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

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-lldb

<details>
<summary>Changes</summary>

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

vg is invalided when the write happens. SVE is reconfigured by reading back the new value from the remote. So far so good.

For SME, we read SVG which in some situations appeared to remain valid but have a value of 0 (perhaps it had never been read). This meant lldb expected the size of za to be 0 bytes and rejected the remote's response.

To fix this, invalidate svg before reconfiguring. This ensures that the value used is the latest one from the remote.

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.

Differential Revision: https://reviews.llvm.org/D158514

---
Full diff: https://github.com/llvm/llvm-project/pull/66768.diff


2 Files Affected:

- (modified) lldb/source/Plugins/Process/gdb-remote/GDBRemoteRegisterContext.cpp (+5) 
- (modified) lldb/test/API/commands/register/register/aarch64_za_register/za_dynamic_resize/TestZAThreadedDynamic.py (+2) 


``````````diff
diff --git a/lldb/source/Plugins/Process/gdb-remote/GDBRemoteRegisterContext.cpp b/lldb/source/Plugins/Process/gdb-remote/GDBRemoteRegisterContext.cpp
index 16dde28f6ee5396..13365dc312f5b66 100644
--- a/lldb/source/Plugins/Process/gdb-remote/GDBRemoteRegisterContext.cpp
+++ b/lldb/source/Plugins/Process/gdb-remote/GDBRemoteRegisterContext.cpp
@@ -781,6 +781,11 @@ 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")

``````````

</details>


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