[llvm] [AArch64] Always add PURECODE flag to empty .text if "+execute-only" is set (PR #132196)
Csanád Hajdú via llvm-commits
llvm-commits at lists.llvm.org
Thu Mar 20 06:11:55 PDT 2025
https://github.com/Il-Capitano updated https://github.com/llvm/llvm-project/pull/132196
>From f31e4d2cfb007aff1a71bacc2778561f3cd866f4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Csan=C3=A1d=20Hajd=C3=BA?= <csanad.hajdu at arm.com>
Date: Thu, 20 Mar 2025 12:56:59 +0100
Subject: [PATCH 1/2] [AArch64] Always add PURECODE flag to empty .text if
"+execute-only" is set
The previous approach only added the `SHF_AARCH64_PURECODE` section flag
to the implicitly created `.text` section if there was any other section
containing the flag already. This doesn't work for the case, where the
module doesn't contain any code.
Now, the `SHF_AARCH64_PURECODE` is always added if the "+execute-only"
target feature is set for the module.
---
.../Target/AArch64/AArch64TargetObjectFile.cpp | 9 +++++++++
.../MCTargetDesc/AArch64ELFStreamer.cpp | 18 ------------------
.../test/CodeGen/AArch64/execute-only-empty.ll | 13 +++++++++++++
3 files changed, 22 insertions(+), 18 deletions(-)
create mode 100644 llvm/test/CodeGen/AArch64/execute-only-empty.ll
diff --git a/llvm/lib/Target/AArch64/AArch64TargetObjectFile.cpp b/llvm/lib/Target/AArch64/AArch64TargetObjectFile.cpp
index 434ae32502d48..b662e75741d38 100644
--- a/llvm/lib/Target/AArch64/AArch64TargetObjectFile.cpp
+++ b/llvm/lib/Target/AArch64/AArch64TargetObjectFile.cpp
@@ -16,6 +16,7 @@
#include "llvm/IR/Module.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCExpr.h"
+#include "llvm/MC/MCSectionELF.h"
#include "llvm/MC/MCStreamer.h"
#include "llvm/MC/MCValue.h"
using namespace llvm;
@@ -27,6 +28,14 @@ void AArch64_ELFTargetObjectFile::Initialize(MCContext &Ctx,
// AARCH64 ELF ABI does not define static relocation type for TLS offset
// within a module. Do not generate AT_location for TLS variables.
SupportDebugThreadLocalLocation = false;
+
+ // Make sure the implicitly created empty .text section has the
+ // SHF_AARCH64_PURECODE flag set if the "+execute-only" target feature is
+ // present.
+ if (TM.getMCSubtargetInfo()->hasFeature(AArch64::FeatureExecuteOnly)) {
+ auto *Text = cast<MCSectionELF>(TextSection);
+ Text->setFlags(Text->getFlags() | ELF::SHF_AARCH64_PURECODE);
+ }
}
void AArch64_ELFTargetObjectFile::emitPersonalityValueImpl(
diff --git a/llvm/lib/Target/AArch64/MCTargetDesc/AArch64ELFStreamer.cpp b/llvm/lib/Target/AArch64/MCTargetDesc/AArch64ELFStreamer.cpp
index 98bd102d8f4c1..9803129608c4b 100644
--- a/llvm/lib/Target/AArch64/MCTargetDesc/AArch64ELFStreamer.cpp
+++ b/llvm/lib/Target/AArch64/MCTargetDesc/AArch64ELFStreamer.cpp
@@ -27,7 +27,6 @@
#include "llvm/MC/MCELFStreamer.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCInst.h"
-#include "llvm/MC/MCObjectFileInfo.h"
#include "llvm/MC/MCSectionELF.h"
#include "llvm/MC/MCStreamer.h"
#include "llvm/MC/MCSubtargetInfo.h"
@@ -501,23 +500,6 @@ void AArch64TargetELFStreamer::finish() {
}
}
- // The mix of execute-only and non-execute-only at link time is
- // non-execute-only. To avoid the empty implicitly created .text
- // section from making the whole .text section non-execute-only, we
- // mark it execute-only if it is empty and there is at least one
- // execute-only section in the object.
- if (any_of(Asm, [](const MCSection &Sec) {
- return cast<MCSectionELF>(Sec).getFlags() & ELF::SHF_AARCH64_PURECODE;
- })) {
- auto *Text =
- static_cast<MCSectionELF *>(Ctx.getObjectFileInfo()->getTextSection());
- for (auto &F : *Text)
- if (auto *DF = dyn_cast<MCDataFragment>(&F))
- if (!DF->getContents().empty())
- return;
- Text->setFlags(Text->getFlags() | ELF::SHF_AARCH64_PURECODE);
- }
-
MCSectionELF *MemtagSec = nullptr;
for (const MCSymbol &Symbol : Asm.symbols()) {
const auto &Sym = cast<MCSymbolELF>(Symbol);
diff --git a/llvm/test/CodeGen/AArch64/execute-only-empty.ll b/llvm/test/CodeGen/AArch64/execute-only-empty.ll
new file mode 100644
index 0000000000000..cdf9b3afe8daf
--- /dev/null
+++ b/llvm/test/CodeGen/AArch64/execute-only-empty.ll
@@ -0,0 +1,13 @@
+; RUN: llc -filetype=obj -mtriple=aarch64 -mattr=+execute-only %s -o %t.o
+; RUN: llvm-readobj -S %t.o | FileCheck %s
+
+; CHECK: Name: .text
+; CHECK-NEXT: Type: SHT_PROGBITS
+; CHECK-NEXT: Flags [
+; CHECK-NEXT: SHF_AARCH64_PURECODE
+; CHECK-NEXT: SHF_ALLOC
+; CHECK-NEXT: SHF_EXECINSTR
+; CHECK-NEXT: ]
+; CHECK-NEXT: Address:
+; CHECK-NEXT: Offset:
+; CHECK-NEXT: Size: 0
>From d9734ca970d62dc4496fcaf7b31dd657a47b845d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Csan=C3=A1d=20Hajd=C3=BA?= <csanad.hajdu at arm.com>
Date: Thu, 20 Mar 2025 14:09:42 +0100
Subject: [PATCH 2/2] Revert removing change in AArch64ELFStreamer.cpp
---
.../MCTargetDesc/AArch64ELFStreamer.cpp | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)
diff --git a/llvm/lib/Target/AArch64/MCTargetDesc/AArch64ELFStreamer.cpp b/llvm/lib/Target/AArch64/MCTargetDesc/AArch64ELFStreamer.cpp
index 9803129608c4b..98bd102d8f4c1 100644
--- a/llvm/lib/Target/AArch64/MCTargetDesc/AArch64ELFStreamer.cpp
+++ b/llvm/lib/Target/AArch64/MCTargetDesc/AArch64ELFStreamer.cpp
@@ -27,6 +27,7 @@
#include "llvm/MC/MCELFStreamer.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCInst.h"
+#include "llvm/MC/MCObjectFileInfo.h"
#include "llvm/MC/MCSectionELF.h"
#include "llvm/MC/MCStreamer.h"
#include "llvm/MC/MCSubtargetInfo.h"
@@ -500,6 +501,23 @@ void AArch64TargetELFStreamer::finish() {
}
}
+ // The mix of execute-only and non-execute-only at link time is
+ // non-execute-only. To avoid the empty implicitly created .text
+ // section from making the whole .text section non-execute-only, we
+ // mark it execute-only if it is empty and there is at least one
+ // execute-only section in the object.
+ if (any_of(Asm, [](const MCSection &Sec) {
+ return cast<MCSectionELF>(Sec).getFlags() & ELF::SHF_AARCH64_PURECODE;
+ })) {
+ auto *Text =
+ static_cast<MCSectionELF *>(Ctx.getObjectFileInfo()->getTextSection());
+ for (auto &F : *Text)
+ if (auto *DF = dyn_cast<MCDataFragment>(&F))
+ if (!DF->getContents().empty())
+ return;
+ Text->setFlags(Text->getFlags() | ELF::SHF_AARCH64_PURECODE);
+ }
+
MCSectionELF *MemtagSec = nullptr;
for (const MCSymbol &Symbol : Asm.symbols()) {
const auto &Sym = cast<MCSymbolELF>(Symbol);
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