* Tom Stellard:
> On 6/7/22 02:18, Florian Weimer wrote:
>> * Ben Cotton:
>>
>>> This change will add new macros which will make it easier for packages
>>> to add and remove their own compiler flags. This strategy is already
>>> used to some extent with feature macros like %{_lto_cflags},
>>> %{_hardening_cflags}, etc, but these new macros will give packagers
>>> even more fine-grained control over the options.
>>>
>>> The proposed macros for adding new flags are:
>>>
>>> %_pkg_extra_cflags
>>> %_pkg_extra_cxxflags
>>> %_pkg_extra_fflags
>>> %_pkg_extra_ldflags
>> Why isn't it possible to use the environment variables for this?
>>
>
> Environment variables won't cover all cases. For example, some packages
> need the flags passed as arguments to make or configure or some other
> build system.
But then you can stick the extra flags into that argument. I don't see
why this additional hook is needed.
>> This is very misleading because in several cases, clearing the those
>> flags will not affect toolchain behavior because the flag in question
>> merely restates the toolchain default. In particular, this applies to
>> -fasynchronous-unwind-tables, and it would apply to -march= and -mcpu=
>> if those were in the list. Likewise to -Wl,-z,relro.
>> Is the goal of this proposal just to achieve a textual flags change
>> (disregarding any change in behavior), or to actually change toolchain
> The goal is to make it easy to remove individual flags so packages can
> get the toolchain behavior they want.
Sorry, this does not answer my question. What if removing the flag does
not actually change toolchain behavior?
>> If the former, I'm not sure if the actual _flag names are useful. Maybe
>> we can add an RPM macro to suppress or replace flags based on the flags
>> as they are used instead. This could also add additional error checking
>> because a name typo in the macro definition will not be immediately
>> obvious.
>>
>
> Can you give an example of what you mean by this?
You could write:
%build_cxxflags_remove -Wp,-D_GLIBCXX_ASSERTIONS
or some similar construct, and -Wp,-D_GLIBCXX_ASSERTIONS would be
removed from the build flags.
>>> With these new macros, the examples from above could be re-written as:
>>>
>>> compiler-rt: %global _pkg_extra_cflags -D_DEFAULT_SOURCE
>>> julia: %global _flag_glibcxx_assertions %{nil}
>> Do you have some background why -D_DEFAULT_SOURCE is needed? Why
>> doesn't upstream detect this?
>>
>
> It was added to workaround this bug:
> https://sourceware.org/bugzilla/show_bug.cgi?id=25271
This has long since been fixed, so the workaround is no longer needed.
-D_GLIBCXX_ASSERTIONS has zero false positives. Removing it does not
make the code that triggers the asserts well-defined. Only the explicit
assertion failure is gone. So it is probably another example of a flag
where removal does not result in the hoped-for change in toolchain
behavior.
Thanks,
Florian
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