https://github.com/pmur created https://github.com/llvm/llvm-project/pull/184641
I found out these attributes are only support on s390x when prototyping my Rust [rfc](https://github.com/rust-lang/rfcs/pull/3917) for expanded instrumented function support. Also, is this the correct/preferred way to insert nop's on x86? >From 1d7b9d74e864672e507975983881e14a1c067f9f Mon Sep 17 00:00:00 2001 From: Paul Murphy <[email protected]> Date: Tue, 3 Mar 2026 14:43:18 -0600 Subject: [PATCH 1/2] [LLVM][CodeGen][X86] Support mnop-mcount and mrecord-mcount attributes Support mnop-mcount and mrecord-mcount attributes when used with the fentry-call=true attribute. Similar to SystemZ, use the mnop-mcount attribute to place a nop instead of a call to __fentry__. Likewise, use the mrecord-mcount attribute to record the location of the call to fentry (or nop if used with the above) to a section named __mcount_loc. --- llvm/lib/Target/X86/X86ISelDAGToDAG.cpp | 14 ++++++++-- llvm/lib/Target/X86/X86MCInstLower.cpp | 18 ++++++++++++ llvm/test/CodeGen/X86/mnop-mcount-01.ll | 26 ++++++++++++++++++ llvm/test/CodeGen/X86/mnop-mcount-02.ll | 10 +++++++ llvm/test/CodeGen/X86/mrecord-mcount-01.ll | 32 ++++++++++++++++++++++ llvm/test/CodeGen/X86/mrecord-mcount-02.ll | 10 +++++++ 6 files changed, 107 insertions(+), 3 deletions(-) create mode 100644 llvm/test/CodeGen/X86/mnop-mcount-01.ll create mode 100644 llvm/test/CodeGen/X86/mnop-mcount-02.ll create mode 100644 llvm/test/CodeGen/X86/mrecord-mcount-01.ll create mode 100644 llvm/test/CodeGen/X86/mrecord-mcount-02.ll diff --git a/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp b/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp index 101ea3e231a5c..aa7efb8a05e1c 100644 --- a/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp +++ b/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp @@ -179,11 +179,19 @@ namespace { bool runOnMachineFunction(MachineFunction &MF) override { // Reset the subtarget each time through. Subtarget = &MF.getSubtarget<X86Subtarget>(); - IndirectTlsSegRefs = MF.getFunction().hasFnAttribute( - "indirect-tls-seg-refs"); + const Function &F = MF.getFunction(); + + IndirectTlsSegRefs = F.hasFnAttribute("indirect-tls-seg-refs"); + + if (F.getFnAttribute("fentry-call").getValueAsString() != "true") { + if (F.hasFnAttribute("mnop-mcount")) + report_fatal_error("mnop-mcount only supported with fentry-call"); + if (F.hasFnAttribute("mrecord-mcount")) + report_fatal_error("mrecord-mcount only supported with fentry-call"); + } // OptFor[Min]Size are used in pattern predicates that isel is matching. - OptForMinSize = MF.getFunction().hasMinSize(); + OptForMinSize = F.hasMinSize(); return SelectionDAGISel::runOnMachineFunction(MF); } diff --git a/llvm/lib/Target/X86/X86MCInstLower.cpp b/llvm/lib/Target/X86/X86MCInstLower.cpp index 4ef4718e1b01c..8bbd40d973fab 100644 --- a/llvm/lib/Target/X86/X86MCInstLower.cpp +++ b/llvm/lib/Target/X86/X86MCInstLower.cpp @@ -26,6 +26,7 @@ #include "llvm/ADT/STLExtras.h" #include "llvm/ADT/SmallString.h" #include "llvm/ADT/StringExtras.h" +#include "llvm/BinaryFormat/ELF.h" #include "llvm/CodeGen/MachineBranchProbabilityInfo.h" #include "llvm/CodeGen/MachineConstantPool.h" #include "llvm/CodeGen/MachineFunction.h" @@ -44,6 +45,7 @@ #include "llvm/MC/MCInst.h" #include "llvm/MC/MCInstBuilder.h" #include "llvm/MC/MCSection.h" +#include "llvm/MC/MCSectionELF.h" #include "llvm/MC/MCStreamer.h" #include "llvm/MC/MCSymbol.h" #include "llvm/MC/TargetRegistry.h" @@ -885,6 +887,22 @@ void X86AsmPrinter::LowerFENTRY_CALL(const MachineInstr &MI, X86MCInstLower &MCIL) { bool Is64Bits = Subtarget->is64Bit(); MCContext &Ctx = OutStreamer->getContext(); + + if (MF->getFunction().hasFnAttribute("mrecord-mcount")) { + MCSymbol *DotSym = OutContext.createTempSymbol(); + OutStreamer->pushSection(); + OutStreamer->switchSection( + Ctx.getELFSection("__mcount_loc", ELF::SHT_PROGBITS, ELF::SHF_ALLOC)); + OutStreamer->emitSymbolValue(DotSym, Is64Bits ? 8 : 4); + OutStreamer->popSection(); + OutStreamer->emitLabel(DotSym); + } + + if (MF->getFunction().hasFnAttribute("mnop-mcount")) { + emitX86Nops(*OutStreamer, 5, Subtarget); + return; + } + MCSymbol *fentry = Ctx.getOrCreateSymbol("__fentry__"); const MCSymbolRefExpr *Op = MCSymbolRefExpr::create(fentry, Ctx); diff --git a/llvm/test/CodeGen/X86/mnop-mcount-01.ll b/llvm/test/CodeGen/X86/mnop-mcount-01.ll new file mode 100644 index 0000000000000..ddefa497659f3 --- /dev/null +++ b/llvm/test/CodeGen/X86/mnop-mcount-01.ll @@ -0,0 +1,26 @@ +; RUN: llc %s -mtriple=x86_64-linux-gnu -o - -verify-machineinstrs \ +; RUN: | FileCheck %s + +define void @test1() #0 { +entry: + ret void + +; CHECK-LABEL: @test1 +; CHECK: callq __fentry__ +; CHECK-NOT: nopl 8(%rax,%rax) +; CHECK: retq +} + +define void @test2() #1 { +entry: + ret void + +; CHECK-LABEL: @test2 +; CHECK-NOT: callq __fentry__ +; CHECK: nopl 8(%rax,%rax) +; CHECK: retq +} + +attributes #0 = { "fentry-call"="true" } +attributes #1 = { "fentry-call"="true" "mnop-mcount" } + diff --git a/llvm/test/CodeGen/X86/mnop-mcount-02.ll b/llvm/test/CodeGen/X86/mnop-mcount-02.ll new file mode 100644 index 0000000000000..d576e0f289818 --- /dev/null +++ b/llvm/test/CodeGen/X86/mnop-mcount-02.ll @@ -0,0 +1,10 @@ +; RUN: not --crash llc %s -mtriple=x86_64-linux-gnu -o - 2>&1 | FileCheck %s +; +; CHECK: LLVM ERROR: mnop-mcount only supported with fentry-call + +define void @test1() #0 { +entry: + ret void +} + +attributes #0 = { "instrument-function-entry-inlined"="mcount" "mnop-mcount" } diff --git a/llvm/test/CodeGen/X86/mrecord-mcount-01.ll b/llvm/test/CodeGen/X86/mrecord-mcount-01.ll new file mode 100644 index 0000000000000..6202a652b8831 --- /dev/null +++ b/llvm/test/CodeGen/X86/mrecord-mcount-01.ll @@ -0,0 +1,32 @@ +; RUN: llc %s -mtriple=x86_64-linux-gnu -o - -verify-machineinstrs \ +; RUN: | FileCheck %s + +define void @test1() #0 { +entry: + ret void + +; CHECK-LABEL: test1: +; CHECK: .section __mcount_loc,"a",@progbits +; CHECK: .quad .Ltmp0 +; CHECK: .text +; CHECK: .Ltmp0: +; CHECK: callq __fentry__ +; CHECK: retq +} + +define void @test2() #1 { +entry: + ret void + +; CHECK-LABEL: test2: +; CHECK: .section __mcount_loc,"a",@progbits +; CHECK: .quad .Ltmp1 +; CHECK: .text +; CHECK: .Ltmp1: +; CHECK: nopl 8(%rax,%rax) +; CHECK-NOT: callq __fentry__ +; CHECK: retq +} + +attributes #0 = { "fentry-call"="true" "mrecord-mcount" } +attributes #1 = { "fentry-call"="true" "mnop-mcount" "mrecord-mcount" } diff --git a/llvm/test/CodeGen/X86/mrecord-mcount-02.ll b/llvm/test/CodeGen/X86/mrecord-mcount-02.ll new file mode 100644 index 0000000000000..a1f80f1840c41 --- /dev/null +++ b/llvm/test/CodeGen/X86/mrecord-mcount-02.ll @@ -0,0 +1,10 @@ +; RUN: not --crash llc %s -mtriple=x86_64-linux-gnu -o - 2>&1 | FileCheck %s +; +; CHECK: LLVM ERROR: mrecord-mcount only supported with fentry-call + +define void @test1() #0 { +entry: + ret void +} + +attributes #0 = { "instrument-function-entry-inlined"="mcount" "mrecord-mcount" } >From 0c14b0aef3af7f3fe282a94513c7cc4cb9c10802 Mon Sep 17 00:00:00 2001 From: Paul Murphy <[email protected]> Date: Wed, 4 Mar 2026 08:47:16 -0600 Subject: [PATCH 2/2] [clang] enable -mnop-mcount -mrecord-mcount for x86_64 These are gated by -mfentry. --- clang/lib/Driver/ToolChains/Clang.cpp | 6 ++++-- clang/test/CodeGen/mnop-mcount.c | 8 ++++++++ clang/test/CodeGen/mrecord-mcount.c | 8 ++++++++ clang/test/Driver/mcount.c | 4 +--- 4 files changed, 21 insertions(+), 5 deletions(-) diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp index e860136aae5b3..2807be2c7edd0 100644 --- a/clang/lib/Driver/ToolChains/Clang.cpp +++ b/clang/lib/Driver/ToolChains/Clang.cpp @@ -6884,14 +6884,16 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA, << A->getAsString(Args) << TripleStr; } if (Arg *A = Args.getLastArg(options::OPT_mnop_mcount)) { - if (Arch == llvm::Triple::systemz) + if (Arch == llvm::Triple::systemz || (TC.getTriple().isX86_64() && + TC.getTriple().isOSBinFormatELF())) A->render(Args, CmdArgs); else D.Diag(diag::err_drv_unsupported_opt_for_target) << A->getAsString(Args) << TripleStr; } if (Arg *A = Args.getLastArg(options::OPT_mrecord_mcount)) { - if (Arch == llvm::Triple::systemz) + if (Arch == llvm::Triple::systemz || (TC.getTriple().isX86_64() && + TC.getTriple().isOSBinFormatELF())) A->render(Args, CmdArgs); else D.Diag(diag::err_drv_unsupported_opt_for_target) diff --git a/clang/test/CodeGen/mnop-mcount.c b/clang/test/CodeGen/mnop-mcount.c index ebb21cc560e37..31b4e995cff02 100644 --- a/clang/test/CodeGen/mnop-mcount.c +++ b/clang/test/CodeGen/mnop-mcount.c @@ -6,6 +6,14 @@ // RUN: %s 2>&1 | FileCheck -check-prefix=NOPG %s // RUN: %clang_cc1 -mnop-mcount -triple s390x-ibm-linux -emit-llvm -o - %s \ // RUN: 2>&1 | FileCheck -check-prefix=NOPG %s +// RUN: %clang_cc1 -pg -mfentry -mnop-mcount -triple x86_64-ibm-linux -emit-llvm \ +// RUN: -o - %s 2>&1 | FileCheck %s +// RUN: not %clang_cc1 -pg -mnop-mcount -triple x86_64-ibm-linux -emit-llvm -o - \ +// RUN: %s 2>&1 | FileCheck -check-prefix=NOMFENTRY %s +// RUN: %clang_cc1 -mfentry -mnop-mcount -triple x86_64-ibm-linux -emit-llvm -o - \ +// RUN: %s 2>&1 | FileCheck -check-prefix=NOPG %s +// RUN: %clang_cc1 -mnop-mcount -triple x86_64-ibm-linux -emit-llvm -o - %s \ +// RUN: 2>&1 | FileCheck -check-prefix=NOPG %s int foo(void) { return 0; diff --git a/clang/test/CodeGen/mrecord-mcount.c b/clang/test/CodeGen/mrecord-mcount.c index 292a807073cef..832d4ee5e3e9f 100644 --- a/clang/test/CodeGen/mrecord-mcount.c +++ b/clang/test/CodeGen/mrecord-mcount.c @@ -6,6 +6,14 @@ // RUN: %s 2>&1 | FileCheck -check-prefix=NOPG %s // RUN: %clang_cc1 -mrecord-mcount -triple s390x-ibm-linux -emit-llvm -o - %s \ // RUN: 2>&1 | FileCheck -check-prefix=NOPG %s +// RUN: %clang_cc1 -pg -mfentry -mrecord-mcount -triple x86_64-ibm-linux -emit-llvm \ +// RUN: -o - %s 2>&1 | FileCheck %s +// RUN: not %clang_cc1 -pg -mrecord-mcount -triple x86_64-ibm-linux -emit-llvm -o - \ +// RUN: %s 2>&1 | FileCheck -check-prefix=NOMFENTRY %s +// RUN: %clang_cc1 -mfentry -mrecord-mcount -triple x86_64-ibm-linux -emit-llvm -o - \ +// RUN: %s 2>&1 | FileCheck -check-prefix=NOPG %s +// RUN: %clang_cc1 -mrecord-mcount -triple x86_64-ibm-linux -emit-llvm -o - %s \ +// RUN: 2>&1 | FileCheck -check-prefix=NOPG %s int foo(void) { return 0; diff --git a/clang/test/Driver/mcount.c b/clang/test/Driver/mcount.c index 70f554745b9c3..72d48b3806fe7 100644 --- a/clang/test/Driver/mcount.c +++ b/clang/test/Driver/mcount.c @@ -1,12 +1,10 @@ // RUN: %clang --target=s390x -c -### %s -mnop-mcount -mrecord-mcount 2>&1 | FileCheck %s +// RUN: %clang --target=x86_64 -c -### %s -mnop-mcount -mrecord-mcount 2>&1 | FileCheck %s // CHECK: "-mnop-mcount" // CHECK: "-mrecord-mcount" -// RUN: not %clang --target=x86_64 -c -### %s -mnop-mcount -mrecord-mcount 2>&1 | FileCheck --check-prefix=ERR1 %s // RUN: not %clang --target=aarch64 -c -### %s -mnop-mcount -mrecord-mcount 2>&1 | FileCheck --check-prefix=ERR2 %s -// ERR1: error: unsupported option '-mnop-mcount' for target 'x86_64' -// ERR1: error: unsupported option '-mrecord-mcount' for target 'x86_64' // ERR2: error: unsupported option '-mnop-mcount' for target 'aarch64' // ERR2: error: unsupported option '-mrecord-mcount' for target 'aarch64' _______________________________________________ cfe-commits mailing list [email protected] https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
