[libunwind] [llvm] [llvm][CompactUnwind] Compact unwind does not support .cfi_signal_frame (PR #186458)
Jon Roelofs via cfe-commits
cfe-commits at lists.llvm.org
Fri Mar 13 10:09:47 PDT 2026
https://github.com/jroelofs created https://github.com/llvm/llvm-project/pull/186458
Fixes libunwind's signal_frame.pass.cpp test on Mach-O platforms.
>From 0df84bf18c4b77314922171540bf2d62ef955b80 Mon Sep 17 00:00:00 2001
From: Jon Roelofs <jonathan_roelofs at apple.com>
Date: Fri, 13 Mar 2026 09:15:20 -0700
Subject: [PATCH] [llvm][CompactUnwind] Compact unwind does not support
.cfi_signal_frame
Fixes libunwind's signal_frame.pass.cpp test on Mach-O platforms.
---
libunwind/test/signal_frame.pass.cpp | 3 --
.../MCTargetDesc/AArch64AsmBackend.cpp | 4 +++
.../Target/ARM/MCTargetDesc/ARMAsmBackend.cpp | 7 ++++
.../Target/X86/MCTargetDesc/X86AsmBackend.cpp | 4 +++
.../arm64-compact-unwind-signal-frame.s | 33 +++++++++++++++++++
.../test/MC/ARM/compact-unwind-signal-frame.s | 24 ++++++++++++++
.../test/MC/X86/compact-unwind-signal-frame.s | 23 +++++++++++++
7 files changed, 95 insertions(+), 3 deletions(-)
create mode 100644 llvm/test/MC/AArch64/arm64-compact-unwind-signal-frame.s
create mode 100644 llvm/test/MC/ARM/compact-unwind-signal-frame.s
create mode 100644 llvm/test/MC/X86/compact-unwind-signal-frame.s
diff --git a/libunwind/test/signal_frame.pass.cpp b/libunwind/test/signal_frame.pass.cpp
index 004029cfe1e90..a4676b15dd942 100644
--- a/libunwind/test/signal_frame.pass.cpp
+++ b/libunwind/test/signal_frame.pass.cpp
@@ -9,9 +9,6 @@
// Ensure that functions marked as signal frames are reported as such.
-// TODO: Investigate this failure on Apple
-// XFAIL: target={{.+}}-apple-{{.+}}
-
// TODO: Figure out why this fails with Memory Sanitizer.
// XFAIL: msan
diff --git a/llvm/lib/Target/AArch64/MCTargetDesc/AArch64AsmBackend.cpp b/llvm/lib/Target/AArch64/MCTargetDesc/AArch64AsmBackend.cpp
index 48213d4da5d9f..eece54692e18c 100644
--- a/llvm/lib/Target/AArch64/MCTargetDesc/AArch64AsmBackend.cpp
+++ b/llvm/lib/Target/AArch64/MCTargetDesc/AArch64AsmBackend.cpp
@@ -580,6 +580,10 @@ class DarwinAArch64AsmBackend : public AArch64AsmBackend {
if (FI->IsMTETaggedFrame)
return CU::UNWIND_ARM64_MODE_DWARF;
+ // Signal frames cannot be encoded in compact unwind.
+ if (FI->IsSignalFrame)
+ return CU::UNWIND_ARM64_MODE_DWARF;
+
ArrayRef<MCCFIInstruction> Instrs = FI->Instructions;
if (Instrs.empty())
return CU::UNWIND_ARM64_MODE_FRAMELESS;
diff --git a/llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp b/llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
index 243fa7b512d0d..28277ece97c91 100644
--- a/llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
+++ b/llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
@@ -1171,13 +1171,20 @@ enum CompactUnwindEncodings {
uint64_t ARMAsmBackendDarwin::generateCompactUnwindEncoding(
const MCDwarfFrameInfo *FI, const MCContext *Ctxt) const {
DEBUG_WITH_TYPE("compact-unwind", llvm::dbgs() << "generateCU()\n");
+
// Only armv7k uses CFI based unwinding.
if (Subtype != MachO::CPU_SUBTYPE_ARM_V7K)
return 0;
+
+ // Signal frames cannot be encoded in compact unwind.
+ if (FI->IsSignalFrame)
+ return CU::UNWIND_ARM_MODE_DWARF;
+
// No .cfi directives means no frame.
ArrayRef<MCCFIInstruction> Instrs = FI->Instructions;
if (Instrs.empty())
return 0;
+
if (!isDarwinCanonicalPersonality(FI->Personality) &&
!Ctxt->emitCompactUnwindNonCanonical())
return CU::UNWIND_ARM_MODE_DWARF;
diff --git a/llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp b/llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp
index 3a1d960304db0..7515c75ab33e1 100644
--- a/llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp
+++ b/llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp
@@ -1306,6 +1306,10 @@ class DarwinX86AsmBackend : public X86AsmBackend {
/// for the CFI instructions.
uint64_t generateCompactUnwindEncoding(const MCDwarfFrameInfo *FI,
const MCContext *Ctxt) const override {
+ // Signal frames cannot be encoded in compact unwind.
+ if (FI->IsSignalFrame)
+ return CU::UNWIND_MODE_DWARF;
+
ArrayRef<MCCFIInstruction> Instrs = FI->Instructions;
if (Instrs.empty()) return 0;
if (!isDarwinCanonicalPersonality(FI->Personality) &&
diff --git a/llvm/test/MC/AArch64/arm64-compact-unwind-signal-frame.s b/llvm/test/MC/AArch64/arm64-compact-unwind-signal-frame.s
new file mode 100644
index 0000000000000..34b0e64a05b3d
--- /dev/null
+++ b/llvm/test/MC/AArch64/arm64-compact-unwind-signal-frame.s
@@ -0,0 +1,33 @@
+// RUN: llvm-mc -triple=arm64-apple-ios -filetype=obj %s -o %t.o
+// RUN: llvm-objdump --macho --unwind-info --dwarf=frames %t.o | FileCheck %s
+
+/// Signal frames cannot be encoded in compact unwind. Verify that
+/// .cfi_signal_frame causes UNWIND_ARM64_MODE_DWARF (0x03000000) to be
+/// emitted in the __compact_unwind section, and that the corresponding DWARF
+/// CIE carries the 'S' augmentation character. A non-signal frame in the
+/// same translation unit is encoded normally (UNWIND_ARM64_MODE_FRAMELESS,
+/// 0x02000000) and needs no DWARF FDE.
+
+ .globl _f
+_f:
+ .cfi_startproc
+ .cfi_signal_frame
+ ret
+ .cfi_endproc
+
+ .globl _g
+_g:
+ .cfi_startproc
+ ret
+ .cfi_endproc
+
+// CHECK: Contents of __compact_unwind section:
+// CHECK: Entry at offset 0x0:
+// CHECK: compact encoding: 0x03000000
+// CHECK: Entry at offset 0x20:
+// CHECK: start: 0x{{.*}} _g
+// CHECK: compact encoding: 0x02000000
+
+// CHECK: .eh_frame contents:
+// CHECK: CIE
+// CHECK: Augmentation: "zRS"
diff --git a/llvm/test/MC/ARM/compact-unwind-signal-frame.s b/llvm/test/MC/ARM/compact-unwind-signal-frame.s
new file mode 100644
index 0000000000000..55fb95f2cd2aa
--- /dev/null
+++ b/llvm/test/MC/ARM/compact-unwind-signal-frame.s
@@ -0,0 +1,24 @@
+// RUN: llvm-mc -triple=armv7k-apple-ios -filetype=obj %s -o %t.o
+// RUN: llvm-objdump --macho --unwind-info --dwarf=frames %t.o | FileCheck %s
+
+/// Signal frames cannot be encoded in compact unwind. Verify that
+/// .cfi_signal_frame causes UNWIND_ARM_MODE_DWARF (0x04000000) to be emitted
+/// in the __compact_unwind section, and that the corresponding DWARF CIE
+/// carries the 'S' augmentation character.
+
+ .globl _f
+_f:
+ .cfi_startproc
+ .cfi_signal_frame
+ bx lr
+ .cfi_endproc
+
+// CHECK: Contents of __compact_unwind section:
+// CHECK: Entry at offset 0x0:
+// CHECK: start: 0x0 _f
+// CHECK: length: 0x4
+// CHECK: compact encoding: 0x04000000
+
+// CHECK: .eh_frame contents:
+// CHECK: CIE
+// CHECK: Augmentation: "zRS"
diff --git a/llvm/test/MC/X86/compact-unwind-signal-frame.s b/llvm/test/MC/X86/compact-unwind-signal-frame.s
new file mode 100644
index 0000000000000..a63f5389aea2f
--- /dev/null
+++ b/llvm/test/MC/X86/compact-unwind-signal-frame.s
@@ -0,0 +1,23 @@
+// RUN: llvm-mc -triple x86_64-apple-macos10.6 -filetype=obj %s -o %t.o
+// RUN: llvm-objdump --macho --unwind-info --dwarf=frames %t.o | FileCheck %s
+
+/// Signal frames cannot be encoded in compact unwind. Verify that
+/// .cfi_signal_frame causes UNWIND_X86_MODE_DWARF (0x04000000) to be emitted
+/// in the __compact_unwind section, and that the corresponding DWARF CIE
+/// carries the 'S' augmentation character.
+
+_f:
+ .cfi_startproc
+ .cfi_signal_frame
+ ret
+ .cfi_endproc
+
+// CHECK: Contents of __compact_unwind section:
+// CHECK: Entry at offset 0x0:
+// CHECK: start: 0x0 _f
+// CHECK: length: 0x1
+// CHECK: compact encoding: 0x04000000
+
+// CHECK: .eh_frame contents:
+// CHECK: CIE
+// CHECK: Augmentation: "zRS"
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