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Re: libcpu_a_CXXFLAGS must be set with '=' before using '+='

From: Mathieu Lirzin
Subject: Re: libcpu_a_CXXFLAGS must be set with '=' before using '+='
Date: Fri, 03 Nov 2017 18:22:59 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/25.3 (gnu/linux)

Jeffrey Walton <address@hidden> writes:

> This is related to Nick and Mathieu's comments about per-object flags
> and use of CXXFLAGS.
> When I change the pattern to:
>   CPU_FLAG = -msse2
>   libcpu_a_SOURCES = cpu.cpp
>   libcpu_a_CXXFLAGS += $(CPU_FLAG)
> I encounter:
> error: libcpu_a_CXXFLAGS must be set with '=' before
> using '+='
> I think there are two or three issues with what I am trying to do, and
> the issue with "+=" is only the most prominent symptom.
> I think this document may be controlling:
> The paragraph that starts with "What we recommend is that you define
> extra flags in separate variables...." is especially interesting to
> me. It is interesting because `CPU_FLAG` will eventually need to be
> computed based on the platform. (Eventually we need: i386 gets -msse2;
> x86_64 gets nothing; ARMv7 gets NEON; and PowerPC gets Power4 and
> Altivec; others get nothing).
> Please forgive my ignorance, but how do I fix this issue such that it
> won't break when I start computing the value of CPU_FLAG in Autoconf?

Maybe I am overlooking something but using '=' shouldn't cause any issue
event if CPU_FLAG is computed from Autoconf.

Mathieu Lirzin
GPG: F2A3 8D7E EB2B 6640 5761  070D 0ADE E100 9460 4D37

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