linux-kernel - Re: cannot build Linux 4.4: arch/mips/kernel/signal.c:142:12: error: ‘struct ucontext’ has no member named ‘uc

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Date:	Tue, 19 Jan 2016 10:01:55 +0000
From:	James Hogan <james.hogan@...tec.com>
To:	Florian Fainelli <f.fainelli@...il.com>
CC:	Heinrich Schuchardt <xypron.glpk@....de>,
	lkml <linux-kernel@...r.kernel.org>, <linux-mips@...ux-mips.org>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Paul Burton <paul.burton@...tec.com>,
	<linux-kbuild@...r.kernel.org>, Michal Marek <mmarek@...e.com>
Subject: Re: cannot build Linux 4.4: arch/mips/kernel/signal.c:142:12: error: ‘struct ucontext’ has no member named ‘uc_extcontext’

Hi Florian,

On Mon, Jan 18, 2016 at 06:22:21PM -0800, Florian Fainelli wrote:
> Le 17/01/2016 06:48, Heinrich Schuchardt a écrit :
> > On 01/17/2016 02:54 PM, Heinrich Schuchardt wrote:
> >>
> >> HEAD is now at afd2ff9... Linux 4.4
> >> arch/mips/kernel/signal.c: In function ‘sc_to_extcontext’:
> >> arch/mips/kernel/signal.c:142:12: error: ‘struct ucontext’ has no member
> >> named ‘uc_extcontext’
> >>   return &uc->uc_extcontext;
> >>             ^
> >> In file included from include/linux/poll.h:11:0,
> >>                  from include/linux/ring_buffer.h:7,
> >>                  from include/linux/trace_events.h:5,
> >>                  from include/trace/syscall.h:6,
> >>                  from include/linux/syscalls.h:81,
> >>                  from arch/mips/kernel/signal.c:26:
> >> arch/mips/kernel/signal.c: In function ‘save_msa_extcontext’:
> >> arch/mips/kernel/signal.c:170:40: error: dereferencing pointer to
> >> incomplete type
> >>
> > 
> > The problem stemmed from make not recognizing that this file was outdated:
> > 
> > Oct 16  2014 arch/mips/include/generated/asm/ucontext.h
> > 
> > Shouldn't make automatically regenerate outdated files?
> 
> The reduced test case can be simplified to these steps:
> 
> git co f1fe2d21f4e1aca8644cea888dc618f0183ad671\^1
> configure your kernel
> ARCH=mips make arch/mips/kernel/signal.o
> git co f1fe2d21f4e1aca8644cea888dc618f0183ad671
> ARCH=mips make arch/mips/kernel/signal.o
> 
> The problem seems to be that if there was a previous build which
> resulted in creating an asm-generic wrapper for a file
> (arch/mips/include/generated/asm/ucontext.h in that case), but this file
> was later moved into an arch-specific, non asm-generic header file, then
> we are just not going to automatically remove this auto-generated
> wrapper, and generate the new one.
> 
> This seems to be aggravated by the fact that commit
> f1fe2d21f4e1aca8644cea888dc618f0183ad671 does not add ucontext.h to
> arch/mips/include/uapi/Kbuild, Paul, James is that intentional?

I suspect it was intended to be exported in kernel headers, for
libc/signal handlers to use, although it isn't referenced by other
headers. Paul?

> 
> After trying to mess a bit with a clean solution, I just gave up and
> decided that this was not worth fixing since it is a very infrequent
> problem.

Thing is it isn't that uncommon. I've lost count of the number of times
I've hit this specific case (especially during bisection), and as Ralf
says, several others have mentioned it on the list, but rm -fr
arch/mips/include/generated always seemed so much easier than fixing
the actual problem.

Anyway, after a bit of fiddling around I think i've fixed this properly
now. I'll submit the patch asap.

Cheers
James

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