[llvm][llvm-readobj] Add NT_ARM_GCS Linux core note type

[DavidSpickett]

The ARM Guarded Control Stack extension (GCS) is similar to existing shadow stack extensions for other architectures.

The core note will include which features of GCS are enabled, which have been locked in their current state, and the stack pointer of the shadow stack.

Note that 0x40f is NT_ARM_POE, FPMR is supported by LLDB and GCS will be soon, POE is not at this time. So NT_ARM_POE will be added when that work starts.

See https://github.com/torvalds/linux/blob/master/include/uapi/linux/elf.h.

[llvmbot]

@llvm/pr-subscribers-objectyaml

@llvm/pr-subscribers-llvm-binary-utilities

Author: David Spickett (DavidSpickett)

Changes

The ARM Guarded Control Stack extension (GCS) is similar to existing shadow stack extensions for other architectures.

The core note will include which features of GCS are enabled, which have been locked in their current state, and the stack pointer of the shadow stack.

Note that 0x40f is NT_ARM_POE, FPMR and GCS will be supported by lldb, POE is not at this time.

---

Full diff: https://github.com/llvm/llvm-project/pull/117545.diff

4 Files Affected:

• (modified) llvm/include/llvm/BinaryFormat/ELF.h (+1)
• (modified) llvm/lib/ObjectYAML/ELFYAML.cpp (+1)
• (modified) llvm/test/tools/llvm-readobj/ELF/note-core.test (+5)
• (modified) llvm/tools/llvm-readobj/ELFDumper.cpp (+1)

diff --git a/llvm/include/llvm/BinaryFormat/ELF.h b/llvm/include/llvm/BinaryFormat/ELF.h
index fd32a6ec19652b..5356843f8ecf1a 100644
--- a/llvm/include/llvm/BinaryFormat/ELF.h
+++ b/llvm/include/llvm/BinaryFormat/ELF.h
@@ -1724,6 +1724,7 @@ enum : unsigned {
   NT_ARM_ZA = 0x40c,
   NT_ARM_ZT = 0x40d,
   NT_ARM_FPMR = 0x40e,
+  NT_ARM_GCS = 0x410,
 
   NT_FILE = 0x46494c45,
   NT_PRXFPREG = 0x46e62b7f,
diff --git a/llvm/lib/ObjectYAML/ELFYAML.cpp b/llvm/lib/ObjectYAML/ELFYAML.cpp
index ca0ea03452d3be..f28e6766f734c0 100644
--- a/llvm/lib/ObjectYAML/ELFYAML.cpp
+++ b/llvm/lib/ObjectYAML/ELFYAML.cpp
@@ -136,6 +136,7 @@ void ScalarEnumerationTraits<ELFYAML::ELF_NT>::enumeration(
   ECase(NT_ARM_ZA);
   ECase(NT_ARM_ZT);
   ECase(NT_ARM_FPMR);
+  ECase(NT_ARM_GCS);
   ECase(NT_FILE);
   ECase(NT_PRXFPREG);
   ECase(NT_SIGINFO);
diff --git a/llvm/test/tools/llvm-readobj/ELF/note-core.test b/llvm/test/tools/llvm-readobj/ELF/note-core.test
index 1196d4b2507241..2c35178a97524b 100644
--- a/llvm/test/tools/llvm-readobj/ELF/note-core.test
+++ b/llvm/test/tools/llvm-readobj/ELF/note-core.test
@@ -265,6 +265,11 @@
 # RUN: llvm-readelf --notes %t_nt_arm_fpmr.o | FileCheck %s --check-prefix=CHECK-GNU  -DDESC="NT_ARM_FPMR (AArch64 Floating Point Mode Register)"
 # RUN: llvm-readobj --notes %t_nt_arm_fpmr.o | FileCheck %s --check-prefix=CHECK-LLVM -DDESC="NT_ARM_FPMR (AArch64 Floating Point Mode Register)"
 
+## Check ELF::NT_ARM_GCS
+# RUN: yaml2obj %s -DTYPE=0x410 -o %t_nt_arm_gcs.o
+# RUN: llvm-readelf --notes %t_nt_arm_gcs.o | FileCheck %s --check-prefix=CHECK-GNU  -DDESC="NT_ARM_GCS (AArch64 Guarded Control Stack state)"
+# RUN: llvm-readobj --notes %t_nt_arm_gcs.o | FileCheck %s --check-prefix=CHECK-LLVM -DDESC="NT_ARM_GCS (AArch64 Guarded Control Stack state)"
+
 ## Check ELF::NT_FILE.
 # RUN: yaml2obj %s -DTYPE=0x46494c45 -o %t_nt_file.o
 # RUN: llvm-readelf --notes %t_nt_file.o | FileCheck %s --check-prefix=CHECK-GNU  -DDESC="NT_FILE (mapped files)"
diff --git a/llvm/tools/llvm-readobj/ELFDumper.cpp b/llvm/tools/llvm-readobj/ELFDumper.cpp
index bb8ec41d87454c..bfca65aad52b44 100644
--- a/llvm/tools/llvm-readobj/ELFDumper.cpp
+++ b/llvm/tools/llvm-readobj/ELFDumper.cpp
@@ -6057,6 +6057,7 @@ const NoteType CoreNoteTypes[] = {
     {ELF::NT_ARM_ZA, "NT_ARM_ZA (AArch64 SME ZA registers)"},
     {ELF::NT_ARM_ZT, "NT_ARM_ZT (AArch64 SME ZT registers)"},
     {ELF::NT_ARM_FPMR, "NT_ARM_FPMR (AArch64 Floating Point Mode Register)"},
+    {ELF::NT_ARM_GCS, "NT_ARM_GCS (AArch64 Guarded Control Stack state)"},
 
     {ELF::NT_FILE, "NT_FILE (mapped files)"},
     {ELF::NT_PRXFPREG, "NT_PRXFPREG (user_xfpregs structure)"},

[jh7370]

LGTM. Perhaps worth getting someone else with ARM knowledge a chance to give it a once over (@smithp35?)

[DavidSpickett]

@omjavaid is about to review the lldb patches even if he doesn't realise yet :)

https://github.com/search?q=repo%3Atorvalds%2Flinux%20NT_ARM_GCS&type=code should help validate it.

POE (permission overlay extension) support is planned for about a year from now, so I'm not going to add that constant until LLDB needs it.

[omjavaid]

For reference NT_ARM_GCS is defined at:
https://github.com/torvalds/linux/blob/master/include/uapi/linux/elf.h
#define NT_ARM_GCS 0x410 /* ARM GCS state */