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List:       linux-m68k
Subject:    Re: [RFC PATCH 2/2] arch/m68k: Add CONFIG_CPU_HAS_NO_MULDIV32
From:       "George Spelvin" <linux () horizon ! com>
Date:       2016-05-13 2:39:32
Message-ID: 20160513023932.16877.qmail () ns ! horizon ! com
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Finn Thain wrote:
> On Fri, 12 May 2016, George Spelvin wrote:
>> +# Old GCC versions fall back to -m5200 compilation, generating these calls
>> +# even though the CPU doesn't actually need it.  See arch/m68k/Makefile.
>
> The comment is vague. Does anyone know which GCC versions do or don't work 
> like this?

Yes, I looked it up in the archived GCC documentation.  My current patch says:

(commit comment)
    Since the compiler version is not known at Kconfig time, this cannot
    be expressed in a CONFIG_ variable, but instead is handled by some
    Makefile hackery.  This only applies to GCC 4.2.4 and earlier, which
    is hopefully almost everyone, but Documentation/Changes says GCC 3.2.

(arch/m68k/lib/Makefile)
+# GCC 4.2.4 and earlier don't know about ColdFire models that support
+# DIV.L and fall back to -m5200, generating these calls even though the
+# CPU doesn't actually need it.  Not needed on GCC 4.3 or later.
+# See the $(call cc-option ...) lines in arch/m68k/Makefile.
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