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Message-ID: <20161120191257.GX1041@n2100.armlinux.org.uk>
Date: Sun, 20 Nov 2016 19:12:57 +0000
From: Russell King - ARM Linux <linux@...linux.org.uk>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Nicholas Piggin <npiggin@...il.com>, Arnd Bergmann <arnd@...db.de>,
Michal Marek <mmarek@...e.com>,
Adam Borowski <kilobyte@...band.pl>,
Omar Sandoval <osandov@...ndov.com>,
Alexey Dobriyan <adobriyan@...il.com>,
Stephen Rothwell <sfr@...b.auug.org.au>,
Al Viro <viro@...iv.linux.org.uk>,
Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>
Subject: Re: [PATCH 1/2] kbuild: provide include/asm/asm-prototypes.h for ARM
On Sun, Nov 20, 2016 at 10:32:50AM -0800, Linus Torvalds wrote:
> On Sun, Nov 20, 2016 at 5:21 AM, Russell King - ARM Linux
> <linux@...linux.org.uk> wrote:
> > On Tue, Oct 25, 2016 at 07:32:00PM +1100, Nicholas Piggin wrote:
> >>
> >> Michal, what's your thoughts? If you merge my patch 2/2 and skip 1/2, it
> >> should not give any new build warnings or errors, so then arch patches can
> >> go via arch trees. 1/2 could go in after everyone is up to date.
> >
> > So what's the conclusion on this? I've just had a failure due to
> > CONFIG_TRIM_UNUSED_KSYMS reported on ARM, and it looks like (at
> > least some of) patch 1 could resolve it.
>
> Hmm. I've got
>
> cc6acc11cad1 kbuild: be more careful about matching preprocessed asm
> ___EXPORT_SYMBOL
> 4efca4ed05cb kbuild: modversions for EXPORT_SYMBOL() for asm
>
> in my tree. Is that sufficient, or do we still have issues?
Hmm, those seem to have gone in during the last week, so I haven't
tested it yet (build running, but it'll take a while). However, I
don't think they'll solve _this_ problem.
Some of the issue here is that we use a mixture of assembly macros
and preprocessor for the ARM bitops - the ARM bitops are created
with an assembly macro which contains some pre-processor expanded
macros (eg, EXPORT_SYMBOL()).
This means that the actual symbol being exported is not known to
the preprocessor, so doing the "__is_defined(__KSYM_##sym)" inside
"EXPORT_SYMBOL(\name)" becomes "__is_defined(__KSYM_\name)" to the
preprocessor. As "__KSYM_\name" is never defined, it always comes
out as zero, hence we always use __cond_export_sym_0, which omits
the symbol export from the assembly macro definition:
.macro bitop, name, instr
.globl \name ; .align 0 ; \name:
...
.type \name, %function; .size \name, .-\name
.endm
In other words, using preprocessor macros inside an assembly macro
may not work as expected, and now leads to config-specific failures.
--
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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