[Buildroot] [PATCH 1/2] package/pkg-cargo.mk: fix handling of runtime debug builds

[Moritz Bitsch]

Am 22.10.22 um 00:57 schrieb James Hilliard:
> On Fri, Oct 21, 2022 at 5:04 PM Moritz Bitsch <moritz at h6t.eu> wrote:
>>
>> Am 21.10.22 um 18:41 schrieb James Hilliard:
>>> On Fri, Oct 21, 2022 at 2:48 AM Moritz Bitsch <moritz at h6t.eu> wrote:
>>>>
>>>> Am 20.10.22 um 00:12 schrieb James Hilliard:
>>>>
>>>>> On Wed, Oct 19, 2022 at 6:02 PM Moritz Bitsch via buildroot
>>>>> <buildroot at buildroot.org> wrote:
>>>>>> From: Moritz Bitsch <moritz at h6t.eu>
>>>>>>
>>>>>> The cargo --release flag is used to create optimized builds, not supplying
>>>>>> --release has major performance implications.
> 
> Looking at this further the cargo --release flag merely tells cargo to use the
> release profile rather than the dev profile, however the issue of optimizations
> being enabled or not is really a matter of what the profile configuration is,
> right now we are effectively choosing between the default release or default
> dev profile configuration which does not properly match the build settings.
> 
> Instead what we really want to do is configure all cargo profiles based on the
> selected buildroot build settings.
> 
> Unfortunately cargo doesn't have any env variable that selects a profile, but
> we can sidestep this simply by configuring both root profiles(which other
> profiles inherit from).
> 
> I think the existing cargo build flags are fine, I sent a patch which should fix
> the profile configurations so that they match the buildroot build settings, let
> me know if this fixes the optimization issue for you:
> https://lore.kernel.org/buildroot/20221021224448.3502942-1-james.hilliard1@gmail.com/

Thanks, for the detailed response. The mentioned patch works fine for my 
use case. I can reproduce the performance issue/improvement when 
switching between different optimization levels.

>>>>> Is there an env variable we can use to set this instead?
>>>>>
>>>>> Some packages use cargo without the cargo infrastructure, for example
>>>>> we have a number of pyo3(https://pyo3.rs/) based packages that use the
>>>>> cargo env but not the cargo build commands from here.
>>>> I could not find any env variable for switching profiles.
>>>>
>>>> I had a look at python-rtoml, and the used setuptools-rust: supplying
>>>> --debug to
>>>> the "setup.py build" removes the --release flag from the cargo invocation.
>>>
>>> Hmm, there are two pyo3 build backends, only setuptools-rust uses setup.py,
>>> we also have maturin which is pep517 based.
>>
>> I'm in no way a a python expert, so take my words with a grain of salt.
>>
>> I could not find a way to specify what build profile is used by maturin
>> when in a pep517 build. Even if maturin supports the -r flag for release
>> builds when called directly.
> 
> I think the real issue is actually not that the wrong build profile is
> being used
> so much as the build profile configuration itself is wrong.

After looking into some crates with different behavior when built in 
debug or release mode (for example rust-embed) I think that most of them 
check for enabled debug_assertions, which you handle in your patch.

I think the conditional --release switch should be removed. Your patch 
is by far the more precise solution.

>>
>>>
>>>>>> Signed-off-by: Moritz Bitsch <moritz at h6t.eu>
>>>>>> ---
>>>>>>     package/pkg-cargo.mk | 2 +-
>>>>>>     1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/package/pkg-cargo.mk b/package/pkg-cargo.mk
>>>>>> index f7e3f39503..e0556252fa 100644
>>>>>> --- a/package/pkg-cargo.mk
>>>>>> +++ b/package/pkg-cargo.mk
>>>>>> @@ -119,7 +119,7 @@ define $(2)_BUILD_CMDS
>>>>>>                    $$($(2)_CARGO_ENV) \
>>>>>>                    cargo build \
>>>>>>                            --offline \
>>>>>> -                       $$(if $$(BR2_ENABLE_DEBUG),,--release) \
>>>>>> +                       $$(if $$(BR2_ENABLE_RUNTIME_DEBUG),,--release) \
>>>>>>                            --manifest-path Cargo.toml \
>>>>>>                            --locked \
>>>>>>                            $$($(2)_CARGO_BUILD_OPTS)
>>>>>> --
>>>>>> 2.37.3
>>>>>>
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