[Lldb-commits] [lldb] [lldb][RISCV] Implement trap handler unwind plan (PR #166531)

[Georgiy Samoylov via lldb-commits]

================
@@ -302,12 +304,56 @@ static lldb::UnwindPlanSP GetAArch64TrapHandlerUnwindPlan(ConstString name) {
   return unwind_plan_sp;
 }
 
+static lldb::UnwindPlanSP GetRISCVTrapHandlerUnwindPlan(ConstString name) {
+  if (name != "__vdso_rt_sigreturn")
+    return UnwindPlanSP{};
+
+  UnwindPlan::Row row;
+
+  // In the signal trampoline frame, sp points to an rt_sigframe[1], which is:
+  //  - 128-byte siginfo struct
+  //  - ucontext struct:
+  //     - 8-byte long (uc_flags)
+  //     - 8-byte pointer (*uc_link)
+  //     - 24-byte struct (uc_stack)
+  //     - 8-byte struct (uc_sigmask)
+  //     - 120-byte of padding to allow sigset_t to be expanded in the future
+  //     - 8 bytes of padding because sigcontext has 16-byte alignment
+  //     - struct sigcontext uc_mcontext
+  // [1]
+  // https://github.com/torvalds/linux/blob/master/arch/riscv/kernel/signal.c
+
+  constexpr size_t siginfo_size = 128;
+  constexpr size_t uc_flags_size = 8;
+  constexpr size_t uc_link_ptr_size = 8;
+  constexpr size_t uc_stack_size = 24;
+  constexpr size_t uc_sigmask_size = 8;
+  constexpr size_t padding_size = 128;
+
+  constexpr size_t offset = siginfo_size + uc_flags_size + uc_link_ptr_size +
+                            uc_stack_size + uc_sigmask_size + padding_size;
+
+  row.GetCFAValue().SetIsRegisterPlusOffset(gpr_sp_riscv, offset);
+  for (uint32_t reg_num = 0; reg_num <= 31; ++reg_num)
+    row.SetRegisterLocationToAtCFAPlusOffset(reg_num, reg_num * 8, false);
+
+  UnwindPlanSP unwind_plan_sp = std::make_shared<UnwindPlan>(eRegisterKindLLDB);
+  unwind_plan_sp->AppendRow(std::move(row));
+  unwind_plan_sp->SetSourceName("RISC-V Linux sigcontext");
+  unwind_plan_sp->SetSourcedFromCompiler(eLazyBoolYes);
----------------
sga-sc wrote:

I changed this flag to `eLazyBoolNo`, because this unwind plan wasn't emitted by the compiler. In this case linux tells us how to do unwinding.

Also unwinding works correctly both with `eLazyBoolNo` and `eLazyBoolYes` value of this flag

https://github.com/llvm/llvm-project/pull/166531