == support::little);
case Triple::Wasm:
return createWasmDwoObjectWriter(
cast<MCWasmObjectTargetWriter>(std::move(TW)), OS, DwoOS);
default:
report_fatal_error("dwo only supported with ELF and Wasm");
}
}
Optional<MCFixupKind> MCAsmBackend::getFixupKind(StringRef Name) const {
return None;
}
const MCFixupKindInfo &MCAsmBackend::getFixupKindInfo(MCFixupKind Kind) const {
static const MCFixupKindInfo Builtins[] = {
{"FK_NONE", 0, 0, 0},
{"FK_Data_1", 0, 8, 0},
{"FK_Data_2", 0, 16, 0},
{"FK_Data_4", 0, 32, 0},
{"FK_Data_8", 0, 64, 0},
{"FK_Data_6b", 0, 6, 0},
{"FK_PCRel_1", 0, 8, MCFixupKindInfo::FKF_IsPCRel},
{"FK_PCRel_2", 0, 16, MCFixupKindInfo::FKF_IsPCRel},
{"FK_PCRel_4", 0, 32, MCFixupKindInfo::FKF_IsPCRel},
{"FK_PCRel_8", 0, 64, MCFixupKindInfo::FKF_IsPCRel},
{"FK_GPRel_1", 0, 8, 0},
{"FK_GPRel_2", 0, 16, 0},
{"FK_GPRel_4", 0, 32, 0},
{"FK_GPRel_8", 0, 64, 0},
{"FK_DTPRel_4", 0, 32, 0},
{"FK_DTPRel_8", 0, 64, 0},
{"FK_TPRel_4", 0, 32, 0},
{"FK_TPRel_8", 0, 64, 0},
{"FK_SecRel_1", 0, 8, 0},
{"FK_SecRel_2", 0, 16, 0},
{"FK_SecRel_4", 0, 32, 0},
{"FK_SecRel_8", 0, 64, 0},
{"FK_Data_Add_1", 0, 8, 0},
{"FK_Data_Add_2", 0, 16, 0},
{"FK_Data_Add_4", 0, 32, 0},
{"FK_Data_Add_8", 0, 64, 0},
{"FK_Data_Add_6b", 0, 6, 0},
{"FK_Data_Sub_1", 0, 8, 0},
{"FK_Data_Sub_2", 0, 16, 0},
{"FK_Data_Sub_4", 0, 32, 0},
{"FK_Data_Sub_8", 0, 64, 0},
{"FK_Data_Sub_6b", 0, 6, 0}};
assert((size_t)Kind <= array_lengthof(Builtins) && "Unknown fixup kind");
return Builtins[Kind];
}
bool MCAsmBackend::fixupNeedsRelaxationAdvanced(
const MCFixup &Fixup, bool Resolved, uint64_t Value,
const MCRelaxableFragment *DF, const MCAsmLayout &Layout,
const bool WasForced) const {
if (!Resolved)
return true;
return fixupNeedsRelaxation(Fixup, Value, DF, Layout);
}