[llvm] 1952dba - [MC,ELF] Extract CREL encoder code
Fangrui Song via llvm-commits
llvm-commits at lists.llvm.org
Mon Jul 8 09:28:19 PDT 2024
Author: Fangrui Song
Date: 2024-07-08T09:28:09-07:00
New Revision: 1952dba49abdda848512d11fc68c031a0a21ec50
URL: https://github.com/llvm/llvm-project/commit/1952dba49abdda848512d11fc68c031a0a21ec50
DIFF: https://github.com/llvm/llvm-project/commit/1952dba49abdda848512d11fc68c031a0a21ec50.diff
LOG: [MC,ELF] Extract CREL encoder code
The extracted ELFObjectWriter.cpp code will be reused by llvm-objcopy
support (#97521).
Added:
llvm/include/llvm/MC/MCELFExtras.h
Modified:
llvm/include/llvm/BinaryFormat/ELF.h
llvm/lib/MC/ELFObjectWriter.cpp
Removed:
################################################################################
diff --git a/llvm/include/llvm/BinaryFormat/ELF.h b/llvm/include/llvm/BinaryFormat/ELF.h
index 32cc9ff8cbb78..456cffff6b4a7 100644
--- a/llvm/include/llvm/BinaryFormat/ELF.h
+++ b/llvm/include/llvm/BinaryFormat/ELF.h
@@ -22,6 +22,7 @@
#include "llvm/ADT/StringRef.h"
#include <cstdint>
#include <cstring>
+#include <type_traits>
namespace llvm {
namespace ELF {
@@ -1430,6 +1431,14 @@ struct Elf64_Rela {
}
};
+// In-memory representation of CREL. The serialized representation uses LEB128.
+template <bool Is64> struct Elf_Crel {
+ std::conditional_t<Is64, uint64_t, uint32_t> r_offset;
+ uint32_t r_symidx;
+ uint32_t r_type;
+ std::conditional_t<Is64, int64_t, int32_t> r_addend;
+};
+
// Relocation entry without explicit addend or info (relative relocations only).
typedef Elf64_Xword Elf64_Relr; // offset/bitmap for relative relocations
diff --git a/llvm/include/llvm/MC/MCELFExtras.h b/llvm/include/llvm/MC/MCELFExtras.h
new file mode 100644
index 0000000000000..2c0718886a11b
--- /dev/null
+++ b/llvm/include/llvm/MC/MCELFExtras.h
@@ -0,0 +1,63 @@
+//===- MCELFExtras.h - Extra functions for ELF ------------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_MC_MCELFEXTRAS_H
+#define LLVM_MC_MCELFEXTRAS_H
+
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/bit.h"
+#include "llvm/BinaryFormat/ELF.h"
+#include "llvm/Support/LEB128.h"
+#include "llvm/Support/raw_ostream.h"
+
+#include <cstdint>
+#include <type_traits>
+
+namespace llvm::ELF {
+// Encode relocations as CREL to OS. ToCrel is responsible for converting a
+// const RelocsTy & to an Elf_Crel.
+template <bool Is64, class RelocsTy, class F>
+void encodeCrel(raw_ostream &OS, RelocsTy Relocs, F ToCrel) {
+ using uint = std::conditional_t<Is64, uint64_t, uint32_t>;
+ uint OffsetMask = 8, Offset = 0, Addend = 0;
+ uint32_t SymIdx = 0, Type = 0;
+ for (const auto &R : Relocs)
+ OffsetMask |= ToCrel(R).r_offset;
+ const int Shift = llvm::countr_zero(OffsetMask);
+ encodeULEB128(Relocs.size() * 8 + ELF::CREL_HDR_ADDEND + Shift, OS);
+ for (const auto &R : Relocs) {
+ auto CR = ToCrel(R);
+ auto DeltaOffset = static_cast<uint>((CR.r_offset - Offset) >> Shift);
+ Offset = CR.r_offset;
+ uint8_t B = (DeltaOffset << 3) + (SymIdx != CR.r_symidx) +
+ (Type != CR.r_type ? 2 : 0) +
+ (Addend != uint(CR.r_addend) ? 4 : 0);
+ if (DeltaOffset < 0x10) {
+ OS << char(B);
+ } else {
+ OS << char(B | 0x80);
+ encodeULEB128(DeltaOffset >> 4, OS);
+ }
+ // Delta symidx/type/addend members (SLEB128).
+ if (B & 1) {
+ encodeSLEB128(static_cast<int32_t>(CR.r_symidx - SymIdx), OS);
+ SymIdx = CR.r_symidx;
+ }
+ if (B & 2) {
+ encodeSLEB128(static_cast<int32_t>(CR.r_type - Type), OS);
+ Type = CR.r_type;
+ }
+ if (B & 4) {
+ encodeSLEB128(std::make_signed_t<uint>(CR.r_addend - Addend), OS);
+ Addend = CR.r_addend;
+ }
+ }
+}
+} // namespace llvm::ELF
+
+#endif
diff --git a/llvm/lib/MC/ELFObjectWriter.cpp b/llvm/lib/MC/ELFObjectWriter.cpp
index 5cba6eb15b5c9..59d796b419b35 100644
--- a/llvm/lib/MC/ELFObjectWriter.cpp
+++ b/llvm/lib/MC/ELFObjectWriter.cpp
@@ -23,6 +23,7 @@
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCContext.h"
+#include "llvm/MC/MCELFExtras.h"
#include "llvm/MC/MCELFObjectWriter.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCFixup.h"
@@ -903,44 +904,14 @@ void ELFWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
WriteWord(EntrySize); // sh_entsize
}
-template <class uint>
+template <bool Is64>
static void encodeCrel(ArrayRef<ELFRelocationEntry> Relocs, raw_ostream &OS) {
- uint OffsetMask = 8, Offset = 0, Addend = 0;
- uint32_t SymIdx = 0, Type = 0;
- // hdr & 4 indicates 3 flag bits in delta offset and flags members.
- for (const ELFRelocationEntry &Entry : Relocs)
- OffsetMask |= Entry.Offset;
- const int Shift = llvm::countr_zero(OffsetMask);
- encodeULEB128(Relocs.size() * 8 + ELF::CREL_HDR_ADDEND + Shift, OS);
- for (const ELFRelocationEntry &Entry : Relocs) {
- // The delta offset and flags member may be larger than uint64_t. Special
- // case the first byte (3 flag bits and 4 offset bits). Other ULEB128 bytes
- // encode the remaining delta offset bits.
- auto DeltaOffset = static_cast<uint>((Entry.Offset - Offset) >> Shift);
- Offset = Entry.Offset;
- uint32_t CurSymIdx = Entry.Symbol ? Entry.Symbol->getIndex() : 0;
- uint8_t B = (DeltaOffset << 3) + (SymIdx != CurSymIdx) +
- (Type != Entry.Type ? 2 : 0) + (Addend != Entry.Addend ? 4 : 0);
- if (DeltaOffset < 0x10) {
- OS << char(B);
- } else {
- OS << char(B | 0x80);
- encodeULEB128(DeltaOffset >> 4, OS);
- }
- // Delta symidx/type/addend members (SLEB128).
- if (B & 1) {
- encodeSLEB128(static_cast<int32_t>(CurSymIdx - SymIdx), OS);
- SymIdx = CurSymIdx;
- }
- if (B & 2) {
- encodeSLEB128(static_cast<int32_t>(Entry.Type - Type), OS);
- Type = Entry.Type;
- }
- if (B & 4) {
- encodeSLEB128(std::make_signed_t<uint>(Entry.Addend - Addend), OS);
- Addend = Entry.Addend;
- }
- }
+ using uint = std::conditional_t<Is64, uint64_t, uint32_t>;
+ ELF::encodeCrel<Is64>(OS, Relocs, [&](const ELFRelocationEntry &R) {
+ uint32_t SymIdx = R.Symbol ? R.Symbol->getIndex() : 0;
+ return ELF::Elf_Crel<Is64>{static_cast<uint>(R.Offset), SymIdx, R.Type,
+ std::make_signed_t<uint>(R.Addend)};
+ });
}
void ELFWriter::writeRelocations(const MCAssembler &Asm,
@@ -989,9 +960,9 @@ void ELFWriter::writeRelocations(const MCAssembler &Asm,
}
} else if (TO && TO->Crel) {
if (is64Bit())
- encodeCrel<uint64_t>(Relocs, W.OS);
+ encodeCrel<true>(Relocs, W.OS);
else
- encodeCrel<uint32_t>(Relocs, W.OS);
+ encodeCrel<false>(Relocs, W.OS);
} else {
for (const ELFRelocationEntry &Entry : Relocs) {
uint32_t Symidx = Entry.Symbol ? Entry.Symbol->getIndex() : 0;
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