linux-kernel - Re: [PATCH v2 02/17] vdso: Clean header inclusion in getrandom

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Message-ID: <ZsyAbP4GOP1eCSI8@zx2c4.com>
Date: Mon, 26 Aug 2024 15:17:32 +0200
From: "Jason A. Donenfeld" <Jason@...c4.com>
To: Christophe Leroy <christophe.leroy@...roup.eu>
Cc: Michael Ellerman <mpe@...erman.id.au>,
	Nicholas Piggin <npiggin@...il.com>,
	Naveen N Rao <naveen@...nel.org>, Andy Lutomirski <luto@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>, Theodore Ts'o <tytso@....edu>,
	Arnd Bergmann <arnd@...db.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Vincenzo Frascino <vincenzo.frascino@....com>,
	Shuah Khan <shuah@...nel.org>, linuxppc-dev@...ts.ozlabs.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-arch@...r.kernel.org, linux-mm@...ck.org,
	linux-trace-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v2 02/17] vdso: Clean header inclusion in getrandom

On Mon, Aug 26, 2024 at 12:45:40PM +0200, Christophe Leroy wrote:
> 
> 
> Le 26/08/2024 à 10:58, Jason A. Donenfeld a écrit :
> > On Mon, Aug 26, 2024 at 10:37:49AM +0200, Christophe Leroy wrote:
> >>
> >>
> >> Le 26/08/2024 à 10:07, Jason A. Donenfeld a écrit :
> >>> On Thu, Aug 22, 2024 at 09:13:10AM +0200, Christophe Leroy wrote:
> >>>>    
> >>>> +#define _PAGE_SIZE (1UL << CONFIG_PAGE_SHIFT)
> >>>> +#define _PAGE_MASK (~(_PAGE_SIZE - 1))
> >>>
> >>> If PAGE_SIZE isn't defined at this point, why not just call it PAGE_SIZE
> >>> instead of _PAGE_SIZE? But if that's the case, why not put the vdso
> >>> definition of PAGE_SIZE into some vdso header included by this file?
> >>
> >> It was working ok on powerpc but on x86 I got:
> > 
> > Seems like there might be some more fiddling to do, then? Or did you
> > conclude it's impossible?
> 
> Maybe someone who knows x86 in details could helps but after a first 
> look I gave up because it looks very x86 specific, indeed that's 
> x86/asm/vdso/gettimeofday.h that pulls several x86/asm/ headers , and 
> the same type of issue might arise for any new architecture coming in.
> 
> For me it looked cleaner to just do as commit cffaefd15a8f ("vdso: Use 
> CONFIG_PAGE_SHIFT in vdso/datapage.h") and not use PAGE_SIZE at all. But 
> I didn't want to directly use (1UL << CONFIG_PAGE_SHIFT) and (~(1UL << 
> (CONFIG_PAGE_SHIFT - 1))) in the code directly hence the new macros with 
> a leading underscore to avoid any conflict with existing macros.

If that's the case and you can't sort it out or it's impossible, then it
seems like adding #ifndef PAGE_SIZE, #define... inside of some vdso header
(not inside getrandom.c) would make sense.

Jason