Re: [PATCH] Handling SIGSETXID used by glibc NPTL setuid/setgid

[Laurent Vivier]

Le 28/01/2020 à 10:26, Peter Maydell a écrit :
> On Thu, 16 Jan 2020 at 11:58, Matus Kysel <address@hidden> wrote:
>>
>> Used same style to handle another glibc reserved signal SIGSETXID (33),
>> that is used by glibc NPTL setuid/setgid functions. This should fix problems
>> with application using those functions and failing with error
>> "qemu:handle_cpu_signal received signal outside vCPU context".
>>
>> Signed-off-by: Matus Kysel <address@hidden>
>> ---
>>  linux-user/signal.c | 13 +++++++++----
>>  1 file changed, 9 insertions(+), 4 deletions(-)
>>
>> diff --git a/linux-user/signal.c b/linux-user/signal.c
>> index 0128bde4d2..c59221fd0a 100644
>> --- a/linux-user/signal.c
>> +++ b/linux-user/signal.c
>> @@ -66,11 +66,16 @@ static uint8_t host_to_target_signal_table[_NSIG] = {
>>      [SIGPWR] = TARGET_SIGPWR,
>>      [SIGSYS] = TARGET_SIGSYS,
>>      /* next signals stay the same */
>> -    /* 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.  */
>> +    /*
>> +     * Nasty hack: Swap SIGRTMIN and SIGRTMIN + 1 with SIGRTMAX and 
>> SIGRTMAX - 1
>> +     * to avoid overlap with host libpthread (NPTL glibc) signals.
>> +     * This assumes no one actually uses SIGRTMAX and SIGRTMAX - 1 :-/
>> +     * To fix this properly we need to do manual signal delivery multiplexed
>> +     * over a single host signal.
>> +     */
>>      [__SIGRTMIN] = __SIGRTMAX,
>> +    [__SIGRTMIN + 1] = __SIGRTMAX - 1,
>> +    [__SIGRTMAX - 1] = __SIGRTMIN + 1,
>>      [__SIGRTMAX] = __SIGRTMIN,
>>  };
>>  static uint8_t target_to_host_signal_table[_NSIG];
>> --
>> 2.17.1
> 
> This is a long-standing known problem, but doing this is likely
> to break currently-working guest binaries (notably things written
> in Go). See for example the discussion on this thread:
> https://lists.gnu.org/archive/html/qemu-devel/2019-08/msg03804.html

Peter,

I try to fix this problem and I'd like to find a reproducer for the Go
problem.

I tried to write an "hello world" program and run it in an arm64/bionic
chroot but there is no problem (with and without this patch).

Any hints?

Thanks,
Laurent