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

[Laurent Vivier]

Le 29/01/2020 à 17:12, Laurent Vivier a écrit :
> 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?

Markus has sent me the information.

I'm able to reproduce the problem with an "Hello World" go program and
go 1.10 (basically ubuntu bionic/arm64).

Thanks,
Laurent