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erts: Fix undefined behavior of driver start callback #11435

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93911ad
erts: Fix undefined behavior of driver start callback
sverker Aug 6, 2026
0e6ef38
erts: Remove documentation for system drivers start callback
sverker Aug 6, 2026
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8 changes: 1 addition & 7 deletions erts/doc/references/driver_entry.md
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Original file line number Diff line number Diff line change
Expand Up @@ -114,14 +114,8 @@ typedef struct erl_drv_entry {
int (*init)(void); /* Called at system startup for statically
linked drivers, and after loading for
dynamically loaded drivers */
#ifndef ERL_SYS_DRV
ErlDrvData (*start)(ErlDrvPort port, char *command);
/* Called when open_port/2 is invoked,
return value -1 means failure */
#else
ErlDrvData (*start)(ErlDrvPort port, char *command, SysDriverOpts* opts);
/* Special options, only for system driver */
#endif
/* Called when open_port/2 is invoked */
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void (*stop)(ErlDrvData drv_data);
/* Called when port is closed, and when the
emulator is halted */
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4 changes: 3 additions & 1 deletion erts/emulator/beam/global.h
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Expand Up @@ -225,7 +225,9 @@ struct erts_driver_t_ {
DE_Handle *handle;
erts_mtx_t *lock;
ErlDrvEntry *entry;
ErlDrvData (*start)(ErlDrvPort port, char *command, SysDriverOpts* opts);
ErlDrvData (*start)(ErlDrvPort port, char *command);
ErlDrvData (*start_sys_drv)(ErlDrvPort port, char *command,
SysDriverOpts* opts);
void (*stop)(ErlDrvData drv_data);
void (*finish)(void);
void (*flush)(ErlDrvData drv_data);
Expand Down
32 changes: 23 additions & 9 deletions erts/emulator/beam/io.c
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Expand Up @@ -93,7 +93,7 @@ static erts_atomic64_t bytes_in;
static erts_atomic64_t bytes_out;

static void deliver_result(Port *p, Eterm sender, Eterm pid, Eterm res);
static int init_driver(erts_driver_t *, ErlDrvEntry *, DE_Handle *);
static int init_driver(erts_driver_t *, ErlDrvEntry *, DE_Handle *, bool);
static void terminate_port(Port *p);
static void pdl_init(void);
static int driver_failure_term(ErlDrvPort ix, Eterm term, int eof);
Expand Down Expand Up @@ -685,7 +685,7 @@ erts_open_driver(erts_driver_t* driver, /* Pointer to driver. */
&opts->high_msgq_watermark);

error_number = error_type = 0;
if (driver->start) {
if (driver->start || driver->start_sys_drv) {
ERTS_MSACC_PUSH_STATE_M();
if (ERTS_IS_P_TRACED_FL(port, F_TRACE_SCHED_PORTS)) {
trace_sched_ports_where(port, am_in, am_open);
Expand All @@ -710,7 +710,13 @@ erts_open_driver(erts_driver_t* driver, /* Pointer to driver. */
}
#endif

drv_data = (*driver->start)(ERTS_Port2ErlDrvPort(port), name, opts);
if (driver->start_sys_drv) {
drv_data = (*driver->start_sys_drv)(ERTS_Port2ErlDrvPort(port),
name, opts);
}
else {
drv_data = (*driver->start)(ERTS_Port2ErlDrvPort(port), name);
}
if (((SWord) drv_data) == -1)
error_type = -1;
else if (((SWord) drv_data) == -2) {
Expand Down Expand Up @@ -3024,10 +3030,10 @@ void erts_init_io(int port_tab_size,
erts_tsd_set(driver_list_lock_status_key, (void *) 1);
erts_rwmtx_rwlock(&erts_driver_list_lock);

init_driver(&fd_driver, &fd_driver_entry, NULL);
init_driver(&spawn_driver, &spawn_driver_entry, NULL);
init_driver(&fd_driver, &fd_driver_entry, NULL, true);
init_driver(&spawn_driver, &spawn_driver_entry, NULL, true);
#ifndef __WIN32__
init_driver(&forker_driver, &forker_driver_entry, NULL);
init_driver(&forker_driver, &forker_driver_entry, NULL, true);
#endif
erts_init_static_drivers();
for (dp = driver_tab; dp->de != NULL; dp++)
Expand Down Expand Up @@ -7547,7 +7553,8 @@ no_stop_select_callback(ErlDrvEvent event, void* private)
((DE)->major_version == (MAJOR) && (DE)->minor_version >= (MINOR)))

static int
init_driver(erts_driver_t *drv, ErlDrvEntry *de, DE_Handle *handle)
init_driver(erts_driver_t *drv, ErlDrvEntry *de, DE_Handle *handle,
bool is_system_driver)
{
drv->name_atom = erts_atom_put((byte*)de->driver_name,
sys_strlen(de->driver_name),
Expand All @@ -7570,7 +7577,14 @@ init_driver(erts_driver_t *drv, ErlDrvEntry *de, DE_Handle *handle)
}
drv->entry = de;

drv->start = de->start;
if (is_system_driver) {
drv->start = NULL;
drv->start_sys_drv = de->start;
}
else {
drv->start = (ErlDrvData (*)(ErlDrvPort, char *)) de->start;
drv->start_sys_drv = NULL;
}
drv->stop = de->stop;
drv->finish = de->finish;
drv->flush = de->flush;
Expand Down Expand Up @@ -7651,7 +7665,7 @@ int erts_add_driver_entry(ErlDrvEntry *de, DE_Handle *handle,
}

if (!err) {
err = init_driver(dp, de, handle);
err = init_driver(dp, de, handle, false);

if (taint) {
erts_add_taint(dp->name_atom);
Expand Down
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