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From: Alexander Graf <agraf@csgraf.de>
To: Richard Henderson <richard.henderson@linaro.org>,
	Peter Maydell <peter.maydell@linaro.org>
Cc: "Eduardo Habkost" <ehabkost@redhat.com>,
	"Philippe Mathieu-Daudé" <philmd@redhat.com>,
	"QEMU Developers" <qemu-devel@nongnu.org>,
	"Cameron Esfahani" <dirty@apple.com>,
	"Roman Bolshakov" <r.bolshakov@yadro.com>,
	qemu-arm <qemu-arm@nongnu.org>, "Frank Yang" <lfy@google.com>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Peter Collingbourne" <pcc@google.com>
Subject: Re: [PATCH v8 16/19] hvf: arm: Implement PSCI handling
Date: Mon, 13 Sep 2021 12:06:20 +0200	[thread overview]
Message-ID: <6fe284da-6989-f837-adda-1aa722f0d345@csgraf.de> (raw)
In-Reply-To: <8e0879b6-23c0-8f14-fd96-4d72f1d640c1@linaro.org>


On 12.09.21 23:40, Richard Henderson wrote:
> On 9/12/21 2:37 PM, Alexander Graf wrote:
>>
>> On 12.09.21 23:20, Richard Henderson wrote:
>>> On 9/12/21 1:36 PM, Alexander Graf wrote:
>>>>> I think the callsites would be clearer if you made the function
>>>>> return true for "PSCI call handled", false for "not recognised,
>>>>> give the guest an UNDEF". Code like
>>>>>            if (hvf_handle_psci_call(cpu)) {
>>>>>                stuff;
>>>>>            }
>>>>>
>>>>> looks like the 'stuff' is for the "psci call handled" case,
>>>>> which at the moment it isn't.
>>>>
>>>>
>>>> This function merely follows standard C semantics along the lines
>>>> of "0
>>>> means success, !0 is error". Isn't that what you would usually expect?
>>>
>>> No, not really.  I expect stuff that returns error codes to return
>>> negative integers on failure.  I expect stuff that returns a boolean
>>> success/failure to return true on success.
>>
>>
>> Fair, I'll change it to return -1 then. Thanks!
>
> Not quite the point I was making.  If the only two return values are
> -1/0, then bool false/true is in fact more appropriate.


If the whole code base adheres to it, maybe. The big problem with using
true/false as return values for functions that don't make it very
explicit (have an is in their name or use gerund for example). QEMU uses
a lot of 0 == success internally.

If you now add bools to the a code base that already uses int returns a
lot, you always need to look up what a function actually returns if the
caller treats it as bool (if, ?, assert, etc), making code review and
reasoning about code flows extremely hard. I've had one too many
occasions where I called an innocently looking API and put the assert()
the wrong way around for example.

I don't think we can solve this problem here, but IMHO the only sensible
way to get to good readability would be to have functions that return
success/failure return a libc defined struct that indicates the error.
Then check for success explicitly on every caller site. Overloading bool
or int for success/failure return is just bad :).


Alex



  reply	other threads:[~2021-09-13 10:23 UTC|newest]

Thread overview: 66+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-19 20:22 [PATCH v8 00/19] hvf: Implement Apple Silicon Support Alexander Graf
2021-05-19 20:22 ` [PATCH v8 01/19] hvf: Move assert_hvf_ok() into common directory Alexander Graf
2021-05-27 10:00   ` Sergio Lopez
2021-05-19 20:22 ` [PATCH v8 02/19] hvf: Move vcpu thread functions " Alexander Graf
2021-05-27 10:01   ` Sergio Lopez
2021-05-19 20:22 ` [PATCH v8 03/19] hvf: Move cpu " Alexander Graf
2021-05-27 10:02   ` Sergio Lopez
2021-05-19 20:22 ` [PATCH v8 04/19] hvf: Move hvf internal definitions into common header Alexander Graf
2021-05-27 10:04   ` Sergio Lopez
2021-05-19 20:22 ` [PATCH v8 05/19] hvf: Make hvf_set_phys_mem() static Alexander Graf
2021-05-27 10:06   ` Sergio Lopez
2021-05-19 20:22 ` [PATCH v8 06/19] hvf: Remove use of hv_uvaddr_t and hv_gpaddr_t Alexander Graf
2021-05-27 10:07   ` Sergio Lopez
2021-05-19 20:22 ` [PATCH v8 07/19] hvf: Split out common code on vcpu init and destroy Alexander Graf
2021-05-27 10:09   ` Sergio Lopez
2021-05-19 20:22 ` [PATCH v8 08/19] hvf: Use cpu_synchronize_state() Alexander Graf
2021-05-27 10:15   ` Sergio Lopez
2021-05-19 20:22 ` [PATCH v8 09/19] hvf: Make synchronize functions static Alexander Graf
2021-05-27 10:15   ` Sergio Lopez
2021-05-19 20:22 ` [PATCH v8 10/19] hvf: Remove hvf-accel-ops.h Alexander Graf
2021-05-27 10:16   ` Sergio Lopez
2021-05-19 20:22 ` [PATCH v8 11/19] hvf: Introduce hvf vcpu struct Alexander Graf
2021-05-27 10:18   ` Sergio Lopez
2021-05-19 20:22 ` [PATCH v8 12/19] hvf: Simplify post reset/init/loadvm hooks Alexander Graf
2021-05-27 10:20   ` Sergio Lopez
2021-05-19 20:22 ` [PATCH v8 13/19] hvf: Add Apple Silicon support Alexander Graf
2021-05-27 10:55   ` Sergio Lopez
2021-06-15 10:21   ` Peter Maydell
2021-06-27 20:40     ` Alexander Graf
2021-05-19 20:22 ` [PATCH v8 14/19] arm/hvf: Add a WFI handler Alexander Graf
2021-05-27 10:53   ` Sergio Lopez
2021-06-15 10:38   ` Peter Maydell
2021-05-19 20:22 ` [PATCH v8 15/19] hvf: arm: Implement -cpu host Alexander Graf
2021-05-27 11:18   ` Sergio Lopez
2021-06-15 10:56   ` Peter Maydell
2021-09-12 20:23     ` Alexander Graf
2021-09-13  8:28       ` Peter Maydell
2021-09-13 10:46         ` Alexander Graf
2021-09-13 10:52           ` Peter Maydell
2021-09-13 11:46             ` Alexander Graf
2021-09-13 11:48               ` Peter Maydell
2021-09-13 11:55                 ` Alexander Graf
2021-05-19 20:22 ` [PATCH v8 16/19] hvf: arm: Implement PSCI handling Alexander Graf
2021-05-27 11:20   ` Sergio Lopez
2021-06-15 12:54   ` Peter Maydell
2021-09-12 20:36     ` Alexander Graf
2021-09-12 21:20       ` Richard Henderson
2021-09-12 21:37         ` Alexander Graf
2021-09-12 21:40           ` Richard Henderson
2021-09-13 10:06             ` Alexander Graf [this message]
2021-09-13 10:30               ` Philippe Mathieu-Daudé
2021-05-19 20:22 ` [PATCH v8 17/19] arm: Add Hypervisor.framework build target Alexander Graf
2021-05-27 11:20   ` Sergio Lopez
2021-06-15 10:59   ` Peter Maydell
2021-05-19 20:22 ` [PATCH v8 18/19] arm: Enable Windows 10 trusted SMCCC boot call Alexander Graf
2021-05-27 11:21   ` Sergio Lopez
2021-06-15 11:02   ` Peter Maydell
2021-06-27 21:12     ` Alexander Graf
2021-05-19 20:22 ` [PATCH v8 19/19] hvf: arm: Handle Windows 10 SMC call Alexander Graf
2021-05-27 11:22   ` Sergio Lopez
2021-06-15  9:31   ` Peter Maydell
2021-06-27 21:07     ` Alexander Graf
2021-05-19 20:45 ` [PATCH v8 00/19] hvf: Implement Apple Silicon Support no-reply
2021-06-03 13:43 ` Peter Maydell
2021-06-03 13:53   ` Alexander Graf
2021-06-15 12:54   ` Peter Maydell

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