On Tue, 4 Feb 2020 at 17:11, Laurent Vivier <laur...@vivier.eu> wrote:
>
> Some RT signals can be in use by glibc,
> it's why SIGRTMIN (34) is generally greater than __SIGRTMIN (32).
>
> So SIGRTMIN cannot be mapped to TARGET_SIGRTMIN.
>
> Instead of swapping only SIGRTMIN and SIGRTMAX, map all the
> range [TARGET_SIGRTMIN ... TARGET_SIGRTMAX - X] to
> [__SIGRTMIN + X ... SIGRTMAX ]
> (SIGRTMIN is __SIGRTMIN + X).
>
> Signed-off-by: Laurent Vivier <laur...@vivier.eu>
> ---
In general I think this is a good approach to trying to deal
with this long-standing issue in a pragmatic and not too
complicated way, so thanks for writing this patchset. I have
some fairly minor comments on the code below.
>
> Notes:
> v2: ignore error when target sig <= TARGET_NSIG but host sig > SIGRTMAX
> replace i, j by target_sig, host_sig
> update signal_table_init() trace message
>
> linux-user/signal.c | 37 ++++++++++++++++++++++++++++++-------
> linux-user/trace-events | 3 +++
> 2 files changed, 33 insertions(+), 7 deletions(-)
>
> diff --git a/linux-user/signal.c b/linux-user/signal.c
> index c1e664f97a7c..e7e5581a016f 100644
> --- a/linux-user/signal.c
> +++ b/linux-user/signal.c
> @@ -498,18 +498,23 @@ static int core_dump_signal(int sig)
>
> static void signal_table_init(void)
> {
> - int host_sig, target_sig;
> + int host_sig, target_sig, count;
>
> /*
> - * Nasty hack: Reverse SIGRTMIN and SIGRTMAX to avoid overlap with
> - * host libpthread signals. This assumes no one actually uses SIGRTMAX
> :-/
> - * To fix this properly we need to do manual signal delivery multiplexed
> - * over a single host signal.
> + * some RT signals can be in use by glibc,
> + * it's why SIGRTMIN (34) is generally greater than __SIGRTMIN (32)
> */
> - host_to_target_signal_table[__SIGRTMIN] = __SIGRTMAX;
> - host_to_target_signal_table[__SIGRTMAX] = __SIGRTMIN;
> + for (host_sig = SIGRTMIN; host_sig <= SIGRTMAX; host_sig++) {
> + target_sig = host_sig - SIGRTMIN + TARGET_SIGRTMIN;
> + if (target_sig <= TARGET_NSIG) {
> + host_to_target_signal_table[host_sig] = target_sig;
> + }
> + }
So the effect of this is that we now support target signals
starting from TARGET_SIGRTMIN and going up until we run out
of host realtime signals that the host libc hasn't reserved ?
That seems reasonable, since glibc at least uses only the
lower 2 rt signals and probably nobody's using the upper ones.
But this would be a good place to have a comment explaining
the limitation (and that if it needed to be fixed we'd have
to multiplex guest signals onto a single host signal). You
could also mention that attempts to configure the "missing"
signals via sigaction will be silently ignored.
> /* generate signal conversion tables */
> + for (target_sig = 1; target_sig <= TARGET_NSIG; target_sig++) {
> + target_to_host_signal_table[target_sig] = _NSIG; /* poison */
> + }
> for (host_sig = 1; host_sig < _NSIG; host_sig++) {
> if (host_to_target_signal_table[host_sig] == 0) {
> host_to_target_signal_table[host_sig] = host_sig;
> @@ -519,6 +524,15 @@ static void signal_table_init(void)
> target_to_host_signal_table[target_sig] = host_sig;
> }
> }
> +
> + if (TRACE_SIGNAL_TABLE_INIT_BACKEND_DSTATE()) {
This isn't the right way to conditionalize expensive stuff
that's only used in trace events. You want to use
trace_event_get_state_backends() (see docs/devel/tracing.txt
for details).
> + for (target_sig = 1, count = 0; target_sig <= TARGET_NSIG;
> target_sig++) {
> + if (target_to_host_signal_table[target_sig] == _NSIG) {
> + count++;
> + }
> + }
> + trace_signal_table_init(count);
> + }
> }
>
> void signal_init(void)
> @@ -817,6 +831,8 @@ int do_sigaction(int sig, const struct target_sigaction
> *act,
> int host_sig;
> int ret = 0;
>
> + trace_signal_do_sigaction_guest(sig, TARGET_NSIG);
> +
> if (sig < 1 || sig > TARGET_NSIG || sig == TARGET_SIGKILL || sig ==
> TARGET_SIGSTOP) {
> return -TARGET_EINVAL;
> }
> @@ -847,6 +863,13 @@ int do_sigaction(int sig, const struct target_sigaction
> *act,
>
> /* we update the host linux signal state */
> host_sig = target_to_host_signal(sig);
> + trace_signal_do_sigaction_host(host_sig, TARGET_NSIG);
> + if (host_sig > SIGRTMAX) {
> + /* we don't have enough host signals to map all target signals */
> + qemu_log_mask(LOG_UNIMP, "Unsupported target signal #%d,
> ignored\n",
> + sig);
> + return 0;
We should have a comment here mentioning why we don't return
an error code here (and explicitly noting that the Go runtime
is the major one which we don't want to upset).
> + }
> if (host_sig != SIGSEGV && host_sig != SIGBUS) {
> sigfillset(&act1.sa_mask);
> act1.sa_flags = SA_SIGINFO;
> diff --git a/linux-user/trace-events b/linux-user/trace-events
> index f6de1b8befc0..0296133daeb6 100644
> --- a/linux-user/trace-events
> +++ b/linux-user/trace-events
> @@ -1,6 +1,9 @@
> # See docs/devel/tracing.txt for syntax documentation.
>
> # signal.c
> +signal_table_init(int i) "number of unavailable signals: %d"
> +signal_do_sigaction_guest(int sig, int max) "target signal %d (MAX %d)"
> +signal_do_sigaction_host(int sig, int max) "host signal %d (MAX %d)"
> # */signal.c
> user_setup_frame(void *env, uint64_t frame_addr) "env=%p
> frame_addr=0x%"PRIx64
> user_setup_rt_frame(void *env, uint64_t frame_addr) "env=%p
> frame_addr=0x%"PRIx64
thanks
-- PMM
