Re: [PATCH v4 4/4] meson: Warn when TCI is selected but TCG backend is available

From: Stefan Weil <sw@weilnetz.de>
To: "Alex Bennée" <alex.bennee@linaro.org>
Cc: "Thomas Huth" <thuth@redhat.com>,
	"Daniel P. Berrangé" <berrange@redhat.com>,
	"Richard Henderson" <richard.henderson@linaro.org>,
	qemu-devel@nongnu.org, "Paolo Bonzini" <pbonzini@redhat.com>,
	"Philippe Mathieu-Daudé" <philmd@redhat.com>
Subject: Re: [PATCH v4 4/4] meson: Warn when TCI is selected but TCG backend is available
Date: Tue, 26 Jan 2021 20:44:35 +0100	[thread overview]
Message-ID: <89209f1b-29ad-e5df-6d45-b2480db4775e@weilnetz.de> (raw)
In-Reply-To: <875z3jy3tt.fsf@linaro.org>

Am 26.01.21 um 18:24 schrieb Alex Bennée:
> I'm going to go out on a limb and guess you have commit:
>
>    23a77b2d18 (build-system: clean up TCG/TCI configury)
>
> which temporarily has the effect of disabling TCI. See
>
>    Subject: Re: [PATCH v4 1/4] configure: Fix --enable-tcg-interpreter
>    From: Paolo Bonzini <pbonzini@redhat.com>
>    Message-ID: <2b8b6291-b54c-b285-ae38-21f067a8497d@redhat.com>
>    Date: Mon, 25 Jan 2021 17:36:42 +0100
>
> with that fix fixed I see the same failures as Richard:
>
>    ./qemu-arm ./tests/tcg/arm-linux-user/fcvt > /dev/null
>    TODO ../../tcg/tci.c:614: tcg_qemu_tb_exec()
>    ../../tcg/tci.c:614: tcg fatal error
>    qemu: uncaught target signal 11 (Segmentation fault) - core dumped
>    fish: “./qemu-arm ./tests/tcg/arm-linu…” terminated by signal SIGSEGV (Address boundary error)
>
> which does raise the question before today when was the last time anyone
> attempted to run check-tcg on this?

Yes, I tested with latest git master and did not notice that 
--enable-tcg-interpreter was broken.

Paolo's patch fixed that.I could reproduce the fatal assertions which 
were all caused by the same missing TCG opcode implementation.

I have sent a trivial patch which adds that implementation and fixes all 
segmentation faults.

>> Daniel, regarding your comment: TCI has 100 % test coverage for the
>> productive code lines.
> By what tests? The fact you don't hit asserts in your day to day testing
> doesn't mean there are features missing that are easily tripped up or
> that TCI got it right.

I was not talking about the TODO assertions. When I wrote TCI, I only 
enabled and included code which was triggered by my testing - that's why 
I said the productive code lines have 100 % test coverage. TODO 
assertions are not productive code, but debug code which were made to 
detect new test cases. They were successful, too, because they were 
triggered by some tests in `make check-tcg`.

>> All code lines which were never tested raise an
>> assertion, so can easily be identified (and fixed as soon as there is a
>> test case which triggers such an assertion). The known deficits are
>> speed, missing TCG opcodes, unimplemented TCG opcodes because of missing
>> test cases and missing support for some host architectures.

As soon as I was aware of the new test cases, adding the missing TCG 
opcode implementation was not difficult.

> Passing check-tcg would be a minimum for me.

It should pass now unless you get timeouts for some tests. Please tell 
me if more TODO assertions are triggered by new tests.

Stefan