[MC] Emit a jump table size section #101962
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This patch will make LLVM emit a jump table size section containing tuples of (jump table address, entry count) in object files. This section is useful for tools that need to statically reconstruct the control flow of executables. The name of the new section is .debug_llvm_jump_table_sizes because that makes both llvm-strip and GNU strip remove it. At the moment this is only enabled by default for the PS5 target.
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@llvm/pr-subscribers-clang @llvm/pr-subscribers-llvm-binary-utilities Author: Nabeel Omer (omern1) ChangesThis patch will make LLVM emit a jump table size section containing tuples of (jump table address, entry count) in object files. This section is useful for tools that need to statically reconstruct the control flow of executables. The name of the new section is .debug_llvm_jump_table_sizes because that makes both llvm-strip and GNU strip remove it. At the moment this is only enabled by default for the PS5 target. Full diff: https://github.com/llvm/llvm-project/pull/101962.diff 9 Files Affected:
diff --git a/clang/lib/Driver/ToolChains/PS4CPU.cpp b/clang/lib/Driver/ToolChains/PS4CPU.cpp
index a9e612c44da06..f9a9e995fff8e 100644
--- a/clang/lib/Driver/ToolChains/PS4CPU.cpp
+++ b/clang/lib/Driver/ToolChains/PS4CPU.cpp
@@ -265,6 +265,8 @@ void tools::PS5cpu::Linker::ConstructJob(Compilation &C, const JobAction &JA,
CmdArgs.push_back(D.getLTOMode() == LTOK_Thin ? "--lto=thin"
: "--lto=full");
+ AddLTOFlag("-emit-jump-table-sizes-section");
+
if (UseJMC)
AddLTOFlag("-enable-jmc-instrument");
@@ -483,6 +485,12 @@ void toolchains::PS4PS5Base::addClangTargetOptions(
else
CC1Args.push_back("-fvisibility-externs-nodllstorageclass=keep");
}
+
+ // Enable jump table sizes section for PS5.
+ if (getTriple().isPS5()) {
+ CC1Args.push_back("-mllvm");
+ CC1Args.push_back("-emit-jump-table-sizes-section");
+ }
}
// PS4 toolchain.
diff --git a/clang/test/Driver/ps4-ps5-toolchain.c b/clang/test/Driver/ps4-ps5-toolchain.c
index 444e9df24714b..c9987c2b5758b 100644
--- a/clang/test/Driver/ps4-ps5-toolchain.c
+++ b/clang/test/Driver/ps4-ps5-toolchain.c
@@ -11,3 +11,8 @@
// RUN: %clang %s -### -target x86_64-sie-ps5 -flto 2>&1 | FileCheck %s --check-prefix=LTO
// LTO-NOT: error:
// LTO-NOT: unable to pass LLVM bit-code
+
+// Verify that the jump table sizes section is enabled.
+// RUN: %clang %s -target x86_64-sie-ps5 -### 2>&1 | FileCheck -check-prefix=JUMPTABLESIZES %s
+// JUMPTABLESIZES: "-mllvm" "-emit-jump-table-sizes-section"
+// JUMPTABLESIZES: "-plugin-opt=-emit-jump-table-sizes-section"
diff --git a/llvm/docs/Extensions.rst b/llvm/docs/Extensions.rst
index 74ca8cb0aa687..0e209f3fe5cc0 100644
--- a/llvm/docs/Extensions.rst
+++ b/llvm/docs/Extensions.rst
@@ -554,6 +554,12 @@ time. This section is generated when the compiler enables fat LTO. This section
has the ``SHF_EXCLUDE`` flag so that it is stripped from the final executable
or shared library.
+``SHT_LLVM_JT_SIZES`` Section (Jump table addresses and sizes)
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+This section stores pairs of (jump table address, number of entries).
+This information is useful for tools that need to statically reconstruct
+the control flow of executables.
+
CodeView-Dependent
------------------
diff --git a/llvm/include/llvm/BinaryFormat/ELF.h b/llvm/include/llvm/BinaryFormat/ELF.h
index fb39bb4b10b37..7bec01688783d 100644
--- a/llvm/include/llvm/BinaryFormat/ELF.h
+++ b/llvm/include/llvm/BinaryFormat/ELF.h
@@ -1121,6 +1121,7 @@ enum : unsigned {
SHT_LLVM_BB_ADDR_MAP = 0x6fff4c0a, // LLVM Basic Block Address Map.
SHT_LLVM_OFFLOADING = 0x6fff4c0b, // LLVM device offloading data.
SHT_LLVM_LTO = 0x6fff4c0c, // .llvm.lto for fat LTO.
+ SHT_LLVM_JT_SIZES = 0x6fff4c0d, // LLVM jump tables sizes.
// Android's experimental support for SHT_RELR sections.
// https://android.googlesource.com/platform/bionic/+/b7feec74547f84559a1467aca02708ff61346d2a/libc/include/elf.h#512
SHT_ANDROID_RELR = 0x6fffff00, // Relocation entries; only offsets.
diff --git a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
index b64fe83959eb1..05624d2728bfd 100644
--- a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
@@ -107,6 +107,7 @@
#include "llvm/Pass.h"
#include "llvm/Remarks/RemarkStreamer.h"
#include "llvm/Support/Casting.h"
+#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/FileSystem.h"
@@ -155,6 +156,11 @@ static cl::bits<PGOMapFeaturesEnum> PgoAnalysisMapFeatures(
"Enable extended information within the SHT_LLVM_BB_ADDR_MAP that is "
"extracted from PGO related analysis."));
+static cl::opt<bool> EmitJumpTableSizesSection(
+ "emit-jump-table-sizes-section",
+ cl::desc("Emit a section containing jump table addresses and sizes"),
+ cl::Hidden, cl::init(false));
+
STATISTIC(EmittedInsts, "Number of machine instrs printed");
char AsmPrinter::ID = 0;
@@ -2764,6 +2770,26 @@ void AsmPrinter::emitJumpTableInfo() {
for (const MachineBasicBlock *MBB : JTBBs)
emitJumpTableEntry(MJTI, MBB, JTI);
}
+
+ if (EmitJumpTableSizesSection && !JT.empty()) {
+ MCSymbolELF *LinkedToSym = cast<MCSymbolELF>(CurrentFnSym);
+ int Flags = F.hasComdat() ? ELF::SHF_GROUP : 0;
+ StringRef GroupName = F.hasComdat() ? F.getComdat()->getName() : "";
+
+ MCSection *JumpTableSizesSection = OutContext.getELFSection(
+ ".debug_llvm_jump_table_sizes", ELF::SHT_LLVM_JT_SIZES, Flags, 0, GroupName,
+ F.hasComdat(), MCSection::NonUniqueID, LinkedToSym);
+
+ OutStreamer->switchSection(JumpTableSizesSection);
+
+ for (unsigned JTI = 0, E = JT.size(); JTI != E; ++JTI) {
+ const std::vector<MachineBasicBlock *> &JTBBs = JT[JTI].MBBs;
+ OutStreamer->emitSymbolValue(GetJTISymbol(JTI),
+ TM.getProgramPointerSize());
+ OutStreamer->emitIntValue(JTBBs.size(), TM.getProgramPointerSize());
+ }
+ }
+
if (!JTInDiffSection)
OutStreamer->emitDataRegion(MCDR_DataRegionEnd);
}
diff --git a/llvm/lib/MC/MCParser/ELFAsmParser.cpp b/llvm/lib/MC/MCParser/ELFAsmParser.cpp
index e8a22d3defd6e..c4536441665fa 100644
--- a/llvm/lib/MC/MCParser/ELFAsmParser.cpp
+++ b/llvm/lib/MC/MCParser/ELFAsmParser.cpp
@@ -677,6 +677,8 @@ bool ELFAsmParser::ParseSectionArguments(bool IsPush, SMLoc loc) {
Type = ELF::SHT_LLVM_OFFLOADING;
else if (TypeName == "llvm_lto")
Type = ELF::SHT_LLVM_LTO;
+ else if (TypeName == "llvm_jt_sizes")
+ Type = ELF::SHT_LLVM_JT_SIZES;
else if (TypeName.getAsInteger(0, Type))
return TokError("unknown section type");
}
diff --git a/llvm/lib/MC/MCSectionELF.cpp b/llvm/lib/MC/MCSectionELF.cpp
index 5cd6590fb626d..25e62b70b5e2a 100644
--- a/llvm/lib/MC/MCSectionELF.cpp
+++ b/llvm/lib/MC/MCSectionELF.cpp
@@ -172,6 +172,8 @@ void MCSectionELF::printSwitchToSection(const MCAsmInfo &MAI, const Triple &T,
OS << "llvm_offloading";
else if (Type == ELF::SHT_LLVM_LTO)
OS << "llvm_lto";
+ else if (Type == ELF::SHT_LLVM_JT_SIZES)
+ OS << "llvm_jt_sizes";
else
OS << "0x" << Twine::utohexstr(Type);
diff --git a/llvm/lib/Object/ELF.cpp b/llvm/lib/Object/ELF.cpp
index e47a40b8715dd..c66736fb2c919 100644
--- a/llvm/lib/Object/ELF.cpp
+++ b/llvm/lib/Object/ELF.cpp
@@ -319,6 +319,7 @@ StringRef llvm::object::getELFSectionTypeName(uint32_t Machine, unsigned Type) {
STRINGIFY_ENUM_CASE(ELF, SHT_LLVM_BB_ADDR_MAP);
STRINGIFY_ENUM_CASE(ELF, SHT_LLVM_OFFLOADING);
STRINGIFY_ENUM_CASE(ELF, SHT_LLVM_LTO);
+ STRINGIFY_ENUM_CASE(ELF, SHT_LLVM_JT_SIZES)
STRINGIFY_ENUM_CASE(ELF, SHT_GNU_ATTRIBUTES);
STRINGIFY_ENUM_CASE(ELF, SHT_GNU_HASH);
STRINGIFY_ENUM_CASE(ELF, SHT_GNU_verdef);
diff --git a/llvm/test/CodeGen/X86/jump-table-size-section.ll b/llvm/test/CodeGen/X86/jump-table-size-section.ll
new file mode 100644
index 0000000000000..4a259aecd72b6
--- /dev/null
+++ b/llvm/test/CodeGen/X86/jump-table-size-section.ll
@@ -0,0 +1,97 @@
+; RUN: llc %s -o - -emit-jump-table-sizes-section -verify-machineinstrs --relocation-model=pic | FileCheck --check-prefix=CHECK %s
+; RUN: llc %s -o - -verify-machineinstrs --relocation-model=pic | FileCheck --check-prefix=NOFLAG %s
+
+; This test verifies the jump table size section. Currently only enabled by default on the PS5 target.
+
+$foo1 = comdat any
+
+; Ensure proper comdat handling.
+define void @foo1(i32 %x, ptr %to) comdat {
+
+; CHECK-LABEL: foo1
+; CHECK: .section .debug_llvm_jump_table_sizes,"G",@llvm_jt_sizes,foo1,comdat
+; CHECK-NEXT: .quad .LJTI0_0
+; CHECK-NEXT: .quad 6
+
+; NOFLAG-LABEL: foo1
+; NOFLAG-NOT: .section .debug_llvm_jump_table_sizes
+
+entry:
+ switch i32 %x, label %default [
+ i32 0, label %bb0
+ i32 1, label %bb1
+ i32 2, label %bb2
+ i32 3, label %bb3
+ i32 4, label %bb4
+ i32 5, label %bb4
+ ]
+bb0:
+ store i32 0, ptr %to
+ br label %exit
+bb1:
+ store i32 1, ptr %to
+ br label %exit
+bb2:
+ store i32 2, ptr %to
+ br label %exit
+bb3:
+ store i32 3, ptr %to
+ br label %exit
+bb4:
+ store i32 4, ptr %to
+ br label %exit
+exit:
+ ret void
+default:
+ unreachable
+}
+
+define void @foo2(i32 %x, ptr %to) {
+
+; CHECK-LABEL: foo2
+; CHECK: .section .debug_llvm_jump_table_sizes
+; CHECK-NEXT: .quad .LJTI1_0
+; CHECK-NEXT: .quad 5
+
+; NOFLAG-LABEL: foo2
+; NOFLAG-NOT: .section .debug_llvm_jump_table_sizes
+
+entry:
+ switch i32 %x, label %default [
+ i32 0, label %bb0
+ i32 1, label %bb1
+ i32 2, label %bb2
+ i32 3, label %bb3
+ i32 4, label %bb4
+ ]
+bb0:
+ store i32 0, ptr %to
+ br label %exit
+bb1:
+ store i32 1, ptr %to
+ br label %exit
+bb2:
+ store i32 2, ptr %to
+ br label %exit
+bb3:
+ store i32 3, ptr %to
+ br label %exit
+bb4:
+ store i32 4, ptr %to
+ br label %exit
+exit:
+ ret void
+default:
+ unreachable
+}
+
+; Ensure that the section isn't produced if there is no jump table.
+
+define void @foo3(i32 %x, ptr %to) {
+
+; CHECK-LABEL: foo3
+; CHECK-NOT: .section .debug_llvm_jump_table_sizes
+
+exit:
+ ret void
+}
|
|
@llvm/pr-subscribers-backend-x86 Author: Nabeel Omer (omern1) ChangesThis patch will make LLVM emit a jump table size section containing tuples of (jump table address, entry count) in object files. This section is useful for tools that need to statically reconstruct the control flow of executables. The name of the new section is .debug_llvm_jump_table_sizes because that makes both llvm-strip and GNU strip remove it. At the moment this is only enabled by default for the PS5 target. Full diff: https://github.com/llvm/llvm-project/pull/101962.diff 9 Files Affected:
diff --git a/clang/lib/Driver/ToolChains/PS4CPU.cpp b/clang/lib/Driver/ToolChains/PS4CPU.cpp
index a9e612c44da06..f9a9e995fff8e 100644
--- a/clang/lib/Driver/ToolChains/PS4CPU.cpp
+++ b/clang/lib/Driver/ToolChains/PS4CPU.cpp
@@ -265,6 +265,8 @@ void tools::PS5cpu::Linker::ConstructJob(Compilation &C, const JobAction &JA,
CmdArgs.push_back(D.getLTOMode() == LTOK_Thin ? "--lto=thin"
: "--lto=full");
+ AddLTOFlag("-emit-jump-table-sizes-section");
+
if (UseJMC)
AddLTOFlag("-enable-jmc-instrument");
@@ -483,6 +485,12 @@ void toolchains::PS4PS5Base::addClangTargetOptions(
else
CC1Args.push_back("-fvisibility-externs-nodllstorageclass=keep");
}
+
+ // Enable jump table sizes section for PS5.
+ if (getTriple().isPS5()) {
+ CC1Args.push_back("-mllvm");
+ CC1Args.push_back("-emit-jump-table-sizes-section");
+ }
}
// PS4 toolchain.
diff --git a/clang/test/Driver/ps4-ps5-toolchain.c b/clang/test/Driver/ps4-ps5-toolchain.c
index 444e9df24714b..c9987c2b5758b 100644
--- a/clang/test/Driver/ps4-ps5-toolchain.c
+++ b/clang/test/Driver/ps4-ps5-toolchain.c
@@ -11,3 +11,8 @@
// RUN: %clang %s -### -target x86_64-sie-ps5 -flto 2>&1 | FileCheck %s --check-prefix=LTO
// LTO-NOT: error:
// LTO-NOT: unable to pass LLVM bit-code
+
+// Verify that the jump table sizes section is enabled.
+// RUN: %clang %s -target x86_64-sie-ps5 -### 2>&1 | FileCheck -check-prefix=JUMPTABLESIZES %s
+// JUMPTABLESIZES: "-mllvm" "-emit-jump-table-sizes-section"
+// JUMPTABLESIZES: "-plugin-opt=-emit-jump-table-sizes-section"
diff --git a/llvm/docs/Extensions.rst b/llvm/docs/Extensions.rst
index 74ca8cb0aa687..0e209f3fe5cc0 100644
--- a/llvm/docs/Extensions.rst
+++ b/llvm/docs/Extensions.rst
@@ -554,6 +554,12 @@ time. This section is generated when the compiler enables fat LTO. This section
has the ``SHF_EXCLUDE`` flag so that it is stripped from the final executable
or shared library.
+``SHT_LLVM_JT_SIZES`` Section (Jump table addresses and sizes)
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+This section stores pairs of (jump table address, number of entries).
+This information is useful for tools that need to statically reconstruct
+the control flow of executables.
+
CodeView-Dependent
------------------
diff --git a/llvm/include/llvm/BinaryFormat/ELF.h b/llvm/include/llvm/BinaryFormat/ELF.h
index fb39bb4b10b37..7bec01688783d 100644
--- a/llvm/include/llvm/BinaryFormat/ELF.h
+++ b/llvm/include/llvm/BinaryFormat/ELF.h
@@ -1121,6 +1121,7 @@ enum : unsigned {
SHT_LLVM_BB_ADDR_MAP = 0x6fff4c0a, // LLVM Basic Block Address Map.
SHT_LLVM_OFFLOADING = 0x6fff4c0b, // LLVM device offloading data.
SHT_LLVM_LTO = 0x6fff4c0c, // .llvm.lto for fat LTO.
+ SHT_LLVM_JT_SIZES = 0x6fff4c0d, // LLVM jump tables sizes.
// Android's experimental support for SHT_RELR sections.
// https://android.googlesource.com/platform/bionic/+/b7feec74547f84559a1467aca02708ff61346d2a/libc/include/elf.h#512
SHT_ANDROID_RELR = 0x6fffff00, // Relocation entries; only offsets.
diff --git a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
index b64fe83959eb1..05624d2728bfd 100644
--- a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
@@ -107,6 +107,7 @@
#include "llvm/Pass.h"
#include "llvm/Remarks/RemarkStreamer.h"
#include "llvm/Support/Casting.h"
+#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/FileSystem.h"
@@ -155,6 +156,11 @@ static cl::bits<PGOMapFeaturesEnum> PgoAnalysisMapFeatures(
"Enable extended information within the SHT_LLVM_BB_ADDR_MAP that is "
"extracted from PGO related analysis."));
+static cl::opt<bool> EmitJumpTableSizesSection(
+ "emit-jump-table-sizes-section",
+ cl::desc("Emit a section containing jump table addresses and sizes"),
+ cl::Hidden, cl::init(false));
+
STATISTIC(EmittedInsts, "Number of machine instrs printed");
char AsmPrinter::ID = 0;
@@ -2764,6 +2770,26 @@ void AsmPrinter::emitJumpTableInfo() {
for (const MachineBasicBlock *MBB : JTBBs)
emitJumpTableEntry(MJTI, MBB, JTI);
}
+
+ if (EmitJumpTableSizesSection && !JT.empty()) {
+ MCSymbolELF *LinkedToSym = cast<MCSymbolELF>(CurrentFnSym);
+ int Flags = F.hasComdat() ? ELF::SHF_GROUP : 0;
+ StringRef GroupName = F.hasComdat() ? F.getComdat()->getName() : "";
+
+ MCSection *JumpTableSizesSection = OutContext.getELFSection(
+ ".debug_llvm_jump_table_sizes", ELF::SHT_LLVM_JT_SIZES, Flags, 0, GroupName,
+ F.hasComdat(), MCSection::NonUniqueID, LinkedToSym);
+
+ OutStreamer->switchSection(JumpTableSizesSection);
+
+ for (unsigned JTI = 0, E = JT.size(); JTI != E; ++JTI) {
+ const std::vector<MachineBasicBlock *> &JTBBs = JT[JTI].MBBs;
+ OutStreamer->emitSymbolValue(GetJTISymbol(JTI),
+ TM.getProgramPointerSize());
+ OutStreamer->emitIntValue(JTBBs.size(), TM.getProgramPointerSize());
+ }
+ }
+
if (!JTInDiffSection)
OutStreamer->emitDataRegion(MCDR_DataRegionEnd);
}
diff --git a/llvm/lib/MC/MCParser/ELFAsmParser.cpp b/llvm/lib/MC/MCParser/ELFAsmParser.cpp
index e8a22d3defd6e..c4536441665fa 100644
--- a/llvm/lib/MC/MCParser/ELFAsmParser.cpp
+++ b/llvm/lib/MC/MCParser/ELFAsmParser.cpp
@@ -677,6 +677,8 @@ bool ELFAsmParser::ParseSectionArguments(bool IsPush, SMLoc loc) {
Type = ELF::SHT_LLVM_OFFLOADING;
else if (TypeName == "llvm_lto")
Type = ELF::SHT_LLVM_LTO;
+ else if (TypeName == "llvm_jt_sizes")
+ Type = ELF::SHT_LLVM_JT_SIZES;
else if (TypeName.getAsInteger(0, Type))
return TokError("unknown section type");
}
diff --git a/llvm/lib/MC/MCSectionELF.cpp b/llvm/lib/MC/MCSectionELF.cpp
index 5cd6590fb626d..25e62b70b5e2a 100644
--- a/llvm/lib/MC/MCSectionELF.cpp
+++ b/llvm/lib/MC/MCSectionELF.cpp
@@ -172,6 +172,8 @@ void MCSectionELF::printSwitchToSection(const MCAsmInfo &MAI, const Triple &T,
OS << "llvm_offloading";
else if (Type == ELF::SHT_LLVM_LTO)
OS << "llvm_lto";
+ else if (Type == ELF::SHT_LLVM_JT_SIZES)
+ OS << "llvm_jt_sizes";
else
OS << "0x" << Twine::utohexstr(Type);
diff --git a/llvm/lib/Object/ELF.cpp b/llvm/lib/Object/ELF.cpp
index e47a40b8715dd..c66736fb2c919 100644
--- a/llvm/lib/Object/ELF.cpp
+++ b/llvm/lib/Object/ELF.cpp
@@ -319,6 +319,7 @@ StringRef llvm::object::getELFSectionTypeName(uint32_t Machine, unsigned Type) {
STRINGIFY_ENUM_CASE(ELF, SHT_LLVM_BB_ADDR_MAP);
STRINGIFY_ENUM_CASE(ELF, SHT_LLVM_OFFLOADING);
STRINGIFY_ENUM_CASE(ELF, SHT_LLVM_LTO);
+ STRINGIFY_ENUM_CASE(ELF, SHT_LLVM_JT_SIZES)
STRINGIFY_ENUM_CASE(ELF, SHT_GNU_ATTRIBUTES);
STRINGIFY_ENUM_CASE(ELF, SHT_GNU_HASH);
STRINGIFY_ENUM_CASE(ELF, SHT_GNU_verdef);
diff --git a/llvm/test/CodeGen/X86/jump-table-size-section.ll b/llvm/test/CodeGen/X86/jump-table-size-section.ll
new file mode 100644
index 0000000000000..4a259aecd72b6
--- /dev/null
+++ b/llvm/test/CodeGen/X86/jump-table-size-section.ll
@@ -0,0 +1,97 @@
+; RUN: llc %s -o - -emit-jump-table-sizes-section -verify-machineinstrs --relocation-model=pic | FileCheck --check-prefix=CHECK %s
+; RUN: llc %s -o - -verify-machineinstrs --relocation-model=pic | FileCheck --check-prefix=NOFLAG %s
+
+; This test verifies the jump table size section. Currently only enabled by default on the PS5 target.
+
+$foo1 = comdat any
+
+; Ensure proper comdat handling.
+define void @foo1(i32 %x, ptr %to) comdat {
+
+; CHECK-LABEL: foo1
+; CHECK: .section .debug_llvm_jump_table_sizes,"G",@llvm_jt_sizes,foo1,comdat
+; CHECK-NEXT: .quad .LJTI0_0
+; CHECK-NEXT: .quad 6
+
+; NOFLAG-LABEL: foo1
+; NOFLAG-NOT: .section .debug_llvm_jump_table_sizes
+
+entry:
+ switch i32 %x, label %default [
+ i32 0, label %bb0
+ i32 1, label %bb1
+ i32 2, label %bb2
+ i32 3, label %bb3
+ i32 4, label %bb4
+ i32 5, label %bb4
+ ]
+bb0:
+ store i32 0, ptr %to
+ br label %exit
+bb1:
+ store i32 1, ptr %to
+ br label %exit
+bb2:
+ store i32 2, ptr %to
+ br label %exit
+bb3:
+ store i32 3, ptr %to
+ br label %exit
+bb4:
+ store i32 4, ptr %to
+ br label %exit
+exit:
+ ret void
+default:
+ unreachable
+}
+
+define void @foo2(i32 %x, ptr %to) {
+
+; CHECK-LABEL: foo2
+; CHECK: .section .debug_llvm_jump_table_sizes
+; CHECK-NEXT: .quad .LJTI1_0
+; CHECK-NEXT: .quad 5
+
+; NOFLAG-LABEL: foo2
+; NOFLAG-NOT: .section .debug_llvm_jump_table_sizes
+
+entry:
+ switch i32 %x, label %default [
+ i32 0, label %bb0
+ i32 1, label %bb1
+ i32 2, label %bb2
+ i32 3, label %bb3
+ i32 4, label %bb4
+ ]
+bb0:
+ store i32 0, ptr %to
+ br label %exit
+bb1:
+ store i32 1, ptr %to
+ br label %exit
+bb2:
+ store i32 2, ptr %to
+ br label %exit
+bb3:
+ store i32 3, ptr %to
+ br label %exit
+bb4:
+ store i32 4, ptr %to
+ br label %exit
+exit:
+ ret void
+default:
+ unreachable
+}
+
+; Ensure that the section isn't produced if there is no jump table.
+
+define void @foo3(i32 %x, ptr %to) {
+
+; CHECK-LABEL: foo3
+; CHECK-NOT: .section .debug_llvm_jump_table_sizes
+
+exit:
+ ret void
+}
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✅ With the latest revision this PR passed the C/C++ code formatter. |
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Is there a previous discussion (e.g., RFC) about this? Did you consider alternative approaches? (E.g., just a spontaneous idea, adding a specially named symbol for every jump table where the symbol size is the size of the jump table; entry size (4/8) could be encoded in the name like I'm not a fan of |
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The |
No, this isn't being proposed for the DWARF standard. Though, searching through the DWARF standard I couldn't find anywhere saying that the I feel like there's a case for this prefix as GNU Also, the choice of |
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Conventionally, When designing new sections, we should not adapt to the --strip-all-gnu behavior. Jump tables exhibit diverse structures. For instance, consider llvm/test/CodeGen/ARM/jump-table-tbh.ll and Mach-O's .data_region. |
Thanks, it appears that you're suggesting removing the
Jump tables of type |
compnerd
reviewed
Aug 20, 2024
| @@ -2764,6 +2770,27 @@ void AsmPrinter::emitJumpTableInfo() { | |||
| for (const MachineBasicBlock *MBB : JTBBs) | |||
| emitJumpTableEntry(MJTI, MBB, JTI); | |||
| } | |||
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| if (EmitJumpTableSizesSection && TM.getTargetTriple().isOSBinFormatELF() && | |||
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Outside of flags and section name, this is pretty generic. Why not open this to all object fully formats?
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I've added support for COFF (hopefully correctly). I'm completely unfamiliar with MachO so I suggest that we leave that for a followup.
| @@ -0,0 +1,97 @@ | |||
| ; RUN: llc %s -o - -emit-jump-table-sizes-section -verify-machineinstrs --relocation-model=pic | FileCheck --check-prefix=CHECK %s | |||
| ; RUN: llc %s -o - -verify-machineinstrs --relocation-model=pic | FileCheck --check-prefix=NOFLAG %s | |||
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You will need explicit triples - these tests may be run where the default target is not PS5 and the default object file format is not ELF.
compnerd
reviewed
Aug 31, 2024
| COFF::IMAGE_SCN_CNT_INITIALIZED_DATA | COFF::IMAGE_SCN_MEM_READ | | ||
| COFF::IMAGE_SCN_LNK_COMDAT | COFF::IMAGE_SCN_MEM_DISCARDABLE, | ||
| F.getComdat()->getName(), COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE); | ||
| } else |
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Braces here would be nice to match the other side.
| COFF::IMAGE_SCN_MEM_READ | | ||
| COFF::IMAGE_SCN_MEM_DISCARDABLE); | ||
| } else { | ||
| return; |
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Can you change this to an early return please?
compnerd
approved these changes
Sep 2, 2024
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Hi, I really like this design and am trying to apply it to more architectures, such as x86. However, it seems that the jump table is not properly mapped to the instruction that references it. Do you have any suggestions on how to correctly associate the jump table with the corresponding assembly instruction? Please let me know if I’m misunderstanding anything. |
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Hi @ruotongyu,
I'm not sure what you mean here, this patch is really architecture independent and already works on X86. I maybe be misunderstanding you here though.
That's unfortunately something that I did not have time to do in this patch but #112606 is trying to achieve that. |
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This patch will make LLVM emit a jump table size section containing tuples of (jump table address, entry count) in object files. This section is useful for tools that need to statically reconstruct the control flow of executables.
The name of the new section is .debug_llvm_jump_table_sizes because that makes both llvm-strip and GNU strip remove it.
At the moment this is only enabled by default for the PS5 target.