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relax feature
From 87f6adc2acf635a0a4c294217fb54c55eee3a06c Mon Sep 17 00:00:00 2001
From: Jinyang He <hejinyang@loongson.cn>
Date: Wed, 24 Jan 2024 09:17:49 +0800
Subject: [PATCH 08/14] [LoongArch] Insert nops and emit align reloc when
handle alignment directive (#72962)
Refer to RISCV, we will fix up the alignment if linker relaxation
changes code size and breaks alignment. Insert enough Nops and emit
R_LARCH_ALIGN relocation type so that linker could satisfy the alignment
by removing Nops.
It does so only in sections with the SHF_EXECINSTR flag.
In LoongArch psABI v2.30, R_LARCH_ALIGN requires symbol index. The
lowest 8 bits of addend represent alignment and the other bits of addend
represent the maximum number of bytes to emit.
(cherry picked from commit c51ab483e6c2d991a01179584705b83fbea1940d)
Change-Id: Iba30702c9dda378acfae0b1f1134926fa838a368
---
llvm/lib/MC/MCExpr.cpp | 2 +-
.../MCTargetDesc/LoongArchAsmBackend.cpp | 67 ++++++++++++++++
.../MCTargetDesc/LoongArchAsmBackend.h | 15 ++++
.../MCTargetDesc/LoongArchFixupKinds.h | 4 +-
.../Relocations/align-non-executable.s | 27 +++++++
.../MC/LoongArch/Relocations/relax-addsub.s | 15 +++-
.../MC/LoongArch/Relocations/relax-align.s | 79 +++++++++++++++++++
7 files changed, 205 insertions(+), 4 deletions(-)
create mode 100644 llvm/test/MC/LoongArch/Relocations/align-non-executable.s
create mode 100644 llvm/test/MC/LoongArch/Relocations/relax-align.s
diff --git a/llvm/lib/MC/MCExpr.cpp b/llvm/lib/MC/MCExpr.cpp
index a561fed11179..79808a58d81c 100644
--- a/llvm/lib/MC/MCExpr.cpp
+++ b/llvm/lib/MC/MCExpr.cpp
@@ -711,7 +711,7 @@ static void AttemptToFoldSymbolOffsetDifference(
if (DF) {
Displacement += DF->getContents().size();
} else if (auto *AF = dyn_cast<MCAlignFragment>(FI);
- AF && Layout &&
+ AF && Layout && AF->hasEmitNops() &&
!Asm->getBackend().shouldInsertExtraNopBytesForCodeAlign(
*AF, Count)) {
Displacement += Asm->computeFragmentSize(*Layout, *AF);
diff --git a/llvm/lib/Target/LoongArch/MCTargetDesc/LoongArchAsmBackend.cpp b/llvm/lib/Target/LoongArch/MCTargetDesc/LoongArchAsmBackend.cpp
index 8d82327b2e2b..8c482356402f 100644
--- a/llvm/lib/Target/LoongArch/MCTargetDesc/LoongArchAsmBackend.cpp
+++ b/llvm/lib/Target/LoongArch/MCTargetDesc/LoongArchAsmBackend.cpp
@@ -17,10 +17,13 @@
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCELFObjectWriter.h"
+#include "llvm/MC/MCExpr.h"
+#include "llvm/MC/MCSection.h"
#include "llvm/MC/MCValue.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/EndianStream.h"
#include "llvm/Support/LEB128.h"
+#include "llvm/Support/MathExtras.h"
#define DEBUG_TYPE "loongarch-asmbackend"
@@ -177,6 +180,70 @@ void LoongArchAsmBackend::applyFixup(const MCAssembler &Asm,
}
}
+// Linker relaxation may change code size. We have to insert Nops
+// for .align directive when linker relaxation enabled. So then Linker
+// could satisfy alignment by removing Nops.
+// The function returns the total Nops Size we need to insert.
+bool LoongArchAsmBackend::shouldInsertExtraNopBytesForCodeAlign(
+ const MCAlignFragment &AF, unsigned &Size) {
+ // Calculate Nops Size only when linker relaxation enabled.
+ if (!AF.getSubtargetInfo()->hasFeature(LoongArch::FeatureRelax))
+ return false;
+
+ // Ignore alignment if MaxBytesToEmit is less than the minimum Nop size.
+ const unsigned MinNopLen = 4;
+ if (AF.getMaxBytesToEmit() < MinNopLen)
+ return false;
+ Size = AF.getAlignment().value() - MinNopLen;
+ return AF.getAlignment() > MinNopLen;
+}
+
+// We need to insert R_LARCH_ALIGN relocation type to indicate the
+// position of Nops and the total bytes of the Nops have been inserted
+// when linker relaxation enabled.
+// The function inserts fixup_loongarch_align fixup which eventually will
+// transfer to R_LARCH_ALIGN relocation type.
+// The improved R_LARCH_ALIGN requires symbol index. The lowest 8 bits of
+// addend represent alignment and the other bits of addend represent the
+// maximum number of bytes to emit. The maximum number of bytes is zero
+// means ignore the emit limit.
+bool LoongArchAsmBackend::shouldInsertFixupForCodeAlign(
+ MCAssembler &Asm, const MCAsmLayout &Layout, MCAlignFragment &AF) {
+ // Insert the fixup only when linker relaxation enabled.
+ if (!AF.getSubtargetInfo()->hasFeature(LoongArch::FeatureRelax))
+ return false;
+
+ // Calculate total Nops we need to insert. If there are none to insert
+ // then simply return.
+ unsigned Count;
+ if (!shouldInsertExtraNopBytesForCodeAlign(AF, Count))
+ return false;
+
+ MCSection *Sec = AF.getParent();
+ MCContext &Ctx = Asm.getContext();
+ const MCExpr *Dummy = MCConstantExpr::create(0, Ctx);
+ // Create fixup_loongarch_align fixup.
+ MCFixup Fixup =
+ MCFixup::create(0, Dummy, MCFixupKind(LoongArch::fixup_loongarch_align));
+ const MCSymbolRefExpr *MCSym = getSecToAlignSym()[Sec];
+ if (MCSym == nullptr) {
+ // Create a symbol and make the value of symbol is zero.
+ MCSymbol *Sym = Ctx.createNamedTempSymbol("la-relax-align");
+ Sym->setFragment(&*Sec->getBeginSymbol()->getFragment());
+ Asm.registerSymbol(*Sym);
+ MCSym = MCSymbolRefExpr::create(Sym, Ctx);
+ getSecToAlignSym()[Sec] = MCSym;
+ }
+
+ uint64_t FixedValue = 0;
+ unsigned Lo = Log2_64(Count) + 1;
+ unsigned Hi = AF.getMaxBytesToEmit() >= Count ? 0 : AF.getMaxBytesToEmit();
+ MCValue Value = MCValue::get(MCSym, nullptr, Hi << 8 | Lo);
+ Asm.getWriter().recordRelocation(Asm, Layout, &AF, Fixup, Value, FixedValue);
+
+ return true;
+}
+
bool LoongArchAsmBackend::shouldForceRelocation(const MCAssembler &Asm,
const MCFixup &Fixup,
const MCValue &Target) {
diff --git a/llvm/lib/Target/LoongArch/MCTargetDesc/LoongArchAsmBackend.h b/llvm/lib/Target/LoongArch/MCTargetDesc/LoongArchAsmBackend.h
index 657f5ca5e731..71bbd003888a 100644
--- a/llvm/lib/Target/LoongArch/MCTargetDesc/LoongArchAsmBackend.h
+++ b/llvm/lib/Target/LoongArch/MCTargetDesc/LoongArchAsmBackend.h
@@ -17,7 +17,9 @@
#include "MCTargetDesc/LoongArchFixupKinds.h"
#include "MCTargetDesc/LoongArchMCTargetDesc.h"
#include "llvm/MC/MCAsmBackend.h"
+#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCFixupKindInfo.h"
+#include "llvm/MC/MCSection.h"
#include "llvm/MC/MCSubtargetInfo.h"
namespace llvm {
@@ -27,6 +29,7 @@ class LoongArchAsmBackend : public MCAsmBackend {
uint8_t OSABI;
bool Is64Bit;
const MCTargetOptions &TargetOptions;
+ DenseMap<MCSection *, const MCSymbolRefExpr *> SecToAlignSym;
public:
LoongArchAsmBackend(const MCSubtargetInfo &STI, uint8_t OSABI, bool Is64Bit,
@@ -45,6 +48,15 @@ public:
uint64_t Value, bool IsResolved,
const MCSubtargetInfo *STI) const override;
+ // Return Size with extra Nop Bytes for alignment directive in code section.
+ bool shouldInsertExtraNopBytesForCodeAlign(const MCAlignFragment &AF,
+ unsigned &Size) override;
+
+ // Insert target specific fixup type for alignment directive in code section.
+ bool shouldInsertFixupForCodeAlign(MCAssembler &Asm,
+ const MCAsmLayout &Layout,
+ MCAlignFragment &AF) override;
+
bool shouldForceRelocation(const MCAssembler &Asm, const MCFixup &Fixup,
const MCValue &Target) override;
@@ -79,6 +91,9 @@ public:
std::unique_ptr<MCObjectTargetWriter>
createObjectTargetWriter() const override;
const MCTargetOptions &getTargetOptions() const { return TargetOptions; }
+ DenseMap<MCSection *, const MCSymbolRefExpr *> &getSecToAlignSym() {
+ return SecToAlignSym;
+ }
};
} // end namespace llvm
diff --git a/llvm/lib/Target/LoongArch/MCTargetDesc/LoongArchFixupKinds.h b/llvm/lib/Target/LoongArch/MCTargetDesc/LoongArchFixupKinds.h
index 178fa6e5262b..78414408f21f 100644
--- a/llvm/lib/Target/LoongArch/MCTargetDesc/LoongArchFixupKinds.h
+++ b/llvm/lib/Target/LoongArch/MCTargetDesc/LoongArchFixupKinds.h
@@ -108,7 +108,9 @@ enum Fixups {
// 20-bit fixup corresponding to %gd_hi20(foo) for instruction lu12i.w.
fixup_loongarch_tls_gd_hi20,
// Generate an R_LARCH_RELAX which indicates the linker may relax here.
- fixup_loongarch_relax = FirstLiteralRelocationKind + ELF::R_LARCH_RELAX
+ fixup_loongarch_relax = FirstLiteralRelocationKind + ELF::R_LARCH_RELAX,
+ // Generate an R_LARCH_ALIGN which indicates the linker may fixup align here.
+ fixup_loongarch_align = FirstLiteralRelocationKind + ELF::R_LARCH_ALIGN,
};
} // end namespace LoongArch
} // end namespace llvm
diff --git a/llvm/test/MC/LoongArch/Relocations/align-non-executable.s b/llvm/test/MC/LoongArch/Relocations/align-non-executable.s
new file mode 100644
index 000000000000..47834acd9521
--- /dev/null
+++ b/llvm/test/MC/LoongArch/Relocations/align-non-executable.s
@@ -0,0 +1,27 @@
+## A label difference separated by an alignment directive, when the
+## referenced symbols are in a non-executable section with instructions,
+## should generate ADD/SUB relocations.
+## https://github.com/llvm/llvm-project/pull/76552
+
+# RUN: llvm-mc --filetype=obj --triple=loongarch64 --mattr=+relax %s \
+# RUN: | llvm-readobj -r - | FileCheck --check-prefixes=CHECK,RELAX %s
+# RUN: llvm-mc --filetype=obj --triple=loongarch64 --mattr=-relax %s \
+# RUN: | llvm-readobj -r - | FileCheck %s
+
+.section ".dummy", "a"
+.L1:
+ la.pcrel $t0, sym
+.p2align 3
+.L2:
+.dword .L2 - .L1
+
+# CHECK: Relocations [
+# CHECK-NEXT: Section ({{.*}}) .rela.dummy {
+# CHECK-NEXT: 0x0 R_LARCH_PCALA_HI20 sym 0x0
+# RELAX-NEXT: 0x0 R_LARCH_RELAX - 0x0
+# CHECK-NEXT: 0x4 R_LARCH_PCALA_LO12 sym 0x0
+# RELAX-NEXT: 0x4 R_LARCH_RELAX - 0x0
+# RELAX-NEXT: 0x8 R_LARCH_ADD64 .L2 0x0
+# RELAX-NEXT: 0x8 R_LARCH_SUB64 .L1 0x0
+# CHECK-NEXT: }
+# CHECK-NEXT: ]
diff --git a/llvm/test/MC/LoongArch/Relocations/relax-addsub.s b/llvm/test/MC/LoongArch/Relocations/relax-addsub.s
index cd01332afd0b..18e0ede5e293 100644
--- a/llvm/test/MC/LoongArch/Relocations/relax-addsub.s
+++ b/llvm/test/MC/LoongArch/Relocations/relax-addsub.s
@@ -28,12 +28,23 @@
# RELAX: Relocations [
# RELAX-NEXT: Section ({{.*}}) .rela.text {
+# RELAX-NEXT: 0x4 R_LARCH_ALIGN {{.*}} 0x4
# RELAX-NEXT: 0x10 R_LARCH_PCALA_HI20 .L1 0x0
# RELAX-NEXT: 0x10 R_LARCH_RELAX - 0x0
# RELAX-NEXT: 0x14 R_LARCH_PCALA_LO12 .L1 0x0
# RELAX-NEXT: 0x14 R_LARCH_RELAX - 0x0
# RELAX-NEXT: }
# RELAX-NEXT: Section ({{.*}}) .rela.data {
+# RELAX-NEXT: 0x10 R_LARCH_ADD8 .L3 0x0
+# RELAX-NEXT: 0x10 R_LARCH_SUB8 .L2 0x0
+# RELAX-NEXT: 0x11 R_LARCH_ADD16 .L3 0x0
+# RELAX-NEXT: 0x11 R_LARCH_SUB16 .L2 0x0
+# RELAX-NEXT: 0x13 R_LARCH_ADD32 .L3 0x0
+# RELAX-NEXT: 0x13 R_LARCH_SUB32 .L2 0x0
+# RELAX-NEXT: 0x17 R_LARCH_ADD64 .L3 0x0
+# RELAX-NEXT: 0x17 R_LARCH_SUB64 .L2 0x0
+# RELAX-NEXT: 0x1F R_LARCH_ADD_ULEB128 .L3 0x0
+# RELAX-NEXT: 0x1F R_LARCH_SUB_ULEB128 .L2 0x0
# RELAX-NEXT: 0x20 R_LARCH_ADD8 .L4 0x0
# RELAX-NEXT: 0x20 R_LARCH_SUB8 .L3 0x0
# RELAX-NEXT: 0x21 R_LARCH_ADD16 .L4 0x0
@@ -57,7 +68,7 @@
# RELAX: Hex dump of section '.data':
# RELAX-NEXT: 0x00000000 04040004 00000004 00000000 00000004
-# RELAX-NEXT: 0x00000010 0c0c000c 0000000c 00000000 0000000c
+# RELAX-NEXT: 0x00000010 00000000 00000000 00000000 00000000
# RELAX-NEXT: 0x00000020 00000000 00000000 00000000 00000000
# RELAX-NEXT: 0x00000030 00000000 00000000 00000000 000000
@@ -78,7 +89,7 @@
.word .L2 - .L1
.dword .L2 - .L1
.uleb128 .L2 - .L1
-## TODO Handle alignment directive.
+## With relaxation, emit relocs because the .align makes the diff variable.
.byte .L3 - .L2
.short .L3 - .L2
.word .L3 - .L2
diff --git a/llvm/test/MC/LoongArch/Relocations/relax-align.s b/llvm/test/MC/LoongArch/Relocations/relax-align.s
new file mode 100644
index 000000000000..294fd9fb916c
--- /dev/null
+++ b/llvm/test/MC/LoongArch/Relocations/relax-align.s
@@ -0,0 +1,79 @@
+## The file testing Nop insertion with R_LARCH_ALIGN for relaxation.
+
+# RUN: llvm-mc --filetype=obj --triple=loongarch64 --mattr=-relax %s -o %t
+# RUN: llvm-objdump -d %t | FileCheck %s --check-prefix=INSTR
+# RUN: llvm-readobj -r %t | FileCheck %s --check-prefix=RELOC
+# RUN: llvm-mc --filetype=obj --triple=loongarch64 --mattr=+relax %s -o %t.r
+# RUN: llvm-objdump -d %t.r | FileCheck %s --check-prefixes=INSTR,RELAX-INSTR
+# RUN: llvm-readobj -r %t.r | FileCheck %s --check-prefixes=RELOC,RELAX-RELOC
+
+.text
+break 0
+# INSTR: break 0
+
+## Not emit R_LARCH_ALIGN if alignment directive is less than or equal to
+## minimum code alignment(a.k.a 4).
+.p2align 2
+.p2align 1
+.p2align 0
+
+## Not emit instructions if max emit bytes less than min nop size.
+.p2align 4, , 2
+
+## Not emit R_LARCH_ALIGN if alignment directive with specific padding value.
+## The behavior is the same as GNU assembler.
+break 1
+.p2align 4, 1
+# INSTR-NEXT: break 1
+# INSTR-COUNT-2: 01 01 01 01
+
+break 2
+.p2align 4, 1, 12
+# INSTR-NEXT: break 2
+# INSTR-COUNT-3: 01 01 01 01
+
+break 3
+.p2align 4
+# INSTR-NEXT: break 3
+# INSTR-COUNT-3: nop
+
+break 4
+.p2align 5
+.p2align 4
+# INSTR-NEXT: break 4
+# INSTR-COUNT-3: nop
+# RELAX-INSTR-COUNT-7: nop
+
+break 5
+.p2align 4, , 11
+# INSTR-NEXT: break 5
+# RELAX-INSTR-COUNT-3: nop
+
+break 6
+## Not emit the third parameter.
+.p2align 4, , 12
+# INSTR-NEXT: break 6
+# INSTR-NEXT: nop
+# INSTR-NEXT: nop
+# RELAX-INSTR-NEXT: nop
+
+ret
+# INSNR-NEXT: ret
+
+## Test the symbol index is different from .text.
+.section .text2, "ax"
+.p2align 4
+break 7
+
+# RELOC: Relocations [
+# RELAX-RELOC-NEXT: Section ({{.*}}) .rela.text {
+# RELAX-RELOC-NEXT: 0x24 R_LARCH_ALIGN .Lla-relax-align0 0x4
+# RELAX-RELOC-NEXT: 0x34 R_LARCH_ALIGN .Lla-relax-align0 0x5
+# RELAX-RELOC-NEXT: 0x50 R_LARCH_ALIGN .Lla-relax-align0 0x4
+# RELAX-RELOC-NEXT: 0x60 R_LARCH_ALIGN .Lla-relax-align0 0xB04
+# RELAX-RELOC-NEXT: 0x70 R_LARCH_ALIGN .Lla-relax-align0 0x4
+# RELAX-RELOC-NEXT: }
+# RELAX-RELOC-NEXT: Section ({{.*}}) .rela.text2 {
+# RELAX-RELOC-NEXT: 0x0 R_LARCH_ALIGN .Lla-relax-align1 0x4
+# RELAX-RELOC-NEXT: }
+# RELOC-NEXT: ]
--
2.20.1
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