Re: [PATCH 00/13] tools/nolibc: riscv: Add full rv32 support

From: Zhangjin Wu <falcon@tinylab.org>
To: w@1wt.eu
Cc: falcon@tinylab.org, linux-kernel@vger.kernel.org,
	linux-kselftest@vger.kernel.org, linux-riscv@lists.infradead.org,
	thomas@t-8ch.de
Subject: Re: [PATCH 00/13] tools/nolibc: riscv: Add full rv32 support
Date: Tue, 30 May 2023 18:06:29 +0800	[thread overview]
Message-ID: <20230530100629.383892-1-falcon@tinylab.org> (raw)
In-Reply-To: <20230529113143.GB2762@1wt.eu>

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Hi, Thomas, Willy

> Hi Thomas,
> 
> On Mon, May 29, 2023 at 10:45:40AM +0200, Thomas Weißschuh wrote:
> > <lots of implementation>
> > 
> > > usage:
> > > 
> > >     $ gcc -o nolibc-test tools/testing/selftests/nolibc/nolibc-test.c
> > >     $ ./nolibc-test
> > >     ...
> > >     35 gettimeofday_tz = 0                                           [OK]
> > >     36 gettimeofday_tv_tz = 0                                        [OK]
> > >     37 gettimeofday_bad1 = -1                                       [FAIL] (continued by sigaction/siglongjmp/sigsetjmp)
> > >     38 gettimeofday_bad2 = -1                                       [FAIL] (continued by sigaction/siglongjmp/sigsetjmp)
> > >     39 getpagesize = 0                                               [OK]
> > >     40 ioctl_tiocinq = 0                                             [OK]
> > >     41 ioctl_tiocinq = 0                                             [OK]
> > >     ...
> > > 
> > > It did work as expected, but for nolibc, we still need to add sigaction/siglongjump/sigsetjmp support.
> > > 
> > > Will send a patch based on Willy's latest branch, perhaps this may help us to
> > > verify the future sigaction/siglongjump/sigsetjmp for nolibc.
> > > 
> > > ref: https://www.ibm.com/docs/en/i/7.1?topic=ssw_ibm_i_71/apis/sigsetj.html
> > >      https://www.ibm.com/docs/en/zos/2.1.0?topic=functions-siglongjmp-restore-stack-environment-signal-mask
> > 
> > This seems very complicated for fairly limited gain to be honest.
> 
> I agree as well. I'm not denying the fact that one day we may want to
> support signal, longjmp and friends but I'm not convinced we want to
> go through that just to make a few uncertain tests succeed.
>

I agree too, I'm just interested in whether it is able to restore the
whole test after a user-space invalid memory access ;-) 

> > If we really want to keep the current testcase we could also ensure that
> > the pointer does not fall into the first page, as the first page is not
> > mapped under Linux:
> > 
> > 0 <= addr < PAGE_SIZE
> > 
> > Or instead of PAGE_SIZE just hardcode 4096, as that should be the
> > minimum size and and does not require a lookup.
> 
> I would not even do that. It brings nothing to the application layer and
> inflates the code. I'd rather just get rid of the EFAULT test cases that
> rely on an unreliable syscall (i.e. one that may either be a real syscall
> or an emulated one). The value brought by these tests is extremely low
> and they were implemented only because they were easy to do. If they're
> causing pain, let's just drop them.

Thanks, one of the sent v2 patches has dropped both of them.

yesterday, based on the demo code pasted in this email thread, I went
further to implement a cleaner user-space 'efault' handler, with this
handler, it is able to continue next test, and without this handler,
just skip the test, so, it can be used to add future test cases for
sigaction/sigsetjmp/siglongjmp.

besides, a multiple 'run' support is added too, will share the new code
as a new standalone patchset later but I'm not expecting it is
mergeable.

Thanks,
Zhangjin

> 
> Willy