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deps: uv: restore prior signal disposition instead of SIG_DFL (DCP-4748) #4

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deps: uv: restore prior signal disposition instead of SIG_DFL (DCP-4748) #4

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60 changes: 53 additions & 7 deletions deps/uv/src/unix/signal.c
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Original file line number Diff line number Diff line change
Expand Up @@ -32,6 +32,27 @@
# define SA_RESTART 0
#endif

/* Some libcs don't expose NSIG; 65 covers all standard and realtime signals on
* the platforms libuv supports. An out-of-range signum simply skips the
* save/restore path below and keeps the historical SIG_DFL behaviour.
*/
#ifndef NSIG
# define NSIG 65
#endif

/* Remembers the signal disposition that was in effect before libuv first
* installed uv__signal_handler() for a given signum, so that
* uv__signal_unregister_handler() can restore it instead of blindly forcing
* SIG_DFL. Restoring the prior handler is strictly more correct than a reset,
* and on platforms where another runtime owns these signals -- notably
* Android's ART, whose libsigchain logs (and can be destabilised by) any reset
* of a claimed signal to SIG_DFL -- it avoids clobbering that handler.
* Indexed by signum and only touched while the global signal lock is held, so
* it needs no synchronisation of its own.
*/
static struct sigaction uv__signal_saved_sa[NSIG];
static unsigned char uv__signal_saved[NSIG];

typedef struct {
uv_signal_t* handle;
int signum;
Expand Down Expand Up @@ -221,9 +242,10 @@ static void uv__signal_handler(int signum) {
}


static int uv__signal_register_handler(int signum, int oneshot) {
static int uv__signal_register_handler(int signum, int oneshot, int save) {
/* When this function is called, the signal lock must be held. */
struct sigaction sa;
struct sigaction* oldp;

/* XXX use a separate signal stack? */
memset(&sa, 0, sizeof(sa));
Expand All @@ -234,10 +256,23 @@ static int uv__signal_register_handler(int signum, int oneshot) {
if (oneshot)
sa.sa_flags |= SA_RESETHAND;

/* XXX save old action so we can restore it later on? */
if (sigaction(signum, &sa, NULL))
/* Resolve the historical "save old action so we can restore it later on"
* TODO by capturing the previous disposition straight into the per-signum
* slot. `save` is set only on the transition from "no libuv handler" to
* "libuv handler installed" for this signum (see uv__signal_start); the
* oneshot re-registration paths pass save=0 so they never overwrite the
* captured disposition with libuv's own handler.
*/
oldp = NULL;
if (save && signum > 0 && signum < NSIG)
oldp = &uv__signal_saved_sa[signum];

if (sigaction(signum, &sa, oldp))
return UV__ERR(errno);

if (oldp != NULL)
uv__signal_saved[signum] = 1;

return 0;
}

Expand All @@ -246,8 +281,19 @@ static void uv__signal_unregister_handler(int signum) {
/* When this function is called, the signal lock must be held. */
struct sigaction sa;

memset(&sa, 0, sizeof(sa));
sa.sa_handler = SIG_DFL;
/* Restore the disposition captured when uv__signal_register_handler() first
* installed our handler for this signum, if we have it; otherwise fall back
* to the historical SIG_DFL reset. Restoring a non-default handler (e.g.
* ART's on Android) avoids the libsigchain "Setting SIGxxx to SIG_DFL"
* report.
*/
if (signum > 0 && signum < NSIG && uv__signal_saved[signum]) {
sa = uv__signal_saved_sa[signum];
uv__signal_saved[signum] = 0;
} else {
memset(&sa, 0, sizeof(sa));
sa.sa_handler = SIG_DFL;
}

/* sigaction can only fail with EINVAL or EFAULT; an attempt to deregister a
* signal implies that it was successfully registered earlier, so EINVAL
Expand Down Expand Up @@ -413,7 +459,7 @@ static int uv__signal_start(uv_signal_t* handle,
first_handle = uv__signal_first_handle(signum);
if (first_handle == NULL ||
(!oneshot && (first_handle->flags & UV_SIGNAL_ONE_SHOT))) {
err = uv__signal_register_handler(signum, oneshot);
err = uv__signal_register_handler(signum, oneshot, first_handle == NULL);
if (err) {
/* Registering the signal handler failed. Must be an invalid signal. */
uv__signal_unlock_and_unblock(&saved_sigmask);
Expand Down Expand Up @@ -568,7 +614,7 @@ static void uv__signal_stop(uv_signal_t* handle) {
rem_oneshot = handle->flags & UV_SIGNAL_ONE_SHOT;
first_oneshot = first_handle->flags & UV_SIGNAL_ONE_SHOT;
if (first_oneshot && !rem_oneshot) {
ret = uv__signal_register_handler(handle->signum, 1);
ret = uv__signal_register_handler(handle->signum, 1, 0);
assert(ret == 0);
(void)ret;
}
Expand Down