mem — MCP server for process memory introspection

Live process memory introspection, debugger, and valgrind runner. Linux-only (x86_64). Runs as an MCP stdio server for the pi agent.

Tools

Related MCP server: re-gdb

Requirements

• Linux (process_vm_readv/writev, ptrace, /proc)

• ptrace_scope = 0 (or use run tool to spawn child processes)

• valgrind (optional, for valgrind_run)

ptrace_scope limitation

On Ubuntu (default ptrace_scope=1), process_vm_readv and ptrace only work on direct child processes of the MCP server. To inspect a program:

1. Use run to spawn it — the server is its parent, all tools work

2. Or set ptrace_scope=0: echo 0 | sudo tee /proc/sys/kernel/yama/ptrace_scope

3. Or use CAP_SYS_PTRACE

The run tool makes the child fully inspectable without any sysadmin changes.

Debugging workflow

1. run   → spawns the target program, returns PID
2. maps  → read its memory layout
3. mem_read → read bytes from any address
4. attach → ptrace-stop the process
5. registers → read CPU registers (rip, rsp, rax, etc.)
6. mem_write → patch a variable or instruction
7. detach → resume execution
8. valgrind_run → check for memory errors

Wiring

pi.mcpServers in package.json declares the server; the hub merges it into pi's mcp.json when the package is registered (this workspace is a watched hub workspace, so a new package dir wires itself). The command is relative to this dir on purpose — hub resolves it. Build first, then restart pi: pi reads mcp.json at startup.

Build

cd /home/feb/dev/_pi_extensions/mem
cargo build --release

Safety

• mem_write can crash or corrupt the target process.

• attach stops the target process. Always detach when done.

• valgrind jobs run with a timeout (default 300s).

Not wired by default

pi.mcpServers is empty on purpose — 11 tools on every session's surface for a debugger that fires a few times a year is a bad trade. Wire it where you need it, with a .mcp.json in the project root:

{ "mcpServers": { "mem": {
  "command": "/home/feb/dev/_pi_extensions/mem/target/release/mem",
  "args": [], "directTools": true, "lifecycle": "lazy-keep-alive"
} } }