[Lldb-commits] [lldb] [lldb][AArch64] Invalidate SVG prior to reconfiguring ZA regdef (PR #66768)

[David Spickett via lldb-commits]

https://github.com/DavidSpickett updated https://github.com/llvm/llvm-project/pull/66768

>From 8b292d573710e1c37227d6f80b9770220abd658e Mon Sep 17 00:00:00 2001
From: David Spickett <david.spickett at linaro.org>
Date: Tue, 22 Aug 2023 14:42:35 +0100
Subject: [PATCH 1/2] [lldb][AArch64] Invalidate SVG prior to reconfiguring ZA
 regdef

This fixes a bug where writing vg during streaming mode
could prevent you reading za directly afterwards.

vg is invalidated just prior to us reading it in AArch64Reconfigure,
but svg was not. This lead to some situations where vg would be
updated or read from fresh, but svg would not be.

This meant it had some undefined value which lead to errors
that prevented us reading ZA. Likely we receieved a lot more
data than we were expecting.

To fix this, invalidate svg before reconfiguring. This ensures
that the value used is the latest one from the remote and matches
the procedure for SVE's VG.

The bug may depend on timing, I could not find a consistent way
to trigger it. I originally found it when checking whether za
is disabled after a vg change, so I've added checks for that
to TestZAThreadedDynamic.

The SVE VG version of the bug did show up on the buildbot,
but not consistently. So it's possible that TestZAThreadedDynamic
does in fact cover this, but I haven't run it enough times to know.
---
 .../Plugins/Process/gdb-remote/GDBRemoteRegisterContext.cpp  | 5 +++++
 .../za_dynamic_resize/TestZAThreadedDynamic.py               | 2 ++
 2 files changed, 7 insertions(+)

diff --git a/lldb/source/Plugins/Process/gdb-remote/GDBRemoteRegisterContext.cpp b/lldb/source/Plugins/Process/gdb-remote/GDBRemoteRegisterContext.cpp
index b127d3d6213a4aa..72280927471f883 100644
--- a/lldb/source/Plugins/Process/gdb-remote/GDBRemoteRegisterContext.cpp
+++ b/lldb/source/Plugins/Process/gdb-remote/GDBRemoteRegisterContext.cpp
@@ -783,6 +783,11 @@ void GDBRemoteRegisterContext::AArch64Reconfigure() {
   std::optional<uint64_t> svg_reg_value;
   const RegisterInfo *svg_reg_info = m_reg_info_sp->GetRegisterInfo("svg");
   if (svg_reg_info) {
+    // When vg is written it is automatically made invalid. Writing vg will also
+    // change svg if we're in streaming mode but it will not be made invalid
+    // so do this manually so the following read gets the latest svg value.
+    SetRegisterIsValid(svg_reg_info, false);
+
     uint32_t svg_reg_num = svg_reg_info->kinds[eRegisterKindLLDB];
     uint64_t reg_value = ReadRegisterAsUnsigned(svg_reg_num, fail_value);
     if (reg_value != fail_value && reg_value <= 32)
diff --git a/lldb/test/API/commands/register/register/aarch64_za_register/za_dynamic_resize/TestZAThreadedDynamic.py b/lldb/test/API/commands/register/register/aarch64_za_register/za_dynamic_resize/TestZAThreadedDynamic.py
index 65d1071c26b2a34..d2a26ce71bde1d8 100644
--- a/lldb/test/API/commands/register/register/aarch64_za_register/za_dynamic_resize/TestZAThreadedDynamic.py
+++ b/lldb/test/API/commands/register/register/aarch64_za_register/za_dynamic_resize/TestZAThreadedDynamic.py
@@ -125,11 +125,13 @@ def za_test_impl(self, enable_za):
                 self.runCmd("thread select %d" % (idx + 1))
                 self.check_za_register(4, 2)
                 self.runCmd("register write vg 2")
+                self.check_disabled_za_register(2)
 
             elif stopped_at_line_number == thY_break_line1:
                 self.runCmd("thread select %d" % (idx + 1))
                 self.check_za_register(2, 3)
                 self.runCmd("register write vg 4")
+                self.check_disabled_za_register(4)
 
         self.runCmd("thread continue 2")
         self.runCmd("thread continue 3")

>From f00e970f03dea81fccae04ae5fe265d7721fb625 Mon Sep 17 00:00:00 2001
From: David Spickett <david.spickett at linaro.org>
Date: Fri, 6 Oct 2023 16:29:28 +0100
Subject: [PATCH 2/2] Also use the invalidates mechanism to link vg and svg.

---
 .../Process/Utility/RegisterInfoPOSIX_arm64.cpp       | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/lldb/source/Plugins/Process/Utility/RegisterInfoPOSIX_arm64.cpp b/lldb/source/Plugins/Process/Utility/RegisterInfoPOSIX_arm64.cpp
index 60070819cb92699..e6e6c12d0404aed 100644
--- a/lldb/source/Plugins/Process/Utility/RegisterInfoPOSIX_arm64.cpp
+++ b/lldb/source/Plugins/Process/Utility/RegisterInfoPOSIX_arm64.cpp
@@ -374,6 +374,17 @@ void RegisterInfoPOSIX_arm64::AddRegSetSME() {
       std::make_pair(sme_regnum, m_dynamic_reg_infos.size());
   m_dynamic_reg_sets.push_back(g_reg_set_sme_arm64);
   m_dynamic_reg_sets.back().registers = m_sme_regnum_collection.data();
+
+  // When vg is written during streaming mode, svg will also change, as vg and
+  // svg in this state are both showing the streaming vector length.
+  // We model this as vg invalidating svg. In non-streaming mode this doesn't
+  // happen but to keep things simple we will invalidate svg anyway.
+  //
+  // This must be added now, rather than when vg is defined because SME is a
+  // dynamic set that may or may not be present.
+  static const uint32_t vg_invalidates[] = {sme_regnum + 1 /*svg*/,
+                                            LLDB_INVALID_REGNUM};
+  m_dynamic_reg_infos[GetRegNumSMESVG()].invalidate_regs = vg_invalidates;
 }
 
 uint32_t RegisterInfoPOSIX_arm64::ConfigureVectorLengthSVE(uint32_t sve_vq) {