Thank you Peter,
I will address you comments and send a new version of the series.
Laurent
Le 11/02/2020 à 18:05, Peter Maydell a écrit :
> 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
>
