Re: [OE-core] [RFT] GCC 8.1

[Andre McCurdy <armccurdy@gmail.com>]

On Thu, May 10, 2018 at 6:16 PM, Khem Raj <raj.khem@gmail.com> wrote:
> On Thu, May 10, 2018 at 6:11 PM, Andre McCurdy <armccurdy@gmail.com> wrote:
>> On Thu, May 10, 2018 at 6:06 PM, Khem Raj <raj.khem@gmail.com> wrote:
>>> On Thu, May 10, 2018 at 6:00 PM, Andre McCurdy <armccurdy@gmail.com> wrote:
>>>> On Thu, May 10, 2018 at 5:55 PM, Khem Raj <raj.khem@gmail.com> wrote:
>>>>> On Thu, May 10, 2018 at 4:11 PM, Andre McCurdy <armccurdy@gmail.com> wrote:
>>>>>> On Thu, May 10, 2018 at 3:50 PM, Martin Jansa <martin.jansa@gmail.com> wrote:
>>>>>>> On Thu, May 10, 2018 at 03:40:53PM -0700, Andre McCurdy wrote:
>>>>>>>> On Thu, May 10, 2018 at 3:38 PM, Martin Jansa <martin.jansa@gmail.com> wrote:
>>>>>>>> > see
>>>>>>>> > http://lists.openembedded.org/pipermail/openembedded-core/2018-May/150654.html
>>>>>>>>
>>>>>>>> Removing -fno-omit-frame-pointer isn't the same as adding
>>>>>>>> -fomit-frame-pointer. Frame pointers may get enabled depending on the
>>>>>>>> optimisation level etc (ie not only by -fno-omit-frame-pointer).
>>>>>>>
>>>>>>> Should I send v2 adding -fomit-frame-pointer instead of removing
>>>>>>> -fno-omit-frame-pointer?
>>>>>>>
>>>>>>> The v1 fixes the issue for me with default config + DEBUG_BUILD.
>>>>>>
>>>>>> The v1 patch isn't wrong, it's just incomplete (the problem could come
>>>>>> back if someone changes optimisation level or switches gcc to clang,
>>>>>> etc).
>>>>>>
>>>>>> My choice would be a v2 patch which adds -fomit-frame-pointer to
>>>>>> CFLAGS unconditionally for all ARM builds when Thumb is enabled. That
>>>>>> should fix the problem for all optimisation levels etc and avoids
>>>>>> building the main strace binary differently depending on whether or
>>>>>> not ptest is enabled.
>>>>>
>>>>> explicitly adding this option is a poor choice especially for debug
>>>>> builds where we should
>>>>> let the -On level decide and not explicitly ask for either
>>>>> enable/disable frame-pointers
>>>>> that will also make it compiler proof.
>>>>
>>>> Of course, we should let the compiler decide whenever it's possible to do so.
>>>>
>>>> Unfortunately there are cases like this one where frame pointers clash
>>>> with inline assembler and we need to over-rule the compiler's choice.
>>>
>>> Here we are adding -fno-omit-frame-pointer via global opt flags that
>>> is the issue
>>> where we have fallouts from default O options I agree we should teach
>>> this to build
>>> system and help the compiler
>>
>> Since there's NO situation where enabling frame pointers is going to
>> work for this code + ARM + Thumb, I don't see the advantage of leaving
>> anything up to chance. Just explicitly disabling frame pointers is the
>> safest and cleanest option.
>
> In that case what we are saying is that strace has wrong assumptions
> I would think its best to change strace build system to demand this
> option override instead of injecting it externally.

There are many possible / better fixes if we want to patch the strace
sources or Makefiles. I'm not sure if Martin was signing up for that
though :-)