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Re: [PATCH 4/6] accel/tcg: Declare missing cpu_loop_exit*() stubs

From: Claudio Fontana
Subject: Re: [PATCH 4/6] accel/tcg: Declare missing cpu_loop_exit*() stubs
Date: Mon, 18 Jan 2021 11:03:08 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0

On 1/18/21 10:39 AM, Philippe Mathieu-Daudé wrote:
> On 1/18/21 10:29 AM, Claudio Fontana wrote:
>> On 1/17/21 5:48 PM, Philippe Mathieu-Daudé wrote:
>>> cpu_loop_exit*() functions are declared in accel/tcg/cpu-exec-common.c,
>>> and are not available when TCG accelerator is not built. Add stubs so
>>> linking without TCG succeed.
>> The reason why stubs are needed here at all seems to be that that the code
>> calling cpu_loop_exit is not refactored properly yet;
> I agree ...
>> if we look at the example of i386, after the refactoring moving tcg related 
>> code into target/i386/tcg/,
>> (and really even before that I think),
>> the code calling cpu_loop_exit is not built for non-TCG at all, and so we 
>> don't need stubs.
>> I am ok with this anyway, just wanted to convey that I think we should look 
>> at stubs as a necessary evil until all code stops mixing tcg, kvm and other 
>> accels...
>> Thanks,
>> Claudio
>>> Problematic files:
>>> - hw/semihosting/console.c in qemu_semihosting_console_inc()
>>> - hw/ppc/spapr_hcall.c in h_confer()
>>> - hw/s390x/ipl.c in s390_ipl_reset_request()
>>> - hw/misc/mips_itu.c
> ... but I have no clue how to refactore these, as they
> are used in both KVM and TCG.
> How would you do? I'm stuck with the semihosting code
> dependency on ARM since 2 years...
> Phil.

Just naively looking at this, qemu_semihosting_console_inc seems called only by
do_arm_semihosting in target/arm/arm-semi.c,

which in turn is called by linux-user (TCG),

target/arm/m_helper.c in arm_v7m_cpu_do_interrupt(),
which I would assume is TCG only too, just waiting for the TCG/KVM refactoring 
in ARM, which I would assume would make cpu_tcg.c TCG-only,

target/arm/helper.c in handle_semihosting, which is already wrapped in #ifdef 
CONFIG_TCG and is commented with:

* We only see semihosting exceptions in TCG only as they are not                
* trapped to the hypervisor in KVM.                                             

So am I wrong in my assumption that as soon as we are able to separate TCG vs 
KVM in target/arm/ , the issue of hw/semihosting/console.c would be solved?

Did not look at the other cases.



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