Subject: Re: [PATCH v4 0/2] make sigaltstack() compatible with swapcontext()
To: Szabolcs Nagy <nsz@port70.net>
References: <1456781345-8243-1-git-send-email-stsp@list.ru>
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Cc: linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
        Andy Lutomirski <luto@amacapital.net>, Oleg Nesterov <oleg@redhat.com>,
        Shuah Khan <shuahkh@osg.samsung.com>
From: Stas Sergeev <stsp@list.ru>
Message-ID: <56DC92AE.3070707@list.ru>
Date: Sun, 6 Mar 2016 23:27:26 +0300
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06.03.2016 23:02, Szabolcs Nagy пишет:
> * Stas Sergeev <stsp@list.ru> [2016-03-01 00:29:03 +0300]:
>> The following patches make it possible to use swapcontext()
>> in a sighandler that works on sigaltstack.
> i don't think that's possible, the (obsolete) userspace
> *context functions cannot operate on kernel provided
> ucontext_t structs,
It doesn't have to.
It does the normal getcontext()/swapcontext() sequences,
as if it would be switching from any casual code place.
Kernel-provided context structs are completely irrelevant.
For more details please see the test-case I posted in that patch series.
It shows what can be done and how.

>   so they are not usable in signal
> handlers.
Please note the fact that swapcontext() also replaces the
signal mask as part of the context switching. This is a very
strong hint that it was intended to work with signal handlers.
And in fact it perfectly does.
What I want is only to make it friendly to sigaltstack.
I am not making it friendly to signal handlers in general,
because it already is.

> at least not on most target archs.
>
> so i don't understand how the tests can work portably.
If you apply my patch series, you can immediately test
it on any arch you want, thanks to the test-case my patch
adds to the kernel. Please let me know on what arch it fails.