[Lldb-commits] [lldb] [RISCV] Adding `vlenb` register as callee register (PR #165796)

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https://github.com/barsolo2000 created https://github.com/llvm/llvm-project/pull/165796

In recent debug sessions we noticed that GDB debugger is showing more stack trace and lldb.
After enabling unwinding log, it seems like the issue is that the CFA is dependent on the value of vlenb.
vlenb doesn't change in runtime so we can assume its value from frame 0. 

>From 7ad2138ab6a9e61b84575f4f41762778cc7e0ad4 Mon Sep 17 00:00:00 2001
From: Bar Soloveychik <barsolo at fb.com>
Date: Thu, 30 Oct 2025 16:07:24 -0700
Subject: [PATCH] Adding vlenb register as callee register

---
 lldb/source/Plugins/ABI/RISCV/ABISysV_riscv.cpp | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/lldb/source/Plugins/ABI/RISCV/ABISysV_riscv.cpp b/lldb/source/Plugins/ABI/RISCV/ABISysV_riscv.cpp
index b313ca03fb970..d46593358ba6d 100644
--- a/lldb/source/Plugins/ABI/RISCV/ABISysV_riscv.cpp
+++ b/lldb/source/Plugins/ABI/RISCV/ABISysV_riscv.cpp
@@ -798,6 +798,8 @@ bool ABISysV_riscv::RegisterIsCalleeSaved(const RegisterInfo *reg_info) {
           // floating point hardware names
           .Cases("f8", "f9", "f18", "f19", "f20", "f21", "f22", "f23", is_hw_fp)
           .Cases("f24", "f25", "f26", "f27", is_hw_fp)
+          // vlenb is constant and needed for vector unwinding.
+          .Case("vlenb", true)
           .Default(false);
 
   return is_callee_saved;