[clang] [llvm] [MC] Emit a jump table size section (PR #101962)
Nabeel Omer via cfe-commits
cfe-commits at lists.llvm.org
Mon Aug 5 04:24:32 PDT 2024
https://github.com/omern1 created https://github.com/llvm/llvm-project/pull/101962
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.
>From 14f3cb82f0d7e69261bd7e1317bd66392e9a2c2b Mon Sep 17 00:00:00 2001
From: Nabeel Omer <Nabeel.Omer at sony.com>
Date: Mon, 5 Aug 2024 11:50:18 +0100
Subject: [PATCH] [MC] Emit a jump table size section
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.
---
clang/lib/Driver/ToolChains/PS4CPU.cpp | 8 ++
clang/test/Driver/ps4-ps5-toolchain.c | 5 +
llvm/docs/Extensions.rst | 6 ++
llvm/include/llvm/BinaryFormat/ELF.h | 1 +
llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp | 26 +++++
llvm/lib/MC/MCParser/ELFAsmParser.cpp | 2 +
llvm/lib/MC/MCSectionELF.cpp | 2 +
llvm/lib/Object/ELF.cpp | 1 +
.../CodeGen/X86/jump-table-size-section.ll | 97 +++++++++++++++++++
9 files changed, 148 insertions(+)
create mode 100644 llvm/test/CodeGen/X86/jump-table-size-section.ll
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", at 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
+}
More information about the cfe-commits
mailing list