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deps: uv: restore prior signal disposition on Android (DCP-4748) #4

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deps: uv: restore prior signal disposition on Android (DCP-4748) #4

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64 changes: 59 additions & 5 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 +32,25 @@
# define SA_RESTART 0
#endif

/* DCP-4748: Android-only. On Android, ART claims SIGSEGV/SIGBUS/SIGFPE/etc. via
* libsigchain; libuv's usual reset-to-SIG_DFL on the last unwatch clobbers that
* handler and emits an ERROR-level libsigchain log on every embedded
* node::FreeEnvironment(). On Android we instead save the disposition that was
* in effect before libuv installed its handler and restore it on the last
* unwatch. This is deliberately gated to __ANDROID__: bionic round-trips the
* sigaction flags correctly (unlike macOS, which drops SA_RESETHAND -- see
* upstream libuv #4299 / reverted #4216), so no other platform's behaviour is
* touched. The table is indexed by signum and accessed only under the global
* signal lock.
*/
#ifdef __ANDROID__
#ifndef NSIG
# define NSIG 65
#endif
static struct sigaction uv__signal_saved_sa[NSIG];
static unsigned char uv__signal_saved[NSIG];
#endif

typedef struct {
uv_signal_t* handle;
int signum;
Expand Down Expand Up @@ -221,9 +240,10 @@ 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 +254,29 @@ 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))
/* On Android, capture the previous disposition so uv__signal_unregister_handler()
* can restore it instead of resetting to SIG_DFL. `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. Off Android this is a no-op and behaviour is unchanged.
*/
oldp = NULL;
#ifdef __ANDROID__
if (save && signum > 0 && signum < NSIG)
oldp = &uv__signal_saved_sa[signum];
#else
(void) save;
#endif

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

#ifdef __ANDROID__
if (oldp != NULL)
uv__signal_saved[signum] = 1;
#endif

return 0;
}

Expand All @@ -246,8 +285,23 @@ static void uv__signal_unregister_handler(int signum) {
/* When this function is called, the signal lock must be held. */
struct sigaction sa;

/* On Android, restore the disposition captured when uv__signal_register_handler()
* first installed our handler for this signum, if we have it; this avoids the
* libsigchain "Setting SIGxxx to SIG_DFL" report and clobbering ART's handler.
* Off Android, reset to SIG_DFL as upstream does.
*/
#ifdef __ANDROID__
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;
}
#else
memset(&sa, 0, sizeof(sa));
sa.sa_handler = SIG_DFL;
#endif

/* 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 +467,7 @@ 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 +622,7 @@ 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