Fix NULL datagram segfault in parallel slave config FSM

[Copilot]

The parallel-slave-config branch crashes with SIGSEGV in EtherCAT-IDLE because ec_fsm_change_t (and sibling sub-FSMs) inside fsm_slave_config store their own datagram pointer, initialized to NULL and never updated before execution. When ec_fsm_change_state_start() fires, it dereferences fsm->datagram = 0x0.

Changes

• master/fsm_slave.c — ec_fsm_slave_exec(): Propagate the incoming datagram to all config sub-FSMs (fsm_change, fsm_coe_config, fsm_soe_config, fsm_eoe_config) on every cycle — both at config start and during ongoing execution — since the pointer changes each cycle from the ext_ring:

if (fsm->config_running) {
    fsm->fsm_slave_config.datagram = datagram;
    fsm->fsm_change.datagram = datagram;      // was missing — root cause of crash
    fsm->fsm_coe_config.datagram = datagram;
    fsm->fsm_soe_config.datagram = datagram;
#ifdef EC_EOE
    fsm->fsm_eoe_config.datagram = datagram;
#endif
    ...
}

• master/fsm_slave.h: Guard ec_fsm_eoe_t fsm_eoe_config with #ifdef EC_EOE to match the established pattern for EoE-conditional fields.

• master/fsm_slave.c — init/clear: Guard ec_fsm_eoe_init/ec_fsm_eoe_clear for fsm_eoe_config with #ifdef EC_EOE; pass NULL for the eoe argument to ec_fsm_slave_config_init() when EC_EOE is disabled.

Original prompt

Bug Description

The parallel-slave-config branch crashes with a segmentation fault in the EtherCAT-IDLE thread when slaves need configuration. The crash occurs because the sub-FSMs (fsm_change, fsm_coe_config, fsm_soe_config, fsm_eoe_config) inside each slave's fsm_slave_config are initialized with a NULL datagram pointer, and this pointer is never updated before the sub-FSMs are executed.

Crash Backtrace

Thread 5 "EtherCAT-IDLE" received signal SIGSEGV, Segmentation fault.
#0  ec_datagram_prealloc (datagram=0x0, size=2) at ../datagram.c:142
#1  ec_datagram_fpwr (datagram=0x0, ...) at ../datagram.c:297
#2  ec_fsm_change_state_start (fsm=0x7ffff0001008) at ../fsm_change.c:195
#3  ec_fsm_change_exec (fsm=0x7ffff0001008) at ../fsm_change.c:159
#4  ec_fsm_slave_config_enter_init (fsm=0x7ffff0000ee0) at ../fsm_slave_config.c:241
#5  ec_fsm_slave_config_exec (fsm=0x7ffff0000ee0) at ../fsm_slave_config.c:202
#6  ec_fsm_slave_exec (fsm=0x7ffff0000d20, datagram=0x5555555758f8) at ../fsm_slave.c:178
#7  ec_master_exec_slave_fsms (master=0x555555574e30) at ../master.c:1341
#8  ec_master_idle_thread (priv_data=0x555555574e30) at ../master.c:1397

Root Cause

In master/fsm_slave.c, the ec_fsm_slave_init() function initializes the sub-FSMs with NULL datagram pointers:

ec_fsm_change_init(&fsm->fsm_change, NULL);   // NULL datagram!

When ec_fsm_slave_exec() runs, it sets fsm->fsm_slave_config.datagram = datagram but does NOT propagate the datagram pointer to the sub-FSMs (fsm_change, fsm_coe_config, fsm_soe_config, fsm_eoe_config). The ec_fsm_change_t struct stores its own separate datagram pointer, which remains NULL.

When ec_fsm_slave_config_exec() is called, it eventually calls ec_fsm_change_exec() → ec_fsm_change_state_start() → ec_datagram_fpwr(fsm->datagram, ...) where fsm->datagram is 0x0, causing the segfault.

Required Fix

In master/fsm_slave.c, in the ec_fsm_slave_exec() function, propagate the external datagram pointer to ALL sub-FSMs before executing ec_fsm_slave_config_exec(). This must be done both when starting configuration AND on every subsequent execution cycle (since the datagram pointer may change each cycle from the ext_ring):

if (fsm->config_requested && !fsm->config_running) {
    fsm->config_requested = 0;
    fsm->config_running = 1;
    fsm->fsm_slave_config.datagram = datagram;
    fsm->fsm_change.datagram = datagram;          // MUST SET
    fsm->fsm_coe_config.datagram = datagram;      // MUST SET  
    fsm->fsm_soe_config.datagram = datagram;      // MUST SET
    fsm->fsm_eoe_config.datagram = datagram;      // MUST SET
    ec_fsm_slave_config_start(&fsm->fsm_slave_config, fsm->slave);
}

if (fsm->config_running) {
    fsm->fsm_slave_config.datagram = datagram;
    fsm->fsm_change.datagram = datagram;          // MUST SET every cycle
    fsm->fsm_coe_config.datagram = datagram;      // MUST SET every cycle
    fsm->fsm_soe_config.datagram = datagram;      // MUST SET every cycle
    fsm->fsm_eoe_config.datagram = datagram;      // MUST SET every cycle
    // ...
}

Additionally, the fsm_eoe_config field in master/fsm_slave.h (line 82) and its init/clear calls in fsm_slave.c should be guarded with #ifdef EC_EOE to match the convention used elsewhere in the codebase. When EC_EOE is not defined, the ec_fsm_slave_config_init() call should pass NULL for the eoe parameter.

Files to Modify

• master/fsm_slave.c — Propagate datagram to all sub-FSMs in ec_fsm_slave_exec(); guard fsm_eoe_config init/clear with #ifdef EC_EOE
• master/fsm_slave.h — Guard ec_fsm_eoe_t fsm_eoe_config with #ifdef EC_EOE

This pull request was created from Copilot chat.

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