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Date:   Wed, 11 Oct 2023 16:15:15 -0700
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Subject: Re: [PATCH v2 -tip] x86/percpu: Use C for arch_raw_cpu_ptr()
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To:     Ingo Molnar <mingo@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Uros Bizjak <ubizjak@gmail.com>, x86@kernel.org,
        linux-kernel@vger.kernel.org, Nadav Amit <namit@vmware.com>,
        Andy Lutomirski <luto@kernel.org>,
        Brian Gerst <brgerst@gmail.com>,
        Denys Vlasenko <dvlasenk@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Josh Poimboeuf <jpoimboe@redhat.com>
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From:   "H. Peter Anvin" <hpa@zytor.com>
In-Reply-To: <ZScjptMn3fDmMFdg@gmail.com>
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On 10/11/23 15:37, Ingo Molnar wrote:
> 
> * Linus Torvalds <torvalds@linux-foundation.org> wrote:
> 
>>> The only drawback is a larger binary size:
>>>
>>>    text    data     bss     dec     hex filename
>>> 25546594        4387686  808452 30742732        1d518cc vmlinux-new.o
>>> 25515256        4387814  808452 30711522        1d49ee2 vmlinux-old.o
>>>
>>> that increases by 31k (0.123%), probably due to 1578 rdgsbase alternatives.
>>
>> I'm actually surprised that it increases the text size. The 'rdgsbase'
>> instruction should be smaller than a 'mov %gs', so I would have
>> expected the *data* size to increase due to the alternatives tables,
>> but not the text size.
>>
>> [ Looks around ]
>>
>> Oh. It's because we put the altinstructions into the text section.
>> That's kind of silly, but whatever.
> 
> Yeah, we should probably move .altinstructions from init-text to .init.data
> or so? Contains a bunch of other sections too that don't get executed
> directly ... and in fact has some non-code data structures too, such as ...
> ".apicdrivers". :-/
> 
> I suspect people put all that into .text because it was the easiest place
> to modify in the x86 linker script, and linker scripts are arguably scary.
> 

Well, it's more than that; "size" considers all non-writable sections to 
be "text".

	-hpa