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[lldb] Restore register state if PrepareTrivialCall fails #129038

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merged 2 commits into from
Feb 28, 2025
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[lldb] Restore register state if PrepareTrivialCall fails #129038

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[lldb] Restore register state if PrepareTrivialCall fails
DavidSpickett Feb 26, 2025
5f6bce5
no longer relevant
DavidSpickett Feb 28, 2025
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9 changes: 1 addition & 8 deletions lldb/source/Plugins/ABI/AArch64/ABISysV_arm64.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -102,12 +102,7 @@ static Status PushToLinuxGuardedControlStack(addr_t return_addr,
size_t wrote = thread.GetProcess()->WriteMemory(gcspr_el0, &return_addr,
sizeof(return_addr), error);
if ((wrote != sizeof(return_addr) || error.Fail())) {
// When PrepareTrivialCall fails, the register context is not restored,
// unlike when an expression fails to execute. This is arguably a bug,
// see https://github.com/llvm/llvm-project/issues/124269.
// For now we are handling this here specifically. We can assume this
// write will work as the one to decrement the register did.
reg_ctx->WriteRegisterFromUnsigned(gcspr_el0_info, gcspr_el0 + 8);
// gcspr_el0 will be restored by the ThreadPlan's DoTakedown.
return Status("Failed to write new Guarded Control Stack entry.");
}

Expand Down Expand Up @@ -150,8 +145,6 @@ bool ABISysV_arm64::PrepareTrivialCall(Thread &thread, addr_t sp,
if (args.size() > 8)
return false;

// Do this first, as it's got the most chance of failing (though still very
// low).
if (GetProcessSP()->GetTarget().GetArchitecture().GetTriple().isOSLinux()) {
Status err = PushToLinuxGuardedControlStack(return_addr, reg_ctx, thread);
// If we could not manage the GCS, the expression will certainly fail,
Expand Down
13 changes: 12 additions & 1 deletion lldb/source/Target/ThreadPlanCallFunction.cpp
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Expand Up @@ -174,8 +174,20 @@ void ThreadPlanCallFunction::ReportRegisterState(const char *message) {

void ThreadPlanCallFunction::DoTakedown(bool success) {
Log *log = GetLog(LLDBLog::Step);
Thread &thread = GetThread();

if (!m_valid) {
// If ConstructorSetup was succesfull but PrepareTrivialCall was not,
// we will have a saved register state and potentially modified registers.
// Restore those.
if (m_stored_thread_state.register_backup_sp)
if (!thread.RestoreRegisterStateFromCheckpoint(m_stored_thread_state))
LLDB_LOGF(
log,
"ThreadPlanCallFunction(%p): Failed to restore register state from "
"invalid plan that contained a saved register state.",
static_cast<void *>(this));

// Don't call DoTakedown if we were never valid to begin with.
LLDB_LOGF(log,
"ThreadPlanCallFunction(%p): Log called on "
Expand All @@ -185,7 +197,6 @@ void ThreadPlanCallFunction::DoTakedown(bool success) {
}

if (!m_takedown_done) {
Thread &thread = GetThread();
if (success) {
SetReturnValue();
}
Expand Down
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