fix: avoid attr_value_t conversion of new_command result during module init

[Wenzel]

Problem

Loading the tsffs module crashes with a SIGSEGV on newer Simics Base versions, before any target is even set up. load-module tsffs alone is enough to reproduce it — no model required.

Segmentation fault (SIGSEGV) in thread ("simics-scriptbr")
#3  VT_effective_log_level
#4  VT_log_message64
#5  VT_log_error
#6  simics::api::logging::log_error
#7  _simics_module_init
#8  load_module_common.part.0
#9  SIM_load_module

Root cause

Two independent issues compound here.

1. The trigger. init() registers the init-tsffs CLI command by handing a bare new_command(...) call to run_python. SIM_run_python converts the value of a trailing expression to an attr_value_t. Newer Simics Base versions return a CliCommand object from new_command rather than None, and that object has no attr_value_t representation:

SimExc_Type: Failed converting return value from SIM_run_python()
to attr_value_t: unsupported Python object type(_run_python)

The command itself registers fine — I confirmed this by wrapping new_command and observing it return normally. Only the marshalling of the return value fails. #[simics_exception] then promotes the pending exception into an Err.

2. The segfault that hides it. The error path is itself unsound:

let tsffs = Tsffs::create()?;   // *mut ConfClass
...
.map_err(|e| { error!(tsffs, "{e}"); e })

simics::log! casts its object argument with $obj as *mut ConfObject. ConfClass and ConfObject are distinct opaque types, so this raw pointer cast compiles silently, and VT_log_error goes on to read a conf_class_t as a conf_object_t. That is the crash in VT_effective_log_level, and it swallows the actual error message.

Fix

Bind the result of new_command to a variable so the snippet is a statement rather than an expression. Nothing is returned, so no conversion is attempted.

Drop the error! call that passed a ConfClass where a ConfObject was required. The remaining .expect() surfaces any genuine failure without dereferencing an invalid pointer.

Verification

Rebuilt with cargo simics-build -r and loaded the resulting module:

simics> load-module tsffs
simics> init-tsffs
TSFFS initialized. Configure and use it as @tsffs.
simics> @print(tsffs)
<the tsffs 'tsffs'>

Previously this sequence segfaulted at load-module.

Note for maintainers

The unchecked $obj as *mut simics::ConfObject cast in the log! / error! macros in simulator-bindings makes passing a ConfClass a silent, guaranteed segfault. Constraining that parameter to AsConfObject / *mut ConfObject would have turned this into a compile error rather than a crash in module init. Might be worth a separate issue there.

[Copilot]

🟢 Approval recommended

The focused fix addresses both documented crash causes and is covered by existing module-loading integration paths.

Pull request overview

Fixes a module-load crash on newer Simics versions.

Changes:

• Prevents new_command results from being marshalled to attr_value_t.
• Removes unsafe error logging with a ConfClass pointer.

File summaries

File	Description
src/lib.rs	Safely registers init-tsffs during module initialization.

Review details

• Files reviewed: 1/1 changed files
• Comments generated: 0
• Review effort level: Balanced

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